A 13-year-old girl was admitted to the hospital because of dizziness for 3 days and syncope twice. She experienced syncope first during school recess, which lasted for approximately 10 min, accompanied by salivation and urinary incontinence. She was immediately sent to the emergency department of a local hospital. During hospitalization, she suffered syncope for a second time, and she was then transported to our hospital by ambulance.
After admission, physical examination revealed that the child was conscious with a normal heart rate but an irregular heartbeat. Echocardiography showed normal left ventricular systolic function and a normal cardiac structure. Multiple bedside electrocardiograms (ECGs) showed frequent multisource premature ventricular contractions. Holter ECG showed frequent multisource premature ventricular contractions (43,729 beats/day, with some occurring in pairs and some occurring in doublet or triplet patterns) with the R-ON-T phenomenon and Tdp (Figure 1A). The QTc ranged from 410 to 468 ms. For treatment, the patient was administered an intravenous infusion of magnesium sulfate (0.5-1.0 mg/kg h) and potassium to maintain serum potassium concentration at 4.5-5 mmol/L. She received oral propranolol tablets (0.5 mg/kg) every 8 h. After 1 week of treatment, the child recovered and did not experience palpitations or dizziness in the hospital. An ECG showed that the premature ventricular contractions were significantly reduced and that no ventricular tachycardia (VT) occurred, and the QTc was 416 ms (Figure 1B). Occasionally, a biphasic T wave was observed in Lead V2 in this patient in sinus rhythm. Second-generation gene sequencing was performed after receiving approval by the Medical Ethics Committee and parental informed consent. As a result, a heterozygous mutation, namely, c.11714T > C (p.M3905T), in the AKAP9 gene of the patient was detected, which was inherited from her mother (Figure 2), whose ECG was normal without QT prolongation and no history of syncope. This variant has not been previously described in the literature and has also not been previously reported in the Human Gene Mutation Database (HGMD). No other possible causative mutations were found, and no history of related genetic diseases was detected in the family.
After 9 months, the child suffered from syncope and convulsions again during housework. She was transferred to our hospital after cardiopulmonary resuscitation for 2 h. The ECG showed frequent multisource VT with Tdp (Figure 1C). Temporary subclavian pacing was given to the patient, and vasoactive drugs were used to maintain circulatory stability. Oral propranolol tablets were adjusted to 1 mg/kg every 8 h, and the patient received intravenous potassium and magnesium supplementation. The Holter ECG showed that the incidence of ventricular arrhythmia was 19,924 beats in 24 h with no occurrence of Tdp. Considering that the child had syncope after drug treatment, she was implanted with an implantable cardioverter defibrillator (ICD) under general anesthesia after 7 days of stabilization (Figure 3). Her parents were informed that she needed activity restriction and exercise reduction.
Two weeks after discharge from the hospital, the patient developed obvious palpitations, fatigue, dizziness, and a sense of electric shock at night. Because she experienced several suspicious electric shock events, she was readmitted to our hospital. The bedside program control of the ICD confirmed that the child had multiple VT at home, and electrical cardioversion terminated the tachycardia after antitachycardia pacing (ATP) failed. In order to alleviate her anxiety, the ATP function was turned off, the VT judgment threshold was adjusted from 180 beats/min to 200 beats/min, and the energy of the first electric shock was lowered from 30 to 20 J. To reduce the incidence of ventricular arrhythmias, the patient was prescribed oral propafenone tablets (3 mg/kg) every 8 h. A repeated Holter ECG showed that the frequency of ventricular arrhythmias (3,387 beats/day) was significantly lower than before and that the ventricular pacing function was normal. The morphology of the T wave was normal in the lateral precordial leads. No malignant arrhythmia and electric shock events occurred during the 1-, 3-, and 6-month follow-ups. The child returned to school with restricted activities, and her parents were satisfied with the treatment provided.