Furthermore, a recent study demonstrated that concomitant amiodarone therapy may affect outcomes in patients with ischemic VT who are undergoing CA [6]. The above findings may be explained by changes in substrate characteristics and electrogram properties. It is unknown whether concomitant amiodarone therapy affects procedural outcomes in patients with ARVC. Accordingly, the aim of this study was to investigate the substrate characteristics and ablation outcomes between ARVC patients receiving CA with and without concomitant amiodarone therapy.

#### **2. Materials and Methods**

#### *2.1. Study Population*

From 2013 to 2020, we retrospectively screened patients with ARVC who had undergone successful CA of drug-refractory VT in three medical centers (Taipei Veterans General Hospital, Yangon General Hospital, and Taichung Veterans General Hospital). Based on the 2010 modified Task Force criteria, all patients met the diagnosis of definite ARVC [7]. The indications for catheter ablation included the following: (1) individuals with recurrent, sustained monomorphic VT refractory to antiarrhythmic drugs; and (2) symptomatic individuals with a high burden of ventricular ectopy and documented non-sustained VT refractory to antiarrhythmic drugs. Patients without documented sustained VT or successful CA were excluded. Patients had a minimum follow-up period of six months after CA. Written informed consent was obtained in all cases. The institutional review boards of each participating center approved the collection of data. From the electronic medical records, clinical data, such as baseline characteristics, 12 lead ECGs, 24 h Holter monitoring, transthoracic echocardiography, coronary angiography, and electrophysiological (EP)/ablation parameters, were collected for comparison. In the study, patients were divided into two groups based on their use of amiodarone before CA ("Off" amiodarone for at least 8 weeks before ablation and "On" amiodarone within 8 weeks). The use of amiodarone depends on physicians' discretion or intolerable side effects.

#### *2.2. Electrophysiological Study, Mapping, and Ablation*

In previous publications, we described details of an electrophysiological study, substrate mapping, and ablation strategies [8]. After obtaining informed consent, we performed a standardized electrophysiological study on all patients under fasting and sedated conditions. Except for amiodarone, all anti-arrhythmic drugs (AADs) have been discontinued for at least five half-lives prior to CA [8]. The induction protocol and mapping strategy were described in the previous article [9]. Epicardial mapping/ablation is conducted in patients with failed endocardial ablation or in those who may have extensive epicardial involvement and limited abnormal substrates within the endocardium [8]. The RV endocardial bipolar scar and low voltage zone (LVZ) were defined as areas with peak-to-peak bipolar voltage < 0.5 mV and 0.5–1.5 mV, respectively, whereas the RV endocardial unipolar LVZ area was defined as an area with peak-to-peak unipolar voltage < 5.5 mV [10].

The RV epicardial bipolar scar and LVZ were defined as areas with a peak-to-peak bipolar voltage of <0.5 mV and 0.5–1 mV, respectively. The voltage maps were manually edited to avoid intracavitary points. An average bipolar or unipolar voltage was calculated. The scar, LVZ, and areas with abnormal electrograms (defined as either continuous, late, or fragmented potentials during sinus or paced rhythm) were assessed by using the standard surface area measurement tool on the navigation system [11]. When multiple areas of confluent low voltage were present, the aggregate area of the individual regions of interest was calculated. All patients received complete endocardial and/or epicardial substrate

modification targeting the areas with abnormal electrograms. Successful ablation was defined as the non-inducibility of any VTs with or without isoproterenol [8].

#### *2.3. Follow-Up and Recurrences of Ventricular Arrhythmia (VA)*

Patients were followed up at the first, third, and sixth months after CA, as well as every three–six months thereafter. ICD interrogation, ECG, and Holter monitoring were performed. Recurrent VA, defined as sustained VT or VT/VF, requires ICD interventions [12].

#### *2.4. Statistical Analysis*

The continuous and categorical variables were expressed as mean ± standard deviation and percentage, respectively. The Student's *t*-test was used to compare continuous variables, while chi-square tests with or without Yate's correction for continuity or Fisher's exact tests were used for categorical variables, as indicated. A multivariate Cox proportional hazards regression analysis was performed with variables with a *p*-value of less than 0.2 in the univariate analysis for a hazard ratio to predict the VT/VF recurrence. We considered a *p*-value of 0.05 to be statistically significant. The statistical analyses were conducted using the Statistical Package for the Social Sciences, Version 22.0 (IBM Corporation, Armonk, NY, USA).

#### **3. Results**

#### *3.1. Study Population*

3.1.1. Patient Selection and Baseline Characteristics of ARVC Patients

In total, we screened 106 patients who were diagnosed with definite ARVC and had received successful CA of VA (Figure 1). The analysis included 72 patients (67.9%) (age 45.3 ± 14.5 years, 61.1% male) who received CA for clinically documented sustained VT with successful ablation. (Figure 1). Of these, 29 (40.3%) and 43 (59.7%) patients were classified as "off" and "on" amiodarone groups, respectively (Figure 1). The median (25–75%) duration of amiodarone use in patients "on" amiodarone was 11 (4–18) months before CA. The characteristics of these two groups are shown in Table 1. There were fewer men in patients "off" amiodarone (13 (44.8%) vs. 31 (72.1%); *p* = 0.027). Patients "off" amiodarone received more class Ic AAD medications (10 (34.5%) vs. 3 (7.0%); *p* = 0.004). In terms of the other parameters and Task Force criteria, there were no significant differences between the two groups.

**Table 1.** Comparison of baseline characteristics between patients with ARVC "On" and "Off" amiodarone before CA.

#### **Table 1.** *Cont.*

\* According to the 2010 revised Task Force criteria (9). AAD, anti-arrhythmic drug; ARVC, arrhythmogenic right ventricular cardiomyopathy; CA, catheter ablation; LVEF, left ventricular ejection fraction; RVEF, right ventricular ejection fraction.

**Figure 1.** Patient selection in the present study. Patients with ARVC receiving successful CA for ventricular arrhythmia were screened. We enrolled ARVC patients with clinically documented sustained VT, and patients were further categorized into two groups based on their use of amiodarone within the 8 weeks before CA. ARVC = arrhythmogenic right ventricular cardiomyopathy; CA = catheter ablation; VT = ventricular tachycardia.

#### 3.1.2. Endocardial and Epicardial Substrate Characteristics

Epicardial approach was performed in 47 (65.3%) patients, including 12 (41.4%) and 35 (81.4%) patients "off" and "on" amiodarone, respectively (*p* = 0.001). The characteristics of the RV substrate are shown in Table 2. There were no significant differences between the two groups regarding endocardial and epicardial bipolar voltage, unipolar voltage, and LVZ/scar area. The total activation time of the endocardium and epicardium was longer in patients "on" amiodarone than those in patients "off" amiodarone (158.2 ± 31.8 ms vs. 144.0 ± 32.7 ms, *p* < 0.001; 211.2 ± 26.0 ms vs. 183.6 ± 24.2 ms, *p* = 0.002). In addition, the areas of abnormal electrograms within the endocardium and epicardium were significantly larger in patients "on" amiodarone (Figure 2) than those in patients "off" amiodarone (Figure 3). (Endo: 16.8 ± 15.4 cm2 vs. 6.8 ± 5.0 cm2, *p* = 0.001; Epi: 28.2 ± 29.0 cm2 vs. 13.7 ± 21.4 cm2, *p* = 0.024). In the patients with amiodarone before CA, there was no significant difference in the substrate characteristics between patients with amiodarone durations of more than 6 months or not (Supplemental Table S1).

**Table 2.** Comparison of baseline characteristics between patients with ARVC "On" and "Off" amiodarone before ablation.

\* The average of bipolar or unipolar median voltage. ARVC, arrhythmogenic right ventricular cardiomyopathy; RV, right ventricular; VT, ventricular tachycardia.

**Figure 2.** An example of electrophysiological and substrate characteristics in a patient "on" amiodarone before CA. Patients with ARVC "on" amiodarone had a longer total activation time and larger areas with abnormal electrograms. The (**left panel**) showed an endocardial voltage map and activation map with local abnormal electrograms. The (**right panel**) showed an epicardial voltage map and activation map with local abnormal electrograms (\* indicated the location of corresponding signal). "See text for details".

**Figure 3.** An example of electrophysiological and substrate characteristics in a patient "off" amiodarone before CA. The (**left panel**) showed an endocardial voltage map and activation map with local abnormal electrograms. The (**right panel**) showed an epicardial voltage map and activation map with local abnormal electrograms (\* indicated the location of corresponding signal). "See text for details".

#### 3.1.3. Mapping of Ventricular Tachycardia and Catheter Ablation

During the electrophysiological study, 112 VTs (1.6 ± 0.8/patient) were induced, including 37 and 75 VTs in patients "off" and "on" amiodarone, respectively (*p* = 0.008). The mean cycle length of inducible VTs was 306.3 ± 66.1 ms. Of 112 inducible VTs, 61 VTs were mappable (14 in the "off" amiodarone group and 47 in the "on" amiodarone group, *p* = 0.007). Nine of the 61 mappable VT circuits were considered intramural because they lacked identifiable diastolic paths despite simultaneous epicardial and endocardial mapping. Three in the "off" amiodarone and six in the "on" amiodarone, (*p* = 0.731), all identified VT isthmuses and were correlated with areas with abnormal electrograms and abnormal substrates.

Each patient underwent ablation of the isthmus if mappable, and complete elimination of the endocardial and/or epicardial abnormal substrates. In patients "on" amiodarone, the total procedure duration and ablation time were significantly longer than in those "off" amiodarone (220.3 ± 43.9 min vs. 184.5 ± 51.1 min, *p* = 0.019, and 55.4 ± 37.7 min vs. 28.2 ± 24.4 min, *p* = 0.001, respectively). In all patients, non-inducibility of VT was achieved following CA. There were no procedural complications.

#### 3.1.4. Follow-Up

After a follow-up period of 43.2 ± 29.5 months, two patients (2.5%) died of noncardiovascular causes (pneumonia: 2), and 24 (33.3%) experienced VT/VF recurrences. The incidence of VT/VF recurrence was significantly higher in patients "on" amiodarone than those "off" amiodarone (19/43 (44.2%) vs. 5/29 (17.2%), log-rank *p*-value = 0.011, Figure 4A). Among patients "on" amiodarone, the use of amiodarone was continued in 23 cases (53.5%) 3 months after CA. The incidence of VT/VF recurrence among patients on amiodarone before CA was still higher for those with continuous amiodarone use than for those without (14/23 (60.9%) vs. 5/20 (25.0%), log-rank *p*-value = 0.002, Figure 4B). Univariate and multivariate analyses (Table 3) showed that the use of amiodarone before CA (hazard ratio (HR): 3.04, 95% confidence interval (CI): 1.07–8.66, *p* = 0.038) is the only independent predictor of VT/VF recurrence.

**Table 3.** Univariate and multivariate analyses of VT/VF recurrence after catheter ablation.

CA = catheter ablation; CI = confidence interval; HR = hazard ratio; LVEF = left ventricular ejection fraction; RV = right ventricle; RVEF = RV ejection fraction.

**Figure 4.** Kaplan–Meier curve for ablation outcomes during follow-up. (**A**) The Kaplan–Meier curve showed the recurrence-free survival in patients "on" and "off" amiodarone. Higher VT/VF recurrences were observed in patients "on" amiodarone than in those "off" amiodarone. (**B**) The Kaplan–Meier curve demonstrated the VT/VF recurrence-free survival in the patients with or without continuous amiodarone use after the successful ablation in patients "on" amiodarone before CA.

#### **4. Discussion**

#### *4.1. Main Findings*

According to our study, amiodarone use before CA in patients with ARVC is associated with a longer activation time and a greater area of abnormal electrograms within the RV endocardium and epicardium. Despite the similar ablation strategy and endpoints (complete elimination of arrhythmogenic potential and non-inducible VT), VT recurrence was higher in patients "on" amiodarone before CA. Regardless of acute success, patients whose amiodarone use was discontinued 3 months after CA experienced fewer VT recurrences during subsequent follow-up.

#### *4.2. Amiodarone and the Abnormal Substrate*

Amiodarone has been shown to prolong the total QRS duration and result in low amplitude signals in previous studies [13], which is consistent with the present findings that a longer activation time was observed in patients "on" amiodarone compared with those without. One of the main effects of chronic amiodarone therapy is the inhibition of potassium outward currents, which may prolong the action potential duration of the ventricular myocytes and delay conduction velocity [14]. Amiodarone may also increase the refractory periods of ischemic scar tissue and organize fractionated electrograms [15]. Luigi et al. reported that patients with ischemic VT "on" amiodarone had a smaller area of abnormal electrogram compared to those without [6]. These findings suggest that the use of amiodarone may mask "abnormal" electrical activity within the scar tissue in patients with ischemic VT. However, the impact of amiodarone on abnormal electrograms in patients with ARVC or other non-ischemic cardiomyopathies remains to be determined.

In contrast to the above-mentioned study regarding ischemic cardiomyopathy, we found that patients "on" amiodarone had larger areas of abnormal electrograms than those "off" amiodarone. Inconsistent findings as compared to ischemic substrates can be attributed to the following plausible explanations: (1) amiodarone prolongs conduction velocity heterogeneously in fatty-infiltrated myocytes and creates more abnormal electrograms in patients with ARVC; and (2) there is a diversity of disease progression and scarring in ARVCs, which could also contribute to nonuniform ablation outcomes. However, as a result of the study design, we cannot determine the cause-and-effect relationship between amiodarone use and the extent of abnormal electrogram extension in the present study. Further studies focusing on the effects of amiodarone on the diseased substrate in ARVC will be warranted.

#### *4.3. Amiodarone Use and Ablation Outcomes*

In this study, we found that patients who were "on" amiodarone had higher recurrences of VT than those who were "off" amiodarone before CA. These findings may be explained by the following reasons: First, a greater extent of diseased substrates has been observed in amiodarone users, suggesting a worse disease status and/or faster disease progression in these individuals. Previously, we found that the progression of the disease could also cause the expansion of abnormal substrates, which was linked to VT recurrences [8]. The second issue is that, despite the larger area with abnormal electrograms, there were still some arrhythmogenic substrates that were hidden after amiodarone use, as seen in ischemic substrates. As a result, substrate modification could not be performed completely. Moreover, amiodarone could possess good antiarrhythmic properties and prevent ventricular arrhythmias from being induced after CA [16]. Nonetheless, the possibility of this is negated by the findings that these patients were refractory to amiodarone before CA. Furthermore, the pro-arrhythmic effect was reported with a relatively low incidence but was not negligible [4,17]. Amiodarone might prolong the QT interval and cause polymorphic ventricular tachycardia (i.e., torsade de pointes), especially in patients with drug-drug interactions [18]. The above hypothesis might be indirectly supported by the observation that patients with continuous use of amiodarone after ablation experience VT recurrences at higher rates. Amiodarone, however, causes proarrhythmia at a rate of less

than one percent per year [19]. A previous study demonstrated that long-term amiodarone use did not increase mortality or hospitalization [20]. Further investigation is needed to determine the exact reason for the higher incidence of VT recurrence in ARVC patients with amiodarone use before CA.

#### *4.4. Clinical Implications*

To the best of our knowledge, this is the first study to investigate the impact of amiodarone use before CA in patients with ARVC. Amiodarone use before CA can result in distinct substrate characteristics, such as longer activation times and larger areas with abnormal electrograms and was associated with worse ablation outcomes. According to the above findings, we suggest the physician withdraw amiodarone before CA if the patient can tolerate it. Despite the standard ablation strategies and endpoints, VT recurrences were still higher in patients without discontinuation, reflecting the importance of alternative strategies to assess the ablation endpoints in these patients who could not withdraw the amiodarone. Future studies are warranted to address this aspect.

#### *4.5. Limitations*

There were some limitations in the present study. This is a retrospective study in which only patients who had successfully undergone ablation were included. The prescription of amiodarone was based on the clinical physician's discretion. In patients with ARVC before CA, it is difficult to standardize the use of AADs. Furthermore, the use of amiodarone after CA was also at the discretion of the physicians, which may have affected the present findings. In this retrospective study, it is difficult to determine whether the amiodarone or the need for amiodarone affects substrate characteristics and recurrence. Nevertheless, the bias can be minimized by multivariate analysis and collaboration between referral centers. Additionally, epicardial approaches were not performed in all patients. However, even with the above-mentioned differences, there are more patients "on" amiodarone who are undergoing epicardial ablation to achieve the same outcome. In this regard, we concluded that epicardial ablation was not the cause of the differences between the two groups. A prospective study is warranted to validate the impact of amiodarone on the ablation outcome in patients with definite ARVC.

#### **5. Conclusions**

Despite similar ablation strategies and endpoints, amiodarone use before CA may be associated with a higher rate of VT recurrence in patients with ARVC. Higher VT recurrences were observed in ARVC patients who continued to take amiodarone despite the acute success.

**Supplementary Materials:** The following supporting information can be downloaded at: https:// www.mdpi.com/article/10.3390/jcm11247265/s1. Supplemental Table S1. Comparison of substrate characteristics between patients with different periods on amiodarone before ablation.

**Author Contributions:** Conceptualization, C.-Y.L. and F.-P.C.; methodology, C.-Y.L. and F.-P.C.; formal analysis, C.-Y.L. and F.-P.C.; investigation, Y.-J.L., L.-W.L., Y.-F.H., S.-L.C., S.-A.C., C.-H.L., N.N., Y.-C.H., T.-C.T., F.-P.C. and C.-Y.L.; resources, Y.-J.L., L.-W.L., Y.-F.H., S.-L.C., S.-A.C., C.-H.L., N.N., Y.-C.H., T.-C.T., F.-P.C. and C.-Y.L.; data curation, C.-Y.L.; writing—original draft preparation, C.-Y.L. and F.-P.C.; writing—review and editing, C.-Y.L., F.-P.C., N.N., Y.-C.H., C.-H.L., Y.-J.L., S.-L.C., L.-W.L., Y.-F.H., T.-C.T., T.-F.C., J.-N.L., T.-Y.C., L.K., C.-I.W., C.-M.L., S.-H.L., W.-H.C. and S.-A.C.; funding acquisition, C.-Y.L. and F.-P.C. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work was supported by the Ministry of Science and Technology (111-2314-B-075-007- MY3, 109-2314-B-075-076-MY3, 109-2314-B-010-058-MY2, 109-2314-B-075-074-MY3, 109-2314-B-075 -076 -MY3, grant nos. 107-2314-B-010-061-MY2, 106-2314-B-075-006-MY3, 106-2314-B-010-046-MY3, and 106-2314-B-075-073-MY3), Research Foundation of Cardiovascular Medicine, Szu-Yuan Research Foundation of Internal Medicine, and Taipei Veterans General Hospital (grant no. V106C-158, V106C-104, V107B-014, V107C-060, V107C-054, V108C-107, and V109C-113).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of Taipei Veterans General Hospital (2018-07-006B).

**Informed Consent Statement:** Patient consent was waived due to the anonymized nature of the information and the fact that the submission did not include images that might identify the person.

**Data Availability Statement:** The authors confirm that the data supporting the findings of this study are available within the article.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

## *Article* **The Impact of COVID-19 Pandemic on the Clinical Practice Patterns in Atrial Fibrillation: A Multicenter Clinician Survey in China**

**Feng Hu 1, Minhua Zang 1, Lihui Zheng 2, Wensheng Chen 3, Jinrui Guo 4, Zhongpeng Du 5, Erpeng Liang 6, Lishui Shen 7, Xiaofeng Hu 8, Xuelian Xu 9, Gaifeng Hu 10, Aihua Li 11, Jianfeng Huang 1, Yan Yao 2,\* and Jun Pu 1,\***

**Abstract:** The COVID-19 pandemic has severely impacted healthcare systems worldwide. This study investigated cardiologists' opinions on how the COVID-19 pandemic impacted clinical practice patterns in atrial fibrillation (AF). A multicenter clinician survey, including demographic and clinical questions, was administered to 300 cardiologists from 22 provinces in China, in April 2022. The survey solicited information about their treatment recommendations for AF and their perceptions of how the COVID-19 pandemic has impacted their clinical practice patterns for AF. The survey was completed by 213 cardiologists (71.0%) and included employees in tertiary hospitals (82.6%) and specialists with over 10 years of clinical cardiology practice (53.5%). Most respondents stated that there were reductions in the number of inpatients and outpatients with AF in their hospital during the pandemic. A majority of participants stated that the pandemic had impacted the treatment strategies for all types of AF, although to different extents. Compared with that during the assumed non-pandemic period in the hypothetical clinical questions, the selection of invasive interventional therapies (catheter ablation, percutaneous left atrial appendage occlusion) was significantly decreased (all *p* < 0.05) during the pandemic. There was no significant difference in the selection of non-invasive therapeutic strategies (the management of cardiovascular risk factors and concomitant diseases, pharmacotherapy for stroke prevention, heart rate control, and rhythm control) between the pandemic and non-pandemic periods (all *p* > 0.05). The COVID-19 pandemic has had a profound impact on the clinical practice patterns of AF. The selection of catheter ablation and percutaneous left atrial appendage occlusion was significantly reduced, whereas pharmacotherapy was often stated as the preferred option by participating cardiologists.

**Keywords:** COVID-19 pandemic; atrial fibrillation; interventional therapy; catheter ablation; percutaneous left atrial appendage occlusion; pharmacotherapy

**Citation:** Hu, F.; Zang, M.; Zheng, L.; Chen, W.; Guo, J.; Du, Z.; Liang, E.; Shen, L.; Hu, X.; Xu, X.; et al. The Impact of COVID-19 Pandemic on the Clinical Practice Patterns in Atrial Fibrillation: A Multicenter Clinician Survey in China. *J. Clin. Med.* **2022**, *11*, 6469. https://doi.org/10.3390/ jcm11216469

Academic Editors: Tong Liu and Firat Duru

Received: 25 August 2022 Accepted: 29 October 2022 Published: 31 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

The coronavirus disease 2019 (COVID-19) pandemic has severely disrupted medical care systems worldwide [1–5].The adverse influence of the pandemic on the healthcare system has impacted the prevention and treatment of COVID-19 itself, and has destabilized the relationship between clinicians and patients. In particular, the highly contagious and widespread Omicron variant has made the epidemic difficult to control and has presented challenges for the diagnosis and treatment of other common diseases [6,7].

Atrial fibrillation (AF) treatment is a comprehensive and multifaceted strategy involving heart rhythm control, heart rate control, stroke prevention therapy, interventional or surgical therapy, and the management of cardiovascular risk factors and concomitant diseases [8,9]. Several previous studies have found increased morbidity in AF patients who also have COVID-19, which affects their prognosis [10–14]. Zoubi M et al. demonstrated that new-onset AF is a poor prognostic sign in patients with severe COVID-19 [15]. Alkhameys S et al. performed an interrupted time series analysis of anticoagulant prescription between January 2019 and February 2021 using the English Prescribing Dataset. Although the prescription of direct-acting oral anticoagulants during the COVID-19 pandemic increased by 19%, the overall prescription of oral anticoagulants during this period was lower than expected, possibly owing to medication adherence [16]. A recently published questionnaire analysis also revealed that the COVID-19 pandemic significantly impaired the quality of life of patients awaiting AF ablation procedures [17]. Thus, COVID-19 continues to impact the management of AF and brings increasing challenges for clinicians.

However, no relevant studies have extensively investigated the impact of the COVID-19 pandemic on the clinical practice patterns of AF. In the present study, we invited 300 cardiologists from 22 provinces in China, in April 2022, to fill out a questionnaire survey investigating their perspectives on how the COVID-19 pandemic has impacted their treatment strategies for AF patients.

#### **2. Methods**

#### *2.1. Study Design and Participants*

To better understand the impact of the COVID-19 pandemic on AF treatment practices, we conducted a multicenter physician survey of 300 cardiologists in China. Research team members at the Renji Hospital, School of Medicine, Shanghai Jiaotong University, developed and distributed the survey. This survey was implemented using an online questionnaire as the primary source of data collection. The intended target population was physicians in cardiovascular departments who treated patients with AF in their routine clinical work. An initial questionnaire draft informed by the study aims was developed, pilot-tested, and revised from 1 April 2022 to 10 April 2022. A detailed questionnaire including demographic questions and clinical questions was distributed via the WeChat software to 300 cardiologists from 22 provinces in China, in April 2022. The clinician survey was administered anonymously, and all responses were submitted by 30 April 2022. This study was approved by the Institutional Ethics Committee of Renji Hospital Affiliated to Medical College of Shanghai Jiaotong University.

#### *2.2. Questionnaire Design*

The questionnaire, entitled "Clinician Perspectives on the Impact of the COVID-19 Pandemic on the Clinical Practice Patterns in Atrial Fibrillation", consisted of single-choice, multiple-choice, and open-ended free-text response questions (Supplement S1). Questions 1 to 5 collected the participant's demographic information, including years of practice, subspecialty, hospital grade, and province. Questions 6 and 7 aimed to investigate the severity of the COVID-19 pandemic at the participant's location. Questions 8 to 24 were designed to obtain the participant's perspectives on how the COVID-19 pandemic has impacted the clinical practice patterns of AF and their treatment strategy decisions for AF patients during the pandemic. On the basis of the standard recommendations for treating AF in the latest guidelines [8,9], we explored the participant's AF treatment practices via

various clinical scenarios in questions 11 to 19. Because there is an overlap in the treatment strategies for the first diagnosed AF and other types of AF, we did not design separate questions about the first diagnosed AF. In addition, the difference between long-standing persistent AF and permanent AF mainly lies in the therapeutic attitudes of the patient and physician about the rhythm control strategy, and there is no notable difference in the clinical characteristics of these patient groups. Therefore, we combined these two types of AF when designing the questionnaire in accordance with the point of view of physicians. Clinical decisions for emergencies such as hemodynamic instability induced by AF were excluded from the clinical survey. Some rarely used AF treatments, such as AF surgery, hybrid surgical/catheter ablation procedures, atrioventricular node ablation and pacing, and surgical left atrial appendage exclusion were also not included in the questionnaire. This questionnaire defines the "previous non-pandemic period" as the year 2019 before the COVID-19 pandemic outbreak.

#### *2.3. Statistical Analysis*

All statistical analyses were performed using the SPSS 24.0 software (IBM Corp, Armonk, NY, USA). Continuous measures were described as mean ± standard deviation. Categorical measures were described as counts or as the number (percentage) of participants and compared by a Pearson chi-squared test. Standard *p* < 0.05 was considered statistically significant.

#### **3. Results**

#### *3.1. Characteristics of Survey Respondents*

In this multicenter survey, 300 questionnaires were distributed via WeChat. A total of 213 questionnaires were returned with a response rate of 71.0%. The characteristics of the respondents are summarized in Table 1. Among the respondents, 82.6% were employed in tertiary hospitals, 53.5% reported more than 10 years of clinical cardiology practice, 59.6% had cardiac arrhythmia as a subspecialty, and 40.8% were electrophysiologists who performed catheter ablation for arrhythmias. The locations of all participated cardiologists are summarized in Table S1.

#### *3.2. Severity of COVID-19 Pandemic at the Locations of the Participants*

The participating cardiologists were from 22 provinces in China with different levels of severity of the COVID-19 pandemic. The characteristics of the pandemic are summarized in Table 2. Overall, 20.7% of participants reported more than 1000 new COVID-19 cases per day in their province during the week before responding to the survey, and 16.4% worked in a city where there were more than 1000 new COVID-19 cases per day in the week before the survey.

#### *3.3. Impact of COVID-19 Pandemic on the Clinical Practice Patterns in AF*

#### 3.3.1. Impact of COVID-19 Pandemic on the Numbers of AF Inpatients and Outpatients

The vast majority of respondents stated that there was an obvious reduction in the number of inpatients and outpatients with a chief complaint of AF-related symptoms, although in different proportions. Only sporadic respondents reported an increase in such patients, and a small proportion of respondents reported that there was only a slight increase or decrease (Figure 1). Similar results were seen for the number of AF patients who underwent catheter ablation therapy.

#### 3.3.2. Perception of Participating Cardiologists on the Impact of COVID-19 Pandemic on the Clinical Practice Patterns in AF

In questions 20 to 24, participants were asked: "Regarding the treatment of first diagnosed/paroxysmal/persistent/long-standing persistent/permanent AF, at what level do you think the COVID-19 pandemic has impacted you?". The response statistics are shown in Figure 2. Less than one in five participating cardiologists stated that the pandemic had almost no impact on their treatment of first diagnosed, paroxysmal, persistent, and long-standing persistent AF. At the same time, 22.07% thought that the COVID-19 pandemic had almost no influence on their treatment of permanent AF. By contrast, the vast majority of the other participants believed that the COVID-19 pandemic had varying degrees of impact on their AF treatment practices.

**Table 1.** Characteristics of survey respondents (*n =* 213).

**Table 2.** The severity of COVID-19 pandemic at the locations of the participants (*n =* 213).

**Figure 1.** Impact of the COVID-19 pandemic on the numbers of outpatients and inpatients with AF. (**A**) Impact of the COVID-19 pandemic on the number of outpatients with AF. (**B**) Impact of the COVID-19 pandemic on the number of inpatients with AF. (**C**) Impact of the COVID-19 pandemic on the number of AF patients who underwent catheter ablation therapy.

66

(**A**) Cardiologists' perceptions on how the COVID-19 pandemic impacted the clinical practice patterns for first diagnosed AF. (**B**) Cardiologists' perceptions on how the COVID-19 pandemic impacted the clinical practice patterns for paroxysmal AF. (**C**) Cardiologists' perceptions on how the COVID-19 pandemic impacted the clinical practice patterns for persistent AF. (**D**) Cardiologists' perceptions on how the COVID-19 pandemic impacted the clinical practice patterns for long-standing persistent AF. (**E**) Cardiologists' perceptions on how the COVID-19 pandemic impacted the clinical practice patterns for permanent AF.

#### 3.3.3. Impact of COVID-19 Pandemic on the Clinical Practice Patterns in the Paroxysmal AF

Regarding the therapeutic recommendations for patients with paroxysmal AF (Figure 3A), there were no significant differences in the management of cardiovascular risk factors and concomitant diseases or in the use of pharmacotherapy for stroke prevention, heart rate control, and rhythm control among COVID-19-positive patients, COVID-19-negative patients during the pandemic period, and patients in the non-pandemic period. However, only 13.6%, 7.5%, and 4.2% of respondents chose electrical cardioversion, catheter ablation, and percutaneous left atrial appendage occlusion, respectively, for treating COVID-19-positive patients, which were significantly lower responses than for treating COVID-19-negative patients in the pandemic period and patients in the non-pandemic period (all *p* < 0.05). Intergroup analyses revealed that the percentage of respondents recommending catheter ablation for COVID-19-negative patients with paroxysmal AF during the pandemic period was also significantly lower than in the non-pandemic period (all *p* < 0.05).

3.3.4. Impact of COVID-19 Pandemic on the Clinical Practice Patterns in the Persistent AF

For patients with persistent AF, significantly fewer respondents recommended catheter ablation and percutaneous left atrial appendage occlusion for COVID-19-positive patients than for COVID-19-negative patients during the pandemic and patients in the non-pandemic period (all *p* < 0.05) (Figure 3B). Furthermore, compared with respondents who chose either of the two invasive interventional strategies for COVID-19-negative patients during the non-pandemic period, significantly fewer respondents chose either of the strategies for such patients during the pandemic period (all *p* < 0.05).

3.3.5. Impact of COVID-19 Pandemic on the Clinical Practice Patterns in the Long-Standing Persistent or Permanent AF

Regarding the therapeutic recommendations for long-standing persistent or permanent AF (Figure 3C), only 4.2%, 4.2%, and 7.5% of participants chose electrical cardioversion, catheter ablation, and percutaneous left appendage occlusion, respectively, for treating COVID-19-positive patients during the pandemic period. These percentages were significantly lower than for COVID-19-negative patients during the pandemic period and patients in the non-pandemic period (all *p* < 0.05). There was no significant difference in the recommendation of electrical cardioversion, catheter ablation, and percutaneous left atrial appendage occlusion between COVID-19-negative patients during the pandemic period and non-pandemic period (all *p* > 0.05).

#### 3.3.6. Impact of COVID-19 Pandemic on the Invasive Interventional Therapies Recommended by the Participating Cardiologists for AF Patients

As shown in Figure 4, during the COVID-19 pandemic, the recommendations of invasive interventional therapies (catheter ablation and percutaneous left atrial appendage occlusion) were inversely related to the number of new COVID-19 cases in the cities of participating cardiologists (all *p* < 0.05).

**Figure 3.** Therapeutic strategies recommended by the participating cardiologists. (**A**) Recommended therapeutic strategies for paroxysmal AF. (**B**) Recommended therapeutic strategies for persistent AF. (**C**) Recommended therapeutic strategies for long-standing persistent and permanent AF. #, *p* < 0.05.

**Figure 4.** Invasive interventional therapies recommended by the participating cardiologists for AF patients during the COVID-19 pandemic. (**A**) Recommendation of catheter ablation for AF patients during COVID-19 pandemic. (**B**) Recommendation of left atrial appendage occlusion for AF patients during COVID-19 pandemic.

#### **4. Discussion**

The COVID-19 pandemic has had a severe impact on healthcare systems around the world. In this multicenter physician survey, we found that the number of inpatients and outpatients with a chief complaint of AF-related symptoms and the number of AF patients who received catheter ablation therapy decreased during the pandemic period. The overwhelming majority of participating cardiologists stated that the COVID-19 pandemic had markedly affected the treatment strategies for AF patients to varying degrees. Compared with respondents who chose to use treatments for all types of AF in the period before the COVID-19 pandemic, fewer respondents chose to use invasive interventional therapies such as catheter ablation and percutaneous left atrial appendage occlusion during the pandemic period. Meanwhile, physicians were more likely to recommend pharmacotherapy for AF patients.

AF is the most common cardiac arrhythmia in adults and is associated with an increased risk of ischemic stroke, cognitive impairment, and heart failure, and it can be a considerable burden to the patient, their family, and society [18–20]. This study found a significant decrease in the number of inpatients and outpatients with AF treated at a hospital during the pandemic. The main reason for this phenomenon is that AF is a chronic disease, and these patients were likely worried about the potential risk of contracting COVID-19 during their hospital visit. Except for those with severe symptoms, many patients with AF chose at-home oral medication treatment. Meanwhile, some patients were also limited in traveling between regions during the pandemic, limiting their ability to attend hospital visits. Besides, COVID-19 infections among medical staff would dramatically reduce the number of available staff to provide medical services [21,22]. Although some studies identified an improvement in the physician-patient relationship during the COVID-19 pandemic, preventive strategies such as wearing face masks, face shields, and protective clothing, create barriers to effective physician-patient communication and has led to decline in trust in doctors during this challenging period [23,24]. Under such circumstances, the communication and interaction between doctors and patients are vital to ensure the comprehensive clinical management of AF. Because the COVID-19 pandemic led to a reduction in hospital visits by AF patients, it is conceivable that the ongoing pandemic could be accompanied by increases in AF-related complications and disability. In China, there are some measures to devote medical resources to the prevention and control of the COVID-19 pandemic, such as the widespread use of vaccines, nationwide free tests for COVID-19, continuous reshaping of the health emergency system, quick and effective cooperation in the joint prevention and the control of various departments, etc. [25]. The pandemic has harmed China and the global economy. That will pose a severe challenge to the health resources of countries, thereby increasing the medical burden of patients [26]. AF interventional therapies, such as catheter ablation and percutaneous left atrial appendage occlusion, are regularly carried out in general tertiary hospitals and have a unique value in the comprehensive treatment of AF. Compared with other types of medical treatment, catheter ablation can significantly prevent the recurrent of atrial arrhythmias and reduce the AF burden in any type of AF, as revealed by the recently published CABANA (Catheter Ablation versus Antiarrhythmic Drug Therapy for Atrial Fibrillation) trial [27,28]. In the AF patients enrolled in the CABANA trial who also had clinically diagnosed heart failure, catheter ablation also showed superiority for improvements in survival and quality of life when compared with medical therapy [27]. Previous studies have verified that early rhythm control therapy leads to a lower risk of cardiovascular complications in AF patients [29–31]. Emerging clinical evidence has also indicated that percutaneous left atrial appendage occlusion is a safe and effective therapeutic strategy for cardioembolic stroke prevention in non-valvular AF patients [32–35]. With the development of many cities in China, Shanghai has the highest rate of elderly, and the AF burden in the aging population has become substantial. Based on the data from medical insurance in the Shanghai municipal health commission database, the left atrial appendage occlusion, as an effective alternative option for AF-related stroke prevention, showed a significant increment from 0.16% in 2015 to 1.23% in 2020 [36]. Compared to other uncommon therapeutic strategies (AF surgery, hybrid surgical/catheter ablation procedures, atrioventricular node ablation and pacing, and surgical left atrial appendage exclusion), the proportion of left atrial appendage occlusion increased 7.68 times from 2015 to 2020 in Shanghai [36]. The application of left atrial appendage occlusion in AF patients who meet the indications may vary among different provinces in China. However, the present study found that the COVID-19 pandemic decreased the proportion of cardiologists who recommended catheter ablation and percutaneous left atrial appendage occlusion for AF patients (who were either positive or negative for COVID-19) during the pandemic period compared with the proportion during the non-pandemic period. According to data from the Hellenic Cardiology Society Ablation Registry, the number of ablation procedures conducted in 2019 (before the COVID-19 pandemic) and 2020 (during the COVID-19 pandemic) was reduced from 3182 cases to 2759 cases, and the number of atrial fibrillation

ablation procedures was reduced by 13.8% [37]. The Spanish Catheter Ablation Registry data showed that the number of ablation procedures conducted and the success rate were both affected by the COVID-19 pandemic [38]. The quality of life of patients awaiting AF ablation has also been significantly impaired by the COVID-19 pandemic [17]. Moreover, interventional treatment during the pandemic may involve arranging a dedicated catheter room and specialized medical staff, which is a possible reason why fewer physicians chose interventional therapeutics during the pandemic than in the pre-pandemic period.

Non-invasive therapeutic strategies, such as pharmacotherapy for stroke prevention, heart rate control, rhythm control, and the management of risk factors and comorbidities, are essential cornerstones for improving long-term outcomes in patients with AF [8,9]. Handy A et al. evaluated the use of antithrombotic therapy and COVID-19 outcomes in England's nationwide atrial fibrillation cohort. The authors found that pre-existing antithrombotic therapy was associated with lower odds of COVID-19 death in AF patients during the pandemic [39]. At the peak of COVID-19 lockdown, patients with AF-related symptoms faced various medical problems. An effective antiarrhythmic medication may be used carefully in selected AF outpatients to address these problems [40]. In the present study, there was no significant difference in the recommendations of these non-invasive strategies between the pandemic and non-pandemic periods. Although the proportion of participating physicians who recommended basic non-invasive strategies was not small, the reduction in hospital visits by AF patients during the pandemic had a potentially negative impact on the effectiveness of these treatments. Recently, the concept of Internet hospitals has become more common. Depending on the attributes of such a platform, increasing the communication between doctors and patients may be a promising approach to improve the comprehensive treatment of AF patients during the COVID-19 pandemic. Telemedicine is an important complementary strategy for the management and follow-up of some chronic diseases during the pandemic [41–46]. Previous studies have demonstrated that telemedicine could be of great value for the management of many chronic diseases during the epidemic, especially the long-term management of hypertension, chronic heart failure, and atrial fibrillation in the cardiology department during such a challenging period [41–43].

The current study has several limitations. Firstly, this study is a multicenter clinician survey analysis and all participated cardiologists from 22 provinces in China. Given the severity of the COVID-19 pandemic and the distribution of healthcare resources in different countries or regions, the results of this study may be biased in different regions. Secondly, the treatment of AF is complex and requires individual solutions according to guidelines' recommendations. Thus, the hypothetical clinical scenarios based on the questionnaires may not reflect actual practice management accurately. Besides, the conclusions of this clinician survey still need to be confirmed by further clinical studies. Meanwhile, this survey mainly recruited cardiologists in hospitals that can carry out the common interventional therapeutic strategies for AF. Therefore, the higher proportions of respondents specializing in arrhythmia and working in tertiary hospitals also have potential bias.

#### **5. Conclusions**

In summary, the ongoing COVID-19 pandemic has had a profound impact on the clinical practice patterns of AF. During the pandemic period, the selections of catheter ablation and percutaneous left atrial appendage occlusion decreased significantly, whereas pharmacotherapy was often stated as the preferred option by participating cardiologists.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/ 10.3390/jcm11216469/s1, Supplement S1: Clinician Perspectives on the Impact of the COVID-19 Pandemic on the Clinical Practice Patterns in Atrial Fibrillation; Table S1: Locations of participated cardiologists (*n* = 213).

**Author Contributions:** Conceptualization, F.H. and J.P.; methodology, F.H.; software, F.H. and M.Z.; validation, J.P. and Y.Y.; formal analysis, A.L.; investigation, J.H.; data curation, W.C., J.G., Z.D., E.L., L.S., X.H., X.X., Z.D. and G.H.; writing—original draft preparation, F.H.; writing—review and editing, M.Z. and L.Z.; supervision, J.P.; project administration, F.H. and J.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Institutional Ethics Committee of Renji Hospital Affiliated to Medical College of Shanghai Jiaotong University (No.2022096, 15 March 2022).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data used to support the findings of this study are available from the corresponding author upon reasonable request.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

## *Article* **A Four-Stepwise Electrocardiographic Algorithm for Differentiation of Ventricular Arrhythmias Originated from Left Ventricular Outflow Tract**

**Hong-Wei Tan 1,†, Wei-Dong Gao 2,†, Xin-Hua Wang 3, Zhi-Song Chen 1 and Xue-Bo Liu 1,\***

**Abstract:** Several electrocardiographic algorithms have been proposed to identify the site of origin for the ventricular arrhythmias (VAs) from the left ventricular outflow tract (LVOT) versus right ventricular outflow tract. However, the electrocardiographic criteria for distinguishing VAs originated from the different sites of LVOT is lacking. We aimed to develop a simple and efficient ECG algorithm to differentiate LVOT VAs originated from the aortic root, AMC and LV summit. We analyzed 12-lead ECG characteristics of 68 consecutive patients who underwent successful radiofrequency catheter ablation of symptomatic VAs from LVOT. Patients were divided into RCC (right coronary cusp) group (*n* = 8), the L-RCC (the junction between the LCC and RCC) group (*n* = 21), the LCC (left coronary cusp) group (*n* = 24), the aortomitral continuity (AMC) group (*n* = 9) and the LV summit group (*n* = 6) according to the final ablation sites. Measurements with the highest diagnostic performance were modeled into a 4-stepwise algorithm to discriminate LVOT VAs. The performance of this novel algorithm was prospectively tested in a validation cohort of 43 consecutive patients undergoing LVOT VAs ablation. Based on the accuracy of AUC, a 4-stepwise ECG algorithm was developed. First, the QS duration in aVL > 134 ms was used to distinguish VAs from AMC, LV summit and VAs from aortic root (80% sensitivity and 76% specificity). Second, the R duration in II > 155 ms was used to differentiate VAs from LV summit and VAs from AMC (67% sensitivity and 56% specificity). Third, the ratio of III/II < 0.9 was used to discriminate VAs from RCC and VAs from LCC, L-RCC (82% sensitivity and 63% specificity). Fourth, the QS duration of aVR > 130 ms was used to discern VAs from LCC and VAs from L-RCC (75% sensitivity and 62% specificity). In the prospective evaluation, our 4-stepwise ECG algorithm exhibited a good predictive value. We have developed a novel and simple 4-stepwise ECG algorithm with good predictive value to discriminate the AVs from different sites of LVOT.

**Keywords:** ventricular arrhythmias; catheter ablation; electrocardiogram; algorithm; left ventricular outflow tract

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **1. Introduction**

Idiopathic ventricular arrhythmias (VAs) often originate from the left ventricular outflow tract (LVOT) [1–4], and up to one third of all VAs are thought to arise from the LVOT region [5]. Anatomically, LVOT lies in the center of the heart and includes the aortic root, aortomitral continuity (AMC), the superior basal septum and LV summit [3]. LVOT VAs can be successfully treated by endocardial radiofrequency catheter ablation (RFCA) from the aortic root, AMC or from the LV summit via cardiac venous system [3,4]. The surface electrocardiogram (ECG) is a simple and relatively accurate evaluation tool

**Citation:** Tan, H.-W.; Gao, W.-D.; Wang, X.-H.; Chen, Z.-S.; Liu, X.-B. A Four-Stepwise Electrocardiographic Algorithm for Differentiation of Ventricular Arrhythmias Originated from Left Ventricular Outflow Tract. *J. Clin. Med.* **2022**, *11*, 6398. https:// doi.org/10.3390/jcm11216398

Academic Editors: Giuseppe Boriani and Tong Liu

Received: 26 September 2022 Accepted: 27 October 2022 Published: 28 October 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

for localization of VAs before ablation. The electrocardiographic characteristics of VAs originating from the aortic root, AMC and LV summit have been studied [3–5], and several ECG criteria have been proposed to identify the site of origin for the VAs from the LVOT versus right ventricular outflow tract [6–10]. However, the electrocardiographic criterion for distinguishing VAs originating from the different sites of LVOT is still lacking. The aim of our study was to develop a simple and efficient ECG algorithm to differentiate LVOT VAs that originated from the aortic root, AMC and LV summit.

#### **2. Methods**

#### *2.1. Study Design*

This study was designed in 2 phases: (1) a retrospective analysis of successful LVOT VAs ablation cases in order to develop an ECG algorithm; and (2) a prospective cohort study to verify the accuracy and effectiveness of our ECG algorithm.

#### *2.2. Study Populations*

Consecutive patients with symptomatic LVOT VAs who were successfully ablated from January 2019 to December 2020 were included in this study. LVOT VAs were defined as VAs with inferior axis, a R/S transition in lead V3 or earlier and a site of the earliest ventricular activation in the aortic root, AMC and LV summit [11]. Physical examination, 12-lead ECG, 24-h Holter monitor, and echocardiography demonstrated no evidence of structural heart disease in any patients. Baseline characteristics, including age, gender, nature of the clinical arrhythmia, and 12-lead ECG during the VAs, were recorded. All antiarrhythmic drugs were discontinued for at least five-lives before the study. The Institutional Review Board approved the study protocol, and informed consent for the procedure was obtained from all the patients.

#### *2.3. Electrophysiological Study*

All patients underwent electrophysiological examination in the postabsorptive, nonsedated state. A catheter was placed in the right ventricle, or within the distal coronary sinus, via femoral veins if necessary. Surface ECG leads were applied in the standard manner. ECG and intracardiac electrograms were recorded simultaneously by digital multichannel system (EPMed, St Jude Medical or Pruca Cardiolab, GE Healthcare), filtered at 30 to 500 Hz for bipolar electrograms and at 0.05 to 400 Hz for unipolar electrograms. If VAs were not inducible at baseline, intravenous isoproterenol infusion (2–5 ug/min) was administrated to induce the clinical VAs. If clinical arrhythmia failed to occur spontaneously, programmed stimulation was performed. The standard protocol consisted of ventricular stimulation at 2 basic drive cycle length with ≤2 extrastimuli to a minimum coupling interval of 230 ms as described previously [12]. Mapping and pacing were performed using a 7.5Fr, 3.5-mm-tip irrigated ablation catheter (Navistar ThermoCool; Biosense Webster, Diamond Bar, CA, USA) introduced from the right femoral vein for sites in the right ventricular outflow tract and LV summit or right femoral artery for the endocardial LVOT and AMC. Intravenous heparin was administered to maintain an activated clot time > 250 s when mapping at the aortic root and left ventricle.

#### *2.4. Mapping and Radiofrequency Catheter Ablation*

The procedure was performed under the guidance of fluoroscopy and the 3-dimensional electroanatomic mapping system (CARTO 3, Biosense Webster, Diamond Bar, CA). In patients with frequent premature ventricular contractions (PVC), activation mapping was performed in the right ventricular outflow tract, the aortic root, AMC and great cardiac veins. In some cases, the area underneath aortic sinus cusps was reached by an antegrade trans-septal approach as described previously [12]. When PVC was infrequent, pace mapping was performed during sinus rhythm at a pacing cycle length of 500 ms at an output just greater than a diastolic threshold, as previously described [8,13]. The ablation target was defined as the earliest bipolar electrogram preceding the QRS onset during the PVC

and/or an excellent pace map (>11/12 leads) [8]. When the earliest ventricular activation at the intended local site preceded QRS onset by >20 ms [14] and/or excellent pace mapping was achieved, RFCA was performed in temperature-controlled mode with a maximum power of 35 W, temperature limit of 43 ◦C, and flush rate of 20 mL/min in aortic root, AMC and with a maximum power of 30 W, temperature limit of 43 ◦C, and flush rate of 30 mL/min in great cardiac veins. If the impedance was too high (more than 200 Ω, even more), we usually flush the catheter first and wait for the impedance to decrease to less than 180 Ω, then we begin ablation. If the earliest ventricular activation site was identified in RVOT or ablation was performed in RVOT, the patients were excluded from the study. If the VAs require multiple sites (≥2) ablation, the cases were also excluded.

Coronary angiography was performed to assess the course of left and right coronary artery and catheter ablation from the aortic root/coronary cusp; this was only performed if the distance from the electrode tip to the ostium of each left and right coronary ostium was >8 mm as detected by simultaneous coronary angiography [4]. Radiofrequency energy application from the great cardiac veins was performed at sites where the distance to the adjacent coronary artery was >5 mm, as determined by simultaneous coronary angiography [4]. During radiofrequency energy delivery, if a decreased frequency/ elimination of VAs occurred within the initial 15 s, the radiofrequency delivery was continued for 30 to 60 s. Otherwise, the energy delivery was terminated, and the ventricular arrhythmias were re-mapped. Successful ablation was defined as the absence of spontaneous or inducible VAs with isoproterenol infusion (2–5 ug/min) and burst pacing from the RV or LV 30 min after the final radiofrequency application.

#### *2.5. ECG Analysis*

The surface 12-lead ECG were recorded during sinus rhythm and during the VAs at a sweep speed of 100 mm/s for all patients. The electrodes of leads V1 and V2 were placed at the fourth intercostal space with careful attention to minimize the effect of incorrect electrode placement on the QRS morphology [15].The following parameters were measured during clinical VAs: (1) total QRS duration; (2) R wave duration and amplitude of inferior leads (II, III, aVF) and the R wave amplitude ratio of lead III/II; (3) QS wave duration and amplitude in leads aVL and aVR and the QS wave amplitude ratio of aVL/aVR; (4) R and S wave amplitude in leads V1-V6; and (5) the site of R wave transition in the precordial leads. The T-P segment was considered the isoelectric baseline for measurement of R wave and S wave amplitudes. The total QRS duration was measured from the site of earliest initial deflection from the isoelectric line in any lead to the time of latest activation in any lead. The R-wave duration was measured from the site of the earliest initial deflection from the isoelectric line to the time at which the R-wave intersected the isoelectric line [16]. For all cases, QRS measurements were performed before mapping and ablation. The ECG analysis was performed by two experienced investigators blinded to the site of the origin with electronic calipers.

#### *2.6. Procedure Success and Follow-Up*

Acute success was defined as absence of spontaneous or provoked clinical VAs at 30 min after the last radiofrequency energy application. Follow-up was performed by referring physicians or outpatient clinics.

#### *2.7. Statistical Analysis*

Continuous variables are expressed as mean ± SD. Analysis of variance (ANOVA) followed by the Tukey test was used to compare the difference among groups. Categorical variables were compared by a chi-squared test analysis or Fisher's exact test. For those ECG measurements that were significantly different between the anatomical sites, a receiver operating characteristic (ROC) curve was performed to determine cut-offs with optimal performance. These were then subjected to stepwise mechanistic analysis in varying order and combination to derive an algorithm with optimal statistical accuracy and the sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for predicting the origins of VAs were assessed using the standard formula. All statistical analyses were performed using SPSS 15.0 software (SPSS Inc., Chicago, IL, USA), and the differences were considered significant at *p* < 0.05.

#### **3. Results**

#### *3.1. Patient Characteristics*

The study population consisted of 68 patients (28 men, mean age 54 ± 17 years [range, 17–85]) with symptomatic idiopathic sustained ventricular tachycardia (VT; *n* = 2, nonsustained VT (*n* = 5), or premature ventricular contractions (PVCs; *n* = 61). The VAs origin was identified in the LVOT by 3-dimensional mapping and a successful catheter ablation. The patients were further divided into five groups according to the final ablation site which includes the RCC (right coronary cusp) group (*n*= 8), the L-RCC (the junction between the LCC and RCC) group (*n* = 21), the LCC (left coronary cusp) group (*n* = 24), the AMC group (*n* = 9) and the LV summit group (*n* = 6). No structural heart disease was found on physical examination, 12-lead ECG or echocardiography. All patients were refractory to ≥1 antiarrhythmic drug before ablation. The demographic and clinical data are shown in Table 1. There was no significant difference in terms of age, gender, diameter of LV, burdens of VAs and comorbidity. Patients in LV summit groups showed significant longer VAs history than patients in RCC and L-RCC groups.

**Table 1.** Patients and clinical characteristics.

Values are presented as mean ± SD or as n (%). BMI, body mass index; LVd, left ventricular diameter; LVEF, left ventricular ejection fraction; PVC, premature ventricular contraction; VT, ventricular tachycardia. \* *p* < 0.05 compared with RCC group; # *p* < 0.05 compared with L-RCC group.

#### *3.2. Mapping and Ablation*

All patients underwent electrophysiological study and 3-dimensional mapping. The successful ablation site was located in the RCC in 8 patients, L-RCC in 21, LCC in 24, AMC in 9 and LV summit in 6 patients. There were no significant differences in local ventricular activation time relative to QRS onset at the successful ablation sites, or duration of radiofrequency application among groups. Compared to other groups, all patients in the LV summit group demonstrated larger A wave at the ablation site.

#### *3.3. ECG Analysis*

All patients showed R morphology in inferior leads and QS morphology in aVR and aVL. As for the precordial leads, all the patients demonstrated a R/S transition in lead V3 or earlier. Patients in AMC and LV summit groups demonstrated Rs morphology in lead V1 while patients with VAs from aortic root showed rs or rS morphology in lead V1.

The results of the electrocardiographic parameters of the VAs are showed in Tables 2 and 3 and Figure 1. The total QRS duration was significantly increased in the LV summit group than in other groups (*p* < 0.05 or *p* < 0.01) and was significantly increased in the LV summit group than in the AMC group (*p* < 0.05). The R wave duration in lead II, III and aVF was significantly increased in the LV summit group than in RCC, L-RCC, and LCC groups (all *p* < 0.01), and was significantly increased in the AMC group than in the RCC and L-RCC groups (all *p* < 0.01). The R wave duration in lead II showed significant difference between LV summit group and AMC group (*p* < 0.05). The QS duration in lead aVL and aVR was significantly increased in the LV summit group than in VAs from aortic root (all *p* < 0.01), and was significantly increased in the AMC group than in VAs from RCC and L-RCC groups (all *p* < 0.01). The QS duration in lead aVL was significantly increased in the AMC group compared to VAs from LCC (*p* < 0.01).

**Characteristic RCC Group (***n* **= 8) L-RCC Group (***n* **= 21) LCC Group (***n* **= 24) AMC Group (***n* **= 9) LV Summit Group (***n* **= 6)** Total QRS duration (ms) 150 ± 28 142 ± 15 147 ± 13 158 ± 13 # 178 ± 26 \*#&\$ R wave duration (ms) Lead I 100 ± 35 88 ± 33 83 ± 35 73 ± 26 103 ± 41 Lead II 132 ± 13 134 ± 16 142 ± 14 152 ± 11 \*# 171 ± 30 \*#&\$ Lead III 131 ± 11 129 ± 19 139 ± 16 152 ± 11 \*# 169 ± 34 \*#& Lead aVF 130 ± 10 133 ± 17 141 ± 16 151 ± 11 \*# 168 ± 30 \*#& QS wave duration (ms) Lead I (S wave) 35 ± 7 59 ± 23 64 ± 27 81 ± 29 71 ± 46 Lead aVL 113 ± 19 124 ± 18 130 ± 17 \* 147 ± 13 \*#& 153 ± 24 \*#& Lead aVR 125 ± 14 128 ± 14 139 ± 15 \*# 146 ± 14 \*# 155 ± 15 \*#& R wave amplitude (mV) Lead I 0.46 ± 0.27 0.43 ± 0.30 0.32 ± 0.22 0,20 ± 0.11 0.29 ± 0.21 Lead II 1.75 ± 0.33 2.07 ± 0.81 2.11 ± 0.57 1.71 ± 0.28 1.84 ± 0.53 Lead III 1.40 ± 0.45 1.95 ± 0.86 2.18 ± 0.69 \* 1.89 ± 0.39 1.93 ± 0.55 Lead aVF 1.60 ± 0.42 2.05 ± 0.89 2.14 ± 0.59 \* 1.79 ± 0.34 1.86 ± 0.53 The ratio of III/II 0.78 ± 0.15 0.94 ± 0.16\* 1.03 ± 0.13 \* 1.10 ± 0.16 \*# 1.06 ± 0.10 \* QS wave amplitude (mV) Lead I (S wave) 0.07 ± 0.03 0.22 ± 0.13 0.31 ± 0.17 0.39 ± 0.11 0.24 ± 0.16 Lead aVL 0.58 ± 0.29 1.14 ± 0.53 \* 1.24 ± 0.35 \* 1.12 ± 0.21 \* 1.12 ± 0.30 \* Lead aVR 1.02 ± 0.18 1.09 ± 0.42 1.09 ± 0.21 0.79 ± 0.15 #& 0.96 ± 0.25 The ratio of aVL/aVR 0.58 ± 0.28 1.12 ± 0.36 \* 1.20 ± 0.36 \* 1.45 ± 0.38 \*# 1.18 ± 0.18 \*

**Table 2.** Comparison of ECG characteristics of limb leads.

Values are presented as mean ± SD or as n (%). \* *p* < 0.01 compared with RCC group; # *p* < 0.01 compared with L-RCC group; & *p* < 0.01 compared with LCC group; \$ *p* < 0.05 compared with AMC group.

**Table 3.** Comparison of ECG characteristics of precordial leads.

Values are presented as mean ± SD or as n (%). \* *p* < 0.01 compared with RCC group; # *p* < 0.01 compared with L-RCCgroup; & *p* < 0.01 compared with LCC group; \$ *p* < 0.05 compared with AMC group.

The R wave amplitude in Lead III and aVF was significantly higher in VAs localized in LCC compared to VAs originated from RCC (*p* < 0.01). Compared to other groups, the QS wave amplitude in lead aVL was significantly decreased in the RCC group (all *p* < 0.01). The QS wave amplitude in lead aVR was significantly decreased in the AMC group than in the L-RCC and LCC groups (all *p* < 0.01).

**Figure 1.** Examples of the electrocardiographic morphology of ventricular arrhythmias originating from different sites of LVOT. aVLd, The QS duration in aVL; IId, The R duration in II; III/II, The ratio of III/II; aVRd, The QS duration in aVR.

The R wave amplitude ratio of lead III/II was significantly decreased in the RCC group compared to VAs from other groups (all *p* < 0.01). The R wave amplitude ratio of lead III/II was significantly decreased in the L-RCC group than in the AMC group (*p* < 0.01). The QS wave amplitude ratio of aVL/aVR was significantly decreased in the RCC group compared to VAs from other groups (all *p* < 0.01). The QS wave amplitude ratio of aVL/aVR was significantly decreased in the L-RCC group than in the AMC group (*p* < 0.01).

In the precordial leads, the R wave duration and amplitude in Lead V1 and V2 demonstrated a progressive increment with significant difference between VAs from AMC, LV summit and VAs from aortic root, while the S wave duration and amplitude showed a tendency to decrease from aortic root to AMC and LV summit groups.

#### *3.4. Develop a Stepwise ECG Algorithm to Differentiate LVOT VAs*

The ability of ECG parameters to distinguish LVOT VAs was assessed by using an ROC curve. The area under the curve for the ROC curve of the QS duration in aVL was 0.846 [95% confidential interval 0.735–0.956]. The QS duration in aVL >134 ms had 80% sensitivity and 76% specificity for differentiating VAs from AMC, LV summit and VAs from aortic root. The area under the curve for the ROC curve of the R duration in II was 0.667 [95% confidential interval 0.369–0.965]. The R duration in II > 155 ms had 67% sensitivity and 56% specificity for differentiating VAs from AMC and VAs from LV summit. The area under the curve for the ROC curve of the ratio of III/II was 0.833 [95% confidential interval 0.711–0.955]. The ratio of III/II < 0.9 had 82% sensitivity and 63% specificity for differentiating VAs from RCC and VAs from L-RCC, LCC. The area under the curve for the ROC curve of the QS duration in aVR was 0.724 [95% confidential interval 0.573–0.876]. The QS duration in aVR > 130 ms had 75% sensitivity and 62% specificity for differentiating VAs from LCC and VAs from L-RCC (Figure 2).

**Figure 2.** Receiver operating characteristic (ROC) curve of the QS duration in aVL (**A**), the R duration in II (**B**), the ratio of III/II (**C**) and the QS duration in aVR (**D**) to distinguish LVOT VAs.

According to the accuracy of AUC, a stepwise ECG algorithm was developed (Figure 3). First, QS duration in aVL > 134 ms was used to distinguish VAs from AMC, LV summit and VAs from aortic root. Second, R duration in II > 155 ms was used to differentiate VAs from LV summit and VAs from AMC. Third, the ratio of III/II < 0.9 was used to discriminate VAs from RCC and VAs from LCC, L-RCC. Fourth, the QS duration of aVR > 130 ms was used to discern VAs from LCC and VAs from L-RCC.

**Figure 3.** Flowchart of 4-stepwise electrocardiographic algorithm.

#### *3.5. Validation of Four-Stepwise ECG Algorithm in the Prospective Study*

A total of 43 consecutive patients (22 males and 21 females) with a left branch block pattern and inferior axis QRS morphology, and with precordial transition before lead V3 that indicate VAs from LVOT, were selected to verify the effectiveness of our four-stepwise algorithms. All these patients underwent successful RFCA for VAs between January 2021 and December 2021 at the sites of LVOT. The successful ablation site was located in the RCC in 6 patients, L-RCC in 8, LCC in 16, AMC in 5 and LV summit in 8 patients. The QS duration in aVL > 134 ms exhibited 100% sensitivity, 86.7% specificity, 76.5% positive predictive value and 100% negative predictive value for differentiating VAs from AMC, LV summit and VAs from aortic root. The R duration in II > 155 ms had 75.0% sensitivity, 80.0% specificity, 85.7% positive predictive value and 66.7% negative predictive value for differentiating VAs from AMC and VAs from LV summit. The ratio of III/II < 0.9 showed 100% sensitivity, 95.0% specificity, 85.7% positive predictive value and 100% negative predictive value for distinguishing VAs from RCC and VAs from LCC, L-RCC. The QS duration in aVR > 130 ms showed 66.7% sensitivity, 62.5% specificity, 72.7% positive predictive value and 55.6% negative predictive value for differentiating VAs from LCC and VAs from L-RCC (Table 4, Figure 4).

**Table 4.** The accuracy of ECG algorithm for predicting the origins of VAs from LVOT in prospective cohort.

**Figure 4.** Process of validation in the prospective cohort patients.

#### **4. Discussion**

This study explored the surface ECG characteristics of VAs originating from LVOT and we present a simple four-stepwise ECG algorithm to differentiate VAs from different sites of LVOT. We have demonstrated that in patients with VAs when ECG strongly favors an LVOT origin, our four-stepwise ECG algorithm can help localize the likely sites of origin during planning for VAs ablation. First, AMC and LV summit VAs can be differentiated from aortic root VAs by measuring the QS duration in aVL. Then, differentiation between AMC and LV summit VAs can be made by the R duration in II. Third, the ratio of III/II was used to distinguish VAs from RCC and VAs from LCC, L-RCC. Last, LCC VAs could be differentiated from L-RCC VAs by using the QS duration in aVR. For patients referred for catheter ablation of LVOT VAs, this simple ECG measurement might be performed to help plan an ablation strategy and to enhance patient counseling with regard to potential outcome, procedure risk associated with mapping and ablation.

Anatomically, the aortic root occupies a central location within the heart, and the RVOT is located anteriorly and leftward to the aortic root, with the AMC and LV summit anterosuperior to the aortic root. The AMC and the LV summit face each other at the basal portion of the LV muscle between them [5,12]. The aortic root consists of three sinuses of Valsalva. The RCC and LCC are connected with the ventricular musculature at their bases, and the NCC is located between the right and the left atria, immediately anterior to the interatrial septum [13,14]. It has been proven that ventricular myocardial extensions into the aorta beyond ventriculo-arterial junction and these myocardial extensions are the target of ablation [17]. AMC consists of the aortic annulus and the anterior side around the mitral annulus. Although this is a fibrous structure, it is known to be an arrhythmogenic site for ventricular tachyarrhythmias in both normal and diseased heart [18,19]. The LV summit constitutes the superior-most aspect of the LV ostium. It is defined as a triangular region, the apex of which is formed by the bifurcation of the left anterior descending and left circumflex arteries, with its base formed by the arc between the first septal perforator of the left anterior descending artery and the left circumflex artery [5]. The VAs originating from the LV summit can be ablated through the great cardiac vein [5,20].

The ECG characteristics of LVOT VAs are very similar and may even overlap because they all originate from adjacent cardiac structures [21]. It is important to differentiate the ECG characteristics of LVOT VAs in order to safely perform radiofrequency catheter ablation. Ouyang et al. [22] found that a great R wave duration and R/S wave amplitude ratio in lead V1 or V2 reliably predicted an aortic sinus cusp compared with right ventricular outflow tract origin. Lin et al. [23] found that the LCC VAs typically produce a precordial transition by V2, whereas RCC VAs demonstrated a precordial transition by lead V3 and precordial transition is a simple criterion for distinguishing VAs from LCC to RCC. Chen et al. [18] found that AMC VAs showed an early R/S transition pattern in the precordial leads, and VAs from anterior AMC demonstrated equal R and S amplitudes in V2, rS in V1, and R in V3, while VAs from the middle part of the AMC demonstrated a special ('rebound') transition pattern, with which equal R and S amplitudes occurred in V2, and high R waves in V1 and V3. However, one shortcoming of the R wave transition in the precordial leads is the QRS morphology that could alter markedly with an incorrect electrode placement [15]. Komatsu et al. [24] found that The R-wave amplitude ratio in lead III/II, Q-wave amplitude ratio in leads aVL/aVR, and ratio of R wave/S wave in lead V1 were higher in LV summit VAs than in the RVOT and the RCC VAs, the ECG characteristics of LV summit VAs were similar to those in LCC VAs, except for the presence of an initial Q wave in lead I, an initial R wave in lead V1.

In the present study, we have demonstrated that the QS duration in aVL was significantly increased in VAs from AMC and LV summit than in VAs from aortic root, and the QS duration in aVL > 134 ms could be used to distinguish VAs from AMC, LV summit and VAs from aortic root. The R duration in II increased more in the LV summit group than in the AMC group. Anatomically, the aortic root, AMC and LV summit area lie in a continuum from the medial to the lateral, and the QRS duration of VAs from aortic root, AMC and LV summit would be increased gradually as demonstrated in our study because of synchronous rather than sequential ventricular activation [11]. For differentiating VAs from aortic root, we have found that the ratio of III/II was significantly decreased in VAs from RCC compared to VAs from L-RCC and LCC. The LCC typically sits slightly superior to the RCC. As a result, the VAs from LCC have more of an inferior axis relative to the VAs from RCC [23]. We also found that the QS duration of aVR increased in VAs from LCC than in VAs from L-RCC, and the QS duration of aVR > 130 ms can be used to distinguishing VAs from these two sites.

To the best of our knowledge, this study is the first to investigate the surface ECG characteristics of VAs from different sites of LVOT. We found that patients with VAs from different sites of LVOT demonstrated distinct ECG characteristics, and we also presented a simple four-stepwise ECG algorithm with satisfactory sensitivity and specificity to distinguish VAs from different sites of LVOT. The utility of this ECG algorithm to predict the precise origin of LVOT VAs was validated in a prospective cohort, and the algorithm also exhibited a good predictive value in discriminating LVOT VAs. The last step of the algorithm showed relatively low sensitivity and specificity; this would be explained as the population of our study was small, LCC and L-RCC are closely related, and it is difficult for ECG to distinguish VAs from these areas. Our algorithm uses limb leads, which are less influenced by lead position. Moreover, based upon the duration and amplitude of the QRS wave, the algorithm is simple and practicable in routine clinical practice to help plan an ablation strategy and to enhance patient counseling.

#### *Study Limitations*

There were several limitations in the present study. First, the study population was relatively small, which might result in statistical bias, and the results of our study should be validated further in larger populations. Second, the origins of LOVT VAs were defined by the successful ablation sites, which might not be the real origin but anatomically in close proximity to it. Furthermore, the patients requiring multiple sites ablation were excluded from this study, and these may lead to subjective bias. Third, cases with structural heart disease that affect cardiac anatomy were excluded, and the stepwise ECG algorithm would not be suitable for patients with structural heart disease. Fourth, intracardiac echocardiography was not used, only coronary angiography and 3-dimensional electroanatomic mapping were used to determine the final ablation sites; sometimes it is difficult for us to distinguish LCC-RCC VAs from LCC VAs. Finally, the long-term success was not confirmed in this study, as there might be late recurrence cases in these subjects.

#### **5. Conclusions**

We have developed a simple four-stepwise ECG algorithm to discriminate the AVs from different sites of LVOT, and our algorithm demonstrated good predictive value in the prospective cohort. Further studies are warranted to verify our results.

**Author Contributions:** Conceptualization, H.-W.T.; methodology, H.-W.T. and W.-D.G.; formal analysis, W.-D.G. and Z.-S.C.; data curation, H.-W.T., W.-D.G., X.-H.W., Z.-S.C. and X.-B.L.; writing—original draft preparation, H.-W.T. and X.-H.W.; writing—review and editing, X.-B.L.; supervision, X.-B.L.; project administration, X.-B.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** The study was conducted according to the guidelines of the Declaration of Helsinki, and approved by the Ethics Committee of Tongji Hospital, Tongji University School of Medicine, Shanghai, China (No. 2019-157), 19 April 2019.

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The data underlying this article will be shared upon reasonable request to the corresponding author.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

## *Article* **Angiographic Characteristics of the Vein of Marshall in Patients with and without Atrial Fibrillation**

**Lei Ding, Hongda Zhang, Fengyuan Yu, Lijie Mi, Wei Hua, Shu Zhang, Yan Yao and Min Tang \***

Department of Cardiology, State Key Laboratory of Cardiovascular Disease, Cardiovascular Institute, Fuwai Hospital, National Center for Cardiovascular Diseases, Chinese Academy of Medical Sciences, and Peking Union Medical College, Beijing 100037, China

**\*** Correspondence<EMAIL_ADDRESS>
**Abstract:** Background: Ethanol infusion into the vein of Marshall (Et-VOM) is a novel therapeutic treatment for atrial fibrillation (AF). However, few studies have focused on the difference between AF and non-AF patients (presented other types of arrhythmias) regarding the characteristics of the vein of Marshall (VOM). Objective: This study sought to investigate the incidence, morphology, and angiographic characteristics of the VOM. Methods: Coronary sinus (CS) angiography was performed in all patients. The baseline, angiographic characteristics and measurements of VOM dimensions were compared between the AF and non-AF group. Results: CS angiography was performed in 290 patients. The VOM detection rate was higher in the AF group than in the non-AF group (91.8% vs. 84.1%, *p* = 0.044). In the right anterior oblique (RAO) projection, AF patients had significant larger VOM ostium, CS ostium, and CS diameter at VOM ostium than non-AF patients (1.9 ± 0.9 vs. 1.7 ± 0.7 mm, *p* = 0.015; 12.8 ± 4.1 vs. 11.4 ± 3.7 mm, *p* = 0.016; 9.1 ± 3.1 vs. 8.2 ± 2.9 mm, *p* = 0.028, respectively). There was a slight linear correlation between the VOM ostium and the CS ostium diameter as well as left atrial volume (LAV). Conclusion: AF patients seem to have a higher incidence of the VOM, larger VOM ostium, CS ostium, and CS lumen in RAO view. Meanwhile, the VOM ostium may correlate with the CS ostium and LAV.

**Keywords:** atrial fibrillation (AF); vein of Marshall (VOM); ethanol infusion; coronary sinus (CS); coronary sinus ostium (CSo)

#### **1. Introduction**

Radiofrequency catheter ablation (RFCA) has been a well-established treatment for atrial fibrillation (AF) [1–3]. Pulmonary veins (PVs) are the most common ectopic triggers for initiating AF, and the treatment strategy mainly consists of PV isolation (PVI). However, only PVI are inadequate when dealing with persistent AF. Many patients suffer recurrent AF and atrial tachycardia which need a redo procedure.

The vein of Marshall (VOM) is an embryological remnant of the left superior vena cava and has been recognized as an important factor for AF initiation and maintenance [4,5]. In addition, the VOM is an epicardial substrate for maintaining perimitral atrial tachycardia [6]. Previous studies have reported the efficacy and safety of ethanol infusion in the VOM [7–10]. Chemical ablation by ethanol infusion could eliminate non-PV AF triggers and facilitate a bidirectional block of the mitral isthmus [11,12]. However, there are no detailed reports in a large cohort of patients with and without AF on the characteristics of the VOM. Meanwhile, the influence of VOM morphology on Et-VOM is also absent.

This study aimed to investigate the incidence, morphology, and angiographic characteristics of the VOM in patients with and without AF by angiography.

**Citation:** Ding, L.; Zhang, H.; Yu, F.; Mi, L.; Hua, W.; Zhang, S.; Yao, Y.; Tang, M. Angiographic Characteristics of the Vein of Marshall in Patients with and without Atrial Fibrillation. *J. Clin. Med.* **2022**, *11*, 5384. https://doi.org/ 10.3390/jcm11185384

Academic Editor: Tong Liu

Received: 14 August 2022 Accepted: 6 September 2022 Published: 14 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

#### **2. Materials and Methods**

#### *2.1. Population*

This was a prospective, cohort study enrolling all patients with tachyarrhythmias who underwent RFCA in Fuwai Hospital between November 2021 and April 2022. No specific exclusion criteria were used. Clinical data, echocardiographic, and imaging data were documented in the study. All patients provided informed consent prior to the procedure. The study protocols were approved by the Ethics Committee of Fuwai Hospital, Chinese Academy of Medical Sciences and were in accordance with the Declaration of Helsinki (No. 2022-1810). Antiarrhythmic drugs were discontinued for at least five half-life periods prior to the procedure.

#### *2.2. Electrophysiology Study and Catheter Ablation*

All catheters were inserted percutaneously by the Seldinger technique and were advanced into position under fluoroscopic guidance. A 6F decapolar steerable catheter (Triguy, APT Medical, CHN) was inserted into the coronary sinus (CS) through the left femoral vein. Two quadripolar catheters (6F, Triguy, APT Medical, CHN) were advanced into the His bundle position and the right ventricle in patients with supraventricular tachycardia (SVT). The surface electrocardiogram and intracardiac electrograms were continuously monitored and stored in a recording system (C. R. Bard, Inc., Lowell, MA, USA). Left atrial access was attempted by transseptal puncture when needed, and heparin was given. The mapping catheter was advanced via a SL1 long sheath. Each patient underwent the standard electrophysiology study, including programmed stimulation and diagnostic pacing maneuvers [13]. Isoproterenol was administered for patients who could not induce tachycardia by standard procedures. Radiofrequency (RF) energy was delivered from a generator (Stockert, Freiburg, Germany). The RF power setting followed the standards of the different procedures, ranging from 25 to 45 W.

AF ablation mainly consisted of antral PVI and was performed under sedation using midazolam and fentanyl. For persistent AF patients and paroxysmal AF patients who were in AF rhythm before ablation, VOM angiography and ethanol infusion were performed. After ethanol infusion, mitral isthmus was ablated to achieve a bidirectional conduction block. The end points of the procedure were as follows: (1) atrioventricular nodal reentrant tachycardia (AVNRT)—either a slow pathway blocked or a single atrial echo beat at baseline and during isoproterenol infusion without inducing tachycardia; (2) atrioventricular reentrant tachycardia (AVRT)—appearance of decremental antegrade and retrograde atrioventricular conduction and could not induce tachycardia; (3) atrial flutter (AFL)—a bidirectional conduction block confirmed by differential pacing; (4) AF—absence of ostial PV potentials on a circumferential mapping catheter and no atrial capture from multiple pacing sites within the PV ostium. End points had to be fulfilled after a waiting period of 20 min after the last ablation. Additionally, for patients diagnosed with paroxysmal AF, 40 mg of adenosine triphosphate (ATP) and isoproterenol were given to verify the block of PVs and induce AF.

#### *2.3. VOM Angiography and Ethanol Infusion*

After pulmonary vein isolation, the CS was canulated with a SL1 long sheath (8.5F, St. Jude Medical, Inc., St Paul, MN, USA) or a steerable long sheath (8.5-F, Agilis NxT; Abbott) inserted from the right femoral vein. A guiding catheter (6-F Judkins Right [JR] 4; Medtronic, Minneapolis, MN, USA) was proximally positioned inside the CS lumen, and contrast was injected to perform CS angiography. Details of stepwise angiography to identify the VOM were shown in Figure 1. First, the CS angiography in the right anterior oblique (RAO) 30◦ was used. The proximal portion of the valve of Vieussens was targeted and the JR 4 guiding catheter was rotated posteriorly and superiorly to find the ostium of the VOM [14]. In addition, at each location, a small amount of contrast was injected through the guiding catheter to confirm the VOM. Second, if the operator found the suspected VOM, the left anterior oblique (LAO) 30◦ was performed to identify. However, if there was

no suspected VOM, the LAO 30◦ or LAO 30◦ with cranial 30◦ was used to find the VOM. For patients in non-AF group, the VOM angiography was conducted during the waiting period of 20 min.

**Figure 1.** Flowchart of CS angiography, VOM angiography, and ethanol infusion procedure. AF = atrial fibrillation; AT = atrial tachycardia; AVNRT = atrioventricular nodal reentrant tachycardia; AVRT = atrioventricular reentrant tachycardia; CS = coronary sinus; LAO = left anterior oblique; LSPV = left superior pulmonary vein; RAO = right anterior oblique; PAF = paroxysmal atrial fibrillation; PerAF = persistent atrial fibrillation; PVC = premature ventricular contraction; VOM = vein of Marshall.

After identifying the VOM, an angioplasty guidewire (Sion Blue 0.014 inch, Asahi) was advanced into the lumen of the VOM with an over-the-wire balloon preload at the distal portion. An appropriately sized balloon (1.5–2 mm diameter and 8–15 mm length; Boston Scientific, USA) was used depending on the size of the VOM. Subsequently, the balloon was inflated, starting at 1–2 atm, until the operator felt some resistance on the inflator with a maximum of 8–10 atm, and the guidewire was removed. After confirming balloon occlusion, 2 mL of ethanol (95%) was slowly administered over one minute, and the selective angiogram of the VOM was repeated to confirm the myocardial lesion created by ethanol [15]. Following every injection, the balloon was deflated and retracted 1 cm towards the proximal VOM; in the same way, another injection was performed with 2 mL of ethanol. The balloon was retracted until it reached the VOM ostium and a total of 10–12 mL of ethanol was used as a maximum dose.

#### *2.4. Measurements and Definitions*

Measurements of the VOM were performed in the RAO 30◦ and LAO 30◦ or LAO 30◦ with cranial 30◦ (Figure 2). The diameters of the CS ostium (CSo), the VOM ostium, and CS lumen at the VOM ostium were measured in all views. In addition, in the LAO 30◦ or LAO 30◦ with cranial 30◦ (Figure 2A), the distance between the VOM ostium and the CSo, and the angle between the VOM lumen and proximal CS lumen, were measured. Subsequently, in the RAO 30◦ (Figure 2B), operators measured the angle between the VOM lumen and distal CS lumen. According to the number of branches at the VOM ostium, we classified all VOM into two categories (Figure 3). Type I VOM was defined as only one branch and Type II VOM was defined as more than one branch within 1 mm around the VOM ostium.

**Figure 2.** Measurements of the VOM in the LAO/LAO cranial (**A**) and RAO (**B**) views by CS angiography. Segment A and E = diameter of VOM; segment B and F = diameter of the CS at VOM level; segment C and G = diameter of CSo; segment D = distance between VOM ostium and CSo; angle α = angle between VOM and proximal CS; angle β = angle between VOM and distal CS. CS = coronary sinus; CSo = coronary sinus ostium; LAO = left anterior oblique; LSPV = left superior pulmonary vein; MCV = middle cardiac vein; PLV = posterior lateral vein; RAO = right anterior oblique; VOM = vein of Marshall.

#### *2.5. Statistical Analysis*

Statistical analysis and graphing were performed by SPSS IBM 22 (IBM Co., Armonk, NY, USA) and GraphPad Prism 8.0 (GraphPad Software Inc., La Jolla, CA, USA). Continuous data are presented as means ± standard deviation (SD) or the median and interquartile range, depending on the normality of the distribution. Categorical variables are described as frequency counts and percentages. For continuous data, either the student *t*-test or Mann-Whiney *U*-test was carried out for statistical comparisons. For comparisons of categorical data, the chi-squared test was performed. A *p* value less than 0.05 indicated statistical significance.

**Figure 3.** Morphologic classification of the VOM. CS = coronary sinus; CSo = coronary sinus ostium; LAO = left anterior oblique; LSPV = left superior pulmonary vein; MCV = middle cardiac vein; RAO = right anterior oblique; VOM = vein of Marshall.

#### **3. Results**

CS angiography was performed in 290 consecutive patients (age 55.2 ± 13.2 years; 114 females) scheduled for RFCA between November 2021 and April 2022. Of these, 183 (63.1%) patients had AF, 36 (12.4%) had AFL, 29 (10.0%) had AVNRT, 20 (6.9%) had AVRT, 20 (6.9%) had AT, and 47 (16.2%) had ventricular arrhythmias. The AF group consisted of 183 patients, whereas the non-AF group consisted of 107 patients. In the non-AF group, there were no patients that presented previous AF episodes. The baseline characteristics of all patients are summarized in Table 1. Of all the AF patients, there were 85 paroxysmal AF (PAF), 98 persistent AF (PerAF), and 14 patients also had AFL. Patients with AF were significantly older, had a higher rate of hypertension and heart failure, and a higher left atrial volume (LAV) than non-AF patients. Similarly, left ventricular ejection fraction (LVEF's) were significantly lower in the AF group compared with the non-AF group. Meanwhile, the CHA2DS2-VASc score and the HAS-BLED score were 2.0 ± 1.5 and 0.6 ± 0.7, respectively, in AF patients. Other clinical characteristics are detailed in Table 1.

There were 101 patients that underwent ethanol infusion into the VOM (Et-VOM); a total of 8 patients failed Et-VOM and the success rate of Et-VOM was 92.1% (Figure 1). Measurements of angiographic images are shown in Table 2. The VOM detection rate was significantly higher in the AF group than in the non-AF group (91.8% vs. 84.1%, *p* = 0.044). Of all undetectable cases (n = 32), four patients were diagnosed as persistent left superior vena cava (PLSVA) with no statistically significant difference between the two groups (1.1% vs. 1.9%, *p* = 0.584). There was no significant difference between patients with and without AF in morphologic classifications of VOM (*p* = 0.477). In measurements in the RAO view, AF patients had a significantly larger VOM ostium diameter, CSo diameter, and CS diameter at the VOM ostium than non-AF patients (1.9 ± 0.9 vs. 1.7 ± 0.7 mm, *p* = 0.015; 12.8 ± 4.1 vs. 11.4 ± 3.7 mm, *p* = 0.016; 9.1 ± 3.1 vs. 8.2 ± 2.9 mm, *p* = 0.028, respectively), while the VOM-CS angle was similar in both groups. For measurements in the LAO view, AF patients had a smaller VOM-CS angle and larger CSo diameter as well as CS diameter

at the VOM level (144.2 ± 36.8◦ vs. 156.0 ± 12.6◦, *p* = 0.036; 11.7 ± 5.8 vs. 10.1 ± 5.4 mm, *p* = 0.022; 7.2 ± 2.9 vs. 6.5 ± 2.0 mm, *p* = 0.047). Other details are shown in Table 2.

**Table 1.** Clinical characteristics of all patients.

BMI = body mass index; LAV = left atrial volume; LVEF = left ventricular ejection fraction; NYHA-FC = New York Heart Association functional class. \* Variables with *p* value < 0.05.

**Table 2.** Assessment of angiography images.

AF = atrial fibrillation; CS = coronary sinus; CSo = coronary sinus ostium; LAO = left anterior oblique; PLSVA = persistent left superior vena cava; RAO = right anterior oblique; VOM = vein of Marshall. Other abbreviations as Table 1. \* Variables with *p* value < 0.05.

The non-AF patients (n = 76) and AF patients (n = 76) were then matched in a ratio of 1:1 based on age and gender. As a result, there were no significant differences between the two groups except LAV (68.7 ± 25.3 mL vs. 52.2 ± 19.5 mL, *p* < 0.001, Supplementary Table S2). Patients in the AF group still have a significantly higher incidence of the VOM, larger VOM ostium diameter, and CSo diameter in the RAO view (Supplementary Table S3).

We initially investigated the linear correlation between the VOM ostium and age as AF patients were significantly older. We did not find a linear correlation between the VOM ostium and age in the AF group, non-AF group, or the total patient group (Figure 4). Meanwhile, we found that there were no significant differences of detection rate of the VOM, diameter of the VOM, VOM-CS angle, and VOM-to-CSo distance in all views between different genders (Supplementary Table S1). We also found that male patients have a significantly larger CSo diameter in RAO and LAO cranial views (11.6 ± 4.0 vs. 12.7 ± 4.0 mm, *p* = 0.025; 12.0 ± 4.2 vs. 13.4 ± 5.4 mm, *p* = 0.041). In addition, patients with a higher LAV may have a larger VOM in the AF group, while there was no obvious linear correlation in the non-AF group (Figure 4). We also found that patients with a larger CSo or CS diameter at the VOM ostium had a larger VOM ostium in both groups and had a slight linear correlation (*p* < 0.001, Figure 5).

**Figure 4.** (**A**) Correlation between the VOM ostium diameter and age as well as LAV in all patients (n = 290); (**B**) correlation between the VOM ostium diameter and age as well as LAV in AF patients (n = 183); (**C**) correlation between the VOM diameter and age as well as LAV in non-AF patients (n = 107). AF = atrial fibrillation; CS = coronary sinus; CSo = coronary sinus ostium; LAV = left atrial volume; VOM = vein of Marshall.

**Figure 5.** (**A**) Correlation between the VOM ostium diameter and the CSo diameter as well as CS diameter at the VOM level in the RAO plane in all patients (n = 290); (**B**) correlation between the VOM ostium diameter and the CSo diameter as well as CS diameter at the VOM level in the RAO plane in AF patients (n = 183); (**C**) correlation between the VOM ostium diameter and the CSo diameter as well as CS diameter at the VOM level in the RAO plane in non-AF patients (n = 107). AF = atrial fibrillation; CS = coronary sinus; CSo = coronary sinus ostium; RAO = right anterior oblique; VOM = vein of Marshall.

#### **4. Discussion**

In summary, the present study illustrated the difference between AF and non-AF patients regarding the VOM dimensions. The main findings of this study are as follows: (1) AF patients were associated with a significantly higher incidence of the VOM, larger VOM ostium, CSo, and CS lumen at the VOM ostium; (2) there was a slight linear correlation between the diameter of the VOM ostium and CSo as well as the diameter of CS at the VOM level; (3) patients with a larger LAV tend to have a larger VOM ostium.

#### *4.1. Characteristics of the VOM and Difference between Patients with and without AF*

According to previous reports, the incidence of the VOM varied from 21% to 98% in anatomical studies [16,17]. The presence of the VOM ranged from 63% in a study of optimized VOM-CT protocol to 73% [18] in a study of 100 patients undergoing CS angiography [19]. By contrast, in the present study, the overall incidence of the VOM is 89% under the workflow of angiography (Figure 1). As Et-VOM has been proved to benefit outcomes of AF and will be widely used [7,9], the angiography of workflow should be undergone before Et-VOM to identify the VOM, especially for centers that are in the early stage of operating Et-VOM. In addition, we found that patients with AF have a significantly larger VOM ostium, CSo, and CS lumen at the VOM ostium. The CSo diameter is comparable with previous studies [20–22]. Ortale et al. [22] reported that the CSo ranged from 4.0 to 16.0 mm in 37 adult human heart specimens. Another study [21] involved measurements of CSo by angiography and showed that the median diameter of CSo was 10–11 mm in non-AF patients. However, few studies compare the VOM between patients with and without AF. Our study demonstrated that the VOM ostium and the CSo are larger in AF patients and there may be a correlation between them. Results of the present study suggest that anatomic factors may contribute to the genesis of AF. Larger VOM may produce more atrial connections into the left atrium, thus, giving rise to AF. Although the pathogeneses of AF are complicated, other large scale, prospective cohort studies need to be conducted to prove these hypotheses.

#### *4.2. The Morphology Characteristics of the VOM*

Some studies have investigated the morphology of the VOM. Valderrábano et al. [23] pointed that the VOM was varied in branching patterns and 88.6% of patients present venous plexus at the VOM ostium or variable branches into small venules. Kamakura et al. [8] further classified the VOM into three morphologies according to the numbers of branches in the trunk. They found multiple branches in 92%, a large trunk in 5.0%, and no branches in 3.0%. In the present study, we classified the VOM as two categories according to the numbers of branches within 1 mm of the VOM ostium. Type I was over 70% (222/76.6%), while Type II only counts for 23.4%. However, there was no difference between AF and non-AF patients.

#### *4.3. Correlation between the VOM and LAV*

Many studies had reported that the LAV contributes to the pathogenesis of AF [24–28]. An echocardiographic measurement of LAV was shown to be a predictor of new-onset AF in 574 subjects, and prospectively followed for a mean of 1.9 years [24]. Tan et al. [25] also pointed that the LAV index is associated with new-onset AF in embolic strokes of an undetermined source in patients. However, few studies have investigated the correlation between the LAV and left atrial veins. In our study, we found that AF patients tend to have a larger LAV, and there was a weak linear correlation between the LAV and the size of the VOM ostium. As Njoku et al. [26] concluded, a larger LAV may present structural remodeling, atrial hypertrophy, and stretch peri-LA tissues. In this way, an increased LAV may result in a larger VOM ostium. This morphologic variation may be the anatomic substrate for AF pathogenesis, but still needs to be investigated in other large-scaled, prospective cohort studies.

#### *4.4. Limitations*

There are some limitations of this study. First, it is possible that the left atrial appendage (LAA) vein was mistaken as the VOM because it also drains into the CS. However, the LAA vein extends toward the anterior and we confirmed the course of the vein both at RAO and LAO views. Second, the incidence of the VOM remains unclear in the anatomical study; for patients who could not find the VOM, we changed at least two different sites and fluorography angles for angiography. Third, this study consisted of a small sample size, whereas a prospective cohort study with a larger population is necessary to evaluate the correlation between the VOM and LAV. Fourth, the two-dimensional (2D) imaging of angiography may could not assess a 3D structure, including the VOM, adequately; we used as many angiography views as possible to illustrate the characteristics of the VOM. Other techniques, such as 3D quantitative angiography, may mitigate against this limitation.

#### **5. Conclusions**

AF patients appear to have a higher incidence of the VOM, larger VOM ostium, CSo, and CS lumen in the RAO view compared to non-AF patients. Meanwhile, the VOM ostium may correlate with the CS ostium and LAV.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10.3 390/jcm11185384/s1, Table S1: Assessment of angiography images according to gender, Table S2: Clinical characteristics after propensity score matching, Table S3: Assessment of angiography images after propensity score matching.

**Author Contributions:** Conceptualization, M.T.; Data curation, L.M.; Formal analysis, L.D.; Funding acquisition, M.T. and H.Z.; Investigation, F.Y.; Methodology, H.Z. and M.T.; Project administration, W.H. and M.T.; Resources, S.Z. and Y.Y.; Writing—original draft, L.D.; Writing—review & editing, H.Z. All authors have read and agreed to the published version of the manuscript.

**Funding:** National Natural Science Foundation of China (Grant No. U1913210 and No. 82000064).

**Institutional Review Board Statement:** The study was conducted in accordance with the Declaration of Helsinki, and approved by the Ethics Committee of Fuwai Hospital, Chinese Academy of Medical Sciences (No. 2022-1810).

**Informed Consent Statement:** Informed consent was obtained from all subjects involved in the study.

**Data Availability Statement:** The datasets presented in this article are not readily available because research data is confidential. Data sharing requests are required to meet the policies of the hospital and the funder. Requests to access the datasets should be directed to<EMAIL_ADDRESS>
**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

## *Article* **Clinical Efficacy of Catheter Ablation in the Treatment of Vasovagal Syncope**

**Lingping Xu 1,2, Yixin Zhao 3, Yichao Duan 2, Rui Wang 2, Junlong Hou 2, Jing Wang 2, Bin Chen 2, Ye Yang 2, Xianjun Xue 2, Yongyong Zhao 2, Bo Zhang 2, Chaofeng Sun 1,\* and Fengwei Guo 4,\***

**Abstract:** Catheter ablation of ganglionated plexi (GPs) performed as cardioneuroablation in the left atrium (LA) has been reported previously as a treatment for vasovagal syncope (VVS). However, the efficacy and safety of catheter ablation in the treatment of VVS remains unclear. The objective of this study is to explore the efficacy and safety of catheter ablation in the treatment of VVS and to compare the different ganglion-mapping methods for prognostic effects. A total of 108 patients with refractory VVS who underwent catheter ablation were retrospectively enrolled. Patients preferred to use high-frequency stimulation (HFS) (*n* = 66), and anatomic landmark (*n* = 42) targeting is used when HFS failed to induce a positive reaction. The efficacy of the treatment is evaluated by comparing the location and probability of the intraoperative vagal reflex, the remission rate of postoperative syncope symptoms, and the rate of negative head-up tilt (HUT) results. Adverse events are analyzed, and safety is evaluated. After follow-up for 8 (5, 15) months, both HFS mapping and anatomical ablation can effectively improve the syncope symptoms in VVS patients, and 83.7% of patients no longer experienced syncope (<0.001). Both approaches to catheter ablation in the treatment of VVS effectively inhibit the recurrence of VVS; they are safe and effective. Therefore, catheter ablation can be used as a treatment option for patients with symptomatic VVS.

**Keywords:** syncope; vasovagal syncope; catheter ablation; ganglionated plexus; high-frequency stimulation

**1. Introduction**

Vasovagal syncope (VVS), a neuro-mediated syndrome, is a disorder of cardiovascular autonomic regulation and is the most common cause of sudden and transient loss of consciousness caused by cerebral hypoperfusion [1]. Although syncope itself has a good prognosis, VVS causes physical injuries and poor quality of life [2]. The difference in heart rate and blood pressure with a positive HUT indicates that VVS can be divided into cardioinhibitory, vasodepressive, and mixed according to the pattern of hemodynamic changes during syncope attacks [3]. Treatment for VVS has been challenging. Conventional interventions (education, avoiding precipitating factors, and maintaining fluid and salt intake), orthostatic training, pharmacological treatments, and implantable rhythm devices have failed to show good clinical outcomes (25–65% recurrent syncope) [4–6]. The pathophysiological mechanisms that underlie VVS are complex and far from being fully elucidated. Pathological increases in vagal tone may play a significant role in VVS [2]. Posterior vagus ganglion neurons of the heart are mainly distributed in the epicardial fat pad, which transmits information between preganglionic and postganglionic nerve fibers and regulates cardiac rhythm and conduction [7,8]. The search for a more effective therapy

**Citation:** Xu, L.; Zhao, Y.; Duan, Y.; Wang, R.; Hou, J.; Wang, J.; Chen, B.; Yang, Y.; Xue, X.; Zhao, Y.; et al. Clinical Efficacy of Catheter Ablation in the Treatment of Vasovagal Syncope. *J. Clin. Med.* **2022**, *11*, 5371. https://doi.org/10.3390/jcm11185371

Academic Editor: Tong Liu

Received: 7 August 2022 Accepted: 5 September 2022 Published: 13 September 2022

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

aimed at achieving long-term suppression of vagal reflexes is therefore justified. Preliminary studies have shown that catheter ablation of the LA endocardial parasympathetic ganglion is effective in the treatment of refractory VVS and can achieve a good long-term prognosis [9–11]. Here, we describe 108 patients with VVS who underwent LAGP catheter ablation; in this study, we compared high-frequency stimulation (HFS) with anatomic markers and analyzed ablation safety and efficacy.

#### **2. Materials and Methods**

#### *2.1. Patients*

In total, 1425 patients with VVS were diagnosed by the syncope center from January 2018 to January 2021 in Xianyang Central Hospital, China, including 125 patients with VVS who received catheter ablation, in which 8 patients who were lost to follow-up and 9 patients with missing postoperative follow-up data. Finally, a total of 108 patients in our syncope center were retrospectively enrolled.

All patients had (1) fulfilled the diagnostic criteria of VVS proposed by the 2015 Heart Rhythm Society Guideline and underwent cardioneuroablation [4]; (2) there was no improvement in symptoms after drug treatment through optimal salt and liquid intake and physical back pressure training; (3) positive response to HUT; (4) the patients or their family members agreed to accept the study protocol and signed their informed consent.

Exclusion criteria were (1) structural cardiac or cardiopulmonary diseases (cardiac valvular diseases, severe aortic stenosis, acute myocardial infarction within 6 months, pulmonary embolism, pulmonary hypertension, and hypertrophic obstructive cardiomyopathy); (2) cerebrovascular diseases (vascular steal syndromes and seizures); (3) medicationrelated syncope (vasodilators, antipsychotics, and antidiabetics); (4) disease that affected autonomic nerve (diabetes mellitus and nervous system–related diseases) and (5) terminal diseases or New York Heart Association Class III or IV heart failure.

The protocols involving human participants were reviewed and approved by the Institutional Ethics Committee for Biomedical Research of Xianyang Central Hospital. The patients and participants provided written informed consent to participate in this study.

#### *2.2. HUT*

HUT was performed in the morning in patients in a fasting state. A SHUT-100 tilt table (SHUT-100, Standard Healthcare, Jiangsu Province, China) with a footboard for weight bearing and restraining belts was used for the procedure. Subjects underwent a passive phase (tilted at 70◦ for 30 min, if under 18 or over 75 years of age tilted at 60◦). If no symptoms occurred during the passive phase, participants further underwent an additional provocative phase (0.5 mg sublingually administered nitroglycerin and continued to be tilted for an additional 20 min). Continuous ECG monitoring and noninvasive blood pressure measurements were performed. If after diagnosis by 2 or more experienced clinicians, the physician believed that the clinical presentation was consistent with VVS and the HUT nitroglycerin stimulation test result was negative, isoproterenol stimulation of HUT was added (starting with 1 μg/min and increasing by 1 μg/min every 5 min until reaching 3 μg/min, and ending when the average heart rate exceeded 20–25% of the baseline level; the maximum heart rate was not allowed to exceed 150 bpm). A positive response of HUT was defined when syncope or presyncope occurred in the presence of bradycardia (heart rate < 40 bpm) or abrupt hypotension (systolic blood pressure < 70 mmHg or diastolic blood pressure < 40 mmHg) as well as reproduction of the patient's relevant clinical symptoms [3].

#### *2.3. Preablation Preparation*

Before the procedure, all medications were discontinued for at least 5 half-lives. All procedures were performed under local anesthesia. Pulse oximetry and blood pressure were monitored during the procedure. Routinely, the subclavian vein and femoral vein were punctured to place electrodes in the coronary sinus (CS) and right ventricle. Then we used the annular pulmonary vein catheter puncture into the LA through the atrial septum. The 3-dimensional geometry of the LA was conducted under the guidance of the Ensite-Navx Velocity 5.0 system (Abbott) or Carto3 Version 6.0 system (Johnson & Johnson). Target mapping and ablation were performed in the LA using a cold saline irrigated-tip ablation catheter. Patients were preferred to use HFS, and anatomic landmark targeting was used when HFS failed to induce a positive reaction. Patients were divided into an HFS group and an anatomic ablation group according to different operation modes. In the HFS group, HFS mapping was performed on the endocardial surface of the LA to search for positive response points and radiofrequency ablation. In the anatomical ablation group, the ablation endpoint was the disappearance of the vagal response in all GP anatomical regions (i.e., repeated stimulation or ablation in GP no longer showed a positive response).

During the operation, ventricular pacing was automatically output by a temporary pacemaker to avoid ventricular electrode connection with an EP4 stimulator or HFS by ventricular electrode output accidentally caused by the operator. To ensure cerebral perfusion, ablation was stopped when the blood pressure was lower than 70/40 mmHg as assessed by invasive blood pressure monitoring of the radial artery.

#### *2.4. High-Frequency Stimulation-Guided Endocardial Catheter Ablation of GPs in the LA*

HFS (50 Hz, 10–20 mA, 5 s) was applied by an electrophysiological stimulator (St Jude Medical EP4 electrophysiological stimulator) to identify five common GP distribution areas in the LA. GPs site could be anatomically located as follows: left superior GP (located in the superolateral area around the root of the left superior pulmonary vein, LSGP); left inferior GP (located in the inferoposterior area around the root of the left inferior pulmonary vein, LIGP); right anterior GP (located in the superoanterior area around the root of the right superior pulmonary vein, RAGP); right inferior GP (located in the inferoposterior area around the root of the right inferior pulmonary vein, RIGP) and coronary sinus electrodes from 3.4 to 5.6 corresponding to the CSMGP of the endocardial region of the LA [12]. In some patients, GP was widely distributed or displaced, and LIGP was extended to the anterior crest of the left upper pulmonary vein and the anterior wall between the left two lungs (Figure 1). RAGP extends to the top of the right superior pulmonary vein vestibule. The middle of the CS covers the coronal sinus electrode 1.2–7.8 corresponding to the endocardium (Figure 2). When GPs were stimulated by high frequency, an RR interval prolonged by more than 50% and a radial artery invasive pressure decreased by more than 5 mmHg were defined as positive reaction points (Figure 3). These positive reaction points were then ablated (power 35 W, temperature limit 43 ◦C, target force-time integral 400 gs). Each positive point was ablated for 30 s, which was repeated until reached the endpoint. HFS often induces atrial fibrillation. A temporary pacemaker was used if cardiac arrest occurred during the process (heart rate below 40 bpm). After marking positive reaction points, discharge ablation was performed one by one until the endpoint was reached (Figure 4).

#### *2.5. Anatomically Guided Endocardial Catheter Ablation of GP in LA*

The above GP distribution areas were located by ablation, and the 5 GP anatomical positions of the LA chamber were tested and ablated successively from the upper left to the left lateral left, lower left, right front, and lower right (power 35 W, temperature limit 43 °C, target force-time integral 400 gs). Each positive point was ablated for 30 s, which was repeated until all five GPs reached the endpoint.

**Figure 1.** Distribution of GP. (**a**) High-frequency stimulation group. The green dots represent positive spots. The blood pressure and heart rate decreased significantly during high-frequency stimulation, which was widely distributed in the pulmonary vein vestibule. The white dots are negative spots; the heart rate and blood pressure did not change significantly during stimulation. The red dots represent cardiac arrest for >4 s at the time of stimulation. (**b**) Anatomical group. The green points are positive reaction points for anterior wall GP ablation, the yellow points are positive reaction points for posterior wall GP ablation, and the white and blue points are negative points.

**Figure 2.** Distribution of ablation sites for anatomic ablation: LSG, RAGP, LIGP, RIGP, and CSMGP.

**Figure 3.** Ventricular arrest induced by high-frequency stimulation. (**a**) Upper left GPHFS induced 5251 ms of asystole. (**b**) Right anterior GPHFS induced 4350 ms of asystole.

**Figure 4.** (**a**) During RAGP ablation, the heart rate decreased, the temporary pacemaker started pacing below the set frequency, and ablation continued until the positive reaction disappeared. (**b**) Repeated high-frequency stimulation verification after ablation showed no heart rate decline, reaching the ablation endpoint.

#### *2.6. Postablation Follow-Up*

Rivaroxaban 20 mg was taken daily after surgery. Previous medications, including beta blockers, fludrocortisones, and midodrine, were discontinued after the procedure. At a follow-up of 8 (5, 15) months after surgery, an outpatient review of ECG, cardiac ultrasound, 24 h ambulatory ECG monitoring, and HUT was performed. Syncope symptoms were assessed, and recurrent syncope and any associated physical impairment were recorded. Both recurrent syncope and any related physical injuries were carefully documented. Prodromes including transient dizziness, diaphoresis, or fatigue without loss of consciousness were not considered recurrent episodes of syncope. During the follow-up period, a change in HUT from positive (preoperatively) to negative, the lack of recurrence of syncope, or the presence of syncope with 50% fewer episodes than before was considered effective. Any associated perioperative adverse events were recorded in detail to assess safety.

#### *2.7. Statistical Analysis*

All data are reported as the mean ± SD for continuous variables and as the number of subjects (%) for categorical variables. Measurement data of skewness distribution are represented by Median (Q1, Q3). Independent sample t-tests were used to analyze differences between the two groups. Paired T-tests or Wilcoxon rank sum tests were used for comparisons of pre- and post-ablation measures. Categorical variables were compared using Pearson χ2 analysis. A two-sided *p* value < 0.05 indicated statistical significance. Data were analyzed using the SPSS statistical package for Windows, version 22.0 (IBM Corp., Armonk, NY, USA).

#### **3. Results**

#### *3.1. Patient Characteristics*

Comparison of baseline data between the two groups (Table 1). In total, 108 patients participated in this retrospective clinical study. There were no significant differences between the anatomic ablation group (*n* = 42) and the HFS group (*n* = 66). All patients successfully completed catheter ablation. The mean age of the patients was 51.2 ± 15.3 years, and 44.4% of them were males. The 108 patients were classified into the mixed depression type (62.0%), vascular depression type (38.0%), and cardiac depression type (0%) according to the preoperative HUT. Concurrent arrhythmias were as follows: atrial arrhythmias (paroxysmal atrial fibrillation, sustained atrial fibrillation, atrial premature beats, atrial tachycardia, atrial flutter): 41.7%; sinus bradycardia: 5.6%; intermittent atrioventricular block: 1.9%; ventricular arrhythmias (ventricular premature beat, ventricular tachycardia): 25.0%; supraventricular tachycardia (atrioventricular nodule reentrant tachycardia, atrial ventricular reentrant tachycardia): 17.6%.

**Table 1.** Baseline characteristics of the study patients between the two groups.

Data are expressed as the mean (SD), number (%), or *n*. Atrial arrhythmia\*: paroxysmal atrial fibrillation, persistent atrial fibrillation, atrial premature beat, atrial tachycardia, atrial flutter. Ventricular arrhythmias\*: Premature ventricular beat, ventricular tachycardia.

#### *3.2. Catheter Ablation*

Detailed information about the procedures for the following sites is listed in Table 2: LSGP (71.3%), LIGP (17.6%), RAGP (53.7%), RIGP (19.4%), CSMGP (20.4%), no positive reaction (8.3%). The immediate heart rate increased by 15 (3, 30) bpm before and after intraoperative ablation. The recovery time of the sinoatrial node (SNRT) was shortened by 264 (140,359) ms, and the SNRT shortening rate was 19.4%. The invasive pressure of the radial artery decreased by 31.8 ± 22.7 mmHg during ablation, which indicates that there is a positive reaction to ablation.

**Table 2.** Comparison of procedure parameter changes between the two groups.

#### *3.3. Clinical Outcomes*

At a follow-up of 8 (5, 15) months, the patients' symptoms of syncope improved significantly after catheter ablation; 83.7% of patients had no recurrence of syncope (<0.001), and 81.5% had HUT results that turned negative Subgroup analysis showed that anatomical ablation and HFS ablation could effectively improve syncope symptoms (Table 3). During the 8 (5, 15) month follow-up, eight patients (11.9%) underwent a conversion from mixed suppression to vascular suppression (absence of heart rate inhibition and residual blood pressure inhibition). The number of syncope symptoms decreased in 76.9% of the patients compared with the previous attacks (Table 4). At 1-year follow-up, the number of syncope symptoms decreased in 84.3% of the patients compared with the previous attacks (Table 5). Both HFS mapping and anatomical ablation can effectively improve the syncope symptoms in VVS patients (Table 4). A Holter monitoring comparison of 108 VVS patients before and after catheter ablation showed that the mean heart rate (SDNN) of the slowest heart rate was statistically different (Table 6).

**Table 3.** Clinical data of the patients pre- and postablation.

**Table 4.** Short-term follow-up results of syncope symptoms in the two groups.

**Table 5.** One-year follow-up results of syncope symptoms in the two groups.

**Table 6.** Changes in HR and HR variation after ablation during follow-up.

Two patients in the HFS group developed postoperative bradycardia with a ventricular rate of 45–55 bpm and hypotension of 80/50 mmHg. Dopamine and atropine were used to improve the blood pressure and heart rate, and sinus rhythm was restored 72 h later, with blood pressures above 90/60 mmHg. During the follow-up period, syncope or with recurrent precursory symptoms of syncope, such as dizziness, palpitation, and sweating, disappeared, and the HUT turned negative. There were no other surgery-related complications, including malignant arrhythmias, cardiac tamponade, pericarditis, symptoms associated with delayed gastric emptying, or death.

#### **4. Discussion**

The results revealed the following findings: (1) Symptoms associated with syncope were improved by both HFS and anatomic ablation-guided LA ganglion ablation in patients. A total of 83.7% of patients did not experience a recurrence of syncope or any related physical injury during a mean follow-up period of 8 (5, 15) months. (2) Catheter ablation has shown some effectiveness in the treatment of mixed inhibitory VVS, which can effectively relieve heart rate inhibition. (3) Many patients with VVS also have atrial fibrillation, idiopathic premature ventricular beats, and supraventricular tachycardia, and these patients should pay attention to preoperative screening of VVS. In this study, the sample size was significantly increased. Moreover, preoperative and postoperative HUT changes were added to the evaluation of efficacy. Patients with arrhythmias had no hemodynamic disorders and no malignant arrhythmias at the time of the arrhythmia attack. Moreover, no malignant arrhythmias were detected during the syncope episode. HUT induces a decrease in heart rate and/or blood pressure consistent with the patient's clinical symptoms. Therefore, the patient's symptoms were considered to be caused by VVS. Although two patients in our study developed arrhythmias after the invasive procedure, both recovered after drug treatment; consequently, catheter ablation of LAGP did not increase the incidence of sympathetic-related malignant arrhythmias. This unreproduced and non-controlled study is our preliminary experience demonstrating the efficacy and safety of LAGP ablation for the prevention of VVS.

The autonomic nervous system affects the function of the cardiovascular system by regulating the delicate balance between sympathetic and parasympathetic tension. VVS is caused by the imbalance of sympathetic and parasympathetic tension and the negative effect of pathologically increased vagal tone on cardiac conduction and vascular tension [2]. Therefore, some scholars have proposed achieving permanent endocardial denervation by catheter ablation of the epicardial ganglion of the atrial wall from the endocardial surface to treat patients with VVS [13,14]. Professor Pachon published articles in 2005 and 2011 demonstrating that catheter ablation can significantly improve the symptoms of patients with VVS [10,11]. The parasympathetic nerves were found to be more densely distributed in the atrial than the sympathetic nerves, with a proportion between 1.3:1 and 1.6:1, mainly located in the subendocardium of the myocardium [15]. Second, anatomical studies of the internal cardiac nervous system show that GP in the LA is mainly located around the root of the pulmonary veins [16]. Subsequently, Sun Wei reported that LAGP ablation showed good long-term clinical outcomes in a protocol that was performed only on the LA and not the right atrium or atrial septum [9].