Inherited Arrhythmias in the Pediatric Population: An Updated Overview

Genetics, manifestations, and management of catecholaminergic polymorphic ventricular tachycardia

PURPOSE OF REVIEW

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a devastating heritable channelopathy that can lead to sudden cardiac death in children and young adults. This review aims to explore genetics, the cardiac and extracardiac manifestations of mutations associated with CPVT, and the challenges involved with managing phenotypically variable variants.

RECENT FINDINGS

The understanding of the genetics and mechanisms of CPVT continues to grow with recent discoveries including alternative splicing of cardiac TRDN and calmodulin gene variants. Additionally, there is an increasing recognition of the extra-cardiac manifestations such as epilepsy, neurodevelopmental delay, and glucose homeostasis abnormalities in RyR2 variant carriers. Advances in precision medicine, including the development of iPSC-derived cardiomyocytes, are valuable models for developing targeted therapeutics.

SUMMARY

CPVT remains a complex disorder with cardiac and neurological manifestations impacting management. Early genetic testing and personalized treatment, including beta-blockers, flecainide, and ICDs, is important in improving outcomes. Ongoing research into the mechanism of each mutation will help in developing more effective, personalized therapeutics.

Haemodynamic Patterns in Reflex Syncope: Insights from Head-Up Tilt Tests in Adults and Children

Introduction: Vasovagal syncope is a prevalent condition marked by transient loss of consciousness due to abrupt decreases in systemic blood pressure and/or heart rate. Despite its clinical impact, the underlying haemodynamic mechanisms remain poorly defined, and data on age-related differences are limited and sometimes contradictory. Objectives: This study aimed to characterise haemodynamic adaptation patterns during a head-up tilt (HUT) test in adult (≥18 years) and paediatric (<18 years) patients with recurrent reflex syncope, compared with healthy adult controls. We sought to identify distinct temporal haemodynamic signatures and clarify potential age-related differences in syncope mechanisms. Methods: In this prospective observational study, participants underwent continuous beat-to-beat monitoring of cardiac output (CO), stroke volume (SV), heart rate (HR), and total peripheral resistance (TPR) during HUT. Linear mixed-effects models were used to examine time-by-group interactions, and post-hoc analyses were adjusted for multiple comparisons. Effect sizes and confidence intervals (CIs) were reported to quantify the magnitude of differences. Results: A total of 187 fainters (paediatric n = 81, adult n = 106) and 108 non-fainters (including 30 healthy controls) were studied. Compared to adult fainters, paediatric fainters showed a 24% larger decline in CO from baseline (mean difference of 1.1 L/min [95% CI: 0.5-1.7], p = 0.003) and a 15-20 bpm higher peak HR (p = 0.001) during presyncope. Both subgroups experienced significant drops in TPR, which were more pronounced in paediatric fainters (effect size = 0.27, 95% CI: 0.12-0.42). Non-fainters (including controls) maintained relatively stable haemodynamics, with no significant decrease in CO or TPR (p > 0.05). Age-related comparisons indicated a heavier reliance on HR modulation in paediatric fainters, leading to an earlier transition from compensated to pre-syncopal states. Conclusions: These findings demonstrate that paediatric fainters exhibit more abrupt decreases in CO and TPR than adults, alongside higher HR responses during orthostatic stress. Targeted interventions that address this heightened chronotropic dependency-such as tilt-training protocols or strategies to improve venous return-may be particularly beneficial in younger patients. An age-specific approach to diagnosis and management could improve risk stratification, minimise recurrent episodes, and enhance patient outcomes.

The Prognostic Implication of Late Gadolinium Enhancement Quantification and Syncope in Hypertrophic Cardiomyopathy

Background: Risk stratification for sudden cardiac death in hypertrophic cardiomyopathy (HCM) remains challenging. Late gadolinium enhancement (LGE) on cardiac MRI signifies myocardial fibrosis and is linked to adverse outcomes in HCM. However, the threshold of LGE that is clinically significant remains a subject of debate. We hypothesized that even small amounts of LGE (≥ 5%) or a history of syncope are associated with worse outcomes. Methods: Between May 2018 and June 2023, HCM patients were prospectively enrolled at the Medical University of Vienna, Austria, a tertiary referral center. The primary endpoint was a composite of new-onset ventricular tachycardia, appropriate ICD therapy, and all-cause mortality. Results: In total, 230 patients were included. The median age of patients was 56 (IQR 44, 64) years, 40% (n = 94) were female, and 43% (n = 84) had significant left ventricular outflow tract obstruction (LVOTO). Over a median follow-up of 3.2 years, 29 patients (13%) met the composite endpoint. While the ESC HCM risk score was not associated with the primary endpoint, both LGE > 5% (Adj. HR 6.16) and a history of at least one syncope (Adj. HR 3.40) were independently associated with the primary endpoint. These associations were consistent across patients with and without LVOTO. Conclusions: In conclusion, our findings indicate that the combination of a history of syncope together with small amounts of LGE (≥ 5%) in cardiac MRI are associated with unfavorable clinical outcomes in HCM patients.

Cardiac Sarcoidosis and Inherited Cardiomyopathies: Clinical Masquerade or Overlap?

Cardiac sarcoidosis (CS) and inherited cardiomyopathies (inherited CM) are associated with advanced heart failure, cardiac conduction defects, ventricular arrhythmias and sudden cardiac death. Both conditions can have similar clinical presentations. Differentiating between the two disease cohorts is important in delivering specific management to patients, such as immunosuppressive therapy for CS patients and genetic screening for inherited CM. In this review, we examined the existing evidence on the overlap between CS and common inherited CM, such as hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, restrictive cardiomyopathy and dilated cardiomyopathy. In patients where both CS and inherited CM were implicated, CS tended to be diagnosed much later, often when patients presented with complications warranting a workup or cardiac histological confirmation. CS can masquerade as an inherited CM, leading to delays in the instigation of CS therapy. Confirmed dual pathology overlap between inherited CM and CS is rarer. Advanced cardiac imaging, such as cardiovascular magnetic resonance, plays an important role in the clinical workup of both CS and inherited CM. However, findings on cardiac imaging alone often cannot differentiate between the two conditions. Definitive differentiation between CS and inherited CM requires both clinical experience and, at times, a myocardial biopsy.

Particular Aspects of Cardiac Rhythm Disorders in Pediatric Patients

BACKGROUND

Cardiac rhythm disorders in children and adolescents have a high incidence. In certain conditions, sudden death may occur.

MATERIALS AND METHODS

We conducted a prospective study including 199 patients divided into two subgroups: one subgroup of 80 practicing different sports and another one of 119 non-sportive, symptomatic patients. We studied all socio-demographic data, medical histories, and the elements revealed by the clinical and paraclinical examinations.

RESULTS

Only 39 (19.60%) participants did not practice any kind of sport; 46 participants had cases of sudden cardiac death in their families; 60.80% of children and adolescents were exposed to smoking; among the symptomatic group, symptoms like vertigo, chest pain, lipothymia, and palpitations predominated.

CONCLUSIONS

A significant percentage of participants with heart rhythm disorders at risk for sudden death was identified. It is extremely important to identify and restrict them from intense physical exertion and to reassess them periodically in order to reduce the risk of sudden cardiac death.

Cardiac Markers in Pediatric Laboratory Medicine: Critical Review

Currently, there are no validated guidelines or recommendations for how to interpret cardiac biomarkers in the pediatric population. The most commonly used cardiac biomarkers are cardiac troponins and natriuretic peptides, but the clinical value of common cardiac biomarkers in pediatric laboratory medicine is restricted due to age- and sex-specific interpretations, and there are no standardized cut-off values. The results from the studies on reference values, as well as results from clinical studies, are difficult to compare with identical studies due to the heterogeneity of subject characteristics (gestational and chronological age, sex, pubertal status, menstrual cycle, exercise), assay characteristics (type of assay, generation of assay, analytical platform used), and experimental protocol characteristics (prospective or retrospective studies, reference population selection, patient population selection, inclusion and exclusion criteria, number of subjects). Future studies need to establish evidence-based cut-offs for specific indications to optimize utilization and standardize the interpretation of common cardiac biomarkers in neonates, children, and adolescents. The aim of this article was to summarize the current analytical and clinical limitations of cardiac troponins and natriuretic peptides in the pediatric population, as informed by the existing published literature.

A new prediction model for sustained ventricular tachycardia in arrhythmogenic cardiomyopathy

Background

Arrhythmogenic cardiomyopathy (ACM) is an inherited cardiomyopathy characterized by high risks of sustained ventricular tachycardia (sVT) and sudden cardiac death. Identifying patients with high risk of sVT is crucial for the management of ACM.

Methods

A total of 147 ACM patients were retrospectively enrolled in the observational study and divided into training and validation groups. The least absolute shrinkage and selection operator (LASSO) regression model was employed to identify factors associated with sVT. Subsequently, a nomogram was constructed based on multivariable logistic regression analysis. The performance of the nomogram was evaluated using the area under the curve (AUC) of the receiver operating characteristic (ROC) curve and calibration curve. Decision curve analysis was conducted to assess the clinical utility of the nomogram.

Results

Seven parameters were incorporated into the nomogram: age, male sex, syncope, heart failure, T wave inversion in precordial leads, left ventricular ejection fraction (LVEF), SDNN level. The AUC of the nomogram to predict the probability of sVT was 0.867 (95% CI, 0.797-0.938) in the training group and 0.815 (95% CI, 0.673-0.958) in the validation group. The calibration curve demonstrated a good consistency between the actual clinical results and the predicted outcomes. Decision curve analysis indicated that the nomogram had higher overall net benefits in predicting sVT.

Conclusion

We have developed and internally validated a new prediction model for sVT in ACM. This model could serve as a valuable tool to accurately identify ACM patients with high risk of sVT.

Alleviating the Effects of Short QT Syndrome Type 3 by Allele-Specific Suppression of the KCNJ2 Mutant Allele

Short QT syndrome type 3 (SQTS3 or SQT3), which is associated with life-threatening cardiac arrhythmias, is caused by heterozygous gain-of-function mutations in the KCNJ2 gene. This gene encodes the pore-forming α-subunit of the ion channel that carries the cardiac inward rectifier potassium current (IK1). These gain-of-function mutations either increase the amplitude of IK1 or attenuate its rectification. The aim of the present in silico study is to test to which extent allele-specific suppression of the KCNJ2 mutant allele can alleviate the effects of SQT3, as recently demonstrated in in vitro studies on specific heterozygous mutations associated with long QT syndrome type 1 and 2 and short QT syndrome type 1. To this end, simulations were carried out with the two most recent comprehensive models of a single human ventricular cardiomyocyte. These simulations showed that suppression of the mutant allele can, at least partially, counteract the effects of the mutation on IK1 and restore the action potential duration for each of the four SQT3 mutations that are known by now. We conclude that allele-specific suppression of the KCNJ2 mutant allele is a promising technique in the treatment of SQT3 that should be evaluated in in vitro and in vivo studies.

Investigating Inherited Heart Diseases Using Human Induced Pluripotent Stem Cell-Based Models

Inherited heart diseases (IHDs) are caused by genetic mutations that disrupt the physiological structure and function of the heart. Understanding the mechanisms behind these diseases is crucial for developing personalised interventions in cardiovascular medicine. Development of induced pluripotent stem cells, which can then be differentiated to any nucleated adult cell type, has enabled the creation of personalised single-cell and multicellular models, providing unprecedented insights into the pathophysiology of IHDs. This review provides a comprehensive overview of recent advancements in human iPSC models used to dissect the molecular and genetic underpinnings of common IHDs. We examine multicellular models and tissue engineering approaches, such as cardiac organoids, engineered heart tissue, and multicellular co-culture systems, which simulate complex intercellular interactions within heart tissue. Recent advancements in stem cell models offer a more physiologically relevant platform to study disease mechanisms, enabling researchers to observe cellular interactions, study disease progression, and identify therapeutic strategies. By leveraging these innovative models, we can gain deeper insights into the molecular and cellular mechanisms underlying IHDs, ultimately paving the way for more effective diagnostic and therapeutic strategies.

Human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) for modeling cardiac arrhythmias: strengths, challenges and potential solutions

Ion channels and cytoskeletal proteins in the cardiac dyad play a critical role in maintaining excitation-contraction (E-C) coupling and provide cardiac homeostasis. Functional changes in these dyad proteins, whether induced by genetic, epigenetic, metabolic, therapeutic, or environmental factors, can disrupt normal cardiac electrophysiology, leading to abnormal E-C coupling and arrhythmias. Animal models and heterologous cell cultures provide platforms to elucidate the pathogenesis of arrhythmias for basic cardiac research; however, these traditional systems do not truly reflect human cardiac electro-pathophysiology. Notably, patients with the same genetic variants of inherited channelopathies (ICC) often exhibit incomplete penetrance and variable expressivity which underscores the need to establish patient-specific disease models to comprehend the mechanistic pathways of arrhythmias and determine personalized therapies. Patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) inherit the genetic background of the patient and reflect the electrophysiological characteristics of the native cardiomyocytes. Thus, iPSC-CMs provide an innovative and translational pivotal platform in cardiac disease modeling and therapeutic screening. In this review, we will examine how patient-specific iPSC-CMs historically evolved to model arrhythmia syndromes in a dish, and their utility in understanding the role of specific ion channels and their functional characteristics in causing arrhythmias. We will also examine how CRISPR/Cas9 have enabled the establishment of patient-independent and variant-induced iPSC-CMs-based arrhythmia models. Next, we will examine the limitations of using human iPSC-CMs with respect to in vitro arrhythmia modeling that stems from variations in iPSCs or toxicity due to gene editing on iPSC or iPSC-CMs and explore how such hurdles are being addressed. Importantly, we will also discuss how novel 3D iPSC-CM models can better capture in vitro characteristics and how all-optical platforms provide non-invasive and high- throughput electrophysiological data that is useful for stratification of emerging arrhythmogenic variants and drug discovery. Finally, we will examine strategies to improve iPSC-CM maturity, including powerful gene editing and optogenetic tools that can introduce/modify specific ion channels in iPSC-CMs and tailor cellular and functional characteristics. We anticipate that an elegant synergy of iPSCs, novel gene editing, 3D- culture models, and all-optical platforms will offer a high-throughput template to faithfully recapitulate in vitro arrhythmogenic events necessary for personalized arrhythmia monitoring and drug screening process.

Prophylactic ICD Survival Benefit Prediction: Review and Comparison between Main Scores

Current guidelines advocate for the use of prophylactic implantable cardioverter defibrillators (ICDs) for all patients with symptomatic heart failure (HF) with low ejection fraction (EF). As many patients will never use their device and some are prone to device-related complications, scoring systems for delineating subgroups with differential ICD survival benefits are crucial to maximize ICD benefit and mitigate complications. This review summarizes the main scores, including MADIT trial-based Risk Stratification Score (MRSS) and Seattle Heart Failure Model (SHFM), which are based on randomized trials with a control group (HF medication only) and validated on large cohorts of 'real-world' HF patients. Recent studies using cardiac MRI (CMR) to predict ventricular arrhythmia (VA) are mentioned as well. The review shows that most scores could not delineate sustained VA incidence, but rather mortality without prior appropriate ICD therapies. Multiple scores could identify high-risk subgroups with extremely high probability of early mortality after ICD implant. On the other hand, low-risk subgroups were defined, in whom a high ratio of appropriate ICD therapy versus death without prior appropriate ICD therapy was found, suggesting significant ICD survival benefit. Moreover, MRSS and SHFM proved actual ICD survival benefit in low- and medium-risk subgroups when compared with control patients, and no benefit in high-risk subgroups, consisting of 16-20% of all ICD candidates. CMR reliably identified areas of myocardial scar and 'channels', significantly associated with VA. We conclude that as for today, multiple scoring models could delineate patient subgroups that would benefit differently from prophylactic ICD. Due to their modest-moderate predictability, these scores are still not ready to be implemented into clinical guidelines, but could aid decision regarding prophylactic ICD in borderline cases, as elderly patients and those with multiple co-morbidities. CMR is a promising technique which might help delineate patients with a low- versus high-risk for future VA, beyond EF alone. Lastly, genetic analysis could identify specific mutations in a non-negligible percent of patients, and a few of these mutations were found to predict an increased arrhythmic risk.

Antiarrhythmic Drug Use in Pregnancy: Considerations and Safety Profiles

Pregnancy entails notable physiological alterations and hormonal fluctuations that affect the well-being of both the fetus and the mother. Cardiovascular events and arrhythmias are a major concern during pregnancy, especially in women with comorbidities or a history of arrhythmias. This paper provides an overview of the prevalence, therapies, and prognoses of different types of arrhythmias during pregnancy. The administration of antiarrhythmic drugs (AADs) during pregnancy demands careful consideration because of their possible effect on the mother and fetus. AADs can cross the placenta or be present in breast milk, potentially leading to adverse effects such as teratogenicity, growth restriction, or premature birth. The safety profiles of different classes of AADs are discussed. Individualized treatment approaches and close monitoring of pregnant women prescribed AADs are essential to ensure optimal maternal and fetal outcomes.

A rare case report of catecholaminergic polymorphic ventricular tachycardia with an uncommon CALM2 mutation

Background

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a primary arrhythmia disorder characterized by syncope or sudden cardiac death and typically caused by a gain-of-function of the Ryanodine Receptor Type 2 (RyR2) mutation. Calmodulin is a calcium-binding protein responsible for many intracellular signalling pathways and disruptions in function or regulation may lead to potentially fatal arrhythmias. We present a case of a young patient with CPVT found to have an unusual, potentially causative, Calmodulin 2-a protein coding gene (CALM2) mutation.

Case summary

A 21-year-old female with autism was brought to the ED following cardiac arrest. Bidirectional ventricular tachycardia was captured on electrocardiogram. Propranolol was initiated, and patient had no further episodes of ventricular arrhythmia. A subcutaneous implantable cardioverter defibrillator (ICD) was implanted, and further genetics testing was done. Rapid Whole Genome Sequencing (PGnome®-RAPID) resulted heterozygous variant of uncertain significance in CALM2 gene NM_001743.5 for variant c.136G>A.

Discussion

To the authors' knowledge, this is the third known record of such mutation in accordance with the International Calmodulin Registry (n = 74). Identification of CALM mutations can help advance the understanding of genetic underpinnings of arrhythmias and underscore necessity of genetic screening and personalized treatment strategies. Subcutaneous ICDs offer a promising therapeutic option while minimizing risks associated with traditional transvenous ICDs.

Exploring Hypertrophic Cardiomyopathy Biomarkers through Integrated Bioinformatics Analysis: Uncovering Novel Diagnostic Candidates

HCM is a heterogeneous monogenic cardiac disease that can lead to arrhythmia, heart failure, and atrial fibrillation. This study aims to identify biomarkers that have a positive impact on the treatment, diagnosis, and prediction of HCM through bioinformatics analysis. We selected the GSE36961 and GSE180313 datasets from the Gene Expression Omnibus (GEO) database for differential analysis. GSE36961 generated 6 modules through weighted gene co-expression network analysis (WGCNA), with the green and grey modules showing the highest positive correlation with HCM (green module: cor = 0.88, p = 2e - 48; grey module: cor = 0.78, p = 4e - 31). GSE180313 generated 17 modules through WGCNA, with the turquoise module exhibiting the highest positive correlation with HCM (turquoise module: cor = 0.92, p = 6e - 09). We conducted GO and KEGG pathway analysis on the intersection genes of the selected modules from GSE36961 and GSE180313 and intersected their GO enriched pathways with the GO enriched pathways of endothelial cell subtypes calculated after clustering single-cell data GSE181764, resulting in 383 genes on the enriched pathways. Subsequently, we used LASSO prediction on these 383 genes and identified RTN4, COL4A1, and IER3 as key genes involved in the occurrence and development of HCM. The expression levels of these genes were validated in the GSE68316 and GSE32453 datasets. In conclusion, RTN4, COL4A1, and IER3 are potential biomarkers of HCM, and protein degradation, mechanical stress, and hypoxia may be associated with the occurrence and development of HCM.

Patterns of Left Ventricular Remodelling in Children and Young Patients with Hypertrophic Cardiomyopathy

Introduction: The aim of this study was to evaluate the age at onset, clinical course, and patterns of left ventricular (LV) remodelling during follow-up in children and young patients with hypertrophic cardiomyopathy (HCM). Methods: We included consecutive patients with sarcomeric or non-syndromic HCM below 18 years old. Three pre-specified patterns of LV remodelling were assessed: maximal LV wall thickness (MLVWT) thickening; MLVWT thinning with preserved LV ejection fraction; and MLVWT thinning with progressive reduction in LV ejection fraction (hypokinetic end-stage evolution). Results: Fifty-three patients with sarcomeric/non-syndromic HCM (mean age 9.4 ± 5.5 years, 68% male) fulfilled the inclusion criteria. In total, 32 patients (60%) showed LV remodelling: 3 patients (6%) exhibited MLVWT thinning; 16 patients (30%) showed MLVWT thickening; and 13 patients (24%) progressed to hypokinetic end-stage HCM. Twenty-one patients (40%) had no LV remodelling during follow-up. In multivariate analysis, MLVWT was a predictor of the hypokinetic end-stage remodelling pattern during follow-up (OR 1.17 [95%CI 1.01-1.36] per 1 mm increase, p-value 0.043), regardless of sarcomeric variants and New York Heart Association class. Two patients with sarcomeric HCM, showing a pattern of MLVWT regression during childhood, experienced progression during adolescence. Conclusions: Different patterns of LV remodelling were observed in a cohort of children with sarcomeric/non-syndromic HCM. Interestingly, a pattern of progressive MLVWT thinning during childhood, with new progression of MLVWT during adolescence, was noted. A better understanding of the remodelling mechanisms in children with sarcomeric HCM may be relevant to defining the timing and possible efficacy of new targeted therapies in the preclinical stage of the disease.

Syncope in the Emergency Department: A Practical Approach

Syncope is a common condition encountered in the emergency department (ED), accounting for about 0.6-3% of all ED visits. Despite its high frequency, a widely accepted management strategy for patients with syncope in the ED is still missing. Since syncope can be the presenting condition of many diseases, both severe and benign, most research efforts have focused on strategies to obtain a definitive etiologic diagnosis. Nevertheless, in everyday clinical practice, a definitive diagnosis is rarely reached after the first evaluation. It is thus troublesome to aid clinicians' reasoning by simply focusing on differential diagnoses. With the current review, we would like to propose a management strategy that guides clinicians both in the identification of conditions that warrant immediate treatment and in the management of patients for whom a diagnosis is not immediately reached, differentiating those that can be safely discharged from those that should be admitted to the hospital or monitored before a final decision. We propose the mnemonic acronym RED-SOS: Recognize syncope; Exclude life-threatening conditions; Diagnose; Stratify the risk of adverse events; Observe; decide on the Setting of care. Based on this acronym, in the different sections of the review, we discuss all the elements that clinicians should consider when assessing patients with syncope.

Loss of protein phosphatase 2A regulatory subunit PPP2R5A is associated with increased incidence of stress-induced proarrhythmia

Background

Protein phosphatase 2A (PP2A) is a serine/threonine-selective holoenzyme that controls Ca2+ homeostasis and contractility of the heart via dephosphorylation of regulatory proteins. In some genetically modified mouse models with increased arrhythmogenicity, a reduced expression of the regulatory subunit B56α of PP2A was found as a concomitant effect. Whether there is a general correlation between the abundance of B56α and the promotion of cardiac arrhythmogenesis remains unclear.

Methods

The aim of this study was therefore to investigate the role of PP2A-B56α in the propensity for arrhythmic activity in the heart. The experimental analysis of this question has been addressed by using a mouse model with deletion of the PP2A-B56α gene, PPP2R5A (KO), in comparison to wild-type animals (WT). Evidence for arrhythmogenicity was investigated in whole animal, isolated heart and cardiomyocytes by ECG, recording of monophasic action potential (MAP) induced by programmed electrical stimulation (PES), measurement of Ca2+ transients under increased pacing frequencies and determination of total K+ channel currents (I K).

Results

ECG measurements showed a prolongation of QT time in KO vs. WT. KO mice exhibited a higher rate of premature ventricular contractions in the ECG. MAP measurements in Langendorff-perfused KO hearts showed increased episodes of ventricular tachyarrhythmia induced by PES. However, the KO hearts showed values for MAP duration that were similar to those in WT hearts. In contrast, KO showed more myocardial cells with spontaneous arrhythmogenic Ca2+ transient events compared to WT. The whole-cell patch-clamp technique applied to ventricular cardiomyocytes revealed comparable peak potassium channel current densities between KO and WT.

Conclusion

These findings support the assumption that a decrease or even the loss of PP2A-B56α leads to an increased propensity of triggered arrhythmias. This could be based on the increased spontaneous Ca2+ tansients observed.

Troponin T Assessment Allows for Identification of Mutation Carriers among Young Relatives of Patients with LMNA-Related Dilated Cardiomyopathy

Background:LMNA-related dilated cardiomyopathy (LMNA-DCM) caused by mutations in the lamin A/C gene (LMNA) is one of the most common forms of hereditary DCM. Due to the high risk of mutation transmission to offspring and the high incidence of ventricular arrhythmia and sudden death even before the onset of heart failure symptoms, it is very important to identify LMNA-mutation carriers. However, many relatives of LMNA-DCM patients do not report to specialized centers for clinical or genetic screening. Therefore, an easily available tool to identify at-risk subjects is needed. Methods: We compared two cohorts of young, asymptomatic relatives of DCM patients who reported for screening: 29 LMNA mutation carriers and 43 individuals from the control group. Receiver operating characteristic (ROC) curves for potential indicators of mutation carriership status were analyzed. Results: PR interval, N-terminal pro-B-type natriuretic peptide (NT-proBNP), and high-sensitivity cardiac troponin T (hscTnT) serum levels were higher in the LMNA mutation carrier cohort. Neither group differed significantly with regard to creatinine concentration or left ventricular ejection fraction. The best mutation carriership discriminator was hscTnT level with an optimal cut-off value at 5.5 ng/L, for which sensitivity and specificity were 86% and 93%, respectively. The median hscTnT level was 11.0 ng/L in LMNA mutation carriers vs. <3.0 ng/L in the control group, p < 0.001. Conclusions: Wherever access to genetic testing is limited, LMNA mutation carriership status can be assessed reliably using the hscTnT assay. Among young symptomless relatives of LMNA-DCM patients, a hscTnT level >5.5 ng/L strongly suggests mutation carriers.

Catheter Ablation for Channelopathies: When Is Less More?

Ventricular fibrillation (VF) is a common cause of sudden cardiac death in patients with channelopathies, particularly in the young population. Although pharmacological treatment, cardiac sympathectomy, and implantable cardioverter defibrillators (ICD) have been the mainstay in the management of VF in patients with channelopathies, they are associated with significant adverse effects and complications, leading to poor quality of life. Given these drawbacks, catheter ablation has been proposed as a therapeutic option for patients with channelopathies. Advances in imaging techniques and modern mapping technologies have enabled increased precision in identifying arrhythmia triggers and substrate modification. This has aided our understanding of the underlying pathophysiology of ventricular arrhythmias in channelopathies, highlighting the roles of the Purkinje network and the epicardial right ventricular outflow tract in arrhythmogenesis. This review explores the role of catheter ablation in managing the most common channelopathies (Brugada syndrome, congenital long QT syndrome, short QT syndrome, and catecholaminergic polymorphic ventricular tachycardia). While the initial results for ablation in Brugada syndrome are promising, the long-term efficacy and durability of ablation in different channelopathies require further investigation. Given the genetic and phenotypic heterogeneity of channelopathies, future studies are needed to show whether catheter ablation in patients with channelopathies is associated with a reduction in VF, and psychological distress stemming from recurrent ICD shocks, particularly relative to other available therapeutic options (e.g., quinidine in high-risk Brugada patients).

Primary Electrical Heart Disease-Principles of Pathophysiology and Genetics

Primary electrical heart diseases, often considered channelopathies, are inherited genetic abnormalities of cardiomyocyte electrical behavior carrying the risk of malignant arrhythmias leading to sudden cardiac death (SCD). Approximately 54% of sudden, unexpected deaths in individuals under the age of 35 do not exhibit signs of structural heart disease during autopsy, suggesting the potential significance of channelopathies in this group of age. Channelopathies constitute a highly heterogenous group comprising various diseases such as long QT syndrome (LQTS), short QT syndrome (SQTS), idiopathic ventricular fibrillation (IVF), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), and early repolarization syndromes (ERS). Although new advances in the diagnostic process of channelopathies have been made, the link between a disease and sudden cardiac death remains not fully explained. Evolving data in electrophysiology and genetic testing suggest previously described diseases as complex with multiple underlying genes and a high variety of factors associated with SCD in channelopathies. This review summarizes available, well-established information about channelopathy pathogenesis, genetic basics, and molecular aspects relative to principles of the pathophysiology of arrhythmia. In addition, general information about diagnostic approaches and management is presented. Analyzing principles of channelopathies and their underlying causes improves the understanding of genetic and molecular basics that may assist general research and improve SCD prevention.