Impact of the method of calculating 30-day readmission rate after hospitalization for heart failure. Data from the VancOuver CoastAL Acute Heart Failure (VOCAL-AHF) registry

BACKGROUND

Thirty-day readmission rate after heart failure (HF) hospitalization is widely used to evaluate healthcare quality. Methodology may substantially influence estimated rates. We assessed the impact of different definitions on HF and all-cause readmission rates.

METHODS

Readmission rates were examined in 1,835 patients discharged following HF hospitalization using 64 unique definitions derived from five methodological factors: (1) ICD-10 codes (broad vs narrow), (2) index admission selection (single admission only first-in-year vs. random sample; or multiple admissions in year with vs. without 30-day blanking period), (3) variable denominator (number alive at discharge vs. number alive at 30-days), (4) follow-up period start (discharge date vs day following discharge), and (5) annual reference-period (calendar vs fiscal). The impact of different factors was assessed using linear-regression.

RESULTS

The calculated 30-day readmission rate for HF varied more than 2-fold depending solely on the methodological approach (6.5% to 15.0%). All-cause admission rates exhibited similar variation (18.8% to 29.9%). The highest rates included all consecutive index admissions (HF 11.1-15.0%, all-cause 24.0-29.9%), and lowest only one index admission per patient per year (HF 6.5-11.3%, all-cause 18.8-22.7%). When including multiple index admissions and compared to blanking the 30-days post-discharge, not blanking was associated with 2.3% higher readmission rates. Selecting a single admission per year with a first-in-year approach lowered readmission rates by 1.5%, while random-sampling admissions lowered estimates further by 5.2% (p<0.001).

CONCLUSION

Calculated 30-day readmission rates varied more than 2-fold by altering methods. Transparent and consistent methods are needed to ensure reproducible and comparable reporting.

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.

Novel Magnetic Resonance Imaging Tools for Hypertrophic Cardiomyopathy Risk Stratification

Hypertrophic cardiomyopathy (HCM) is a common genetic disorder with a well described risk of sudden cardiac death; however, risk stratification has remained a challenge. Recently, novel parameters in cardiac magnetic resonance imaging (CMR) have shown promise in helping to improve upon current risk stratification paradigms. In this manuscript, we have reviewed novel CMR risk markers and their utility in HCM. The results of the review showed that T1, extracellular volume, CMR feature tracking, and other miscellaneous novel CMR variables have the potential to improve sudden death risk stratification and may have additional roles in diagnosis and prognosis. The strengths and weaknesses of these imaging techniques, and their potential utility and implementation in HCM risk stratification are discussed.

Advances in Hypertrophic Cardiomyopathy Disease Modelling Using hiPSC-Derived Cardiomyocytes

The advent of human induced pluripotent stem cells (hiPSCs) and their capacity to be differentiated into beating human cardiomyocytes (CMs) in vitro has revolutionized human disease modelling, genotype-phenotype predictions, and therapeutic testing. Hypertrophic cardiomyopathy (HCM) is a common inherited cardiomyopathy and the leading known cause of sudden cardiac arrest in young adults and athletes. On a molecular level, HCM is often driven by single pathogenic genetic variants, usually in sarcomeric proteins, that can alter the mechanical, electrical, signalling, and transcriptional properties of the cell. A deeper knowledge of these alterations is critical to better understanding HCM manifestation, progression, and treatment. Leveraging hiPSC-CMs to investigate the molecular mechanisms driving HCM presents a unique opportunity to dissect the consequences of genetic variants in a sophisticated and controlled manner. In this review, we summarize the molecular underpinnings of HCM and the role of hiPSC-CM studies in advancing our understanding, and we highlight the advances in hiPSC-CM-based modelling of HCM, including maturation, contractility, multiomics, and genome editing, with the notable exception of electrophysiology, which has been previously covered.

The 2023 Canadian Cardiovascular Society Clinical Practice Update on Management of the Patient With a Prolonged QT Interval

A prolonged QT interval on the electrocardiogram is associated with an increased risk of the torsades de pointes form of ventricular arrhythmia resulting in syncope, sudden cardiac arrest or death, or misdiagnosis as a seizure disorder. The cause of QT prolongation can be congenital and inherited as an autosomal dominant variant, or it can be transient and acquired, often because of QT-prolonging drugs or electrolyte abnormalities. Automated measurement of the QT interval can be inaccurate, especially when the baseline electrocardiogram is abnormal, and manual verification is recommended. In this clinical practice update we provide practical tips about measurement of the QT interval, diagnosis, and management of congenital long QT syndrome and acquired prolongation of the QT interval. For congenital long QT syndrome, certain β-adrenergic-blocking drugs are highly effective, and implantable defibrillators are infrequently required. Many commonly prescribed drugs such as antidepressants and antibiotics can prolong the QT interval, and recommendations are provided on their safe use.

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.

Left Ventricular Systolic Dysfunction in Patients Diagnosed With Hypertrophic Cardiomyopathy During Childhood: Insights From the SHaRe Registry

BACKGROUND

The development of left ventricular systolic dysfunction (LVSD) in hypertrophic cardiomyopathy (HCM) is rare but serious and associated with poor outcomes in adults. Little is known about the prevalence, predictors, and prognosis of LVSD in patients diagnosed with HCM as children.

METHODS

Data from patients with HCM in the international, multicenter SHaRe (Sarcomeric Human Cardiomyopathy Registry) were analyzed. LVSD was defined as left ventricular ejection fraction <50% on echocardiographic reports. Prognosis was assessed by a composite of death, cardiac transplantation, and left ventricular assist device implantation. Predictors of developing incident LVSD and subsequent prognosis with LVSD were assessed using Cox proportional hazards models.

RESULTS

We studied 1010 patients diagnosed with HCM during childhood (<18 years of age) and compared them with 6741 patients with HCM diagnosed as adults. In the pediatric HCM cohort, median age at HCM diagnosis was 12.7 years (interquartile range, 8.0-15.3), and 393 (36%) patients were female. At initial SHaRe site evaluation, 56 (5.5%) patients with childhood-diagnosed HCM had prevalent LVSD, and 92 (9.1%) developed incident LVSD during a median follow-up of 5.5 years. Overall LVSD prevalence was 14.7% compared with 8.7% in patients with adult-diagnosed HCM. Median age at incident LVSD was 32.6 years (interquartile range, 21.3-41.6) for the pediatric cohort and 57.2 years (interquartile range, 47.3-66.5) for the adult cohort. Predictors of developing incident LVSD in childhood-diagnosed HCM included age <12 years at HCM diagnosis (hazard ratio [HR], 1.72 [CI, 1.13-2.62), male sex (HR, 3.1 [CI, 1.88-5.2), carrying a pathogenic sarcomere variant (HR, 2.19 [CI, 1.08-4.4]), previous septal reduction therapy (HR, 2.34 [CI, 1.42-3.9]), and lower initial left ventricular ejection fraction (HR, 1.53 [CI, 1.38-1.69] per 5% decrease). Forty percent of patients with LVSD and HCM diagnosed during childhood met the composite outcome, with higher rates in female participants (HR, 2.60 [CI, 1.41-4.78]) and patients with a left ventricular ejection fraction <35% (HR, 3.76 [2.16-6.52]).

CONCLUSIONS

Patients with childhood-diagnosed HCM have a significantly higher lifetime risk of developing LVSD, and LVSD emerges earlier than for patients with adult-diagnosed HCM. Regardless of age at diagnosis with HCM or LVSD, the prognosis with LVSD is poor, warranting careful surveillance for LVSD, especially as children with HCM transition to adult care.

Increased Ca2+ Transient Underlies RyR2-Related Left Ventricular Noncompaction

BACKGROUND

A loss-of-function cardiac ryanodine receptor (RyR2) mutation, I4855M+/-, has recently been linked to a new cardiac disorder termed RyR2 Ca2+ release deficiency syndrome (CRDS) as well as left ventricular noncompaction (LVNC). The mechanism by which RyR2 loss-of-function causes CRDS has been extensively studied, but the mechanism underlying RyR2 loss-of-function-associated LVNC is unknown. Here, we determined the impact of a CRDS-LVNC-associated RyR2-I4855M+/- loss-of-function mutation on cardiac structure and function.

METHODS

We generated a mouse model expressing the CRDS-LVNC-associated RyR2-I4855M+/- mutation. Histological analysis, echocardiography, ECG recording, and intact heart Ca2+ imaging were performed to characterize the structural and functional consequences of the RyR2-I4855M+/- mutation.

RESULTS

As in humans, RyR2-I4855M+/- mice displayed LVNC characterized by cardiac hypertrabeculation and noncompaction. RyR2-I4855M+/- mice were highly susceptible to electrical stimulation-induced ventricular arrhythmias but protected from stress-induced ventricular arrhythmias. Unexpectedly, the RyR2-I4855M+/- mutation increased the peak Ca2+ transient but did not alter the L-type Ca2+ current, suggesting an increase in Ca2+-induced Ca2+ release gain. The RyR2-I4855M+/- mutation abolished sarcoplasmic reticulum store overload-induced Ca2+ release or Ca2+ leak, elevated sarcoplasmic reticulum Ca2+ load, prolonged Ca2+ transient decay, and elevated end-diastolic Ca2+ level upon rapid pacing. Immunoblotting revealed increased level of phosphorylated CaMKII (Ca2+-calmodulin dependent protein kinases II) but unchanged levels of CaMKII, calcineurin, and other Ca2+ handling proteins in the RyR2-I4855M+/- mutant compared with wild type.

CONCLUSIONS

The RyR2-I4855M+/- mutant mice represent the first RyR2-associated LVNC animal model that recapitulates the CRDS-LVNC overlapping phenotype in humans. The RyR2-I4855M+/- mutation increases the peak Ca2+ transient by increasing the Ca2+-induced Ca2+ release gain and the end-diastolic Ca2+ level by prolonging Ca2+ transient decay. Our data suggest that the increased peak-systolic and end-diastolic Ca2+ levels may underlie RyR2-associated LVNC.

Current gaps in knowledge in inherited arrhythmia syndromes

The 3 most common inherited arrhythmia syndromes-Brugada syndrome, congenital long QT syndrome and catecholaminergic polymorphic ventricular tachycardia-were initially described in the previous century. Since then, research has evolved, which has enabled us to identify patients prior to the onset of potentially life-threatening symptoms. However, there are significant gaps in knowledge that complicate clinical management of these patients today. With this review paper, we aim to highlight the most important knowledge gaps in clinical research of these inherited arrhythmia syndromes.

Gene Therapy for Catecholaminergic Polymorphic Ventricular Tachycardia

Over the last three decades, the genetic basis of various inherited arrhythmia syndromes has been elucidated, providing key insights into cardiomyocyte biology and various regulatory pathways associated with cellular excitation, contraction, and repolarisation. As varying techniques to manipulate genetic sequence, gene expression, and different cellular pathways have become increasingly defined and understood, the potential to apply various gene-based therapies to inherited arrhythmia has been explored. The promise of gene therapy has generated significant interest in the medical and lay press, providing hope for sufferers of seemingly incurable disorders to imagine a future without repeated medical intervention, and, in the case of various cardiac disorders, without the risk of sudden death. In this review, we focus on catecholaminergic polymorphic ventricular tachycardia (CPVT), discussing the clinical manifestations, genetic basis, and molecular biology, together with current avenues of research related to gene therapy.

RYR2-ryanodinopathies: from calcium overload to calcium deficiency

The sarcoplasmatic reticulum (SR) cardiac ryanodine receptor/calcium release channel RyR2 is an essential regulator of cardiac excitation-contraction coupling and intracellular calcium homeostasis. Mutations of the RYR2 are the cause of rare, potentially lethal inherited arrhythmia disorders. Catecholaminergic polymorphic ventricular tachycardia (CPVT) was first described more than 20 years ago and is the most common and most extensively studied cardiac ryanodinopathy. Over time, other distinct inherited arrhythmia syndromes have been related to abnormal RyR2 function. In addition to CPVT, there are at least two other distinct RYR2-ryanodinopathies that differ mechanistically and phenotypically from CPVT: RYR2 exon-3 deletion syndrome and the recently identified calcium release deficiency syndrome (CRDS). The pathophysiology of the different cardiac ryanodinopathies is characterized by complex mechanisms resulting in excessive spontaneous SR calcium release or SR calcium release deficiency. While the vast majority of CPVT cases are related to gain-of-function variants of the RyR2 protein, the recently identified CRDS is linked to RyR2 loss-of-function variants. The increasing number of these cardiac 'ryanodinopathies' reflects the complexity of RYR2-related cardiogenetic disorders and represents an ongoing challenge for clinicians. This state-of-the-art review summarizes our contemporary understanding of RYR2-related inherited arrhythmia disorders and provides a systematic and comprehensive description of the distinct cardiac ryanodinopathies discussing clinical aspects and molecular insights. Accurate identification of the underlying type of cardiac ryanodinopathy is essential for the clinical management of affected patients and their families.

Population Prevalence of Premature Truncating Variants in Plakophilin-2 and Association With Arrhythmogenic Right Ventricular Cardiomyopathy: A UK Biobank Analysis

BACKGROUND

Truncating variants in the desmosomal gene PKP2 (PKP2tv) cause arrhythmogenic right ventricular cardiomyopathy (ARVC) yet display varied penetrance and expressivity.

METHODS

We identified individuals with PKP2tv from the UK Biobank (UKB) and determined the prevalence of an ARVC phenotype and other cardiovascular traits based on clinical and procedural data. The PKP2tv minor allelic frequency in the UKB was compared with a second cohort of probands with a clinical diagnosis of ARVC (ARVC cohort), with a figure of 1:5000 assumed for disease prevalence. In silico predictors of variant pathogenicity (combined annotation-dependent depletion and Splice AI [Illumina, Inc.]) were assessed.

RESULTS

PKP2tv were identified in 193/200 643 (0.10%) UKB participants, with 47 unique PKP2tv. Features consistent with ARVC were present in 3 (1.6%), leaving 190 with PKP2tv without manifest disease (UKB cohort; minor allelic frequency 4.73×10-4). The ARVC cohort included 487 ARVC probands with 144 distinct PKP2tv, with 25 PKP2tv common to both cohorts. The odds ratio for ARVC for the 25 common PKP2tv was 0.047 (95% CI, 0.001-0.268; P=2.43×10-6), and only favored ARVC (odds ratio >1) for a single variant, p.Arg79*. In silico variant analysis did not differentiate PKP2tv between the 2 cohorts. Atrial fibrillation was over-represented in the UKB cohort in those with PKP2tv (7.9% versus 4.3%; odds ratio, 2.11; P=0.005).

CONCLUSIONS

PKP2tv are prevalent in the population and associated with ARVC in only a small minority, necessitating a more detailed understanding of how PKP2tv cause ARVC in combination with associated genetic and environmental risk factors.

The design and rationale of the Advancing Cardiac Care Unit-based Rapid Assessment and Treatment of hypErcholesterolemia (ACCURATE) study

Familial hypercholesterolemia (FH) is an inherited condition characterized by elevated low-density lipoprotein cholesterol (LDL-C) levels and premature atherosclerotic cardiovascular disease (ASCVD). Despite being the most common inherited cardiovascular disorder, it is still highly underdiagnosed and undertreated worldwide. We designed the Advancing Cardiac Care Unit-based Rapid Assessment and Treatment of hypErcholesterolemia (ACCURATE) study to test the hypothesis that opportunistic genetic testing for FH among patients hospitalized for acute coronary syndrome (ACS) will increase the diagnosis of FH and improve patient outcomes. ACCURATE is a non-randomized, controlled trial of patients <60 years old admitted to an acute cardiac unit with ACS and elevated LDL-C levels. The first cohort will consist of a control group of patients presenting with ACS who will be treated according to usual standard-of-care. The second cohort will consist of patients presenting with ACS in whom research-based genetic testing for FH will be performed during hospitalization and the results returned to the treating physicians. The primary endpoint will be the number of patients with a new diagnosis of FH. The secondary endpoints will be the proportion of patients who undergo intensification of lipid-lowering therapy, the lowest LDL-C level achieved, and the proportion of patients reaching guideline recommended lipid targets in the 12 months after the index ACS. To our knowledge, ACCURATE represents the first clinical trial of genetic testing for FH in the acute cardiac care setting and is expected to help identify optimal approaches to increase the diagnosis and treatment of FH.

A Population-Based Study of Unexplained/Lone Atrial Fibrillation: Temporal Trends, Management, and Outcomes

Background

Previous studies on lone/unexplained atrial fibrillation and atrial flutter (AF) did not exclude patients with contemporary secondary AF triggers. We characterized unexplained AF using a strict definition, and compared it to secondary AF.

Methods

In this population-based study, unexplained AF was defined by the lack of any identifiable triggering medical/surgical diagnosis. Comparisons by AF type (unexplained vs secondary), age-of-onset (≤ / > 65 years), and sex were undertaken. Data were acquired by linking 6 population databases maintained by the Alberta Ministry of Health over a 9-year period (April 2006 to March 2015). The primary composite outcome of stroke, transient ischemic attack, thromboembolism, and/or death was assessed.

Results

There were 33,150 incident AF diagnoses identified, including 1145 patients (3.5%) with unexplained AF, 931 (81.2%) of whom were aged ≤ 65 years (2.8% of diagnoses, and 79% male). Patients with unexplained AF less often received rate/rhythm-control drugs (P < 0.0001), but they more often underwent electrical cardioversion (P < 0.0001) vs secondary AF patients. Men were younger at unexplained AF diagnosis (45 [interquartile range: 34-59] vs 58 [interquartile range: 40-69] years; P < 0.001). After adjusting for age at diagnosis, there were no sex-based differences in the primary outcome. Event-free survival in young unexplained AF (age ≤ 65 years) was 99.4% at 1 year and 98.3% at 3 years. At 3 years, hospitalization(s)/emergency visit(s) for noncardiovascular reasons and for AF occurred in 56.6% and 23.8% of these patients, respectively.

Conclusions

Using a strict contemporary definition of unexplained AF, this study shows that the condition is rare, predominantly male, and has excellent event-free survival. However, the high rate of acute hospital utilization after diagnosis is concerning.

Using hiPSC-CMs to Examine Mechanisms of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited cardiac arrhythmia condition, triggered by physical or acute emotional stress, that predominantly expresses early in life. Gain-of-function mutations in the cardiac ryanodine receptor gene (RYR2) account for the majority of CPVT cases, causing substantial disruption of intracellular calcium (Ca²⁺ ) homeostasis particularly during the periods of β-adrenergic receptor stimulation. However, the highly variable penetrance, patient outcomes, and drug responses observed in clinical practice remain unexplained, even for patients with well-established founder RyR2 mutations. Therefore, investigation of the electrophysiological consequences of CPVT-causing RyR2 mutations is crucial to better understand the pathophysiology of the disease. The development of strategies for reprogramming human somatic cells to human induced pluripotent stem cells (hiPSCs) has provided a unique opportunity to study inherited arrhythmias, due to the ability of hiPSCs to differentiate down a cardiac lineage. Employment of genome editing enables generation of disease-specific cell lines from healthy and diseased patient-derived hiPSCs, which subsequently can be differentiated into cardiomyocytes. This paper describes the means for establishing an hiPSC-based model of CPVT in order to recapitulate the disease phenotype in vitro and investigate underlying pathophysiological mechanisms. The framework of this approach has the potential to contribute to disease modeling and personalized medicine using hiPSC-derived cardiomyocytes. © 2021 Wiley Periodicals LLC.

An International Multi-Center Cohort Study on β-blockers for the Treatment of Symptomatic Children with Catecholaminergic Polymorphic Ventricular Tachycardia

Background: Symptomatic children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for recurrent arrhythmic events. Beta-blockers (BBs) decrease this risk, but studies comparing individual BBs in sizeable cohorts are lacking. We aimed to assess the association between risk for arrhythmic events and type of BB in a large cohort of symptomatic children with CPVT. Methods: From two international registries of patients with CPVT, RYR2 variant-carrying symptomatic children (defined as syncope or sudden cardiac arrest prior to BB initiation and age at start of BB therapy <18 years), treated with a BB were included. Cox-regression analyses with time-dependent covariates for BB and potential confounders were used to assess the hazard ratio (HR). The primary outcome was the first occurrence of sudden cardiac death, sudden cardiac arrest, appropriate implantable cardioverter-defibrillator shock, or syncope. The secondary outcome was the first occurrence of any of the primary outcomes except syncope. Results: We included 329 patients (median age at diagnosis 12 [interquartile range, 7-15] years, 35% females). Ninety-nine (30.1%) patients experienced the primary and 74 (22.5%) experienced the secondary outcome during a median follow-up of 6.7 [interquartile range, 2.8-12.5] years. Two-hundred sixteen patients (66.0%) used a non-selective BB (predominantly nadolol [n=140] or propranolol [n=70]) and 111 (33.7%) used a β1-selective BB (predominantly atenolol [n=51], metoprolol [n=33], or bisoprolol [n=19]) as initial BB. Baseline characteristics did not differ. The HR for both the primary and secondary outcomes were higher for β1-selective compared with non-selective BBs (HR, 2.04 95% CI, 1.31-3.17; and HR, 1.99; 95% CI, 1.20-3.30, respectively). When assessed separately, the HR for the primary outcome was higher for atenolol (HR, 2.68; 95% CI, 1.44-4.99), bisoprolol (HR, 3.24; 95% CI, 1.47-7.18), and metoprolol (HR, 2.18; 95% CI, 1.08-4.40) compared with nadolol, but did not differ from propranolol. The HR of the secondary outcome was only higher in atenolol compared with nadolol (HR, 2.68; 95% CI, 1.30-5.55). Conclusions: B1-selective BBs were associated with a significantly higher risk for arrhythmic events in symptomatic children with CPVT compared with non-selective BBs, specifically nadolol. Nadolol, or propranolol if nadolol is unavailable, should be the preferred BB for treating symptomatic children with CPVT.

Clinical and Functional Characterization of Ryanodine Receptor 2 Variants Implicated in Calcium-Release Deficiency Syndrome

Importance

Calcium-release deficiency syndrome (CRDS), which is caused by loss-of-function variants in cardiac ryanodine receptor 2 (RyR2), is an emerging cause of ventricular fibrillation. However, the lack of complex polymorphic/bidirectional ventricular tachyarrhythmias during exercise stress testing (EST) may distinguish it from catecholaminergic polymorphic ventricular tachycardia (CPVT). Recently, in the first clinical series describing the condition, mouse and human studies showed that the long-burst, long-pause, short-coupled ventricular extra stimulus (LBLPS) electrophysiology protocol reliably induced CRDS ventricular arrhythmias. Data from larger populations with CRDS and its associated spectrum of disease are lacking.

Objective

To further insight into CRDS through international collaboration.

Design, Setting, and Participants

In this multicenter observational cohort study, probands with unexplained life-threatening arrhythmic events and an ultrarare RyR2 variant were identified. Variants were expressed in HEK293 cells and subjected to caffeine stimulation to determine their functional impact. Data were collected from September 1, 2012, to March 6, 2021, and analyzed from August 9, 2015, to March 6, 2021.

Main Outcomes and Measures

The functional association of RyR2 variants found in putative cases of CRDS and the associated clinical phenotype(s).

Results

Of 10 RyR2 variants found in 10 probands, 6 were loss-of-function, consistent with CRDS (p.E4451del, p.F4499C, p.V4606E, p.R4608Q, p.R4608W, and p.Q2275H) (in 4 [67%] male and 2 [33%] female probands; median age at presentation, 22 [IQR, 8-34] years). In 5 probands with a documented trigger, 3 were catecholamine driven. During EST, 3 probands with CRDS had no arrhythmias, 1 had a monomorphic couplet, and 2 could not undergo EST (deceased). Relatives of the decedents carrying the RyR2 variant did not have EST results consistent with CPVT. After screening 3 families, 13 relatives were diagnosed with CRDS, including 3 with previous arrhythmic events (23%). None had complex ventricular tachyarrhythmias during EST. Among the 19 confirmed cases with CRDS, 10 had at least 1 life-threatening event at presentation and/or during a median follow-up of 7 (IQR, 6-18) years. Two of the 3 device-detected ventricular fibrillation episodes were induced by a spontaneous LBLPS-like sequence. β-Blockers were used in 16 of 17 surviving patients (94%). Three of 16 individuals who were reportedly adherent to β-blocker therapy (19%) had breakthrough events.

Conclusions and Relevance

The results of this study suggest that calcium-release deficiency syndrome due to RyR2 loss-of-function variants mechanistically and phenotypically differs from CPVT. Ventricular fibrillation may be precipitated by a spontaneous LBLPS-like sequence of ectopy; however, CRDS remains difficult to recognize clinically. These data highlight the need for better diagnostic tools and treatments for this emerging condition.

Proband and family member disease penetrance in cardiac genetic secondary findings

Background

Broad genomic screening including whole exome sequencing (ES) is increasingly used in clinical care. Families may elect to receive pathogenic and likely pathogenic genetic variants in 30 genes associated with inherited cardiac disorders recommended as reportable by the ACMG, termed cardiac secondary findings (CSF). Most families (91%) opt to receive CSF for the proband, and 73% of parents opt to receive CSF for themselves1.

Our initial experience of 33 patients with 22 different CSF identified a low diagnostic yield and high proportion of patients referred for evaluation with non-reportable findings, with only 4 CSF classified as P/LP (4/22; 18%). Three patients (9%) had concordant clinical findings but none met diagnostic criteria2.

Purpose

The purpose of this analysis was to evaluate the genetic and clinical findings in a secondary cohort.

Methods

All patients who presented to a joint familial cardiogenetic clinic were included. Identified CSF were categorized by 2015 ACMG criteria for variant classification. Clinical evaluation was performed using contemporaneous diagnostic criteria based on potential phenotypes associated with identified CSF. Variant classification and clinical findings were compared in the initial and secondary cohorts. The study was approved by the Institutional Review Board.

Results

Forty patients (20 male; age 19.5±15.9 years) from 20 families were evaluated with 19 different CSF. The variant consequence was missense (12), frameshift (6) and premature stop codon (1), and ACMG classification was pathogenic/likely pathogenic in 15/19 (79%) (p&lt;0.01).

Complete clinical evaluation was performed in 35 (88%) individuals and is ongoing in 5. Concordant findings were identified in 12/35 (34%) (p&lt;0.04) including 5 adults and 7 children. CSF and associated phenotype included TTN – LV dilatation (1); KCNQ1 – LQTS (5); DSP – arrhythmogenic cardiomyopathy (ACM) (4); RYR2 – CPVT (1); SCN5A – 1st degree AV block (1).

Two patients were symptomatic prior to diagnosis; a 16-year-old female with palpitations and ventricular ectopy considered benign (DSP), and a 41-year-old female with syncope and documented torsade de pointes experienced before cascade screening (KCNQ1).

Three patients received defibrillators on primary (ACM) or secondary (LQTS) prevention indications and 2 received ILRs (ACM). Beta-blockers were prescribed for 5 with LQTS (3), CPVT (1) and KCNQ1 CSF but no phenotype (2). Avoidance of provocative medication was recommended for 11. Ten patients with pathogenic CSF (MYBPC3 (2), RYR2 (1), SCN5A (4), KCNH2 (3)) had no discernable phenotype.

Conclusions

In this secondary analysis there was a marked increase in the proportion of pathogenic/likely pathogenic CSF and associated clinical findings, including those necessitating significant management strategies. This data may help inform results disclosure and referral streams for patients with CSF.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): The Mannion and Roberts Families Table 1

Human RyR2 (Ryanodine Receptor 2) Loss-of-Function Mutations: Clinical Phenotypes and In Vitro Characterization

[Figure: see text].

Pediatric Catecholaminergic Polymorphic Ventricular Tachycardia: A Translational Perspective for the Clinician-Scientist

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare and potentially lethal inherited arrhythmia disease characterized by exercise or emotion-induced bidirectional or polymorphic ventricular tachyarrhythmias. The median age of disease onset is reported to be approximately 10 years of age. The majority of CPVT patients have pathogenic variants in the gene encoding the cardiac ryanodine receptor, or calsequestrin 2. These lead to mishandling of calcium in cardiomyocytes resulting in after-depolarizations, and ventricular arrhythmias. Disease severity is particularly pronounced in younger individuals who usually present with cardiac arrest and arrhythmic syncope. Risk stratification is imprecise and long-term prognosis on therapy is unknown despite decades of research focused on pediatric CPVT populations. The purpose of this review is to summarize contemporary data on pediatric CPVT, highlight knowledge gaps and present future research directions for the clinician-scientist to address.

Cardiac ryanodine receptor calcium release deficiency syndrome

Cardiac ryanodine receptor (RyR2) gain-of-function mutations cause catecholaminergic polymorphic ventricular tachycardia, a condition characterized by prominent ventricular ectopy in response to catecholamine stress, which can be reproduced on exercise stress testing (EST). However, reports of sudden cardiac death (SCD) have emerged in EST-negative individuals who have loss-of-function (LOF) RyR2 mutations. The clinical relevance of RyR2 LOF mutations including their pathogenic mechanism, diagnosis, and treatment are all unknowns. Here, we performed clinical and genetic evaluations of individuals who suffered from SCD and harbored an LOF RyR2 mutation. We carried out electrophysiological studies using a programed electrical stimulation protocol consisting of a long-burst, long-pause, and short-coupled (LBLPS) ventricular extra-stimulus. Linkage analysis of RyR2 LOF mutations in six families revealed a combined logarithm of the odds ratio for linkage score of 11.479 for a condition associated with SCD with negative EST. A RyR2 LOF mouse model exhibited no catecholamine-provoked ventricular arrhythmias as in humans but did have substantial cardiac electrophysiological remodeling and an increased propensity for early afterdepolarizations. The LBLPS pacing protocol reliably induced ventricular arrhythmias in mice and humans having RyR2 LOF mutations, whose phenotype is otherwise concealed before SCD. Furthermore, treatment with quinidine and flecainide abolished LBLPS-induced ventricular arrhythmias in model mice. Thus, RyR2 LOF mutations underlie a previously unknown disease entity characterized by SCD with normal EST that we have termed RyR2 Ca²⁺ release deficiency syndrome (CRDS). Our study provides insights into the mechanism of CRDS, reports a specific CRDS diagnostic test, and identifies potentially efficacious anti-CRDS therapies.

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.

Potential overdiagnosis of long QT syndrome using exercise stress and QT stand testing in children and adolescents with a low probability of disease

BACKGROUND

Long QT syndrome (LQTS) is a dangerous arrhythmia disorder that often presents in childhood and adolescence. The exercise stress test (EST) and QT-stand test may unmask QT interval prolongation at key heart rate transition points in LQTS, but their utility in children is debated.

OBJECTIVE

To determine if the QT-stand test or EST can differentiate children with a low probability of LQTS from those with confirmed LQTS.

METHODS

This retrospective study compares the corrected QT intervals (QTc) of children (<19 years) during the QT-stand test and EST. Patients were divided into three groups for comparison: confirmed LQTS (n = 14), low probability of LQTS (n = 14), and a control population (n = 9).

RESULTS

Using the Bazett formula, confirmed LQTS patients had longer QTc intervals than controls when supine, standing, and at 3-4 min of recovery (p ≤ .01). Patients with a low probability of LQTS had longer QTc duration upon standing (p = .018) and at 1 min of recovery (p = .016) versus controls. There were no significant QTc differences at any transition point between low probability and confirmed LQTS. Using the Fridericia formula, differences in QTc between low probability and confirmed LQTS were also absent at the transition points examined, except at 1 min into exercise, where low probability patients had shorter QTc intervals (437 vs. 460 ms, p = .029).

CONCLUSION

The diagnostic utility of the QT stand test and EST remains unclear in pediatric LQTS. The formula used for heart rate correction may influence accuracy, and dynamic T-U wave morphology changes may confound interpretation in low probability situations.

The Interplay Between Titin, Polygenic Risk, and Modifiable Cardiovascular Risk Factors in Atrial Fibrillation

BACKGROUND

Common and rare variants, including those in the gene for the cardiac structural protein titin (TTN), have been implicated in the risk of developing atrial fibrillation (AF). However, the effect of genetic variants on risk of AF compared with established modifiable risk factors is unclear. The objective of this study was to evaluate the risk of AF and associated cardiovascular complications in TTN variant carriers and examine interactions between TTN variants or common variants and modifiable AF risk factors.

METHODS

We used whole exome sequencing data of 49,881 individuals and genotyping data of 408,572 individuals from the UK Biobank to examine the associations of TTN variants, polygenic risk, and 4 risk factors (hypertension, diabetes, obesity, and smoking) with AF. Adjusted hazard ratios (aHRs) were calculated with the use of Cox proportional hazards models.

RESULTS

TTN variant carrier status was associated with a higher risk of AF (aHR 2.10, 95% CI 1.59-2.79; P = 2.54 × 10^-7) and higher risk of dilated cardiomyopathy in AF patients (aHR 10.39, 95% CI 5.31-20.33; P = 8.37 × 10^-12). We identified additive effects between TTN variants and polygenic risk with hypertension, diabetes, obesity, and smoking on the risk of AF.

CONCLUSIONS

Genetic and modifiable cardiovascular risk factors contribute to the probability of developing AF. Our findings highlight the potential utility of incorporating data from targeted sequencing or genotyping of common variants to further inform AF risk stratification and aggressive management of modifiable cardiovascular risk factors.

Implantable cardioverter-defibrillators in previously undiagnosed patients with catecholaminergic polymorphic ventricular tachycardia resuscitated from sudden cardiac arrest

AIMS

In patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), implantable cardioverter-defibrillator (ICD) shocks are sometimes ineffective and may even trigger fatal electrical storms. We assessed the efficacy and complications of ICDs placed in patients with CPVT who presented with a sentinel event of sudden cardiac arrest (SCA) while undiagnosed and therefore untreated.

METHODS AND RESULTS

We analysed 136 patients who presented with SCA and in whom CPVT was diagnosed subsequently, leading to the initiation of guideline-directed therapy, including β-blockers, flecainide, and/or left cardiac sympathetic denervation. An ICD was implanted in 79 patients (58.1%). The primary outcome of the study was sudden cardiac death (SCD). The secondary outcomes were composite outcomes of SCD, SCA, appropriate ICD shocks, and syncope. After a median follow-up of 4.8 years, SCD had occurred in three patients (3.8%) with an ICD and none of the patients without an ICD (P = 0.1). SCD, SCA, or appropriate ICD shocks occurred in 37 patients (46.8%) with an ICD and 9 patients (15.8%) without an ICD (P < 0.0001). Inappropriate ICD shocks occurred in 19 patients (24.7%) and other device-related complications in 22 patients (28.9%).

CONCLUSION

In previously undiagnosed patients with CPVT who presented with SCA, an ICD was not associated with improved survival. Instead, the ICD was associated with both a high rate of appropriate ICD shocks and inappropriate ICD shocks along with other device-related complications. Strict adherence to guideline-directed therapy without an ICD may provide adequate protection in these patients without all the potential disadvantages of an ICD.

An International Multicenter Evaluation of Inheritance Patterns, Arrhythmic Risks, and Underlying Mechanisms of CASQ2-Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

Genetic variants in calsequestrin-2 (CASQ2) cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), although isolated reports have identified arrhythmic phenotypes among heterozygotes. Improved insight into the inheritance patterns, arrhythmic risks, and molecular mechanisms of CASQ2-CPVT was sought through an international multicenter collaboration.

METHODS

Genotype-phenotype segregation in CASQ2-CPVT families was assessed, and the impact of genotype on arrhythmic risk was evaluated using Cox regression models. Putative dominant CASQ2 missense variants and the established recessive CASQ2-p.R33Q variant were evaluated using oligomerization assays and their locations mapped to a recent CASQ2 filament structure.

RESULTS

A total of 112 individuals, including 36 CPVT probands (24 homozygotes/compound heterozygotes and 12 heterozygotes) and 76 family members possessing at least 1 presumed pathogenic CASQ2 variant, were identified. Among CASQ2 homozygotes and compound heterozygotes, clinical penetrance was 97.1% and 26 of 34 (76.5%) individuals had experienced a potentially fatal arrhythmic event with a median age of onset of 7 years (95% CI, 6-11). Fifty-one of 66 CASQ2 heterozygous family members had undergone clinical evaluation, and 17 of 51 (33.3%) met diagnostic criteria for CPVT. Relative to CASQ2 heterozygotes, CASQ2 homozygote/compound heterozygote genotype status in probands was associated with a 3.2-fold (95% CI, 1.3-8.0; P=0.013) increased hazard of a composite of cardiac syncope, aborted cardiac arrest, and sudden cardiac death, but a 38.8-fold (95% CI, 5.6-269.1; P<0.001) increased hazard in genotype-positive family members. In vitro turbidity assays revealed that p.R33Q and all 6 candidate dominant CASQ2 missense variants evaluated exhibited filamentation defects, but only p.R33Q convincingly failed to dimerize. Structural analysis revealed that 3 of these 6 putative dominant negative missense variants localized to an electronegative pocket considered critical for back-to-back binding of dimers.

CONCLUSIONS

This international multicenter study of CASQ2-CPVT redefines its heritability and confirms that pathogenic heterozygous CASQ2 variants may manifest with a CPVT phenotype, indicating a need to clinically screen these individuals. A dominant mode of inheritance appears intrinsic to certain missense variants because of their location and function within the CASQ2 filament structure.

Heart Rate Recovery After Exercise Is Associated With Arrhythmic Events in Patients With Catecholaminergic Polymorphic Ventricular Tachycardia

Background:

Risk stratification in catecholaminergic polymorphic ventricular tachycardia remains ill defined. Heart rate recovery (HRR) immediately after exercise is regulated by autonomic reflexes, particularly vagal tone, and may be associated with symptoms and ventricular arrhythmias in patients with catecholaminergic polymorphic ventricular tachycardia. Our objective was to evaluate whether HRR after maximal exercise on the exercise stress test (EST) is associated with symptoms and ventricular arrhythmias.

Methods:

In this retrospective observational study, we included patients ≤65 years of age with an EST without antiarrhythmic drugs who attained at least 80% of their age- and sex-predicted maximal HR. HRR in the recovery phase was calculated as the difference in heart rate (HR) at maximal exercise and at 1 minute in the recovery phase (ΔHRR1′).

Results:

We included 187 patients (median age, 36 years; 68 [36%] symptomatic before diagnosis). Pre-EST HR and maximal HR were equal among symptomatic and asymptomatic patients. Patients who were symptomatic before diagnosis had a greater ΔHRR1′ after maximal exercise (43 [interquartile range, 25–58] versus 25 [interquartile range, 19–34] beats/min; P <0.001). Corrected for age, sex, and relatedness, patients in the upper tertile for ΔHRR1′ had an odds ratio of 3.4 (95% CI, 1.6–7.4) of being symptomatic before diagnosis ( P <0.001). In addition, ΔHRR1′ was higher in patients with complex ventricular arrhythmias at EST off antiarrhythmic drugs (33 [interquartile range, 22–48] versus 27 [interquartile range, 20–36] beats/min; P =0.01). After diagnosis, patients with a ΔHRR1′ in the upper tertile of its distribution had significantly more arrhythmic events as compared with patients in the other tertiles ( P =0.045).

Conclusions:

Catecholaminergic polymorphic ventricular tachycardia patients with a larger HRR following exercise are more likely to be symptomatic and have complex ventricular arrhythmias during the first EST off antiarrhythmic drug.

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.

Chronotropic incompetence as a risk predictor in children and young adults with catecholaminergic polymorphic ventricular tachycardia

INTRODUCTION

Risk stratification tools for catecholaminergic polymorphic ventricular tachycardia (CPVT) are limited. The exercise stress test (EST) is the most important diagnostic and prognostic test. We aimed to determine whether heart rate (HR) and blood pressure (BP) response during EST were associated with the risk of arrhythmias.

MATERIALS AND METHODS

We studied the association between HR and BP response and ventricular arrhythmia burden on EST in 20 CPVT patients. HR reserve values <80% and ≤62% were used to define chronotropic incompetence (CI) off and on therapy, respectively. Symptoms and ventricular arrhythmia score (VAS) in all patients with respect to CI and BP during index EST off therapy and on maximal therapy were compared.

RESULTS

CI in CPVT patients off therapy was associated with a worse VAS during EST (P = .046). Patients with CI also more frequently presented with syncope and/or cardiac arrest compared to patients with a normal chronotropic response (P = .008). Once on therapy, patients with CI had similar VAS compared to patients without CI (P = .50), suggesting that treatment attenuates risk related to CI. Patients with CI also had a lower peak systolic BP (P = .041) which persisted on maximal therapy (P = .033).

CONCLUSION

Untreated CPVT patients with CI have more ventricular arrhythmias than those without CI. This may serve as a simple disease prognosticator that can be modified by antiarrhythmic therapy. A mechanistic link between CI and arrhythmia susceptibility remains unknown. Larger studies are needed to confirm and establish the mechanism of these findings.

Pregnancy in Catecholaminergic Polymorphic Ventricular Tachycardia

OBJECTIVES

This investigation was a retrospective study of catecholaminergic polymorphic ventricular tachycardia (CPVT) patients in Canada and the Netherlands to compare pregnancy, postpartum, and nonpregnant event rates.

BACKGROUND

CPVT is characterized by life-threatening arrhythmias during exertion or emotional stress. The arrhythmic risk in CPVT patients during pregnancy is unknown.

METHODS

Baseline demographics, genetics, treatment, and pregnancy complications were reviewed. Event rate calculations assumed a 40-week pregnancy and 24-week postpartum period.

RESULTS

Ninety-six CPVT patients had 228 pregnancies (median 2 pregnancies per patient; range: 1 to 10; total: 175.4 pregnant patient-years). The median age of CPVT diagnosis was 40.7 years (range: 12 to 84 years), with a median follow-up of 2.9 years (range: 0 to 20 years; total 448.1 patient-years). Most patients had pregnancies before CPVT diagnosis (82%). Pregnancy and postpartum cardiac events included syncope (5%) and an aborted cardiac arrest (1%), which occurred in patients who were not taking beta-blockers. Other complications included miscarriages (13%) and intrauterine growth restriction (1 case). There were 6 cardiac events (6%) during the nonpregnant period. The pregnancy and postpartum event rates were 1.71 and 2.85 events per 100 patient-years, respectively, and the combined event rate during the pregnancy and postpartum period was 2.14 events per 100 patient-years. These rates were not different from the nonpregnant event rate (1.46 events per 100 patient-years).

CONCLUSIONS

The combined pregnancy and postpartum arrhythmic risk in CPVT patients was not elevated compared with the nonpregnant period. Most patients had pregnancies before diagnosis, and all patients with events were not taking beta-blockers at the time of the event.

The clinical and genetic spectrum of catecholaminergic polymorphic ventricular tachycardia: findings from an international multicentre registry

Aims

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an ion channelopathy characterized by ventricular arrhythmia during exertion or stress. Mutations in RYR2-coded Ryanodine Receptor-2 (RyR2) and CASQ2-coded Calsequestrin-2 (CASQ2) genes underlie CPVT1 and CPVT2, respectively. However, prognostic markers are scarce. We sought to better characterize the phenotypic and genotypic spectrum of CPVT, and utilize molecular modelling to help account for clinical phenotypes.

Methods and results

This is a Pediatric and Congenital Electrophysiology Society multicentre, retrospective cohort study of CPVT patients diagnosed at <19 years of age and their first-degree relatives. Genetic testing was undertaken in 194 of 236 subjects (82%) during 3.5 (1.4-5.3) years of follow-up. The majority (60%) had RyR2-associated CPVT1. Variant locations were predicted based on a 3D structural model of RyR2. Specific residues appear to have key structural importance, supported by an association between cardiac arrest and mutations in the intersubunit interface of the N-terminus, and the S4-S5 linker and helices S5 and S6 of the RyR2 C-terminus. In approximately one quarter of symptomatic patients, cardiac events were precipitated by only normal wakeful activities.

Conclusion

This large, multicentre study identifies contemporary challenges related to the diagnosis and prognostication of CPVT patients. Structural modelling of RyR2 can improve our understanding severe CPVT phenotypes. Wakeful rest, rather than exertion, often precipitated life-threatening cardiac events.

Catecholaminergic polymorphic ventricular tachycardia patients with multiple genetic variants in the PACES CPVT Registry

BACKGROUND

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is often a life-threatening arrhythmia disorder with variable penetrance and expressivity. Little is known about the incidence or outcomes of CPVT patients with ≥2 variants.

METHODS

The phenotypes, genotypes and outcomes of patients in the Pediatric and Congenital Electrophysiology Society CPVT Registry with ≥2 variants in genes linked to CPVT were ascertained. The American College of Medical Genetics & Genomics (ACMG) criteria and structural mapping were used to predict the pathogenicity of variants (3D model of pig RyR2 in open-state).

RESULTS

Among 237 CPVT subjects, 193 (81%) had genetic testing. Fifteen patients (8%) with a median age of 9 years (IQR 5-12) had ≥2 variants. Sudden cardiac arrest occurred in 11 children (73%), although none died during a median follow-up of 4.3 years (IQR 2.5-6.1). Thirteen patients (80%) had at least two RYR2 variants, while the remaining two patients had RYR2 variants plus variants in other CPVT-linked genes. Among all variants identified, re-classification of the commercial laboratory interpretation using ACMG criteria led to the upgrade from variant of unknown significance (VUS) to pathogenic/likely pathogenic (P/LP) for 5 variants, and downgrade from P/LP to VUS for 6 variants. For RYR2 variants, 3D mapping using the RyR2 model suggested that 2 VUS by ACMG criteria were P/LP, while 2 variants were downgraded to likely benign.

CONCLUSIONS

This severely affected cohort demonstrates that a minority of CPVT cases are related to ≥2 variants, which may have implications on family-based genetic counselling. While multi-variant CPVT patients were at high-risk for sudden cardiac arrest, there are insufficient data to conclude that this genetic phenomenon has prognostic implications at present. Further research is needed to determine the significance and generalizability of this observation. This study also shows that a rigorous approach to variant re-classification using the ACMG criteria and 3D mapping is important in reaching an accurate diagnosis, especially in the multi-variant population.

A Population-Based Study of Syncope in the Young

BACKGROUND

The prevalence, hospitalization patterns, and outcomes of pediatric and adolescent syncope have not been rigorously characterized.

METHODS

Patients < 20 years presenting to an emergency department (ED) with a primary diagnosis of syncope (International Classification of Diseases, 10th revision, code R55) between fiscal year (FY) 2006/2007 and FY 2013/2014 in the province of Alberta, Canada were grouped according to discharge status from the ED, ie, (1) admitted to hospital and (2) discharged without admission. Temporal trends and differences in baseline characteristics, medication use, and outcomes between admitted and discharged patients were examined.

RESULTS

The prevalence of syncope increased from 143/100,000 population in FY 2006/2007 to 166/100,000 population in FY 2013/2014 (P < 0.01). The majority of the 11,488 patients who presented to the ED with syncope were discharged home (n = 11,214 [98%]). Cardiac disease was present in 12.7% and thoracic conditions were present in 8% of the study population. A majority of patients (66.2% admitted and 56.4% discharged; P = 0.018) were taking a prescription drug in the year before presentation. By 30 days, 26.1% of admitted patients had a second ED presentation and 8.1% had a rehospitalization. Among discharged patients, the 30-day repeated ED presentation rate was 11.7% and the hospitalization rate was 1.1%. By 1 year, the rates of repeated ED visits increased to 64.1% and 47.5%, and rehospitalization rates increased to 21.4% and 6.8% among admitted and discharged patients, respectively.

CONCLUSIONS

Our data suggest that pediatric and adolescent syncope is increasing in prevalence and represents a growing public health problem. This population has a high burden of comorbidities that likely contribute to increased health care resource use and polypharmacy.

Functional characterization of a novel hERG variant in a family with recurrent sudden infant death syndrome: Retracting a genetic diagnosis

Long QT syndrome (LQTS) is the most common cardiac ion channelopathy and has been found to be responsible for approximately 10% of sudden infant death syndrome (SIDS) cases. Despite increasing use of broad panels and now whole exome sequencing (WES) in the investigation of SIDS, the probability of identifying a pathogenic mutation in a SIDS victim is low. We report a family-based study who are afflicted by recurrent SIDS in which several members harbor a variant, p.Pro963Thr, in the C-terminal region of the human-ether-a-go-go (hERG) gene, published to be responsible for cases of LQTS type 2. Functional characterization was undertaken due to the variable phenotype in carriers, the discrepancy with published cases, and the importance of identifying a cause for recurrent deaths in a single family. Studies of the mutated ion channel in in vitro heterologous expression systems revealed that the mutation has no detectable impact on membrane surface expression, biophysical gating properties such as activation, deactivation and inactivation, or the amplitude of the protective current conducted by hERG channels during early repolarization. These observations suggest that the p.Pro963Thr mutation is not a monogenic disease-causing LQTS mutation despite evidence of co-segregation in two siblings affected by SIDS. Our findings demonstrate some of the potential pitfalls in post-mortem molecular testing and the importance of functional testing of gene variants in determining disease-causation, especially where the impacts of cascade screening can affect multiple generations.