Citations

Abstract Background Pathogenic variants in the lamin A/C gene (LMNA) can lead to a wide range of phenotypes from dilated and arrhythmogenic cardiomyopathies and conduction abnormalities to partial lipodystrophies. This case highlights a coincidental pathogenic LMNA variant identified in a patient with sudden cardiac arrest (SCA). We demonstrate the need for careful interpretation of pathogenic variants identified in cardiomyopathy genes by highlighting a case in which a coincidental pathogenic LMNA variant was found in a patient with premature ventricular complex (PVC)-induced ventricular fibrillation (VF). Case summary We present the case of a 16-year-old male with SCA secondary to VF. Genetic testing identified a maternally inherited pathogenic variant in LMNA annotated c.1961dup; p.T655Nfs*49. The patient received an implantable cardiac defibrillator and was discharged on nadolol. The patient’s two brothers were also variant-positive. However, the patient and both brothers had normal chamber dimensions on echocardiogram and no late gadolinium enhancement on cardiac magnetic resonance imaging. The family members with the variant were recommended to have prophylactic implantable cardiac defibrillators and thus sought a second opinion. The patient received an appropriate shock and device interrogation identified PVCs. Electrophysiology study identified PVC-induced VF which was ablated with no recurrent ventricular arrhythmias/implantable cardioverter defibrillator therapies over 8 months of follow-up. Although the variant in LMNA could lead to cardiac arrest, the clinical phenotype was consistent with a non-genetic aetiology. The family members were told to have periodic cardiac evaluation. Discussion This case demonstrates the identification of a coincidental pathogenic variant in a cardiomyopathy gene in a patient with cardiac arrest. Although this variant could lead to cardiomyopathy, it appears the cardiac arrest was not due to the pathogenic variant. This highlights the need to consider the clinical phenotype when interpreting genetic test results for cardiomyopathies even in the presence of a positive genetic test result.

Background: Sudden cardiac arrest (SCA) and sudden unexplained death (SUD) are feared sequelae of many genetic heart diseases. In rare circumstances, pathogenic variants in cardiomyopathy-susceptibility genes may result in electrical instability leading to SCA/SUD before any structural manifestations of underlying cardiomyopathy are evident. Methods: Collectively, 38 unexplained SCA survivors (21 males; mean age at SCA 26.4±13.1 years), 68 autopsy-inconclusive SUD cases (46 males; mean age at death 20.4±9.0 years) without disease-causative variants in the channelopathy genes, and 973 ostensibly healthy controls were included. Following exome sequencing, ultrarare (minor allele frequency ≤0.00005 in any ethnic group within Genome Aggregation Database [gnomAD, N=141 456 individuals]) nonsynonymous variants identified in 24 Clinical Genome Resource adjudicated definitive/strong evidence cardiomyopathy-susceptibility genes were analyzed. Eligible variants were adjudicated as pathogenic, likely pathogenic, or variant of uncertain significance in accordance with current American College of Medical Genetics and Genomics guidelines. Results: Overall, 7 out of 38 (18.4%) SCA survivors and 14 out of 68 (20.5%) autopsy-inconclusive, channelopathic-negative SUD cases had at least one pathogenic/likely pathogenic or a variant of uncertain significance nonsynonymous variant within a strong evidence, cardiomyopathy-susceptibility gene. Following American College of Medical Genetics and Genomics criterion variant adjudication, a pathogenic or likely pathogenic variant was identified in 3 out of 38 (7.9%; P =0.05) SCA survivors and 8 out of 68 (11.8%; P =0.0002) autopsy-inconclusive SUD cases compared to 20 out of 973 (2.1%) European controls. Interestingly, the yield of pathogenic/likely pathogenic variants was significantly greater in autopsy-inconclusive SUD cases with documented interstitial fibrosis (4/11, 36%) compared with only 4 out of 57 (7%, P <0.02) SUD cases without ventricular fibrosis. Conclusions: Our data further supports the inclusion of strong evidence cardiomyopathy-susceptibility genes on the genetic testing panels used to evaluate unexplained SCA survivors and autopsy-inconclusive/negative SUD decedents. However, to avoid diagnostic miscues, the careful interpretation of genetic test results in patients without overt phenotypes is vital.

Background: Symptomatic children with catecholaminergic polymorphic ventricular tachycardia (CPVT) are at risk for recurrent arrhythmic events. β-Blockers decrease this risk, but studies comparing individual β-blockers in sizeable cohorts are lacking. We aimed to assess the association between risk for arrhythmic events and type of β-blocker in a large cohort of symptomatic children with CPVT. Methods: From 2 international registries of patients with CPVT, RYR2 variant–carrying symptomatic children (defined as syncope or sudden cardiac arrest before β-blocker initiation and age at start of β-blocker therapy <18 years), treated with a β-blocker were included. Cox regression analyses with time-dependent covariates for β-blockers 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 outcome 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 nonselective β-blocker (predominantly nadolol [n=140] or propranolol [n=70]) and 111 (33.7%) used a β1-selective β-blocker (predominantly atenolol [n=51], metoprolol [n=33], or bisoprolol [n=19]) as initial β-blocker. Baseline characteristics did not differ. The HRs for both the primary and secondary outcomes were higher for β1-selective compared with nonselective β-blockers (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: β1-selective β-blockers were associated with a significantly higher risk for arrhythmic events in symptomatic children with CPVT compared with nonselective β-blockers, specifically nadolol. Nadolol, or propranolol if nadolol is unavailable, should be the preferred β-blocker for treating symptomatic children with CPVT.

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic arrhythmia syndrome characterized by adrenergically-triggered ventricular arrhythmias, syncope, and sudden cardiac death. Several small studies suggest that atrial arrhythmias (AAs) are common in patients with CPVT. Objective: To determine the incidence and type of AAs observed within a large, single-center cohort of CPVT cases as well as the efficacy and durability of AA-directed management. Methods: In this retrospective study, the electronic medical record of 129 patients (52% female; average age at diagnosis 20.8  15.3 years) with CPVT (95% with a putative CPVT1-causative RYR2 variant) between 01/2000 and 09/2019 were reviewed for electrocardiographic evidence of AAs. Clinical features and efficacy of pharmacologic and ablation therapy were assessed. Results: Overall, 10/129 (7.8%) CPVT patients, all RYR2 variant-positive, had evidence of an AA (atrial fibrillation/flutter in 6, atrial tachycardia in 3, and supraventricular tachycardia in 1). The median age at AA diagnosis was 23 (14.2-35.5) years. 8/10 of patients experienced symptoms attributed to their AA, including inappropriate shocks. All patients were trialed on anti-arrhythmics, including -blockers, and/or flecainide. Owing to drug failure (1/10), drug intolerance (1/10), or patient preference (2/10); 4/10 patients received an ablation. Over a median follow-up of 23.5 (4.5-63) months, no AA recurrences were observed. Conclusion: Compared to prior studies, the incidence of AAs in this large, single-center referral cohort of CPVT patients was substantially lower (7.8% vs. 26%-35%). Although larger multi-center studies are needed to confirm, this study suggests that ablation is efficacious and durable in CPVT-associated AAs.

Background: Prior epidemiological studies demonstrated that the p.D85N-Potassium voltage-gated channel subfamily E member 1 (KCNE1) common variant reduces repolarization reserve and predisposes to drug-induced QT prolongation/torsades de pointes. We sought to develop a cellular model for drug-induced long QT syndrome using a patient-specific induced pluripotent stem cell-derived cardiomyocyte (iPSC-CM). Methods: p.D85N-KCNE1 iPSCs were generated from a 23-year-old female with an exaggerated heart rate-corrected QT interval response to metoclopramide (ΔQTc of 160 ms). Clustered regularly interspaced short palindromic repeats-associated 9 technology was used to generate gene-corrected isogenic iPSCs. Field potential duration and action potential duration (APD) were measured from iPSC-CMs. Results: At baseline, p.D85N-KCNE1 iPSC-CMs displayed significantly longer field potential duration (281±15 ms, n=13 versus 223±8.6 ms, n=14, P <0.01) and action potential duration at 90% repolarization (APD90; 579±22 ms, n=24 versus 465±33 ms, n=26, P <0.01) than isogenic-control iPSC-CMs. Dofetilide at a concentration of 2 nM increased significantly field potential duration (379±20 ms, n=13, P <0.01) and APD90 (666±11 ms, n=46, P <0.01) in p.D85N-KCNE1 iPSC-CMs but not in isogenic-control. The effect of dofetilide on APD90 (616±54 ms, n=7 versus 526±54 ms, n=10, P <0.05) was confirmed by Patch-clamp. Interestingly, treatment of p.D85N-KCNE1 iPSC-CMs with estrogen at a concentration of 1 nM exaggerated further dofetilide-induced APD90 prolongation (696±9 ms, n=81, P <0.01) and caused more early afterdepolarizations (11.7%) compared with isogenic control (APD90: 618±8 ms, n=115 and early afterdepolarizations: 2.6%, P <0.05). Conclusions: This iPSC-CM study provides further evidence that the p.D85N-KCNE1 common variant in combination with environmental factors such as QT prolonging drugs and female sex is proarrhythmic.

Background: Heart rate–corrected QT interval (QTc) prolongation, whether secondary to drugs, genetics including congenital long QT syndrome, and/or systemic diseases including SARS-CoV-2–mediated coronavirus disease 2019 (COVID-19), can predispose to ventricular arrhythmias and sudden cardiac death. Currently, QTc assessment and monitoring relies largely on 12-lead electrocardiography. As such, we sought to train and validate an artificial intelligence (AI)–enabled 12-lead ECG algorithm to determine the QTc, and then prospectively test this algorithm on tracings acquired from a mobile ECG (mECG) device in a population enriched for repolarization abnormalities. Methods: Using >1.6 million 12-lead ECGs from 538 200 patients, a deep neural network (DNN) was derived (patients for training, n = 250 767; patients for testing, n = 107 920) and validated (n = 179 513 patients) to predict the QTc using cardiologist-overread QTc values as the “gold standard”. The ability of this DNN to detect clinically-relevant QTc prolongation (eg, QTc ≥500 ms) was then tested prospectively on 686 patients with genetic heart disease (50% with long QT syndrome) with QTc values obtained from both a 12-lead ECG and a prototype mECG device equivalent to the commercially-available AliveCor KardiaMobile 6L. Results: In the validation sample, strong agreement was observed between human over-read and DNN-predicted QTc values (−1.76±23.14 ms). Similarly, within the prospective, genetic heart disease–enriched dataset, the difference between DNN-predicted QTc values derived from mECG tracings and those annotated from 12-lead ECGs by a QT expert (−0.45±24.73 ms) and a commercial core ECG laboratory [10.52±25.64 ms] was nominal. When applied to mECG tracings, the DNN’s ability to detect a QTc value ≥500 ms yielded an area under the curve, sensitivity, and specificity of 0.97, 80.0%, and 94.4%, respectively. Conclusions: Using smartphone-enabled electrodes, an AI DNN can predict accurately the QTc of a standard 12-lead ECG. QTc estimation from an AI-enabled mECG device may provide a cost-effective means of screening for both acquired and congenital long QT syndrome in a variety of clinical settings where standard 12-lead electrocardiography is not accessible or cost-effective.

AbstractBackgroundUnfortunately, some patients with long QT syndrome (LQTS) experience breakthrough cardiac events (BCEs) despite maximal therapy. Small studies have shown that refractory LQTS cases may benefit from intentional permanent atrial pacing (IPAP). As such, we sought to determine the genotype‐specific utilization and efficacy of IPAP in a single‐center LQTS registry.Methods and ResultsIn this retrospective study, electronic medical records from 1065 patients diagnosed with LQTS were used to identify individuals that received IPAP. Pre‐ and post‐IPAP heart rate, heart rate‐corrected QT (QTc) values, annual BCE rate, and IPAP‐related complications were compared between genotypes. BCEs were defined as LQTS‐associated syncope/seizures, sustained ventricular arrhythmia (VA)‐terminating ICD therapies, and sudden cardiac arrest/death.Overall, 52 out of 1065 LQTS patients received adjunctive IPAP therapy (77% female; median age 18.5 [interquartile range, 1–35.5] years; 73% with prior VA). Over an average IPAP follow‐up of 121 ± 82 months, the average heart rate increased from 65.8 ± 20.4 bpm to 78.9 ± 17.1 bpm; (p < .01) and the average QTc decreased from 533.4 ± 66.6 to 488.3 ± 52.4 ms; (p < .01). The mean BCE rate dropped from 0.88 to 0.19 per patient‐year (p = .01), driven by a marked decrease in the LQT2 cohort (1.01 BCE/year to 0.02 BCE/year; p = .003). No serious IPAP‐related complications were observed.ConclusionIn high‐risk LQTS patients, namely those with recalcitrant LQT2, IPAP appears to be a safe and efficacious adjunct therapy. The beneficial effects of IPAP may stem from attenuating the QTc and circumventing a pause‐dependent trigger. Whether IPAP might obviate the need for an ICD in some instances warrants further study.

Abstract Background/Introduction Truncating variants in TTN-encoded titin (TTNtvs) underlie ∼25% of familial dilated cardiomyopathy (DCM) cases. In addition, TTNtvs are over-represented in alcoholic, peripartum, and chemotherapy-induced CM suggesting that risk factors may play a substantive role in the penetrance and expressivity of TTN-mediated DCM. Purpose To determine the prevalence and clinical impact of risk factors for TTN-mediated DCM within a single center cohort of unrelated patients with pathogenic (P)/likely pathogenic (LP) TTNtvs. Methods In this retrospective study, an institutionally developed natural language processing algorithm was used to identify all TTNtv-positive patients evaluated clinically between 01/2012 and 12/2019. Each TTNtv was then mapped to the TTN reference sequence (NM_133378.4) and classified according to a strict interpretation of the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines. After exclusion of individuals with complex congenital heart disease, ischemic heart disease, and those without ACMG P/LP TTNtvs, available medical records were reviewed for risk factors such as long-term heavy alcohol consumption (&gt;80 grams/day), cardiotoxic chemotherapy exposure, morbid obesity (body mass index &gt;40), biopsy/imaging-confirmed myocarditis, peripartum/tachycardia-mediated CM, and valvular heart disease. Results Overall, 33 ACMG P/LP TTNtv-positive patients were identified (40% female; mean age at presentation 45±16 years; mean LVEF at presentation 38%±17%). Of note, 17/33 (52%) presented with heart failure (HF) and 4/33 (12%) presented with sustained ventricular arrhythmias (VAs). The remaining 12 (36%) TTNtv-positive patients presented with incidentally detected asymptomatic left ventricular systolic dysfunction (n=9) or as a result of genetic cascade screening (n=3). In comparison to TTNtv-positive patients with non-HF presentations, those with HF had worse left ventricular function (mean LVEF: 26% ± 11% vs 51% ±12%; p&lt;0.001) and were more likely to have ≥1 risk factor [11/17 (65%) vs 4/16 (25%); p=0.04]. Unexpectedly, the 7 TTNtv-positive patients that presented with (n=4) or subsequently developed (n=3) sustained VAs were younger at the time of presentation (34±13 years vs 48±15 years; p=0.04) and displayed a similar degree of left ventricular dysfunction to those without sustained VAs (mean LVEF: 42% ± 17% vs 36% ± 17%; p=ns). Interestingly, the only risk factor over-represented amongst those with sustained VAs was bileaflet mitral valve prolapse [3/7 (43%) vs 0/26 (0%); p=0.006]. Conclusion The majority of TTNtv-positive patients (14/23; 61%) with a history of HF and/or sustained VAs possessed ≥1 acquired risk factor providing further evidence that gene-environment interaction(s) exert a crucial role in the manifestation of TTN-mediated disease. Funding Acknowledgement Type of funding source: None