Genetic causes of sudden cardiac death in the young

Stem cell models of inherited arrhythmias

Inherited arrhythmias are a heterogeneous group of conditions that confer risk of sudden death. Many inherited arrhythmias have been linked to pathogenic genetic variants that result in ion channel dysfunction, although current genetic testing panels fail to identify variants in many patients, potentially secondary to their underlying substrates being oligogenic or polygenic. Here we review the current state of knowledge surrounding the cellular mechanisms of inherited arrhythmias generated from stem cell models with a focus on integrating genetic and mechanistic data. The utility and limitations of human induced pluripotent stem cell models in disease modeling and drug development are also explored with a particular focus on examples of pharmacogenetics and precision medicine. We submit that progress in understanding inherited arrhythmias is likely to be made by using human induced pluripotent stem cells to model probable polygenic cases as well as to interrogate the diverse and potentially complex molecular networks implicated by genome-wide association studies.

Short-coupled ventricular fibrillation represents a distinct phenotype among latent causes of unexplained cardiac arrest: a report from the CASPER registry

AIMS

The term idiopathic ventricular fibrillation (IVF) describes survivors of unexplained cardiac arrest (UCA) without a specific diagnosis after clinical and genetic testing. Previous reports have described a subset of IVF individuals with ventricular arrhythmia initiated by short-coupled trigger premature ventricular contractions (PVCs) for which the term short-coupled ventricular fibrillation (SCVF) has been proposed. The aim of this article is to establish the phenotype and frequency of SCVF in a large cohort of UCA survivors.

METHODS AND RESULTS

We performed a multicentre study including consecutive UCA survivors from the CASPER registry. Short-coupled ventricular fibrillation was defined as otherwise unexplained ventricular fibrillation initiated by a trigger PVC with a coupling interval of <350 ms. Among 364 UCA survivors, 24/364 (6.6%) met diagnostic criteria for SCVF. The diagnosis of SCVF was obtained in 19/24 (79%) individuals by documented ventricular fibrillation during follow-up. Ventricular arrhythmia was initiated by a mean PVC coupling interval of 274 ± 32 ms. Electrical storm occurred in 21% of SCVF probands but not in any UCA proband (P < 0.001). The median time to recurrent ventricular arrhythmia in SCVF was 31 months. Recurrent ventricular fibrillation resulted in quinidine administration in 12/24 SCVF (50%) with excellent arrhythmia control.

CONCLUSION

Short-coupled ventricular fibrillation is a distinct primary arrhythmia syndrome accounting for at least 6.6% of UCA. As documentation of ventricular fibrillation onset is necessary for the diagnosis, most cases are diagnosed at the time of recurrent arrhythmia, thus the true prevalence of SCVF remains still unknown. Quinidine is effective in SCVF and should be considered as first-line treatment for patients with recurrent episodes.

Pathogenesis of arrhythmogenic cardiomyopathy: role of inflammation

Arrhythmogenic cardiomyopathy (AC) is an inherited disease characterized by progressive breakdown of heart muscle, myocardial tissue death, and fibrofatty replacement. In most cases of AC, the primary lesion occurs in one of the genes encoding desmosomal proteins, disruption of which increases membrane fragility at the intercalated disc. Disrupted, exposed desmosomal proteins also serve as epitopes that can trigger an autoimmune reaction. Damage to cell membranes and autoimmunity provoke myocardial inflammation, a key feature in early stages of the disease. In several preclinical models, targeting inflammation has been shown to blunt disease progression, but translation to the clinic has been sparse. Here we review current understanding of inflammatory pathways and how they interact with injured tissue and the immune system in AC. We further discuss the potential role of immunomodulatory therapies in AC.

An International Multicenter Evaluation of Type 5 Long QT Syndrome: A Low Penetrant Primary Arrhythmic Condition

BACKGROUND

Insight into type 5 long QT syndrome (LQT5) has been limited to case reports and small family series. Improved understanding of the clinical phenotype and genetic features associated with rare KCNE1 variants implicated in LQT5 was sought through an international multicenter collaboration.

METHODS

Patients with either presumed autosomal dominant LQT5 (N = 229) or the recessive Type 2 Jervell and Lange-Nielsen syndrome (N = 19) were enrolled from 22 genetic arrhythmia clinics and 4 registries from 9 countries. KCNE1 variants were evaluated for ECG penetrance (defined as QTc >460 ms on presenting ECG) and genotype-phenotype segregation. Multivariable Cox regression was used to compare the associations between clinical and genetic variables with a composite primary outcome of definite arrhythmic events, including appropriate implantable cardioverter-defibrillator shocks, aborted cardiac arrest, and sudden cardiac death.

RESULTS

A total of 32 distinct KCNE1 rare variants were identified in 89 probands and 140 genotype positive family members with presumed LQT5 and an additional 19 Type 2 Jervell and Lange-Nielsen syndrome patients. Among presumed LQT5 patients, the mean QTc on presenting ECG was significantly longer in probands (476.9±38.6 ms) compared with genotype positive family members (441.8±30.9 ms, P<0.001). ECG penetrance for heterozygous genotype positive family members was 20.7% (29/140). A definite arrhythmic event was experienced in 16.9% (15/89) of heterozygous probands in comparison with 1.4% (2/140) of family members (adjusted hazard ratio [HR] 11.6 [95% CI, 2.6-52.2]; P=0.001). Event incidence did not differ significantly for Type 2 Jervell and Lange-Nielsen syndrome patients relative to the overall heterozygous cohort (10.5% [2/19]; HR 1.7 [95% CI, 0.3-10.8], P=0.590). The cumulative prevalence of the 32 KCNE1 variants in the Genome Aggregation Database, which is a human database of exome and genome sequencing data from now over 140 000 individuals, was 238-fold greater than the anticipated prevalence of all LQT5 combined (0.238% vs 0.001%).

CONCLUSIONS

The present study suggests that putative/confirmed loss-of-function KCNE1 variants predispose to QT prolongation, however, the low ECG penetrance observed suggests they do not manifest clinically in the majority of individuals, aligning with the mild phenotype observed for Type 2 Jervell and Lange-Nielsen syndrome patients.

Sudden cardiac death in young athletes with long QT syndrome: the role of genetic testing and cardiovascular screening

INTRODUCTION

Sudden cardiac death (SCD) of young athletes during competition or training is a tragic event. The long QT syndrome (LQTS) is an arrythmogenic disorder characterized by prolonged ventricular repolarization leading to torsade de pointes evident at electrocardiogram (ECG). Implantable cardioverter defibrillator is an option to revert ventricular fibrillation to sinus rhythm, although the implantation may result in denial of sports participations to the athlete. The authors reviewed the current literature on LQTS in young athletes, to clarify the role of different screening technologies to prevent SCD.

SOURCES OF DATA

A systematic review of the literature was performed applying the PRISMA guidelines according to the PRISMA checklist and algorithm. A comprehensive search of PubMed, Medline, CINAHL, Cochrane, Embase and Google Scholar databases using various combinations of the keywords: 'QT', 'syndrome', 'screening', 'young', 'athletes', 'genetic', 'electrocardiogram', 'echocardiography' and 'prevention' were used.

AREAS OF AGREEMENT

Young athletes with LQTS are at greater risk of SCD.

AREAS OF CONTROVERSY

Different detection screening technologies, including ECG monitoring and genetic testing, are recommended, even though their role is not fully understood.

GROWING POINTS

ECG and genetic testing screening programmes could reduce the incidence of SCD, and they may positively impact on the health and safety of young athletes during sport.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further studies should analyze other modalities of screening to allow early detection of cardiovascular conditions to prevent SCD in young athletes.

Applying High-Resolution Variant Classification to Cardiac Arrhythmogenic Gene Testing in a Demographically Diverse Cohort of Sudden Unexplained Deaths

BACKGROUND

Genetic variant interpretation contributes to testing yield differences reported for sudden unexplained death. Adapting a high-resolution variant interpretation framework, which considers disease prevalence, reduced penetrance, genetic heterogeneity, and allelic contribution to determine the maximum tolerated allele count in gnomAD, we report an evaluation of cardiac channelopathy and cardiomyopathy genes in a large, demographically diverse sudden unexplained death cohort that underwent thorough investigation in the United States' largest medical examiner's office.

METHODS AND RESULTS

The cohort has 296 decedents: 147 Blacks, 64 Hispanics, 49 Whites, 22 Asians, and 14 mixed ethnicities; 142 infants (1 to 11 months), 39 children (1 to 17 years), 74 young adults (18 to 34 years), and 41 adults (35 to 55 years). Eighty-nine cardiac disease genes were evaluated. Using a high-resolution variant interpretation workflow, we classified 17 variants as pathogenic or likely pathogenic (2 of which were incidental findings and excluded in testing yield analysis), 46 novel variants of uncertain significance, and 130 variants of uncertain significance. Nine pathogenic or likely pathogenic variants in ClinVar were reclassified to likely benign and excluded in testing yield analysis. The yields of positive cases by ethnicity and age were 21.4% in mixed ethnicities, 10.2% Whites, 4.5% Asians, 3.1% Hispanics, and 2% Blacks; 7.7% children, 7.3% in adults, 5.4% young adults, and 2.8% infants. The percentages of uncertain cases with variants of uncertain significance by ethnicity were 45.5% in Asians, 45.3% Hispanics, 44.20% Blacks, 36.7% Whites, and 14.3% in mixed ethnicities.

CONCLUSIONS

High-resolution variant interpretation provides diagnostic accuracy and healthcare efficiency. Under-represented populations warrant greater inclusion in future studies.

J-Wave Syndromes: Electrocardiographic and Clinical Aspects

Early repolarization, Brugada syndrome, and pathologic J waves have been described for decades, but only recently experimental and clinical data have allowed reconciliation of Brugada and Early Repolarization under the common definition of J-wave syndromes. The concept was derived from studies showing, in both conditions, the presence of transmural dispersion of repolarization, localized conduction abnormalities, and abnormal transition between QRS and ST segment on electrocardiogram. Although several clinical studies have addressed the clinical presentation and epidemiology of J-wave syndromes, relevant knowledge gaps exist. Incomplete pathophysiologic understanding and uncertain electrocardiographic definitions limit effective risk stratification. Here, we review the current knowledge and recommendations for diagnosis and clinical management of these arrhythmogenic disorders.