An international multicenter cohort study on implantable cardioverter-defibrillators for the treatment of symptomatic children with catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) may cause sudden cardiac death (SCD) despite medical therapy. Therefore, implantable cardioverter-defibrillators (ICDs) are commonly advised. However, there are limited data on the outcomes of ICD use in children.

OBJECTIVE

The purpose of this study was to compare the risk of arrhythmic events in pediatric patients with CPVT with and without ICD.

METHODS

We compared the risk of SCD in patients with RYR2 (ryanodine receptor 2) variants and phenotype-positive symptomatic patients with CPVT with and without ICD who were younger than 19 years and had no history of sudden cardiac arrest at phenotype diagnosis. The primary outcome was SCD; secondary outcomes were composite end points of SCD, sudden cardiac arrest, or appropriate ICD shocks with or without arrhythmic syncope.

RESULTS

The study included 235 patients, 73 with ICD (31.1%) and 162 without ICD (68.9%). Over a median follow-up of 8.0 years (interquartile range 4.3-13.4 years), SCD occurred in 7 patients (3.0%), of whom 4 (57.1%) were noncompliant with medications and none had an ICD. Patients with ICD had a higher risk of both secondary composite outcomes (without syncope: hazard ratio 5.85; 95% confidence interval 3.40-10.09; P < .0001; with syncope: hazard ratio 2.55; 95% confidence interval 1.50-4.34; P = .0005). Thirty-one patients with ICD (42.5%) experienced appropriate shocks, 18 (24.7%) inappropriate shocks, and 21 (28.8%) device-related complications.

CONCLUSION

SCD events occurred only in the no ICD group and in those not on optimal medical therapy. Patients with ICD had a high risk of appropriate and inappropriate shocks, which may be reduced with appropriate device programming. Severe ICD complications were common, and risks vs benefits of ICDs need to be considered.

The frequency of gene variant reclassification and its impact on clinical management in the inherited arrhythmia clinic

BACKGROUND

Genetic testing in the inherited arrhythmia clinic informs risk stratification, clinical management, and family screening. Periodic review of variant classification is recommended as supporting evidence accrues over time. However, there is limited reporting of real-world data on the frequency and impact of variant reclassification.

OBJECTIVE

The purpose of this study was to determine the burden of variant reclassification in our inherited arrhythmia clinic and the impact on clinical management.

METHODS

Genetic testing reports for patients referred to our clinic from 2004-2020 were reviewed. Reported variants were reinvestigated using ClinVar, VarSome, and a literature review. Classification was updated using the American College of Medical Genetics and Genomics (ACMG) criteria and tested for association with arrhythmic events and modification of medical management.

RESULTS

We identified 517 patients (median age 37 years) who underwent gene panel testing. A variant of uncertain significance (VUS) was reported for 94 patients (18.2%) and more commonly identified when using large gene panels (P <.001). A total of 28 of 87 unique VUSs (32.2%) were reclassified to pathogenic/likely pathogenic (n = 11) or benign/likely benign (n = 17). Of 138 originally reported pathogenic variants, 7 (5.1%) lacked support using ACMG criteria. Variant reclassification was not associated with arrhythmic events; however, it did impact genotype-specific counseling and future therapeutic options.

CONCLUSION

In our large real-world patient cohort, we identify a clinically important proportion of both pathogenic variants and VUSs with evidence for reclassification. These findings highlight the need for informed pretest counseling, a regular structured review of variants reported in genetic testing, and the potential benefits to patients for supporting genotype-guided therapy.

Calcium Release Deficiency Syndrome: A New Inherited Arrhythmia Syndrome

Calcium release deficiency syndrome (CRDS) is a newly described form of inherited arrhythmia caused by damaging loss-of-function variants in the cardiac ryanodine receptor (RyR2). Unlike the prototypical RyR2 gain-of-function channelopathy, known as catecholaminergic polymorphic ventricular tachycardia, patients with CRDS are predisposed to sudden death usually in the absence of any electrical abnormalities at rest or during stress electrocardiography. This makes diagnosis incredibly challenging, however, an invasive electrophysiologic test appears to be effective in unmasking the phenotype, called the long-burst, long-pause, short-coupled ventricular extra-stimulus protocol. Optimal therapies for patients with CRDS remain unestablished, although flecainide appears to be a promising candidate drug.

Evaluation of age at symptom onset, proband status, and sex as predictors of disease severity in pediatric catecholaminergic polymorphic ventricular tachycardia

BACKGROUND

Children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for sudden death, and a risk stratification tool does not exist.

OBJECTIVE

The purpose of this study was to determine whether proband status, age at symptom onset, and/or sex are independent predictors of cardiac events.

METHODS

A multicenter, ambispective, cohort of pediatric CPVT patients was categorized by sex, proband status, and age at symptom onset (D1: first decade of life [symptom onset <10 years] or D2: second decade of life [symptom onset 10-18 years, inclusive]). Demographics, therapy, genetics, and outcomes were compared between groups.

RESULTS

A total of 133 patients were included and stratified into 58 D1 and 75 D2 patients (68 female and 65 male; 106 probands and 27 relatives). Localization of RYR2 variants to hotspots differed based on proband status and age at symptom onset. The cardiac event rate was 33% (n = 44/133), inclusive of a 3% (n = 4/133) mortality rate, over a median of 6 years (interquartile range 3-11) after time of symptom onset. Proband status, rather than age at of symptom onset or sex, was an independent predictor of time to first cardiac event (P = .008; hazard ratio = 4.4). The 5-, 10- and 15-year event-free survival rates for probands were 77%, 56%, and 46%, respectively, and for relatives were 96%, 91%, and 86%, respectively. Event risk after diagnosis was 48% (32/67) in patients on β-blocker or flecainide alone vs 10% (5/48) in patients on β-blocker plus flecainide and/or left cardiac sympathetic denervation (P <.001).

CONCLUSION

Proband status, but not age at symptom onset or male sex, independently predicted an earlier onset of cardiac events. A larger sample size would enable a comprehensive investigation of other risk factors.

Diagnostic yield in victims of sudden cardiac death and their relatives

AIMS

International guidelines recommend cardiogenetic screening in families with sudden cardiac death (SCD) if the suspected cause is an inherited cardiac disease. The aim was to assess the diagnostic yield of inherited cardiac diseases in consecutively referred SCD families.

METHODS AND RESULTS

In this single-centre retrospective study, we consecutively included families referred to our tertiary unit between 2005 and 2018 for screening due to SCD. Following evaluation of premortem medical records and postmortem findings for the proband, the families underwent a guideline-based screening protocol. Relatives were followed and cardiovascular events registered. In total, 304 families with 695 relatives were included. In probands, mean age at death was 39 years (75% males) and in relatives mean age at screening was 35 years (47% males). The proband-diagnosis was established through autopsy findings (n = 89), genetic analyses (n = 7), or based on premortem findings (n = 21). In the remaining 187 families with borderline/no diagnosis in the proband, screening of relatives yielded a diagnosis in 26 additional families. In total, an inherited cardiac disease was identified in 143 out of 304 families (47%). In relatives, 73 (11%) were diagnosed. Arrhythmogenic right ventricular cardiomyopathy (n = 16) was the most common diagnosis. During follow-up (mean 5.5 years), a low rate of serious cardiac events was observed (no SCD events).

CONCLUSION

Forty-seven percent of SCD families were diagnosed. Eleven percent of the screened relatives received a definite diagnosis and were offered treatment according to guidelines. A low rate of serious cardiovascular events was observed among SCD relatives.

Inherited arrhythmia syndrome predisposing to sudden cardiac death

Inherited arrhythmia (IA) is one of the main causes of sudden cardiac death (SCD) in young people, and is reported to be a more prevalent cause of SCD in Asia than in Western countries. IAs are a group of genetic disorders caused by mutations in genes encoding cardiac ion channels, leading to electrophysiological characteristics that often occur in the absence of structural abnormalities. Channelopathies, such as long QT syndrome and Brugada syndrome, carry a potential risk of life-threatening ventricular tachyarrhythmias that predispose to SCD, although early prediction and prevention of the risk remain challenging. Recent advances in genetic testing have facilitated risk stratification as well as a precise diagnosis for IA, despite ongoing debates about the implications. Herein, we provide epidemiological data, a pathophysiological overview, and the current clinical approach to IAs related to SCD. In addition, we review the general issues arising from genetic testing for IAs.

Pregnancy in catecholaminergic polymorphic ventricular tachycardia: therapeutic optimization and multidisciplinary care are key to success

Women of child-bearing age comprise a large proportion of the patients followed by inherited arrhythmia clinics. Despite being a rare and dangerous diagnosis, cardiac and obstetric care providers should know that catecholaminergic polymorphic ventricular tachycardia (CPVT) is not a contraindication to pregnancy. In fact, pregnancy was not associated with an increased risk of CPVT-associated arrhythmias in a recent large cohort study, and most guideline-based anti-arrhythmic drug treatments are life-saving and carry a low risk of teratogenesis. In principle, the potential for CPVT destabilization may be more likely to occur after anti-arrhythmic drugs are decreased or stopped during pregnancy, when an implantable cardioverter defibrillator (ICD) shock exacerbates catecholamine release, or if adrenaline surges are triggered by labor and delivery. Therefore, all pregnant women should be followed by a cardio-obstetrics team with extensive knowledge of CPVT diagnosis, as well as arrhythmia risk stratification fand management. This multidisciplinary care should begin preconception and involve counseling on preimplantation genetic testing, choosing safe and effective anti-arrhythmic drugs, stopping contraindicated medications, optimal programming of ICDs, and planning for the brief hyper-adrenergic period of labor and delivery. The latest data on pregnancy in CPVT is reviewed here and the optimal care for this rare and complex patient population outlined.

Catecholaminergic polymorphic ventricular tachycardia in pregnancy: a case report

Introduction

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic disorder that can cause fatal tachyarrhythmias brought on by physical or emotional stress. There is little reported in the literature regarding management of CPVT in pregnancy much less during labor.

Case presentation

A gravida 2, para 1 presented to our high-risk clinic at 15 weeks gestation with known CPVT. The Caucasian female patient had been diagnosed after experiencing a cardiac arrest following a motor vehicle accident and found to have a pathogenic cardiac ryanodine receptor mutation. An implantable cardioverter defibrillator was placed at that time. Her pregnancy was uncomplicated, and she was medically managed with metoprolol, flecainide, and verapamil. Her labor course and successful vaginal delivery were uncomplicated and involved a multidisciplinary team comprising specialists in electrophysiology, maternal fetal medicine, anesthesiology, general obstetrics, lactation, and neonatology.

Conclusions

CPVT is likely underdiagnosed and, given that cardiovascular disease is a leading cause of death in pregnancy, it is important to bring further awareness to the diagnosis and management of this inherited arrhythmia syndrome in pregnancy.

Editorial commentary: When should the patient with an inherited cardiac disease have an ICD?

The implantable cardioverter defibrillator (ICD) is often considered a routine intervention for an inherited heart rhythm disorder (IHRD) despite there being little to no randomized data for non-ischemic indications. Furthermore, existing IHRD studies often do not report adverse ICD outcomes, and observational data increasingly show that complications are under-recognized. Only recently have tools emerged to address the rational use of ICDs for specific forms of IHRD, although the acceptable risk of device complications remains unestablished. Here, we summarize the evidence of ICD benefit and harm in IHRD, highlight current knowledge gaps, and propose alternative and adjunctive options to the transvenous ICD.

Caring for the pregnant woman with an inherited arrhythmia syndrome

Pregnancy is a period of increased cardiovascular risk in a woman's life. In the setting of an inherited arrhythmia syndrome (IAS), cardiologists and obstetricians may be unfamiliar with cardiovascular optimization and risk stratification in pregnancy. Historically, there were little data addressing the safety of pregnancy in these rare disorders. Recent advances suggest that no type of IAS represents an absolute contraindication to pregnancy. However, it is imperative that obstetric and cardiovascular clinicians understand the major forms of IAS and how they affect the risks and course of pregnancy. This includes any disease-specific proarrhythmic triggers unique to pregnancy, such as the postpartum period in long QT syndrome (especially type 2), which poses the greatest risk of arrhythmias, and the adrenergic nature of labor and delivery, which is relevant to catecholaminergic polymorphic ventricular tachycardia. Fortunately, several effective antiarrhythmic options exist that pose little fetal risk. IAS-specific optimization of implantable cardioverter-defibrillator algorithms, drug therapy, and a maternal cardiac plan addressing the antepartum, labor, and delivery and postpartum periods reduces the risk. Where evidence does not exist, there are plausible mechanistic considerations to guide clinicians. To achieve optimal outcomes, early involvement of an expert pregnancy heart team comprising obstetrics, genetics, cardiology, and anesthesiology team members and a shared decision-making approach to IAS issues in pregnancy are needed.

Family Communication About Genetic Risk of Hereditary Cardiomyopathies and Arrhythmias: an Integrative Review

Screening for hereditary cardiomyopathies and arrhythmias (HCA) may enable early detection, treatment, targeted surveillance, and result in effective prevention of debilitating complications and sudden cardiac death. Screening at-risk family members for HCA is conducted through cascade screening. Only half of at-risk family members are screened for HCA. To participate in screening, at-risk family members must be aware of their risk. This often relies on communication from diagnosed individuals to their relatives. However, family communication is not well understood and is ripe for developing interventions to improve screening rates. Until very recently, family communication of genetic risk has been mostly studied in non-cardiac disease. Using this non-cardiac literature, we developed the family communication of genetic risk (FCGR) conceptual framework. The FCGR has four main elements of the communication process: influential factors, communication strategies, communication occurrence, and reaction to communication. Using the FCGR, we conducted an integrated review of the available literature on genetic risk communication in HCA families. Descriptive analysis of 12 articles resulted in the development of categories describing details of the FCGR elements in the context of HCA. This review synthesizes what is known about influential factors, communication strategies, communication occurrence, and outcomes of communication in the context of HCA.

The accessibility and utilization of genetic testing for inherited heart rhythm disorders: a Canadian cross-sectional survey study

The genetic basis of many sudden death-related conditions has been elucidated. These include inherited arrhythmias and arrhythmogenic cardiomyopathies, termed inherited heart rhythm disorders (IHRD). Advising on and interpreting genetic testing is challenging for the general cardiologist. This has led to the development of interdisciplinary clinics for IHRD in varying stages of establishment in Canada. We sought the viewpoints and patterns of practice of Canadian IHRD experts, and assessed their ability to access genetic testing for IHRD using a national cross-sectional survey. Of 56 participants, most were physicians (68%) or genetic counselors (19%). Despite working collaboratively, most genetic counselors (59%) were either not satisfied or only somewhat satisfied with their relationships with physicians. Ninety percent of participants were involved in offering genetic evaluation, including 80% who felt that testing was usually/always accessible. Most offered genetic testing to confirm clinical diagnosis and/or direct family screening. Post-mortem genetic analysis was sought by 69% of respondents; however, a lack of retained tissue and/or poor tissue preparation hindered this process. Family screening was usually recommended in the setting of a pathogenic/likely pathogenic variant. The most commonly perceived barrier to genetic testing was cost to the healthcare system. More than a quarter of patients waited ≥ 6 months for funding. An ability to engage at-risk relatives was rated as limited/poor by 34% of participants. Despite the establishment of several interdisciplinary clinics, timely access to affordable testing, supported by strong team communication, continues to be a barrier to genetic testing in Canada.

Syncope in patients with inherited arrhythmias

Syncope, a common symptom of cerebral ischemia often shows a multifactorial etiopathogenesis. Although inherited arrhythmias causing syncope is uncommon, such an occurrence could be a warning sign preceding cardiac arrest. Long QT syndrome (LQTS) is a typical inherited arrhythmia causing syncope in children. Early diagnosis and treatment of LQTS using beta-blockers prevents recurrent syncope in LQTS. Brugada syndrome, another typical inherited arrhythmia causes syncope or sudden cardiac arrest in young individuals. Syncope as a symptom is useful for risk stratification of fatal arrhythmias and in selection of appropriate therapy. Catecholaminergic polymorphic ventricular tachycardia, another rare inherited arrhythmia causing recurrent syncope is associated with poor outcomes without medication. Early detection and therapeutic intervention improve prognosis; thus, correct diagnosis of syncope is imperative in cases of these inherited arrhythmias. We describe syncope associated with three typical inherited arrhythmias and discuss various diagnostic modalities.

Masked inherited primary arrhythmia syndromes in sudden cardiac death patients accompanied by coronary vasospasm

BACKGROUND/AIMS

Coronary vasospasms are one of the important causes of sudden cardiac death (SCD). Provocation of coronary vasospasms can be useful, though some results may lead to false positives, with patients potentially experiencing recurrent SCD despite appropriate medical treatments. We hypothesized that it is not coronary vasospasms but inherited primary arrhythmia syndromes (IPAS) that underlie the development of SCD.

METHODS

We analyzed 74 consecutive patients (3.8%) who survived out-of-hospital cardiac arrest among 1,986 patients who had angiographically proven coronary vasospasms. Electrical abnormalities were evaluated in serial follow-up electrocardiograms (ECGs) during and after the index event for a 3.9 years median follow-up. Major clinical events were defined as the composite of death and recurrent SCD events.

RESULTS

Forty five patients (60.8%) displayed electrocardiographic abnormalities suggesting IPAS: Brugada type patterns in six (8.2%), arrhythmogenic right ventricular dysplasia patterns in three (4.1%), long QT syndrome pattern in one (2.2%), and early repolarization in 38 (51.4%). Patients having major clinical events showed more frequent Brugada type patterns, early repolarization, and more diffuse multivessel coronary vasospasms. Brugada type pattern ECGs (adjusted hazard ratio [HR], 4.22; 95% confidence interval [CI], 1.16 to 15.99; p = 0.034), and early repolarization (HR, 2.97; 95% CI, 1.09 to 8.10; p = 0.034) were ultimately associated with an increased risk of mortality.

CONCLUSIONS

Even though a number of aborted SCD survivors have coronary vasospasms, some also have IPAS, which has the potential to cause SCD. Therefore, meticulous evaluations and follow-ups for IPAS are required in those patients.

Induced pluripotent stem cell technology and inherited arrhythmia syndromes

Inherited arrhythmia syndromes, including familial long QT syndrome, catecholaminergic polymorphic ventricular tachycardia, and Brugada syndrome, can cause life-threatening arrhythmias and are responsible for a significant proportion of sudden deaths in the young. Identification of genetic mutations and pathophysiological changes that underlie disease development can inform clinical practice and guide novel drug development. However, disease mechanisms in a large number of patients remain elusive and pharmacologic treatment is suboptimal, so many patients rely on implantable cardioverter-defibrillator therapy. Induced pluripotent stem cell models of disease facilitate analysis of disease mechanisms in patient-specific cardiomyocytes, overcoming limitations of animal models and human tissue restrictions. This review outlines how studies using induced pluripotent stem cell-derived cardiomyocytes are contributing to our understanding of the mechanisms that underpin disease pathogenesis and their potential to facilitate new pharmacologic therapies and personalized medicine.

KCNJ2 mutation causes an adrenergic-dependent rectification abnormality with calcium sensitivity and ventricular arrhythmia

BACKGROUND

KCNJ2 mutations are associated with a variety of inherited arrhythmia syndromes including catecholaminergic polymorphic ventricular tachycardia 3.

OBJECTIVE

To characterize the detailed cellular mechanisms of the clinically recognized KCNJ2 mutation R67Q.

METHODS

Kir2.1 current density was measured from COS-1 cells transiently transfected with wild-type human Kir-2.1 (WT-Kir2.1) and/or a heterozygous missense mutation in KCNJ2 (R67Q-Kir2.1) by using the whole-cell voltage clamp technique. Catecholamine activity was simulated with protein kinase A-stimulating cocktail exposure. Phosphorylation-deficient mutants, S425N-Kir2.1 and S425N-Kir2.1/R67Q-S425N-Kir2.1, were used in a separate set of experiments. HA- or Myc-Tag-WT-Kir2.1 and HA-Tag-R67Q-Kir2.1 were used for confocal imaging.

RESULTS

A 33-year-old woman presented with a catecholaminergic polymorphic ventricular tachycardia-like clinical phenotype and was found to have KCNJ2 missense mutation R67Q. Treatment with nadolol and flecainide resulted in the complete suppression of arrhythmias and symptom resolution. Under baseline conditions, R67Q-Kir2.1 expressed alone did not produce inward rectifier current while cells coexpressing WT-Kir2.1 and R67Q-Kir2.1 demonstrated the rectification index (RI) similar to that of WT-Kir2.1. After PKA stimulation, R67Q-Kir2.1/WT-Kir2.1 failed to increase peak outward current density; WT-Kir2.1 increased by 46% (n = 5), while R67Q-Kir2.1/WT-Kir2.1 decreased by 6% (n = 6) (P = .002). Rectification properties in R67Q-Kir2.1/WT-Kir2.1 demonstrated sensitivity to calcium with a decreased RI in the high-calcium pipette solution (RI 20.3% ± 4.1%) than in the low-calcium pipette solution (RI 36.5% ± 5.7%) (P < .05). Immunostaining of WT-Kir2.1 and R67Q-Kir2.1 individually and together showed a normal membrane expression pattern and colocalization by using the Pearson correlation coefficient.

CONCLUSIONS

R67Q-Kir2.1 is associated with an adrenergic-dependent clinical and cellular phenotype with rectification abnormality enhanced by increased calcium. These findings are a significant advancement of our knowledge and understanding of the phenotype-genotype relationship of arrhythmia syndromes related to KCNJ2 mutations.

In silico investigation of a KCNQ1 mutation associated with familial atrial fibrillation

Mutations in transmembrane domains of the KCNQ1 subunit of the I(Ks) potassium channel have been associated with familial atrial fibrillation. We have investigated mechanisms by which the S1 domain S140G KCNQ1 mutation influences atrial arrhythmia risk and, additionally, whether it can affect ventricular electrophysiology. In perforated-patch recordings, S140G-KCNQ1+KCNE1 exhibited leftward-shifted activation, slowed deactivation and marked residual current. In human atrial action potential (AP) simulations, AP duration and refractoriness were shortened and rate-dependence flattened. Simulated I(Ks) but not I(Kr) block offset AP shortening produced by the mutation. In atrial tissue simulations, temporal vulnerability to re-entry was little affected by the S140G mutation. Spatial vulnerability was markedly increased, leading to more stable and stationary spiral wave re-entry in 2D stimulations, which was offset by I(Ks) block, and to scroll waves in 3D simulations. These changes account for vulnerability to AF with this mutation. Ventricular AP clamp experiments indicate a propensity for increased ventricular I(Ks) with the S140G KCNQ1 mutation and ventricular AP simulations showed model-dependent ventricular AP abbreviation.