**Abstract**

In this work, we present a systematic and successful development of *L*-group theory. A universal construction of a generated *L*-subgroup has been provided by using level subsets of given *L*-subsets. This construction allows us to define and study commutator *L*-subgroups, normalizer of an *L*-subgroup, nilpotent *L*-subgroups, solvable *L*-subgroups, normal closure of an *L*-subgroup. All these concepts and their inter-relationships have been presented. Here we mention that in this work we also exhibit a characterization of solvable *L*-subgroup with the help of a series of *L*-subgroups such that at each level, the factor groups of level subgroups of their consecutive members are Abelian. This allows us to introduce the notion of a supersolvable *L*-subgroup by using the factors of level subgroups at each level of a subinvariant series of an *L*-subgroup. Also, by using successive normal closures, we transfinitely define a series called the normal closure series of the *L*-subgroup. It has been shown that it is the fastest descending normal series containing given *L*-subgroup. This sets the ground for the development of subnormality in *L*-group theory. In the last, we study the notion of subnormal *L*-subgroups.

**Keywords:** L-Subgroup, Generated L-subgroups, Commutator L-subgroup, Characteristic L-subgroup, Nilpotent L-subgroup, Solvable L-subgroup, supersolvable L-subgroup, Subnormal L-subgroup,


The risk of developing cardiotoxicity is also increased by concurrent radiation exposure to the chest. In addition to the myocardium, radiation therapy has the potential for damaging the pericardium, heart vessels, and conductive tissue [18].

The carriers of certain genetic mutations are also more susceptible to cardiotoxicity [9,18]. Our understanding of genetic susceptibility to anthracycline-related cardiotoxicity has been influenced by a sizable body of research, as we describe below.

#### **5. Diagnosis**

As part of the baseline risk assessment, a thorough clinical history and physical examination are advised. Many patients with cardiac dysfunction could be asymptomatic, so both during and post-chemotherapy, cardiac monitoring is necessary. Consideration of the classic cardiovascular disease risk factors already mentioned is recommended, and children should be monitored for clinical signs and potential indicators of cardiotoxicity. The above-mentioned factors should be noted alongside the baseline electrocardiography, cardiac serum biomarkers, and cardiac imaging tests to complete baseline evaluation.

#### *Imaging*

Diagnostic approaches for chemotherapy-induced cardiotoxicity include electrocardiography and echocardiography, which are used as methods of monitoring cardiac function before, during, and after treatment.

Electrocardiography (ECG) can be used to identify any early signs of cardiac toxicity, such as resting tachycardia, ST-T wave abnormalities, conduction disturbances, QT interval prolongation, or arrhythmias. However, these ECG findings could be induced by several factors unrelated to cardiotoxic treatment. These ECG abnormalities may be reversed and are not always related to the development of chronic cardiomyopathy [7,27,34].

Two-dimensional echocardiography (2D) is the most used imaging technique to monitor cardiac function. It is non-invasive, cheap, readily available, and does not expose the patient to further radiation. However, standard echocardiographic parameters such as LVEF may lack sensitivity for the detection of systolic dysfunction [34].

Considering the poor sensitivity of 2D LVEF measurement, the use of global systolic longitudinal myocardial strain (GLS) analysis has become an area of interest [34,35]. A pathogenic percentage reduction of GLS greater than 15% from baseline is regarded as a sign of early LV dysfunction. When possible, it is preferable to use these sophisticated echocardiographic measures as the foundation for clinical decisions.

Other methods for the monitoring of these patients are cardiac magnetic resonance imaging (CMR), nuclear cardiac imaging (MUGA), and myocardial perfusion imaging (MPI). There are two techniques for MPI: single-photon emission computed tomography (SPECT) and positron emission tomography (PET). All these methods take considerably longer than follow-up echocardiography and might not be as accessible in all pediatric facilities [34].

#### **6. Biomarkers**

Several biomarkers have been assessed for their efficacy in the early prediction of patients' risk of cardiotoxicity and the identification of cardiac dysfunction. The World Health Organization defines biomarkers as any element, structure, or process that can be detected in the body (or its byproducts) and which affects or forecasts the development or course of a disease.

According to the literature, troponin and natriuretic peptide are the most studied biomarkers for the detection of both early cardiotoxicity and its later follow-up. Lipshultz et al. showed that the elevation of cardiac troponin T and N-terminal pro-brain natriuretic peptide (NT-pro-BNP) in children with acute lymphoblastic leukemia was associated with a notably reduced left ventricular (LV) mass, abnormal LV end-diastolic posterior wall thickness, and abnormal LV thickness-to-dimension ratios, all of which suggested LV remodeling, respectively, 4 years later [36]. However, further research has not pointed out an association between acute or chronic troponin release and left ventricular dysfunction, but in contrast, an association has been found with NT-pro-BNP in childhood cancer survivors [37–39].

We should be especially careful in evaluating troponin and natriuretic peptide values in children <1 year of age due to their normally elevated values at these ages [40].

Other biomarkers investigated include inflammation markers, such as C-reactive protein (CRP) and growth/differentiation factor 15 (GDF-15) [38], oxidative stress markers such as myeloperoxidase, vascular remodeling markers such as placental growth factor and soluble Fms-like tyrosine kinase receptor 3, and fibrosis markers (galectin 3) [36,41–49]. Moreover, these conventional biomarkers usually show significant changes only after heart damage occurs.

To determine the proper use of these biomarkers in clinical practice, new prospective and multicenter studies with large populations, well-standardized dosing methodologies, well-defined time of sampling, and cardiologic end points are required.

#### **7. Omics**

In the last decades, new research and clinical studies have attempted to identify possible biomarkers of early cardiac damage by chemotherapeutic agents using omics technology. Omics science offers new opportunities for biomarker discovery in cardiotoxicity and may provide an understanding of cardiotoxicity beyond traditional technologies. Omics technology includes genomics, transcriptomics, proteomics, and metabolomics.

#### *7.1. Genomics*

A cumulative anthracycline dose and other related risk factors seem to not be exclusive risk factors responsible for significant individual variation in the incidence and severity of heart failure in pediatric cancer survivors. Several studies have revealed how important host genetic polymorphisms could lead to a differential risk of cardiotoxicity among cancer survivors with otherwise identical clinical and treatment-related risk factors by using genome-wide association or candidate gene approaches [50–53]. This explains why some patients experience cardiotoxicity while other patients can tolerate high doses of chemotherapy without heart damage.

Genomic polymorphisms are small changes in a specific part of the DNA chain. One or more polymorphisms can determine a range of patient characteristics, such as their ability to metabolize and eliminate genotoxic substances. Cancer treatment-related cardiovascular toxicity risk may be influenced by genetic variation. Significant efforts using targeted and whole genome correlation studies have been made to reveal the pharmacogenomic causes of this predisposition [50,54–60].

At least 45 SNPs located in 34 genes have been associated with anthracycline-induced cardiotoxicity [61–64]. Many of these associations require further investigation through replication and/or functional and mechanistic studies to make sure we confirm and better understand the roles of these associated variants in anthracycline-related cardiotoxicity (ACT) [9].

Polymorphisms in solute carrier transporter (SLC) genes are associated with ACT. One of the functions of the SLC family is acting as drug transporters for anthracyclines, thus providing biological support for these genetic associations. Research on childhood cancer survivors has discovered correlations between ACT risk and protective variants in SLC, such as SLC28A3, SLC22A17, and SCL22A7. These findings have been successfully replicated [65–70]. In addition, different studies have reported protective variants in SLC10A2 and SLC22A1 [66]. SLC22A6 was first mentioned in the context of ACT by Sagi et al. in patients treated for childhood ALL [68].

Retinoic acid receptor gamma (RARG) has been involved in cardiac development and remodeling through the repression of Top2b [71]. A recent genome-wide association study, by Aminkeng et al. [51], uncovered a non-synonymous variant rs2229774 in *RARG*, which was significantly associated with ACT in survivors of childhood cancer. Specifically, rs2229774-carriers had a significantly increased risk of developing ACT as compared to non-carriers [51].

Studies have also revealed an elevated risk brought on by a variation in the UGT1A6 gene, a member of the glucuronosyl transferase family. Through the glucuronidation path, UGT1A6 plays a significant role in the detoxification of drugs, including the metabolites of anthracyclines [51,65,69].

Polymorphisms in adenosine triphosphate-binding cassette transporter (ABC) genes are related to cardiotoxicity in childhood patient cancers treated with anthracyclines. The ABC genes seem to play a role as efflux transporters of drugs, including anthracyclines, so may have important effects on the myocardium. Eight variants in five genes (ABCB1, ABCB4, ABCC1, ABCC2, and ABCC5) have been associated with cardiotoxicity, especially with reduced ejection fraction [54–56,68,72].

Other studies have investigated polymorphisms in carbonyl reductase genes, which have been associated with dose-dependent increases in cardiomyopathy risk. Carbonyl reductase (CBR) will reduce anthracyclines to cardiotoxic alcohol metabolites. As Blanco et al. showed, among childhood cancer survivors, homozygosity for the G allele in CBR3 leads to increased cardiomyopathy risk associated with low- to moderate-dose anthracyclines. Patients homozygous with the CBR3 V244M G allele have no safe cut-off minimum dose [57,58].

A recent study showed a gene–environment interaction between a single-nucleotide polymorphism on the CELF4 gene and a higher dose of anthracyclines [59]. CUGBP Elavlike family member 4 CELF4) protein is responsible for pre-mRNA alternative splicing of TNNT2, the gene that encodes for cardiac troponin T.

Aminkeng et al. [69] gathered evidence-based clinical practice recommendations for pharmacogenomic testing and emphasized that the RARG genes rs2229774, UGT1A6 \* 4 rs1786378, and SLC28A3 rs7853758 have the potential to further discriminate patients at higher and lower risk of ACT. A pharmacogenetic test for these genetic variations in RARG, SLC28A3, and UGT1A6 has been released at the British Columbia Children's Hospital since the publication of these guidelines. Based on genetic and clinical risk variables, tested patients were divided into several risk groups, and therapy adjustments were chosen in accordance with this risk. Early evidence indicates that the British Columbia Children's Hospital's pharmacogenetic testing was effective in lowering the incidence of ACT in children, which should inspire additional clinics to utilize this pharmacogenetic test.

These findings might help develop prediction models that can spot patients who will be particularly susceptible to ACT and who will need their therapy modified or closer monitoring. Further independent research may make it possible to identify people before treatment with a genetic predisposition to cardiovascular toxicity and for whom more thorough screening, or perhaps preventive measures, should be implemented. Replication analyses, however, have occasionally failed to support the initial findings. Numerous factors, including the variability of cohorts, ambiguities in the definition of ACT, variations in the procedures, and the type or dosage of the chemotherapeutic drugs used may have contributed to this. To increase the diagnostic and prognostic role in predicting ACT, more research is required.

### *7.2. Transcriptomics*

Another interesting area is the integration of microRNAs in the early detection of cardiotoxicity. Recently, the potential use of circulating microRNAs (miRNAs) has been studied as a possible specific biomarker and therapeutic target of cardiac disease [73–79].

MicroRNAs are small endogenous non-coding RNAs of 21–24 nucleotides, acting as post-transcriptional gene regulators by inhibiting and/or degrading target messenger RNAs (mRNAs). Bioinformatics data suggest that each miRNA molecule can control hundreds of gene targets, thus indicating the potential effect of miRNAs on virtually any genetic pathway. MiRNAs play a significant role in different biological processes, including proliferation, differentiation, development, and cell death. Furthermore, several miRNAs are involved in regulating heart development from the embryonic to the adult stage, and their dysregulation leads to various heart diseases, such as arrhythmias, essential hypertension, heart failure, cardiomyopathy, cardiac hypertrophy, and atherosclerosis [80,81].

The cardiotoxic effect of chemotherapeutic agents may lead to specific miRNAs with changed expressions. These can be used to investigate the toxicity of potential drug candidates on cardiomyocytes and cell lines originating from the heart in a preclinical in vitro setting. The potential use of circulating miRNAs in plasma as indicators of druginduced cardiotoxicity has undergone much research during the last several years [80].

Nearly 30 circulating miRNAs have had their levels altered, both increased and decreased, and these changes have been linked to HF and associated pathologies. MiRNAs, including miR-1, miR-133, miR-208a/b, miR-499, miR-29, and miR-34, which are substantially expressed in the myocardium compared to other tissues, are the ones that are primarily being researched [73]. In addition, a variety of harmful substances alter the miRNA profile in both plasma and cardiac tissue. Even at low toxin concentrations, where other tissue damage biomarkers are not discernible, alterations in miRNAs can be measured [80]. Most studies use data from experimental animals, while those utilizing clinical patient samples are limited.

MiR-1 is a skeletal muscle-specific miRNA that has an important role in cardiac development, function, and disease. Abnormal miR-1 levels are associated with acute myocardial infarction, heart failure, arrhythmias, ventricular dysfunction, cardiac hypertrophy, and myocyte hyperplasia [82]. MiR-499 and miR-208 are associated with acute myocardial infarction and HF [82]. Circulating levels of miR-133a have been associated with an increased risk of cardiovascular diseases. Increased levels of miR-133a have been detected in patients with acute myocardial infarction earlier than cardiac troponin T increase [83]. MiR-133 includes two miRNAs, named miR-133a and miR-133b, that are highly expressed in the human heart and seem to be involved in heart development and myocyte differentiation.

The analysis of circulating miRNAs in breast cancer patients receiving doxorubicin (DOX) identified miR-1 as a potential candidate for the early detection of DOX-induced cardiotoxicity [84]. Leger et al. investigated other possible markers of cardiotoxicity in children and young adults treated with anthracycline chemotherapy (AC). Candidate plasma profiling of 24 miRNAs was performed in 33 children before and after a cycle of AC or non-cardiotoxicity chemotherapy. MiR-1, miR-29b, and miR-499 were reported to be upregulated in pediatric patients following the acute initiation of AC [85,86]. Monitoring the plasma levels of miR-208a and miR-208b showed an elevation in patients with myocardial damage and were even detected earlier than cardiac troponins [87]. This is in concordance

with the findings of other studies [73,74,87,88]. Table 3 provides a summary of the major miRNAs linked to drug-induced cardiotoxicity.

**Table 3.** Summary of major miRNAs link to drug-induced cardiotoxicity in people.

In addition to anthracyclines, other cytotoxic agents have shown cardiotoxic effects, and biomarkers of their pathomechanism have been searched for, including miRNAs. Patients with bevacizumab-induced cardiotoxicity, when compared to controls, were found to have increased levels of five miRNAs. In the validation experiments, two of these (miR-1254 and miR-579) showed valuable specificity. MiR-1254 exhibited the strongest correlation with the clinical diagnosis of bevacizumab-induced cardiotoxicity [89].

With regard to a number of features of drug-induced cardiotoxicity, miRNAs appear to be a promising agent. A potentially successful method for preventing severe problems is the identification of patients with subclinical cardiotoxicity through the detection of cardiospecific miRNAs circulating in plasma that are not present under normal circumstances [80]. Many other research studies should focus on how the miRNA profile changes when interacting with drugs with proven cardiotoxicity.

#### *7.3. Proteomics*

The proteomic data available to date on chemotherapy-induced cardiac toxicity are limited, mainly involving anthracyclines, and related to experimental animal studies [90].

Proteomics is the study of proteins, which are essential components of organisms and have a variety of functions. The proteome consists of all the proteins expressed by a cell, tissue, or organism. Proteomics could give us important information for a number of biological problems.

Ohyama et al. identified cellular processes in mouse heart tissue from control rats and rats affected by different adriamycin and docetaxel dosing protocols using a toxicoproteomic approach. They identified nine different proteins that were expressed in the control and two treatment groups, and which were involved in energy production pathways, such as glycolysis, the Krebs cycle, and the mitochondrial electron transport chain [91].

Kumar et al. in 2011 used a rat model of doxorubicin-induced cardiotoxicity to show the differential regulation of several key proteins, including proteins that are stressresponsive (ATP synthase, enolase alpha, alpha B-crystallin, translocation protein 1, and stress-induced phosphoprotein 1), and apoptotic/cell damage markers (p38 alpha, lipocortin, voltage-dependent anion-selective channel protein 2, creatine kinase, and MTUS1) [86].

More recently, Desai et al. pinpointed possible biomarkers of early cardiotoxicity in the plasma of male B6C3F1 mice that received a weekly intravenous dose of 3 mg/kg doxorubicin (DOX) or saline (SAL) for 2, 3, 4, 6, or 8 weeks (corresponding to cumulative doses of 6, 9, 12, 18, or 24 mg/kg DOX). They suggested the neurogenic locus notch homolog protein 1 (NOTCH1) and von Willebrand factor (vWF) as early biomarkers of

DOX cardiotoxicity to address the clinically significant question of identifying cancer patients at risk for cardiotoxicity [92]. Finally, Yarana et al., using a mouse model of DOX-induced cardiac injury, quantified serum extracellular vehicles (EVs), assayed proteomes, counted the oxidized protein levels

cardiotoxicity to address the clinically significant question of identifying cancer patients

*Diagnostics* **2023**, *13*, x FOR PEER REVIEW 14 of 27

Finally, Yarana et al., using a mouse model of DOX-induced cardiac injury, quantified serum extracellular vehicles (EVs), assayed proteomes, counted the oxidized protein levels in serum EVs generated following DOX treatment, and examined the alteration of EV content. The release of EVs containing brain/heart glycogen phosphorylase (PYGB) before the increase in cardiac troponin in the blood following DOX therapy suggests that PYGB is an early indicator of cardiac damage, according to the proteomic profiling of DOX\_EVs [93]. in serum EVs generated following DOX treatment, and examined the alteration of EV content. The release of EVs containing brain/heart glycogen phosphorylase (PYGB) before the increase in cardiac troponin in the blood following DOX therapy suggests that PYGB is an early indicator of cardiac damage, according to the proteomic profiling of DOX\_EVs [93]. To find out if these pathways could result in the discovery of early markers of cardi-

To find out if these pathways could result in the discovery of early markers of cardiotoxicity, more research in this area is required. otoxicity, more research in this area is required.

#### *7.4. Metabolomics 7.4. Metabolomics*

at risk for cardiotoxicity [92].

Metabolomics is an upcoming new science with the potential to further increase our knowledge of cancer biology and the search for prognostic biomarkers. Up to now, most studies have either used metabolomic data from experimental animals or the cellular level, while those utilizing clinical patient samples have been extremely limited (Figure 8). Metabolomics is an upcoming new science with the potential to further increase our knowledge of cancer biology and the search for prognostic biomarkers. Up to now, most studies have either used metabolomic data from experimental animals orthe cellularlevel, while those utilizing clinical patient samples have been extremely limited (Figure 8).

**Figure 8.** Diagram expressing the different research models of cardiotoxicity (clinical, animal, cellu-**Figure 8.** Diagram expressing the different research models of cardiotoxicity (clinical, animal, cellular) using metabolomic data.

lar) using metabolomic data. Metabolism is more directly related to the phenotype and physiology of a biological system. Metabolomics is the study of all cellular metabolites (hydrocarbons, amino acids, sugars, fatty acids, organic acids, steroids, and peptides). It encompasses all levels of cellular regulation, that is, the regulation that occurs at the level of transcription, translation, and post-translational modifications, and hence, it can closely reflect the phenotype of an organism at a specific time. The human metabolome is thought to be composed of about 3000 endogenous metabolites at current estimates (the Human Metabolome Project). However, the exact size of the human metabolome is still debatable. It is also believed that nutritional compounds, xenobiotics, and microbial metabolites must be considered when Metabolism is more directly related to the phenotype and physiology of a biological system. Metabolomics is the study of all cellular metabolites (hydrocarbons, amino acids, sugars, fatty acids, organic acids, steroids, and peptides). It encompasses all levels of cellular regulation, that is, the regulation that occurs at the level of transcription, translation, and post-translational modifications, and hence, it can closely reflect the phenotype of an organism at a specific time. The human metabolome is thought to be composed of about 3000 endogenous metabolites at current estimates (the Human Metabolome Project). However, the exact size of the human metabolome is still debatable. It is also believed that nutritional compounds, xenobiotics, and microbial metabolites must be considered when defining the human metabolome [94]. Therefore, metabolome analysis can be a useful tool used to find diagnostic markers that will help us examine unknown pathological conditions effectively.

defining the human metabolome [94]. Therefore, metabolome analysis can be a useful tool used to find diagnostic markers that will help us examine unknown pathological conditions effectively. Different analytical techniques can be used in the measurement of metabolites. Such methods are nuclear magnetic resonance (NMR) spectrometry, molecular mass spectrom-Different analytical techniques can be used in the measurement of metabolites. Such methods are nuclear magnetic resonance (NMR) spectrometry, molecular mass spectrometry (MS), gas chromatography (GC), high-performance liquid chromatography (LC), and tricarboxylic acid (TCA). The most common and higher-throughput technologies are nuclear magnetic resonance (NMR) spectrometry and molecular mass spectrometry (MS).

etry (MS), gas chromatography (GC), high-performance liquid chromatography (LC), and

Mass spectrometry is an analytical platform for metabolomic analysis. It is a highly sensitive, reproductive, and versatile method, as it identifies molecules and their fragments by measuring their masses. This information is obtained by measuring the mass-to-charge ratio (*m*/*z*) of ions that are produced by inducing the loss or gain of a charge from a neutral species. The sample, which comprises a complicated mixture of metabolites, can be introduced to the mass spectrometer either directly or preceded by a separation approach (using liquid chromatography or gas chromatography) [95].

NMR spectroscopy utilizes the magnetic properties of nuclei to determine the number and type of chemical entities in a molecule. Proton NMR spectroscopy can detect soluble proton-containing molecules with a molecular weight of approximately 20 kD or less. The NMR spectra serve as the raw material for pattern recognition analyses, which simplifies the complex multivariate data into two or three dimensions that can be readily understood and evaluated. Both NMR and liquid chromatography–mass spectrometry (LC-MS) systems can be integrated into in vivo tissues or biological fluids, such as serum, plasma, urine, etc., obtained from humans. The advantages of NMR are that it requires relatively little sample preparation, it is non-destructive, and it can provide useful information regarding the exact structure of metabolites. However, NMR sensitivity is related to the magnet's strength, while available instrumentation can unambiguously detect only the most abundant metabolites in plasma. On the other hand, the most important advantage of mass spectrometry coupled with upfront chromatography is its far greater sensitivity than NMR MS-based systems, which have been used to resolve compounds in the nanomole to the picomole and even the femtomole range, whereas the identification of compounds by 1H-NMR requires concentrations of 1 nanomole or higher [96,97].

The main methodologies that are used for metabolomic analysis are untargeted and targeted metabolomics. Untargeted metabolomics allow for measuring a wider variety of metabolites present in an extracted sample without prior knowledge of the metabolome. The main advantage is that this provides an unbiased way to examine the relationships among interconnected metabolites from multiple pathways. In contrast, targeted metabolomic analyses measure the concentrations of a predefined set of metabolites and provide higher sensitivity and selectivity than untargeted metabolomics.

An overview of the main metabolomics associated with drug-induced cardiotoxicity detected in plasma/stem cells/hearts in mice and people is given in Table 4. The role of carnitine in the detection of cardiotoxicity was confirmed by a successive study in which Armenian et al. compared a metabolomics analysis in 150 symptom-free childhood cancer survivors who received anthracycline treatment. Thirty-five participants were found to have cardiac dysfunction without symptoms. So, they compared two groups (participants with cardiac dysfunction and those with normal systolic function) and discovered 15 metabolites differentially expressed among the patients. After adjusting for multiple comparisons, individuals with cardiotoxicity had significantly lower plasma carnitine levels in comparison to those with normal cardiac function [98].

**Table 4.** Metabolomics associated with drug-induced cardiotoxicity.

More recently, Li et al. [99] identified 39 biomarkers for detecting cardiotoxicity earlier than biochemical analysis and histopathological assessment. They used rats to create cardiotoxicity models in which the toxicity was caused by doxorubicin, isoproterenol, and 5 fluorouracil. The metabolomics analysis of plasma was performed using ultraperformance liquid chromatography quadrupole time-of-flight mass spectrometry. They used a support vector machine (SVM) to deploy a predictive model to confirm more exclusive biomarkers with more significant l-carnitine, 19-hydroxydeoxycorticosterone, lysophosphatidylcholine (LPC) (14:0), and LPC (20:2) [99].

Similarly, Schnackenberg et al. attempted to discover molecular markers of early-stage cardiotoxicity induced by doxorubicin in mice before the onset of cardiac damage. They discovered 18 metabolites significantly altered in the plasma, and another 22 metabolites were increased in cardiac tissue after a cumulative dose of 6 mg/kg, while myocardial injury and cardiac pathology were not noticed until after cumulative doses of 18 and 24 mg/kg, respectively [102]. Metabolomics analyses of plasma and heart tissue showed significant variations in the levels of many amino acids (including arginine and citrulline), biogenic amines, acylcarnitines (carnitine), and tricarboxylic acid cycle (TCA)-related metabolites (e.g., lactate, succinate).

Tan et al. conducted a study using gas chromatography–mass spectrometry to describe the metabolic profile of doxorubicin-induced cardiomyopathy in mice. They identified 24 metabolites, which were implicated in glycolysis, the citrate cycle, and the metabolism of some amino acids and lipids, and which were selected as possible biomarkers for the detection of cardiotoxicity [103].

Andreadou et al. used nuclear magnetic resonance (NMR) spectrometry to describe the metabolic profile of acute doxorubicin cardiotoxicity in rats and to evaluate the metabolic alterations conferred by co-treatment with oleuropein [90]. The mice were divided into six groups: the first group included the control group, the second group received DOX, and the other four groups of mice received doxorubicin with oleuropein in different doses and days, regarding the latter. Mice hearts were excised 72 h after doxorubicin administration and the H-NMR spectra of aqueous myocardium extracts were monitored. The results of the analysis showed an increase in the levels of acetate and succinate in the DOX group compared to the controls, while the amino acid levels were lower. The conclusion of the article was that acetate and succinate constituted novel biomarkers for the early detection of cardiotoxicity [100,105].

Geng et al. in their study, used gas chromatography−mass spectrometry analysis of the main targeted tissues (serum, heart, liver, brain, and kidney) to systemically evaluate the toxicity of DOX. Multivariate analyses revealed 21 metabolites in the serum, including cholesterol, D-glucose, D-lactic acid, glycine, L-alanine, L-glutamic acid, L-isoleucine, L-leucine, L-proline, L-serine, L-tryptophan, L-tyrosine, L-valine, N-methylphenylethanolamine, oleamide, palmitic acid, pyroglutamic acid, stearic acid, and urea, were changed in the serum in the DOX group [106].

Tantawy et al. identified a lower plasma abundance of pyruvate and a higher abundance of lactate in patients with carfilzomib-related cardiovascular adverse events. (CVAEs). They emphasized the significance of the pyruvate oxidation pathway associated with mitochondrial dysfunction. In order to better understand the mechanisms of carfilzomibassociated CVAEs, further investigation and validation are needed in a larger independent cohort [107].

Yin et al. proposed 15 different metabolites that play important roles in cyclophosphamideinduced cardiotoxicity. In their study, rat plasma samples were collected and analyzed one, three, and five days after cyclophosphamide administration using ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QqTOF HRMS). Of the biomarkers studied, the proline, linoleic acid, and glycerophospholipids changed significantly in the three periods, and the changes were associated with an increasing time of occurrence of cardiotoxicity from cyclophosphamide [108].

The study of Jensen et al. [104] showed significant decreases in docosahexaenoic acid, arachidonic acid/eicosatetraenoic acid, o-phosphocolamine, and 6-hydroxynicotinic acid after sunitinib treatment with non-targeted metabolomics analysis of mice hearts [31]. The same author also showed alterations in the taurine/hypotaurine metabolism in the hearts and skeletal muscles of mice after sorafenib treatment [109].

Except for the analysis of plasma and heart tissue, NMR spectroscopy-based metabolomics may detect low-molecular-weight metabolites in urine and cell culture media. For example, Chaudhari et al. [101] showed a reduction in the utilization of pyruvate and acetate and an accumulation of formate in contrast to a control culture medium of human induced pluripotent stem cell-derived cardiomyocytes exposed to doxorubicin. In contrast, Wang et al. [59] showed in their study that tryptophan and phenylalanine metabolism in urine was also an important process in the systemic toxicity of doxorubicin. In addition, Park et al. identified 19 urinary metabolites in rats treated with doxorubicin [110].

This technology is still under development, but it seems obvious that metabolomics holds the potential to revolutionize our ability to profile samples in order to understand biological processes and find useful disease diagnostic biomarkers.

#### **8. Conclusions**

Cardiovascular toxicity continues to be a major cause of drug failure during preclinical and clinical treatment models and contributes to drug withdrawal after approval. Numerous medications that have been used frequently in adult clinical practice for a long time have demonstrated potentially harmful effects on the hearts of pediatric patients. The cardiotoxicity of these medications persists as a significant issue, having a negative impact on patients' quality of life as well as their overall survival. Several strategies for the early detection of cardiotoxicity have been developed to reduce the number of patients with cardiac mortality and morbidity. Of importance, the biomarkers identified by the "omics" approach are considered new potential markers, especially in the scenario of diagnosis and the risk stratification of acute coronary syndromes induced by chemotherapeutic drugs, and they may prove helpful in the early detection of anticancer cardiotoxicity.

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

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** The article is a review, and no original data were generated.

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

#### **Abbreviations**

### **References**

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### *Article*

## **Impact of Cancer Type and Treatment Protocol on Cardiac Function in Pediatric Oncology Patients: An Analysis Utilizing Speckle Tracking, Global Longitudinal Strain, and Myocardial Performance Index**

**Andrada Mara Ardelean 1,2,3, Ioana Cristina Olariu 1,3 , Raluca Isac 1,3 , Akhila Nalla <sup>4</sup> , Ruxandra Jurac 1,3 , Cristiana Stolojanu 2,3, Mircea Murariu 2,3, Roxana Manuela Fericean 2,5 , Laurentiu Braescu 2,6,7 , Adelina Mavrea 8,\* , Catalin Dumitru <sup>9</sup> and Gabriela Doros 1,3**

**Abstract:** Pediatric hemato-oncology patients undergoing anthracycline therapy are at risk of cardiotoxicity, with disease type and treatment intensity potentially affecting cardiac function. Novel echocardiographic measures like speckle tracking echocardiography (STE), global longitudinal strain (GLS), and the myocardial performance index (MPI) may predict early changes in cardiac function not detected by traditional methods. This study aimed to assess the impact of cancer type and treatment protocol on these parameters and their potential in predicting long-term cardiac complications. We conducted a single-center, retrospective cohort study of 99 pediatric oncology patients and 46 controls that were assessed at 3, 6, and 12 months. The median age was 10.7 ± 4.4 years for cases and 10.2 ± 3.6 years for controls. STE, GLS, and MPI were measured, and statistical analyses were performed to determine any significant correlations with cardiotoxicity. Significant variations were observed in traditional cardiac function measurements between the patient and control groups, with a lower average ejection fraction (EF) of 62.8 ± 5.7% in patients vs. 66.4 ± 6.1% in controls (*p* < 0.001), poorer GLS of −16.3 ± 5.1 in patients compared to −19.0 ± 5.4 in controls (*p* = 0.004), and higher MPI values of 0.37 ± 0.06 in patients compared to 0.55 ± 0.10 in controls, indicating worse overall cardiac function (*p* < 0.001). However, differences in cardiac function measurements by cancer histology or treatment protocol were not statistically significant. Regression analyses showed that the combination of GLS, SMOD, and MPI increased the odds of cardiac toxicity with an odds ratio of 7.30 (95% CI: 2.65–12.81, *p* < 0.001). The study underscores the predictive value of the combined GLS, SMOD, and MPI measurements in pediatric oncology patients undergoing anthracycline treatment for cardiotoxicity. Although variations across cancer types and treatment protocols were not significant, the study emphasizes the potential utility of these novel echocardiographic measures in early

**Citation:** Ardelean, A.M.; Olariu, I.C.; Isac, R.; Nalla, A.; Jurac, R.; Stolojanu, C.; Murariu, M.; Fericean, R.M.; Braescu, L.; Mavrea, A.; et al. Impact of Cancer Type and Treatment Protocol on Cardiac Function in Pediatric Oncology Patients: An Analysis Utilizing Speckle Tracking, Global Longitudinal Strain, and Myocardial Performance Index. *Diagnostics* **2023**, *13*, 2830. https:// doi.org/10.3390/diagnostics13172830

Academic Editors: Emmanouel Hatzipantelis and Maria Kourti

Received: 1 July 2023 Revised: 15 August 2023 Accepted: 30 August 2023 Published: 31 August 2023

**Copyright:** © 2023 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/).

detection and long-term prediction of anthracycline-induced cardiotoxicity. Further studies in larger, multi-center cohorts are required for validation.

**Keywords:** pediatrics; oncology; chemotherapy; cardiac function tests

#### **1. Introduction**

The continued advancements in pediatric oncology have led to a steady increase in survival rates, providing a truly encouraging trend [1]. Despite this promising development, the life-saving interventions, which often include aggressive chemotherapy and radiotherapy, often cause considerable long-term morbidity [2,3]. One of the most significant and alarming late effects is cardiotoxicity [4]. It is well established that cancer treatments, particularly anthracyclines and chest irradiation, can lead to various cardiac complications such as cardiomyopathy, ischemic heart disease, pericarditis, arrythmia, and congestive heart failure [5]. Furthermore, cardiac damage can occur years or even decades after the completion of therapy, adding an extra dimension to this already complex issue [6].

Traditionally, cardiac function in pediatric oncology patients has been monitored using conventional echocardiographic methods such as ejection fraction (EF) and fractional shortening (FS) [7]. However, these measures have significant limitations, since they are influenced by several factors, including loading conditions and heart rate, and may not accurately represent true myocardial function [8]. Moreover, significant reductions in EF and FS often occur late, when irreversible myocardial damage has already occurred [9]. Therefore, there is an urgent need to improve the early detection of cardiotoxicity in this population.

The damaging effects of treatments like anthracyclines on the heart cannot be understated. Anthracyclines are known to induce cardiotoxicity, a significant side effect that can severely affect the quality of life and overall survival of cancer patients, independent of the oncological prognosis [10]. This cardiotoxicity usually starts with myocardial cell injury, progresses to reductions in left ventricular ejection fraction (LVEF), and, if undetected and untreated, can eventually lead to symptomatic heart failure [10]. Specifically, anthracycline-induced cardiotoxicity can manifest even in a subclinical phase, making early detection paramount. Traditional measures like LVEF may not suffice in capturing these early changes. Advanced echocardiographic techniques, such as 2D Speckle tracking echocardiography (STE), have shown the capability of detecting early myocardial changes, especially during chemotherapy [11,12]. Peak systolic global longitudinal strain, a parameter derived from STE, stands out as an especially consistent indicator of early myocardial damage. Thus, the use of STE, GLS, and MPI can be pivotal, not just in detecting these changes, but also in driving the implementation of cardioprotective treatments before irreversible damage ensues.

In recent years, speckle tracking echocardiography (STE), global longitudinal strain (GLS), and the myocardial performance index (MPI) have emerged as promising tools for the evaluation of myocardial function [13,14]. STE is an angle-independent imaging technique that provides a detailed assessment of myocardial deformation [15]. GLS measures the degree of deformation of the myocardium longitudinally and is considered more sensitive and specific for the early detection of myocardial damage than traditional echocardiographic methods [16]. MPI, also known as the Tei index, is a Doppler-derived index that evaluates both systolic and diastolic cardiac function [17]. These innovative techniques may enable us to detect subtle changes in cardiac function and improve patient outcomes.

However, while these novel methods show great promise, there are still many unknowns regarding their utility in pediatric oncology patients [18,19]. Previous studies have been limited by small sample sizes, heterogeneous patient populations, and lack of long-term follow-up data. Moreover, there is limited research on the potential impact of different disease types and treatment intensity on the results of these measures. In

addition, it is unclear whether these measures can predict long-term cardiac outcomes. Early detection of cardiotoxicity is crucial, but it is equally important to understand the implications of these findings. If changes in cardiac function were identified at an early stage, it would be possible to intervene and alter the course of the disease. However, to do this effectively, there is a need to understand how these early changes are associated with long-term outcomes.

Therefore, the hypotheses of the present study are that disease type and treatment intensity have a significant impact on cardiac function as measured by speckle tracking, global longitudinal strain, and the myocardial performance index in pediatric oncology patients. It is assumed that these novel echocardiographic measures can detect early changes in cardiac function that traditional methods cannot. Moreover, these early changes might predict long-term cardiac outcomes in this population. Accordingly, the objectives of this study are to evaluate the impact of cancer type and treatment protocol on cardiac function in pediatric oncology patients; to compare the sensitivity of STE, GLS, and MPI with that of traditional echocardiographic methods for detecting early cardiac dysfunction; and to explore the potential of these measures to predict long-term cardiac complications in this population.

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

#### *2.1. Design and Ethics*

This study was designed as a single-center, retrospective cohort study conducted over a four-year period from 2019 to 2022. The study protocol and ethical considerations were reviewed and approved by an institutional review board (IRB). All study procedures complied with the ethical standards of the 1964 Helsinki declaration and its later amendments. The investigators ensured that confidentiality was maintained, and data privacy was protected according to local data protection laws. The investigators clarified to the parents/guardians that participation was voluntary and that they could withdraw from the study at any time without affecting the child's medical care. Before participation, written informed consent was obtained from the parents or guardians of all pediatric patients. For patients who reached the age of consent during the course of the study, assent was sought in addition to parental consent. The research team ensured that all participants and their guardians fully understood the study's objectives, procedures, potential benefits, and risks.

Studies have consistently highlighted the potential cardiotoxic effects of oncology treatments, especially in pediatric patients. While our research primarily focuses on a specific patient cohort, it is imperative to contextualize our findings within the broader scope of evidence. Several meta-analyses have aggregated results from multiple studies, providing a comprehensive understanding of cardiac effects in pediatric oncology patients across diverse treatment protocols, cancer stages, and demographics. Such meta-analyses underscore the importance of regular cardiac monitoring, especially considering the multifaceted nature of oncology treatments and the variabilities in patient response. By delving deep into the oncological characteristics of our population, such as clinical stage, total dose of cardiotoxic drug administered, and detailed echocardiogram timelines, our study aims to bridge the gaps in knowledge and offer nuanced insights into pediatric cardiac care in oncology settings.

#### *2.2. Inclusion and Exclusion Criteria*

The inclusion criteria were pediatric patients diagnosed with a new oncological pathology requiring anthracycline therapy between 2019 and 2022. Baseline measurements were taken upon the patient's first presentation at the oncology ward, before initiation of any therapeutic interventions. Patients, both neoadjuvant and metastatic, were included to provide a comprehensive view of the impact of different cancer stages on cardiac function. The study focused primarily on the diagnosis of a new oncological pathology and did not differentiate based on the specific stage of cancer. However, the clinical stage of each patient was documented and will be presented in the Results section for a more detailed

understanding. The inclusion criteria comprised: (1) Pediatric patients (aged 0–18 years) diagnosed with a new oncological pathology requiring anthracycline therapy between 2019 and 2023; (2) patients with measurable cardiac function at baseline and at regular intervals during the course of treatment; (3) patients whose clinical and treatment data, including disease type, treatment protocol, and cumulative dosage of anthracyclines and other chemotherapy agents, were available and complete.

On the contrary, the exclusion criteria comprised: (1) Patients with known pre-existing cardiac pathology that could affect the cardiac function measurements; (2) patients who had already started oncological treatment before baseline measurements could be established; (3) patients with any contraindications to echocardiography, such as severe skin condition or chest deformity; (4) patients who initiated treatment at our institution but decided to continue treatment at another facility; and (5) patients with other concurrent severe medical conditions (e.g., severe infections, metabolic diseases, genetic syndromes, etc.) that could independently impact cardiac function.

The control group consisted of healthy children admitted to our hospital for minor conditions such as chest wall pain, syncope spells, minor respiratory infections, or athletes who came in for their mandatory annual check-ups and required a cardiology assessment. The cases and control groups were matched by age, gender, and body mass index. The control group included healthy children admitted to our hospital for various minor conditions. Among these, some were athletes. For the purpose of this study, "athletes" were defined as individuals who engage in regular, structured physical training for a specific sport and participate in competitive events related to that sport at least once a year. Out of all the controls, seven were athletes.

Additional factors including patient age, sex, disease, fractional shortening (FS), leftventricular global longitudinal strain (GLS), Simpson's method of discs (SMOD) measurements, myocardial performance index (MPI), presence of cardiotoxicity, 12-lead electrocardiogram (ECG) findings, echocardiography results, biomarkers of cardiac injury, protocol intensity, surface area (m<sup>2</sup> ), total anthracycline dose, cumulative dosage of other chemotherapy agents (including cytarabine administered intravenously, subcutaneously, and intrathecally, etoposide, cyclophosphamide, vincristine, asparaginase, ifosfamide, methotrexate administered intravenously and intrathecally, mercaptopurine orally, Oncaspar intravenously, mitoxantrone intravenously), and radiation therapy received were collected and analyzed.

#### *2.3. Materials Used and Definitions*

The diagnosis of cardiac toxicity was made by identifying ultrasound alterations after chemotherapy. Cardiac function was measured using a GE VIVID E9 echocardiograph. High-quality images with ECG signals were captured in apical views (3, 4, and 2 chambers). When satisfactory images were obtained, the machine software identified the end-systolic frame and automatically traced the endocardial and epicardial borders, spanning from one end of the mitral annulus to the other. This process generated a region of interest (ROI) that encompassed the entire myocardial wall. Cardiac function measurements were taken at regular intervals post the initiation of therapy. Specifically, echocardiograms were performed every three months. Cardioxane, although not a primary chemotherapy agent under consideration, was documented if administered to any patient.

Adjustments were then made to the ROI manually, and speckle placement was corrected to select for optimal myocardial wall thickness. Speckles, which are myocardial reflectors, were tracked throughout the cardiac cycle to determine myocardial strain. Care was taken not to include the pericardium or the base of the valves to avoid a false reduction in global longitudinal strain (GLS). Decreases in GLS (less negative values, closer to 0) may indicate decreased cardiac function and potentially cardiac injury.

In addition to GLS, cardiac function was assessed using traditional methods such as M mode dimension ejection fraction (Teicholtz) and volume ejection fraction (Simpson's method of disks, SMOD), and tissue Doppler was used to measure the myocardial performance index. The normal range for SMOD is generally considered to be between 55% and 70%, while values below 55% are usually considered indicative of reduced systolic function. Normal MPI values are generally considered to be less than 0.40, and these may vary slightly depending on whether they are measured by tissue Doppler imaging or flow Doppler imaging. Values above 0.40 indicate worsening global cardiac function. Any abnormalities that arose during treatment, such as pericardial or pleural effusion, valve regurgitations or stenoses, pulmonary hypertension, diastolic dysfunction, dilated cardiomyopathy or electrocardiographic modifications, were documented and monitored.

#### *2.4. Statistical Analysis*

Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS v.26). Descriptive statistics were utilized to summarize the data. Continuous variables were expressed as the mean ± standard deviation, while categorical variables were presented as frequencies and percentages. The paired *t*-test was used to compare baseline and post-treatment measurements within the same group, and the independent *t*-test was used to compare differences between the patient and control groups, while the ANOVA test was employed to compare means of more than two groups. Multivariate logistic regression was employed to identify independent predictors of chemotherapy-induced cardiotoxicity, adjusting for potential confounders. Before performing multivariate logistic regression, a univariate analysis was conducted to determine which variables were to be included in the multivariate analysis. Additionally, to assess the effectiveness of our cardiac function measurements against established standards, a predictive analysis was carried out. This involved computing predictive values, sensitivity, and specificity of our measures in relation to the gold standard. The ANOVA test was primarily utilized to compare means of cardiac function measurements at different time points, including baseline, 3 months, 6 months, and 12 months. A *p*-value of less than 0.05 was considered statistically significant. All graphs and tables were created using GraphPad Prism v.9.

#### **3. Results**

#### *3.1. Background Data of Patients*

The current study incorporated a total of 145 participants, including 99 cases and 46 controls (Table 1). The average age of the case group was 10.7 ± 4.4 years, whereas the control group averaged slightly younger at 10.2 ± 3.6 years, without a significant difference. The body mass index (BMI) was comparable between the two groups, with mean BMI values of 20.5 and 21.3 for the cases and control groups, respectively, but with no significant difference. Moreover, the BMI percentile categories displayed a balanced distribution among both case and control groups, and the statistical comparison between the two groups did not yield a significant *p*-value (0.361). Gender distribution in both groups was also similar, with 58.6% of the case group being male compared to 63.0% in the control group. Female participants accounted for 41.4% of the case group and 37.0% of the control group, yielding a *p*-value of 0.610. Therefore, gender did not significantly differ between the two groups. The most common cancer histology was B-cell acute lymphocytic leukemia (B-ALL), followed by T-ALL (14.1%), and acute myeloid leukemia (AML) in 12.1% of cases, as presented in Figure 1.

**Variables \* Cases (***n* **= 99) Controls (***n* **= 46)** *p***-Value**

Age (mean ± SD) 10.7 ± 4.4 10.2 ± 3.6 0.471 Age range 1–18 1–17 –

**Table 1.** Background data of study participants. BMI, kg/m2 (mean ± SD) 20.5 ± 4.6 21.3 ± 5.8 0.308

**Table 1.** Background data of study participants.

\*—Mean and SD compared using Student's *t*-test; BMI—body mass index; SD—standard deviation. \*—Mean and SD compared using Students *t*-test; BMI—body mass index; SD—standard deviation.

*Diagnostics* **2023**, *13*, 2830 6 of 14

**Figure 1.** Prevalence of cancer histology types among the pediatric population. **Figure 1.** Prevalence of cancer histology types among the pediatric population.

#### *3.2. Cardiac Parameters*

the controls (*p* = 0.004).

*3.2. Cardiac Parameters*  Table 2 outlines the analysis of cardiac function measurements between pediatric oncology patients post-chemotherapy (*n* = 99) and healthy controls (*n* = 46). Ejection fraction (EF), a marker of systolic function, showed significant variation between the two cohorts. The mean EF in the cases was 62.8 ± 5.7%, which was lower than that in the controls (66.4 ± 6.1%), and this difference was statistically significant (*p* < 0.001). Additionally, EF distribution across categories revealed that a higher proportion of controls had an EF above 70% (30.4%) compared to that of cases (11.1%), also statistically significant (*p* = 0.005). A similar trend was observed in the global longitudinal strain (GLS) measurement. The cases Table 2 outlines the analysis of cardiac function measurements between pediatric oncology patients post-chemotherapy (*n* = 99) and healthy controls (*n* = 46). Ejection fraction (EF), a marker of systolic function, showed significant variation between the two cohorts. The mean EF in the cases was 62.8 ± 5.7%, which was lower than that in the controls (66.4 ± 6.1%), and this difference was statistically significant (*p* < 0.001). Additionally, EF distribution across categories revealed that a higher proportion of controls had an EF above 70% (30.4%) compared to that of cases (11.1%), also statistically significant (*p* = 0.005). A similar trend was observed in the global longitudinal strain (GLS) measurement. The cases had a mean GLS of −16.3 ± 5.1, whereas the controls had a more negative mean GLS of −19.0 ± 5.4, indicating a more substantial contraction and hence better cardiac function in the controls (*p* = 0.004).

had a mean GLS of −16.3 ± 5.1, whereas the controls had a more negative mean GLS of −19.0 ± 5.4, indicating a more substantial contraction and hence better cardiac function in

± 6.7, *p* < 0.001). The myocardial performance index (MPI), a measure of both systolic and diastolic function, was higher in cases (0.37 ± 0.06) compared to that in controls (0.55 ± 0.10). A higher MPI usually represents worse cardiac performance, reflecting poorer over-

When assessed using Simpsons method of discs (SMOD), the mean score in cases

**Table 2.** Cardiac function measurements between children after chemotherapy and healthy controls.

\*—Mean and SD compared using Student's *t*-test; SD—standard deviation; GLS—global longitudinal strain; SMOD—Simpson's method of discs; MPI—myocardial performance index; ECG—electrocardiogram; EF—ejection fraction.

When assessed using Simpson's method of discs (SMOD), the mean score in cases was found to be 55.1 ± 6.0, which was again significantly lower than that in controls (59.3 ± 6.7, *p* < 0.001). The myocardial performance index (MPI), a measure of both systolic and diastolic function, was higher in cases (0.37 ± 0.06) compared to that in controls (0.55 ± 0.10). A higher MPI usually represents worse cardiac performance, reflecting poorer overall cardiac function in cases (*p* < 0.001). Electrocardiogram (ECG) findings revealed a significantly higher proportion of normal findings in controls (87.0%) compared to that in cases (66.7%, *p* = 0.010). This was mirrored in the cardiac ultrasound findings, with a higher rate of normal findings among controls (76.1%) compared to that in cases (47.5%, *p* = 0.001). Conversely, the percentage of abnormal findings was higher in cases for both ECG and cardiac ultrasound.

Table 3 illustrates the comparison of cardiac function measurements stratified by cancer histology. Although there was variation among the different cancer types, none of the observed differences reached statistical significance. Global longitudinal strain (GLS) was calculated using speckle tracking echocardiography and ranged from −15.3 ± 4.6 in Hodgkin's lymphoma patients to −18.1 ± 5.1 in T-cell acute lymphoblastic leukemia (T-ALL) patients. However, these differences were not statistically significant (*p* = 0.442).

**Table 3.** Cardiac measurements based on cancer histology.

SD—standard deviation; MPI—myocardial performance index; T-ALL—T-cell acute lymphoblastic leukemia; B-ALL—B-cell acute lymphoblastic leukemia; AML—acute myeloid leukemia; GLS—global longitudinal strain; SMOD—Simpson's method of discs; EF—ejection fraction.

Cardiac function measured by Simpson's method of discs (SMOD) ranged from 51.0 ± 6.3 in acute myeloid leukemia (AML) patients to 59.2 ± 6.6 in non-Hodgkin's lymphoma patients. Again, the differences across the various types of cancers did not attain statistical significance (*p* = 0.150). The myocardial performance index (MPI), a combined measure of both systolic and diastolic function, varied between 0.36 ± 0.05 in Hodgkin's lymphoma patients and 0.48 ± 0.09 in medulloblastoma patients, but these variations were not statistically significant (*p* = 0.306). Lastly, mean ejection fraction (EF), a measure of systolic function, varied between 58.0 ± 5.4 in osteosarcoma patients and 64.6 ± 5.5 in non-Hodgkin's lymphoma patients. Despite this range, the differences were not statistically significant (*p* = 0.084).

Table 4 illustrates the cardiac function measurements in relation to the different treatment protocols implemented for the various types of cancer. Despite observable differences in the measurements, none of the variations among the treatments reached statistical significance. Global longitudinal strain (GLS), calculated using speckle tracking echocardiography, varied across treatment protocols from −16.5 ± 4.6 under the EURAMOS protocol to −15.0 ± 4.8 under the RCHOP protocol. However, these variations did not achieve statistical significance (*p* = 0.095). Regarding the Simpson's method of discs (SMOD), values ranged from 55.0 ± 6.6 under the EURAMOS protocol to 60.1 ± 4.3 under the ICE protocol, and this range did not reach statistical significance (*p* = 0.317).

**Table 4.** Cardiac measurements based on treatment protocol.

SD—standard deviation; GLS—global longitudinal strain; SMOD—Simpson's method of discs; MPI—myocardial performance index; AML—acute myeloid leukemia; ALL—acute lymphoid leukemia; BFM—Berlin-Frankfurt-Münster; ABVD (for Hodgkin's lymphoma)—Adriamycin (doxorubicin), bleomycin, vinblastine, and dacarbazine; ICE—ifosfamide, carboplatin, and etoposide; ISPO (for nephroblastoma)—International Society of Pediatric Oncology; RCHOP (for non-Hodgkin's lymphoma)—rituximab, cyclophosphamide, hydroxydaunorubicin (doxorubicin), Oncovin (vincristine), and prednisone; EURAMOS—European and American Osteosarcoma Study Group; CWS (for rhabdomyosarcoma)—Cooperative Weichteilsarkom Studiengruppe; EF—ejection fraction.

The myocardial performance index (MPI), a combined measure of both systolic and diastolic function, varied between 0.39 ± 0.04 under the AML BFM protocol and 0.46 ± 0.12 under the ICE protocol, but these differences were not statistically significant (*p* = 0.063). Ejection fraction (EF), a measure of systolic function, ranged from 57.6 ± 3.9 under the EURAMOS protocol to 62.6 ± 3.8 under the ISPO protocol, but these differences were not statistically significant (*p* = 0.139). The percentage of patients who developed cardiac toxicity also varied by treatment protocol, with the highest occurrence in patients under the ALL BFM protocol (12.1%) and the lowest in multiple protocols, including AML BFM, ICE, ISPO, and RCHOP, each at 2.0%. However, the variance in incidence of cardiac toxicity among the different treatment protocols did not reach statistical significance (*p* = 0.247).

#### *3.3. Risk Evaluation*

Table 5 and Figure 2 show the results of the regression analysis, providing odds ratios for the associations between various cardiac function measurements and the development of cardiac toxicity. The odds ratios have been adjusted for potential confounders. Global longitudinal strain (GLS) alone had an odds ratio of 2.20, indicating that for each unit increase in GLS, the odds of cardiac toxicity were approximately doubled. However, this finding was not statistically significant (95% CI: 0.92–4.31, *p* = 0.106). Simpson's method of discs (SMOD) had a similar odds ratio of 2.16, indicating a slightly more than double increase in the odds of cardiac toxicity for each unit increase in the SMOD measure, but again, this finding was not statistically significant (95% CI: 0.99–5.16, *p* = 0.098).

**Table 5.** Regression analysis for factors associated with cardiac toxicity.

\*—The control group serves as reference; CI—confidence interval; GLS—global longitudinal strain; SMOD—Simpson's method of discs; MPI—myocardial performance index.

**Figure 2.** Risk analysis for factors associated with cardiac toxicity. **Figure 2.** Risk analysis for factors associated with cardiac toxicity.

**4. Discussion**  *4.1. Literature and Current Study Findings*  The present studys findings underscored a significant impact of disease type and treatment intensity on cardiac function in pediatric oncology patients. These results were consistent with the initial hypotheses that traditional echocardiographic methods might not detect early changes in cardiac function that these novel methods can discern. Importantly, these early changes might predict long-term cardiac outcomes in this population, lending further weight to the potential utility of these novel approaches in this clinical context. The observed differences in cardiac function parameters, such as ejection fraction (EF), global longitudinal strain (GLS), the myocardial performance index (MPI), and re-The myocardial performance index (MPI) showed a less marked association, with an odds ratio of 1.24 suggesting only a slight increase in the odds of cardiac toxicity for each unit increase in MPI. This association was also not statistically significant (95% CI: 0.81–4.03, *p* = 0.221). However, combinations of these measures showed stronger and statistically significant associations with cardiac toxicity. The combination of GLS and SMOD had an odds ratio of 4.05, showing a significant quadrupling in the odds of cardiac toxicity (95% CI: 1.33–7.40, *p* < 0.001). Similarly, the combination of GLS and MPI showed a significant increase in the odds of cardiac toxicity, with an odds ratio of 2.49 (95% CI: 1.08–7.24, *p* = 0.030). The combination of SMOD and MPI showed an even greater odds ratio of 5.02, indicating a more than fivefold increase in the odds of cardiac toxicity (95% CI: 2.14–10.09, *p* < 0.001). The combination of all three measurements—GLS, SMOD, and MPI—showed the greatest odds ratio of 7.30, indicating more than a sevenfold increase in the odds of cardiac toxicity (95% CI: 2.65–12.81, *p* < 0.001).

sults from Simpsons method of discs (SMOD), underscored the potential deleterious effects of cancer and its treatment on cardiac function. These findings align with earlier studies, such as Lipshultz et al. [20], which identified a higher risk of cardiac dysfunction

Importantly, our study revealed no statistically significant differences in cardiac function parameters when stratified by cancer histology, suggesting a consistent impact across various cancer types. While this seems to be in contrast to prior research such as that by Mulrooney et al. [21] and Getz et al. [22], it is crucial to consider several factors. First, the chemotherapeutic agents used in those studies were different from those in ours, with some using agents like dexrazoxane instead of doxorubicin for AML. The cardiotoxic profile of different chemotherapy agents can vary widely, potentially accounting for the disparate findings. Additionally, population characteristics, such as the age group, baseline health status, and the presence of other comorbidities, might have been different in these studies, leading to varied results. Moreover, sample size, methodology, and the instruments used to measure cardiac function can also influence findings. For instance, if Mulrooney et al. [21] had a larger sample size, they might have had more statistical power to detect subtle differences that our study could not. Similarly, variations in methodology, such as the time intervals between chemotherapy sessions and cardiac function measure-

The uniform impact of treatment intensity on cardiac function across various protocols, as observed in our study, deviates from previous literature. Studies like Armenian et al. [23] have indicated differential impacts based on treatment protocols. Several reasons could account for this discrepancy. The definition and classification of treatment intensity

chest radiation.

ments, can yield different results.

#### **4. Discussion**

#### *4.1. Literature and Current Study Findings*

The present study's findings underscored a significant impact of disease type and treatment intensity on cardiac function in pediatric oncology patients. These results were consistent with the initial hypotheses that traditional echocardiographic methods might not detect early changes in cardiac function that these novel methods can discern. Importantly, these early changes might predict long-term cardiac outcomes in this population, lending further weight to the potential utility of these novel approaches in this clinical context.

The observed differences in cardiac function parameters, such as ejection fraction (EF), global longitudinal strain (GLS), the myocardial performance index (MPI), and results from Simpson's method of discs (SMOD), underscored the potential deleterious effects of cancer and its treatment on cardiac function. These findings align with earlier studies, such as Lipshultz et al. [20], which identified a higher risk of cardiac dysfunction in childhood cancer survivors, particularly in those exposed to anthracycline therapy or chest radiation.

Importantly, our study revealed no statistically significant differences in cardiac function parameters when stratified by cancer histology, suggesting a consistent impact across various cancer types. While this seems to be in contrast to prior research such as that by Mulrooney et al. [21] and Getz et al. [22], it is crucial to consider several factors. First, the chemotherapeutic agents used in those studies were different from those in ours, with some using agents like dexrazoxane instead of doxorubicin for AML. The cardiotoxic profile of different chemotherapy agents can vary widely, potentially accounting for the disparate findings. Additionally, population characteristics, such as the age group, baseline health status, and the presence of other comorbidities, might have been different in these studies, leading to varied results. Moreover, sample size, methodology, and the instruments used to measure cardiac function can also influence findings. For instance, if Mulrooney et al. [21] had a larger sample size, they might have had more statistical power to detect subtle differences that our study could not. Similarly, variations in methodology, such as the time intervals between chemotherapy sessions and cardiac function measurements, can yield different results.

The uniform impact of treatment intensity on cardiac function across various protocols, as observed in our study, deviates from previous literature. Studies like Armenian et al. [23] have indicated differential impacts based on treatment protocols. Several reasons could account for this discrepancy. The definition and classification of treatment intensity might differ between studies. What was considered "intense" in our study could potentially be "moderate" or "mild" in another. Furthermore, the follow-up duration and intervals to check cardiac function post-treatment could vary, leading to differences in the observed impacts. Lastly, the previous studies might have included more diverse treatment protocols, or their patient population might have had different vulnerabilities to certain treatments. However, it is possible that the robustness and sensitivity of the novel echocardiographic measures used in the present study allowed for a more nuanced and sensitive detection of early cardiac dysfunction, thus capturing changes that traditional methods might have missed.

Interestingly, the regression analysis results showed a significant association between combinations of novel echocardiographic measures (GLS, SMOD, and MPI) and the development of cardiac toxicity. This finding suggests that the combined use of these novel measures might provide more accurate and early detection of cardiac dysfunction in pediatric oncology patients. This supports the contention of several previous studies, such as Thavendiranathan et al. [24] and Poterucha et al. [25], who argued for the combined use of novel echocardiographic measures to improve the prediction of chemotherapy-related cardiac dysfunction. Moreover, this combined approach may have the potential to facilitate early intervention, thus mitigating the risk of long-term cardiac complications in this vulnerable population. This aligns with recent research by Narayan et al. [26], who demonstrated that early detection and intervention can improve cardiac outcomes in pediatric oncology patients.

Our results accentuate that pediatric oncology patients post-chemotherapy demonstrated significant decrements in cardiac function when compared to healthy controls. Parameters such as EF and GLS showcased notably lower values in the cases than in controls, indicative of reduced systolic function and compromised cardiac health, respectively. These findings align with the prevailing literature suggesting potential cardiotoxic effects of certain chemotherapy agents on pediatric patients, warranting heightened surveillance and potential interventions to ameliorate these impacts [27,28]. Additionally, while variations in cardiac measurements based on cancer histology and treatment protocol were noted, these were not statistically significant. This underlines the need for more expansive studies, possibly integrating multi-center data, to discern the nuanced effects of different treatment modalities and disease types on pediatric cardiac health. As childhood cancer survivors continue to live longer due to advances in therapy, understanding these cardiac repercussions becomes paramount for tailoring long-term care and optimizing quality of life.

The findings of this study also highlight the potential predictive value of these novel echocardiographic measures in forecasting long-term cardiac outcomes in pediatric oncology patients. This echoes the findings of studies such as Cheung et al. [29] and Kang et al. [30], which identified a significant correlation between early changes in these measures and long-term cardiac outcomes. Therefore, these results underscore the significant impact of cancer and its treatment on cardiac function in pediatric oncology patients. The present study's use of novel echocardiographic measures (GLS, SMOD, and MPI) offers a valuable approach to detecting early cardiac dysfunction and potentially forecasting long-term cardiac outcomes in this population. These findings underscore the importance of ongoing research in this area to further refine these methods and to develop targeted interventions to mitigate the cardiac risks associated with pediatric oncology treatment. Lastly, there is a need for a follow-up study that looks into the time of initial detection of cardiac function abnormalities by the different echocardiographic methods, spanning a period longer than four years. This would help in drawing a more definitive comparison between traditional and novel measures in predicting anthracycline-induced cardiotoxicity.

#### *4.2. Study Limitations*

While this study provides valuable insights into the potential of speckle tracking echocardiography, global longitudinal strain, and the myocardial performance index as sensitive indicators of early anthracycline-induced cardiotoxicity, it has several limitations. Firstly, the study's single-center, retrospective design might limit the generalizability of its findings. Data from a single institution might not adequately capture the variability of clinical practices across different centers, potentially biasing the results. Furthermore, the retrospective nature of the study might introduce selection bias, with the potential for missing or incomplete data. The reliance on historical records could also lead to information bias due to inaccuracies in documentation. Secondly, the study was conducted over a fouryear period, which might be insufficient to determine the long-term cardiac effects of anthracycline therapy. Late-onset cardiotoxicity can occur many years after treatment cessation; thus, the follow-up period might need to be extended to fully assess these effects.

Additionally, the study did not account for other factors that might influence cardiac function, such as patients' physical activity levels, nutritional status, or other comorbidities. The impact of these confounding variables on cardiac function should be considered in future studies. The exclusion of patients who had started treatment before baseline measurements could be established might have resulted in a selection bias, potentially excluding patients with more aggressive disease who needed immediate treatment. Furthermore, patients with severe infections or metabolic diseases were also excluded, potentially creating a cohort of patients in better overall health than the general population of pediatric oncology patients.

Lastly, while the study included a healthy control group, these controls were patients who sought medical care for minor conditions, possibly introducing a "healthy patient

bias". Furthermore, matching cases and controls by age, gender, and body mass index might not have controlled for all potential confounding variables. Other factors such as socioeconomic status or genetic predispositions might also influence cardiac outcomes and were not considered in this study. Despite these limitations, the study provides valuable insights into the potential use of novel echocardiographic measures to detect early cardiac dysfunction in pediatric oncology patients. Further research, particularly multicenter, prospective studies with longer follow-up periods, is needed to validate these findings and to better understand the long-term cardiac outcomes in this population.

#### **5. Conclusions**

The study concluded that pediatric oncology patients exhibited significant differences in cardiac function post-chemotherapy compared to that of healthy controls, as evidenced by measurements including the ejection fraction (EF), global longitudinal strain (GLS), Simpson's method of discs (SMOD), and the myocardial performance index (MPI). These measurements suggested an increased prevalence of cardiac dysfunction in patients, corroborating the hypothesis that cancer type and treatment intensity significantly impacted cardiac function. Notably, early changes detected by GLS, SMOD, and MPI were associated with long-term cardiac outcomes, establishing these methods as potentially superior to traditional echocardiographic measures in identifying early cardiac dysfunction. However, the variations in cardiac function measurements among different cancer histologies and treatment protocols did not reach statistical significance. Interestingly, the combination of GLS, SMOD, and MPI demonstrated the highest association with the development of cardiac toxicity, indicating a sevenfold increase in risk. While the data indicated a promise of these novel measures, further longitudinal studies, spanning longer durations, are needed to truly validate their long-term predictive value.

**Author Contributions:** Conceptualization, A.M.A. and I.C.O.; methodology, A.M.A. and I.C.O.; software, R.I. and R.J.; validation, R.I. and R.J.; formal analysis, C.S. and M.M.; investigation, C.S. and M.M.; resources, R.M.F.; data curation, R.M.F.; writing—original draft preparation, A.M.A.; writing—review and editing, L.B., C.D. and A.N.; visualization, L.B., C.D., and A.N.; supervision, A.M. and G.D.; project administration, A.M. and G.D. 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 in accordance with the Declaration of Helsinki and approved by the Institutional Review Board of the Emergency Hospital for Children "Louis ¸Turcanu", from Timisoara, Romania.

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

**Data Availability Statement:** Data available on request.

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

#### **References**

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**8. Utilization**

288 Sustainable Growth and Applications in Renewable Energy Sources

*graminis*). Szarvasi-1 energy grass proved to be sensitive to mildew particularly on those sites where intensive growth of the plant occurred due to optimal nutrient and water availability. The mildew infection can cause severe damage on the leaf structure of the plant resulting in total devastation of whole patches. Proper chemical plant protection is needed to avoid significant biomass production loss. Infection of mildew was mediated by old hay bales deposited along the edge of energy grass fields, so the prompt collection and transportation of bales can contribute to lowering the chance of energy grass fields being reinfected. According to our results, chemical protection of energy grass fields must be taken

Ecological invasion of neophyte plant and animal taxa has now become one of the most feared sources of natural habitat degradation according to many nationwide and international surveys (e.g. Molnár et al., 2008) The most frequent method of neophyte introduction is their agricultural use through which their large-scale distribution and successful establishment are intensively supported by human activities. Suggesting new plant taxa to be involved in agricultural production bears the hazard of suggesting a new potential invasive plant too. Hence thorough investigation and consideration must be taken

*Elymus elongatus* is a rare, native plant species to Hungary; consequently its Szarvasi-1 cultivar is much more favourable for agricultural production in Hungary than other exotic biomass grasses. Szarvasi-1 carries genetic material that is derived from only indigenous populations of *E. elongatus* in Hungary. Hence the cultivar can be regarded as an indigenous taxon, so its potential as an ecological hazard in terms of invasivity is low. Since Szarvasi-1 energy grass has a transient seedbank type (i.e. its seeds lose their viability in a year), its cropfields can be transformed into any other crop without the problem of resprouting. High competitive ability as well as fast growth dynamics are the main characters of Szarvasi-1 energy grass when it manages to establish itself completely. As our experiments suggested, weed species can outcompete Szarvasi-1 energy grass individuals if there is only incomplete sprouting and the development of tillers are slow. In this case, the stands of Szarvasi-1 energy grass crop remain open, and weeds can gain a significant advantage in growing and spreading. This is why we expect Szarvasi-1 energy grass not to be able to invade intact natural or semi-natural habitats, not even in the close vicinity of energy grass fields from where the seeds can escape in large quantities. Energy grass can germinate only in anthropogenic habitats where continuous and intensive disturbance takes place (e.g. field margins, dirt roads and banks following man-made canals). Since energy grass cannot spread vegetatively (i.e. with rhizomes), it will not become such a hazardous invasive species as for instance *Solidago gigantea* or *Reynoutria japonica*, at least not in its native

For the rest of the world, it is worth being cautious. From Australia and the US the aggressive spread of energy grass has been reported (e.g. Cox, 2001; Walsh, 2008), where the plant formed homogeneous, closed stands outcompeting all the native elements of the local vegetation. Although this happened only in very close environments to the lands recultivated by *Elymus elongatus* (e.g. steep slopes and bank of canals), this might indicate the possibilities of its invasive spreading, particularly in those countries where natural

specialist herbivores, as well as pathogenic agents of *Elymus elongatus* are missing.

into account similarly to that in the case of any other traditional agricultural crops.

before introducing any new agricultural crop, especially a new biomass plant.

**7. Ecological hazard**

habitat, in Eastern Europe.

The moisture content of the energy grass at harvest can highly influence the possibilities for storage, processing and utilization. Appropriate logistic and storage conditions can be provided by harvesting at the optimal time and the use of bales. In this manner the processing, chopping and direct energetic utilization of low moisture content of the baled fuel can be solved easily. High moisture content causes quality loss and negatively affects the processability and energetic characteristics of the material.

The application forms of energy grass used as fuel are:

The physical and some of the energetic characteristics of the listed fuel forms are different. The characteristics are summarized in Table 5.

\* values were determined based on the average of several measurements

Table 5. The physical and some of the energetic characteristics of the listed fuel assortment

Data show that independently of its form the energy grass has high ash content. It is necessary to mention however that based on technological and laboratorial investigations we have found that the high ash content is mainly caused by external physical contaminants. This can be significantly reduced e.g. by training the operators in maintaining technological discipline and by using the appropriate harvest-, loading-, and storing processes of the raw material. The elemental compositions of the investigated fuels are also different from the ligneous fuels. Chlorine and sulphur content were investigated by CHNS analysis which shows several times higher values compared to premium quality fuels (according to standards). This factor must be considered for energetic utilization. Herbaceous fuels (such as the energy grass) have low ash melting point, which greatly restricts their energetic utilization. The results, which clearly show the change in amount of ash sample plotted against temperature for ligneous and herbaceous fuels, are summarized in Fig. 17. Based on the results of the measurements it can be stated that the ash melting point of the energy grass is 690 C, while the ash melting point of the mixed wood-pellet is 1080 C.

Tall Wheatgrass Cultivar Szarvasi–1 (*Elymus elongatus* subsp. *ponticus* cv. Szarvasi–1)

duct.

systems.

**9. Conclusion**

of the plant.

emission of solid component from boilers.

Szarvasi-1 in the course of annual growth (Fig. 18.).

as a Potential Energy Crop for Semi-Arid Lands of Eastern Europe 291

equipped with "travelling grates" which have a ladder-like structure and consist of more segments. There is another grate, so-called "crawler grate", which was named after its appearance because it resembles a looped ribbon stick. The heat and power plant boiler designs have several solutions. Utilization of the energy grass in coal power-plants was carried out with co-firing which can solve the problem of ash melting. During the combustion of herbaceous fuels higher solid emissions can be measured which mainly deposit in the boiler and exhaust with the flue gas. *The efficiency is highly damaged by deposition on the heat transfer surfaces, and* depending on the composition it can result in corrosive effects in the boiler. In order to prevent this, mechanical or pneumatic equipment should be installed with a dust separator, which cleans automatically the flue

Parallel with this solution it is necessary to reduce the load of solid components of the flue gas, the equipment is usually mounted with cyclone, which allays larger floating particles from flue gas. Electrostatic filter may also be assessed, which significantly reduces the

Another possible method for the energetic utilization of energy grass is the so-called pyrolytic procedure where the fuel is fumigated in a multistage process in an oxygen-low environment. The resultant "grass-gas" will be burnt directly or after a cleaning procedure it will be suitable for use in gas engines for electricity production. Because of the high capital costs these technologies are primarily economical in the case of using high-performance equipment. As a conclusion, it can be stated that problems concerning the use of the herbaceous fuels - including energy grass - in low-and high-performance boilers, directly, or with co-firing technique have been solved. The conditions of the application are determined by the logistic aspects and the current production costs. In the current boiler engineering, considering technical, energetic, environmental and economic aspects, the herbaceous fuels and their boilers may play an important role in the medium power-level market of energy

A new energy crop (*Elymus elongatus* subsp. *ponticus* cv. Szarvasi-1, tall wheatgrass) has recently been introduced to cultivation in Hungary to provide biomass for solid biofuel energy production. The cultivar was developed in Hungary from a native population of *E. elongatus* subsp. *ponticus* for agronomic and energetic purposes. The main goal of our research was to investigate the performance of Szarvasi-1 energy grass under different growing conditions (e.g. soil types, nutrition supply). We focused on the ecological background, biomass yield, weed composition, morphology, ecophysiology and the genetics

The biomass yield of Szarvasi-1 energy grass depends mainly on the presence of macronutrients, soil texture and water availability of fields. Under typical soil nutrient conditions, precipitation has a considerable effect on biomass yield. Average yield of Szarvasi-1 energy grass is as much as 10-15 t DM ha-1 with great spatial and temporal variation depending on weather and habitat conditions. As part of an intensive agricultural management, the use of fertilizers can be a good solution when soil nutrients are inadequate. Nitrogen plays an important role in increasing biomass in any phenophases of

Fig. 17. Ash melting diagram of fuels

The high alkali content, which was adsorbed during the lifetime of the plant, causes the low ash melting point of the energy grass. This causes combustion problems because the ash melting occurs in the operating temperature of boiler. The material can melt and sick onto the surface of the structure elements of the boiler, and this will lead to interior depositions and permanent damage. To solve this problem, new boiler and grate types were developed. The part of the combustion chamber where the fuel burns in solid phase cannot reach high enough temperatures for the ash melting. Continuous movement of the fuel also helps to avoid scorification and interior depositions. Boiler technology was developed so that the fuel is moving on a moving grate in the boiler while the volatile component of the fuel is gasified between 150°C and 400°C**.** The charred roughage falls off the grate to the ash pit before the fuel would be able to reach the critical melting temperature (Fig. 17.). The volatile component is burnt in the second part of the boiler (the so-called post-combustor) where the temperature of the combustion chamber is approx. 800-900°C. The problem of ash melting was solved and sufficient burnout of the combustion gas was also ensured by this new technical solution. Based on this operating principle there are many structural solutions and performances available on the market.

The boilers, which are suitable for energetic utilization of the energy grass, can be ranked into three different groups based on their performance levels.

Due to their structure and size the low power equipments are mainly operated with pellet fuel. These automatic systems are suitable for the combustion of energy grass pellets with appropriate efficiency and low emission. The size of the boiler and the manufacturing cost are greatly increased by the necessary moving grate. These equipments are more robust than the prevalent wood-pellet boilers. Medium power equipments are primarily used in communal and social facilities, which are mainly operated using pellets. They are equipped with "travelling grates" which have a ladder-like structure and consist of more segments. There is another grate, so-called "crawler grate", which was named after its appearance because it resembles a looped ribbon stick. The heat and power plant boiler designs have several solutions. Utilization of the energy grass in coal power-plants was carried out with co-firing which can solve the problem of ash melting. During the combustion of herbaceous fuels higher solid emissions can be measured which mainly deposit in the boiler and exhaust with the flue gas. *The efficiency is highly damaged by deposition on the heat transfer surfaces, and* depending on the composition it can result in corrosive effects in the boiler. In order to prevent this, mechanical or pneumatic equipment should be installed with a dust separator, which cleans automatically the flue duct.

Parallel with this solution it is necessary to reduce the load of solid components of the flue gas, the equipment is usually mounted with cyclone, which allays larger floating particles from flue gas. Electrostatic filter may also be assessed, which significantly reduces the emission of solid component from boilers.

Another possible method for the energetic utilization of energy grass is the so-called pyrolytic procedure where the fuel is fumigated in a multistage process in an oxygen-low environment. The resultant "grass-gas" will be burnt directly or after a cleaning procedure it will be suitable for use in gas engines for electricity production. Because of the high capital costs these technologies are primarily economical in the case of using high-performance equipment. As a conclusion, it can be stated that problems concerning the use of the herbaceous fuels - including energy grass - in low-and high-performance boilers, directly, or with co-firing technique have been solved. The conditions of the application are determined by the logistic aspects and the current production costs. In the current boiler engineering, considering technical, energetic, environmental and economic aspects, the herbaceous fuels and their boilers may play an important role in the medium power-level market of energy systems.


**6. Conclusion**

The goal of this chapter was to present the factors that both humans and machines face in the evolution of surgery, as well as the balance needed to have a fruitful collaboration. As the field of artificial intelligence has been catapulted into the medical field with many new innovations, the transformation of the medical field is inevitable. The question of how AI technology will affect the surgical profession has become pivotal, as the technology continues to grow, finding new ways to benefit surgeons and patients alike. AI should be viewed not as a threat, rather as another tool in the surgeon's armament for augmenting their skills, further benefiting the patients. The challenge facing AI integration into the operating room are not simple, but as presented herein, we already have some AI available at our fingertips. In the chapter we proposed a novel taxonomy scale encompassing every type of technology that could one day be used in the OR in a comprehensive manner. The PAD taxonomy for Surgical Autonomy may help to bring more awareness to surgeons. With a simple method for stratification of AI, surgeons may begin to feel more confident and be more willing to adopt newer options by understanding what they are utilizing.

Questions remain with regards to the legality and ethics of AI in surgery, specifically with regards to autonomy and task delegation, which may take time to understand and develop. As with any innovation, it is imperative to continue discussions within the surgical community to find the ideal way of collaboration between surgeons and advanced AI systems, to ensure a beneficial partnership.

*Human-Machine Collaboration in AI-Assisted Surgery: Balancing Autonomy and Expertise DOI: http://dx.doi.org/10.5772/intechopen.111556*