Inherited Arrhythmias in the Pediatric Population: An Updated Overview

Pediatric cardiomyopathies (CMs) and electrical diseases constitute a heterogeneous spectrum of disorders distinguished by structural and electrical abnormalities in the heart muscle, attributed to a genetic variant. They rank among the main causes of morbidity and mortality in the pediatric population, with an annual incidence of 1.1-1.5 per 100,000 in children under the age of 18. The most common conditions are dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM). Despite great enthusiasm for research in this field, studies in this population are still limited, and the management and treatment often follow adult recommendations, which have significantly more data on treatment benefits. Although adult and pediatric cardiac diseases share similar morphological and clinical manifestations, their outcomes significantly differ. This review summarizes the latest evidence on genetics, clinical characteristics, management, and updated outcomes of primary pediatric CMs and electrical diseases, including DCM, HCM, arrhythmogenic right ventricular cardiomyopathy (ARVC), Brugada syndrome (BrS), catecholaminergic polymorphic ventricular tachycardia (CPVT), long QT syndrome (LQTS), and short QT syndrome (SQTS).

Recent Advances in Inherited Cardiac Arrhythmias and Their Genetic Testing

Inherited arrhythmias, encompassing conditions such as cardiomyopathies, cardiac ion channel disorders, and coronary heart disease, represent the common causes that elevate the threat of sudden cardiac death among adults. Researchers have pinpointed the genes responsible for these hereditary arrhythmias in the last 30 years. Concurrently, it has become clear that the genetic makeup underlying these conditions is more intricate than previously understood. Evolution in DNA sequencing techniques, particularly next-generation sequencing, has empowered us to learn these intricate hereditary characteristics. Genetic testing is crucial in diagnosing, assessing risk, and determining treatment for individuals with these conditions and their family members. The need for collaborative endeavors to comprehend and address these uncommon yet potentially life-threatening disorders is becoming more evident. This review aims to inform readers of the latest advances in understanding hereditary arrhythmias and provide the groundwork for collaborative genetic testing initiatives to characterize these disorders in the general population.

The evolution of gene-guided management of inherited arrhythmia syndromes: Peering beyond monogenic paradigms towards comprehensive genomic risk scores

Inherited arrhythmia syndromes have traditionally been viewed as monogenic forms of disease whose pathophysiology is driven by a single highly penetrant rare genetic variant. Although an accurate depiction of a proportion of genetic variants, the variable penetrance frequently noted in genotype positive families and the presence of sporadic genotype negative cases have long highlighted a more nuanced truth being operative. Coupled with our more recent recognition that many rare variants implicated in inherited arrhythmia syndromes possess unexpectedly high allele frequencies within the general population, these observations have contributed to the realization that a spectrum of pathogenicity exists among clinically relevant genetic variants. Notably, variable mutation pathogenicity and corresponding variable degrees of penetrance emphasize a limitation of contemporary guidelines, which attempt to dichotomize genetic variants as pathogenic or benign. Recognition of the existence of low and intermediate penetrant variants insufficient to be causative for disease in isolation has served to emphasize the importance of additional genetic, clinical, and environmental factors in the pathogenesis of rare inherited arrhythmia syndromes. Despite being rare, it has also become increasingly evident that common genetic variants play critical roles in both heritable channelopathies and cardiomyopathies and in aggregate may even be the primary drivers in certain instances, such as genotype negative Brugada syndrome. Our growing realization that the genetic substrates of inherited arrhythmia syndromes have intricacies that extend beyond traditionally perceived monogenic paradigms has highlighted a potential value of leveraging more comprehensive genomic risk scores for predicting disease development and arrhythmic risk.

Mechanisms and models of cardiac sodium channel inactivation

Shortly after cardiac Na+ channels activate and initiate the action potential, inactivation ensues within milliseconds, attenuating the peak Na+ current, INa, and allowing the cell membrane to repolarize. A very limited number of Na+ channels that do not inactivate carry a persistent INa, or late INa. While late INa is only a small fraction of peak magnitude, it significantly prolongs ventricular action potential duration, which predisposes patients to arrhythmia. Here, we review our current understanding of inactivation mechanisms, their regulation, and how they have been modeled computationally. Based on this body of work, we conclude that inactivation and its connection to late INa would be best modeled with a "feet-on-the-door" approach where multiple channel components participate in determining inactivation and late INa. This model reflects experimental findings showing that perturbation of many channel locations can destabilize inactivation and cause pathological late INa.

Trigger elimination of polymorphic ventricular tachycardia and ventricular fibrillation by catheter ablation: trigger and substrate modification

Ventricular fibrillation (VF) is a malignant arrhythmia, usually initiated by a ventricular premature contraction (VPC) during the vulnerable period of cardiac repolarization. Ablation therapy for VF has been described and increasingly reported. Targets for VF triggers are VPCs preceded by Purkinje potentials or from the right ventricular outflow tract (RVOT) in structurally normal hearts, and VPC triggers preceded by Purkinje potentials in ischemic cardiomyopathy. During the session, mapping should be focused on the earliest activation and determining the earliest potential is the key to a successful ablation. However, suppression of VF can be achieved by not only the elimination of triggering VPCs, but also by substrate modification of possible reentry circuits in the Purkinje network, or between the PA and RVOT. The most important issue before the ablation session is the recording of the 12-lead ECG of the triggering event, which can prove invaluable in regionalizing the origin of the triggering VPC for more detailed mapping. In cases where the VPC is not spontaneous or inducible, ablation may be performed by pace mapping. Further studies are needed to evaluate the precise mechanisms of this arrhythmia.

Modeling Catecholaminergic Polymorphic Ventricular Tachycardia using Induced Pluripotent Stem Cell-derived Cardiomyocytes

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic cardiac disorder characterized by life-threatening arrhythmias induced by physical or emotional stress, in the absence structural heart abnormalities. The arrhythmias may cause syncope or degenerate into cardiac arrest and sudden death which usually occurs during childhood. Recent studies have shown that CPVT is caused by mutations in the cardiac ryanodine receptor type 2 (RyR2) or calsequestrin 2 (CASQ2) genes. Both proteins are key contributors to the intracellular Ca(2+) handling process and play a pivotal role in Ca(2+) release from the sarcoplasmic reticulum to the cytosol during systole. Although the molecular pathogenesis of CPVT is not entirely clear, it was suggested that the CPVT mutations promote excessive sarcoplasmic reticulum Ca(2+) leak, which initiates delayed afterdepolarizations (DADs) and triggered arrhythmias in cardiac myocytes. The recent breakthrough discovery of induced pluripotent stem cells (iPSC) generated from somatic cells (e.g. fibroblasts, keratinocytes) now enables researches to investigate mutated cardiomyocytes generated from the patient's iPSC. To this end, in the present article we review recent studies on CPVT iPSC-derived cardiomyocytes, thus demonstrating in the mutated cells catecholamine-induced DADs and triggered arrhythmias.