Mortality of Inherited Arrhythmia Syndromes

Prognosis and clinical management of asymptomatic family members with RYR2-mediated catecholaminergic polymorphic ventricular tachycardia: a review

Despite its low prevalence, the potential diagnosis of catecholaminergic polymorphic ventricular tachycardia (CPVT) should be at the forefront of a paediatric cardiologists mind in children with syncope during exercise or emotions. Over the years, the number of children with a genetic diagnosis of CPVT due to a (likely) pathogenic RYR2 variant early in life and prior to the onset of symptoms has increased due to cascade screening programmes. Limited guidance for this group of patients is currently available. Therefore, we aimed to summarise currently available literature for asymptomatic patients with a (likely) pathogenic RYR2 variant, particularly the history of CPVT and its genetic architecture, the currently available diagnostic tests and their limitations, and the development of a CPVT phenotype - both electrocardiographically and symptomatic - of affected family members. Their risk of arrhythmic events is presumably low and a phenotype seems to develop in the first two decades of life. Future research should focus on this group in particular, to better understand the development of a phenotype over time, and therefore, to be able to better guide clinical management - including the frequency of diagnostic tests, the timing of the initiation of drug therapy, and lifestyle recommendations.

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).

SCN5A-1795insD founder variant: a unique Dutch experience spanning 7 decades

The SCN5A-1795insD founder variant is a unique SCN5A gene variant found in a large Dutch pedigree that first came to attention in the late 1950s. To date, this is still one of the largest and best described SCN5A founder families worldwide. It was the first time that a single pathogenic variant in SCN5A proved to be sufficient to cause a sodium channel overlap syndrome. Affected family members displayed features of Brugada syndrome, cardiac conduction disease and long QT syndrome type 3, thus encompassing features of both loss and gain of sodium channel function. This brief summary takes us past 70 years of clinical experience and over 2 decades of research. It is remarkable to what extent researchers and clinicians have managed to gain understanding of this complex phenotype in a relatively short time. Extensive clinical, genetic, electrophysiological and molecular studies have provided fundamental insights into SCN5A and the cardiac sodium channel Nav1.5.

Congenital Long QT Syndrome

Congenital long QT syndrome (LQTS) encompasses a group of heritable conditions that are associated with cardiac repolarization dysfunction. Since its initial description in 1957, our understanding of LQTS has increased dramatically. The prevalence of LQTS is estimated to be ∼1:2,000, with a slight female predominance. The diagnosis of LQTS is based on clinical, electrocardiogram, and genetic factors. Risk stratification of patients with LQTS aims to identify those who are at increased risk of cardiac arrest or sudden cardiac death. Factors including age, sex, QTc interval, and genetic background all contribute to current risk stratification paradigms. The management of LQTS involves conservative measures such as the avoidance of QT-prolonging drugs, pharmacologic measures with nonselective β-blockers, and interventional approaches such as device therapy or left cardiac sympathetic denervation. In general, most forms of exercise are considered safe in adequately treated patients, and implantable cardioverter-defibrillator therapy is reserved for those at the highest risk. This review summarizes our current understanding of LQTS and provides clinicians with a practical approach to diagnosis and management.

Provocation Testing and Therapeutic Response in a Newly Described Channelopathy: RyR2 Calcium Release Deficiency Syndrome

BACKGROUND

A novel familial arrhythmia syndrome, cardiac ryanodine receptor (RyR2) calcium release deficiency syndrome (CRDS), has recently been described. We evaluated a large and well characterized family to assess provocation testing, risk factor stratification and response to therapy in CRDS.

METHODS

We present a family with multiple unheralded sudden cardiac deaths and aborted cardiac arrests, primarily in children and young adults, with no clear phenotype on standard clinical testing.

RESULTS

Genetic analysis, including whole genome sequencing, firmly established that a missense mutation in RYR2, Ala4142Thr, was the underlying cause of disease in the family. Functional study of the variant in a cell model showed RyR2 loss-of-function, indicating that the family was affected by CRDS. EPS (Electrophysiological Study) was undertaken in 9 subjects known to carry the mutation, including a survivor of aborted sudden cardiac death, and the effects of flecainide alone and in combination with metoprolol were tested. There was a clear gradation in inducibility of nonsustained and sustained ventricular arrhythmia between subjects at EPS, with the survivor of aborted sudden cardiac death being the most inducible subject. Administration of flecainide substantially reduced arrhythmia inducibility in this subject and abolished arrhythmia in all others. Finally, the effects of additional metoprolol were tested; it increased inducibility in 4/9 subjects.

CONCLUSIONS

The Ala4142Thr mutation of RYR2 causes the novel heritable arrhythmia syndrome CRDS, which is characterized by familial sudden death in the absence of prior symptoms or a recognizable phenotype on ambulatory monitoring or exercise stress testing. We increase the experience of a specific EPS protocol in human subjects and show that it is helpful in establishing the clinical status of gene carriers, with potential utility for risk stratification. Our data provide evidence that flecainide is protective in human subjects with CRDS, consistent with the effect previously shown in a mouse model.

Paediatric/young versus adult patients with long QT syndrome

Introduction

Long QT syndrome (LQTS) is a less prevalent cardiac ion channelopathy than Brugada syndrome in Asia. The present study compared the outcomes between paediatric/young and adult LQTS patients.

Methods

This was a population-based retrospective cohort study of consecutive patients diagnosed with LQTS attending public hospitals in Hong Kong. The primary outcome was spontaneous ventricular tachycardia/ventricular fibrillation (VT/VF).

Results

A total of 142 LQTS (mean onset age=27±23 years old) were included. Arrhythmias other than VT/VF (HR 4.67, 95% CI (1.53 to 14.3), p=0.007), initial VT/VF (HR=3.25 (95% CI 1.29 to 8.16), p=0.012) and Schwartz score (HR=1.90 (95% CI 1.11 to 3.26), p=0.020) were predictive of the primary outcome for the overall cohort, while arrhythmias other than VT/VF (HR=5.41 (95% CI 1.36 to 21.4), p=0.016) and Schwartz score (HR=4.67 (95% CI 1.48 to 14.7), p=0.009) were predictive for the adult subgroup (>25 years old; n=58). A random survival forest model identified initial VT/VF, Schwartz score, initial QTc interval, family history of LQTS, initially asymptomatic and arrhythmias other than VT/VF as the most important variables for risk prediction.

Conclusion

Clinical and ECG presentation varies between the paediatric/young and adult LQTS population. Machine learning models achieved more accurate VT/VF prediction.

Prediction of ventricular arrhythmia in phospholamban p.Arg14del mutation carriers-reaching the frontiers of individual risk prediction

Aims

This study aims to improve risk stratification for primary prevention implantable cardioverter defibrillator (ICD) implantation by developing a new mutation-specific prediction model for malignant ventricular arrhythmia (VA) in phospholamban (PLN) p.Arg14del mutation carriers. The proposed model is compared to an existing PLN risk model.

Methods and results

Data were collected from PLN p.Arg14del mutation carriers with no history of malignant VA at baseline, identified between 2009 and 2020. Malignant VA was defined as sustained VA, appropriate ICD intervention, or (aborted) sudden cardiac death. A prediction model was developed using Cox regression. The study cohort consisted of 679 PLN p.Arg14del mutation carriers, with a minority of index patients (17%) and male sex (43%), and a median age of 42 years [interquartile range (IQR) 27–55]. During a median follow-up of 4.3 years (IQR 1.7–7.4), 72 (10.6%) carriers experienced malignant VA. Significant predictors were left ventricular ejection fraction, premature ventricular contraction count/24 h, amount of negative T waves, and presence of low-voltage electrocardiogram. The multivariable model had an excellent discriminative ability {C-statistic 0.83 [95% confidence interval (CI) 0.78–0.88]}. Applying the existing PLN risk model to the complete cohort yielded a C-statistic of 0.68 (95% CI 0.61–0.75).

Conclusion

This new mutation-specific prediction model for individual VA risk in PLN p.Arg14del mutation carriers is superior to the existing PLN risk model, suggesting that risk prediction using mutation-specific phenotypic features can improve accuracy compared to a more generic approach.

LQTS founder population in Northern Sweden - the natural history of a potentially fatal inherited cardiac disorder

Long QT Syndrome (LQTS) is an autosomal dominant inherited cardiac disorder associated with life-threatening arrhythmias. In northern Sweden, a LQTS founder mutation (p.Y111C, KCNQ1 gene) was verified by genetic haplotype analysis and genealogical studies, and a common ancestor couple was identified. Clinical studies of this population revealed an apparent mild phenotype. However, due to early commencement of prophylactic treatment, the natural history of this disorder cannot be properly assessed based only on clinical data. By using the family tree mortality ratio method (FTMR), we assessed the natural history of the untreated LQTS founder population. The principle of FTMR is to compare the age-specific mortality rates in a historic population harboring an inherited disorder with the corresponding mortality rates in an unaffected control population.Initially, we used the general Swedish population during the same period for comparison and observed an apparent increased longevity in the p.Y111C study population. However, when using a control population born in the same area, we observed no differences regarding overall mortality. Moreover, patterns suggesting age- and sex-stratified excess mortality, in accordance with previous LQTS studies, were evident.This study shows the importance of being aware of historical demographic patterns to avoid misinterpreting when comparing historical data.

Classification, Epidemiology, and Global Burden of Cardiomyopathies

In the past 25 years, major advances were achieved in the nosography of cardiomyopathies, influencing the definition and taxonomy of this important chapter of cardiovascular disease. Nearly, 50% of patients dying suddenly in childhood or adolescence or undergoing cardiac transplantation are affected by cardiomyopathies. Novel cardiomyopathies have been discovered (arrhythmogenic, restrictive, and noncompacted) and added to update the World Health Organization classification. Myocarditis has also been named inflammatory cardiomyopathy. Extraordinary progress accomplished in molecular genetics of inherited cardiomyopathies allowed establishment of dilated cardiomyopathy as mostly cytoskeleton, force transmission disease; hypertrophic-restrictive cardiomyopathies as sarcomeric, force generation disease; and arrhythmogenic cardiomyopathy as desmosome, cell junction disease. Channelopathies (short and long QT, Brugada, and catecholaminergic polymorphic ventricular tachycardia syndromes) should also be considered cardiomyopathies because of electric myocyte dysfunction. Cardiomyopathies are easily diagnosed but treated only with palliative pharmacological or invasive therapy. Curative therapy, thanks to insights into the molecular pathogenesis, has to target the fundamental mechanisms involved in the onset and progression of these conditions.

Impact of clinical and genetic findings on the management of young patients with Brugada syndrome

BACKGROUND

Brugada syndrome (BrS) is an arrhythmogenic disease associated with sudden cardiac death (SCD) that seldom manifests or is recognized in childhood.

OBJECTIVES

The objectives of this study were to describe the clinical presentation of pediatric BrS to identify prognostic factors for risk stratification and to propose a data-based approach management.

METHODS

We studied 106 patients younger than 19 years at diagnosis of BrS enrolled from 16 European hospitals.

RESULTS

At diagnosis, BrS was spontaneous (n = 36, 34%) or drug-induced (n = 70, 66%). The mean age was 11.1 ± 5.7 years, and most patients were asymptomatic (family screening, (n = 67, 63%; incidental, n = 13, 12%), while 15 (14%) experienced syncope, 6(6%) aborted SCD or symptomatic ventricular tachycardia, and 5 (5%) other symptoms. During follow-up (median 54 months), 10 (9%) patients had life-threatening arrhythmias (LTA), including 3 (3%) deaths. Six (6%) experienced syncope and 4 (4%) supraventricular tachycardia. Fever triggered 27% of LTA events. An implantable cardioverter-defibrillator was implanted in 22 (21%), with major adverse events in 41%. Of the 11 (10%) patients treated with hydroquinidine, 8 remained asymptomatic. Genetic testing was performed in 75 (71%) patients, and SCN5A rare variants were identified in 58 (55%); 15 of 32 tested probands (47%) were genotype positive. Nine of 10 patients with LTA underwent genetic testing, and all were genotype positive, whereas the 17 SCN5A-negative patients remained asymptomatic. Spontaneous Brugada type 1 electrocardiographic (ECG) pattern (P = .005) and symptoms at diagnosis (P = .001) were predictors of LTA. Time to the first LTA event was shorter in patients with both symptoms at diagnosis and spontaneous Brugada type 1 ECG pattern (P = .006).

CONCLUSION

Spontaneous Brugada type 1 ECG pattern and symptoms at diagnosis are predictors of LTA events in the young affected by BrS. The management of BrS should become age-specific, and prevention of SCD may involve genetic testing and aggressive use of antipyretics and quinidine, with risk-specific consideration for the implantable cardioverter-defibrillator.

Exercise restrictions for patients with inherited cardiac conditions: Current guidelines, challenges and limitations

Inherited primary arrhythmia syndromes are a clinically heterogeneous group of relatively uncommon but important inherited cardiac conditions that are associated with an increased risk of sudden cardiac death (SCD) in the setting of a structurally normal heart. These include long-QT syndrome (LQTS), Short-QT syndrome (SQTS), Brugada syndrome (BrS) and Catecholaminergic Polymorphic Ventricular Tachycardia (CPVT). The cardiomyopathies represent the other major group of inherited cardiac conditions associated with SCD, of which hypertrophic cardiomyopathy (HCM) is the most common. Exercise is a known trigger of ventricular arrhythmias in many of these conditions, however marked genetic and clinical heterogeneity within individual diseases means that certain patients are at a much greater risk of lethal ventricular arrhythmias during exercise than others. For instance, LQTS type 1 (LQT1) and CPVT patients are at particular risk during exertion, whilst in patients with other genetic variants of LQTS, BrS and SQTS, alternative triggers are more significant precipitants. Many channelopathy (principally Brugada, CPVT) & cardiomyopathy (mainly HCM) patients receive primary or secondary prevention therapy with an implantable cardiac defibrillator (ICD). Exercising with an ICD in situ carries a range of additional risks including inappropriate shocks and lead complications. This review will focus on the risk of exercise-induced SCD in patients with inherited cardiac conditions, the current clinical guidelines in this area and the special consideration of patients with an ICD.

Detailed characterization of familial idiopathic ventricular fibrillation linked to the DPP6 locus

BACKGROUND

Familial idiopathic ventricular fibrillation (IVF) is a severe disease entity and is notoriously difficult to manage because there are no clinical risk indicators for premature cardiac arrest. Previously, we identified a link between familial IVF and a risk haplotype on chromosome 7q36 (involving the arrhythmia gene DPP6).

OBJECTIVE

The purpose of this study was to expand our knowledge of familial IVF and to discuss its (extended) clinical characteristics.

METHODS

We studied 601 family members and probands: 286 DPP6 risk-haplotype positive (haplotype-positive) and 315 DPP6 risk-haplotype negative (haplotype-negative) individuals. Clinical parameters, a combination of all-cause mortality and (aborted) cardiac arrest and differences between haplotype-positives and haplotype-negatives, were evaluated.

RESULTS

There were no differences in electrocardiographic indices between haplotype-positives and haplotype-negatives, or between haplotype-positives with or without events. Cardiac magnetic resonance documented slightly larger ventricular volumes in haplotype-positives compared to controls (P <.05), but these were not clinically useful. Mortality and/or cardiac arrest occurred in 85 haplotype-positives (30%) and 18 haplotype-negatives (6%). Twenty-four haplotype-positives (8% male) were resuscitated from ventricular fibrillation (VF). Documented VF was always elicited by monomorphic short-coupled extrasystoles from the right ventricular apex/lower free wall. Median survival in risk-haplotype haplotype-positives was 70 vs. 93 years for haplotype-negatives (P < .01), with a worse phenotype in males (median survival 63 vs. 83 years in females, P < .01). Implantable cardioverter-defibrillators were implanted in 99 patients (76 [77%] for primary prevention). Two arrhythmic events occurred in the primary prevention group during follow-up (5 ± 3 years).

CONCLUSION

Despite our extensive analysis, the complexity in identifying asymptomatic IVF family members at risk for future arrhythmias based on clinical parameters is once more demonstrated.

Next-generation sequencing for the diagnosis of cardiac arrhythmia syndromes

Inherited arrhythmia syndromes are collectively associated with substantial morbidity, yet our understanding of the genetic architecture of these conditions remains limited. Recent technological advances in DNA sequencing have led to the commercialization of genetic testing now widely available in clinical practice. In particular, next-generation sequencing allows the large-scale and rapid assessment of entire genomes. Although next-generation sequencing represents a major technological advance, it has introduced numerous challenges with respect to the interpretation of genetic variation and has opened a veritable floodgate of biological data of unknown clinical significance to practitioners. In this review, we discuss current genetic testing indications for inherited arrhythmia syndromes, broadly outline characteristics of next-generation sequencing techniques, and highlight challenges associated with such testing. We further summarize future directions that will be necessary to address to enable the widespread adoption of next-generation sequencing in the routine management of patients with inherited arrhythmia syndromes.

Cardiac evaluation of pediatric relatives in sudden arrhythmic death syndrome: a 2-center experience

BACKGROUND

Sudden arrhythmic death syndrome defines a sudden unexpected and unexplained death despite comprehensive pathological and toxicological investigation. Previous studies have focused on evaluation of adult relatives. There is, however, a lack of data in children, leading to highly variable management. We sought to determine the clinical utility of cardiac evaluation in pediatric relatives of sudden arrhythmic death syndrome probands.

METHODS AND RESULTS

Retrospective review was undertaken of pediatric patients with a family history of sudden arrhythmic death syndrome assessed from 2010 to 2013 in 2 centers. Clinical history, cardiac, and genetic investigations were assessed, including diagnoses made after evaluation of adult relatives. A total of 112 pediatric relatives from 61 families were evaluated (median age at presentation, 8 years; range, 0.5-16 years). A probable diagnosis was made in 18 (29.5%) families: Brugada syndrome, 13/18 (72%); long QT syndrome, 3/18 (17%); and catecholaminergic polymorphic ventricular tachycardia, 2/18 (11%). Genetic testing identified mutations in 20% of Brugada syndrome (2/10) and 50% of long QT syndrome (1/2) and catecholaminergic polymorphic ventricular tachycardia families (1/2) who were tested. Pediatric evaluation diagnosed 6/112 relatives (5.4%), increasing to 7% (6/85) if only first-degree relatives were assessed. The only useful diagnostic tests were the 12-lead and exercise electrocardiograms and ajmaline provocation test. The median duration of follow-up was 2.1 years (range, 0.2-8.2 years) with no cardiac events.

CONCLUSIONS

The yield of evaluating pediatric relatives is significant and higher when focused on first-degree relatives and on conditions usually expressed in childhood. We propose a management pathway for these children.

Outcome in phospholamban R14del carriers: results of a large multicentre cohort study

BACKGROUND

The pathogenic phospholamban R14del mutation causes dilated and arrhythmogenic right ventricular cardiomyopathies and is associated with an increased risk of malignant ventricular arrhythmias and end-stage heart failure. We performed a multicentre study to evaluate mortality, cardiac disease outcome, and risk factors for malignant ventricular arrhythmias in a cohort of phospholamban R14del mutation carriers.

METHODS AND RESULTS

Using the family tree mortality ratio method in a cohort of 403 phospholamban R14del mutation carriers, we found a standardized mortality ratio of 1.7 (95% confidence interval, 1.4-2.0) with significant excess mortality starting from the age of 25 years. Cardiological data were available for 295 carriers. In a median follow-up period of 42 months, 55 (19%) individuals had a first episode of malignant ventricular arrhythmias and 33 (11%) had an end-stage heart failure event. The youngest age at which a malignant ventricular arrhythmia occurred was 20 years, whereas for an end-stage heart failure event this was 31 years. Independent risk factors for malignant ventricular arrhythmias were left ventricular ejection fraction <45% and sustained or nonsustained ventricular tachycardia with hazard ratios of 4.0 (95% confidence interval, 1.9-8.1) and 2.6 (95% confidence interval, 1.5-4.5), respectively.

CONCLUSIONS

Phospholamban R14del mutation carriers are at high risk for malignant ventricular arrhythmias and end-stage heart failure, with left ventricular ejection fraction <45% and sustained or nonsustained ventricular tachycardia as independent risk factors. High mortality and a poor prognosis are present from late adolescence. Genetic and cardiac screening is, therefore, advised from adolescence onwards.

Sports preparticipation cardiac screening: what about children?

Sudden cardiac death in young athletes is a devastating event. Screening programs have been proposed to prevent sudden cardiac death in young athletes. Mortality rates and causes of death differ among young adults and children. Children have a considerably lower incidence of sudden cardiac death. Data lack to compare athletes and non-athletes in childhood, but 40-50 % of sudden cardiac death in this age group seems to be related to exercise. Screening programs including history and physical exam are not very sensitive or specific and will result in important numbers of false-positives and false-negatives. Especially, interpretation of ECG in children is different from ECG in adults, with less accurate diagnoses as a consequence. Secondary prevention by widespread education of simple resuscitation techniques and use of automatic external defibrillators if available will probably save as many lives as any screening program.

CONCLUSION

Sufficient data are lacking to support general preparticipation screening with history, physical exam, and ECG in competitive children. Nevertheless, the impact of such a program, together with secondary preventive measures, should be evaluated in large prospective studies.

Current perspectives in genetic cardiovascular disorders: from basic to clinical aspects

We summarize recent advances in the clinical genetics of hypercholesterolemia, hypertrophic cardiomyopathy (HCM), and lethal arrhythmia, all of which are monogenic cardiovascular diseases being essential to understanding the heart and circulatory pathophysiology. Among the issues of hypercholesterolemia which play a pivotal role in development of vascular damages, familial hypercholesterolemia is the common genetic cardiovascular disease; in addition to identifying the gene mutation coding low-density lipoprotein receptor, lipid kinetics in autosomal recessive hypercholesterolemia as well as in proprotein convertase subtilisin/kexin 9 gene mutation were recently demonstrated. As for HCM, some gene mutations were identified to correlate with clinical manifestations. Additionally, a gene polymorphism of the renin-angiotensin system in development of heart failure was identified as a modifier gene. The lethal arrhythmias such as sudden death syndromes, QT prolongation, and Brugada syndrome were found to exhibit gene mutation coding potassium and/or sodium ion channels. Interestingly, functional analysis of these gene mutations helped to identify the role of each gene mutation in developing these cardiovascular disorders. We suggest considering the genetic mechanisms of cardiovascular diseases associated with hyperlipidemia, myocardial hypertrophy, or lethal arrhythmia in terms of not only clinical diagnosis but also understanding pathophysiology of each disease with therapeutic aspects.