Novel Calmodulin Variant p.E46K Associated With Severe Catecholaminergic Polymorphic Ventricular Tachycardia Produces Robust Arrhythmogenicity in Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes.

BACKGROUND: CaM (calmodulin) is a ubiquitously expressed, multifunctional Ca2+ sensor protein that regulates numerous proteins. Recently, CaM missense variants have been identified in patients with malignant inherited arrhythmias, such as long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). However, the exact mechanism of CaM-related CPVT in human cardiomyocytes remains unclear. In this study, we sought to investigate the arrhythmogenic mechanism of CPVT caused by a novel variant using human induced pluripotent stem cell (iPSC) models and biochemical assays. METHODS: We generated iPSCs from a patient with CPVT bearing CALM2 p.E46K. As comparisons, we used 2 control lines including an isogenic line, and another iPSC line from a patient with long QT syndrome bearing CALM2 p.N98S (also reported in CPVT). Electrophysiological properties were investigated using iPSC-cardiomyocytes. We further examined the RyR2 (ryanodine receptor 2) and Ca2+ affinities of CaM using recombinant proteins. RESULTS: We identified a novel de novo heterozygous variant, CALM2 p.E46K, in 2 unrelated patients with CPVT accompanied by neurodevelopmental disorders. The E46K-cardiomyocytes exhibited more frequent abnormal electrical excitations and Ca2+ waves than the other lines in association with increased Ca2+ leakage from the sarcoplasmic reticulum via RyR2. Furthermore, the [3H]ryanodine binding assay revealed that E46K-CaM facilitated RyR2 function especially by activating at low [Ca2+] levels. The real-time CaM-RyR2 binding analysis demonstrated that E46K-CaM had a 10-fold increased RyR2 binding affinity compared with wild-type CaM which may account for the dominant effect of the mutant CaM. Additionally, the E46K-CaM did not affect CaM-Ca2+ binding or L-type calcium channel function. Finally, antiarrhythmic agents, nadolol and flecainide, suppressed abnormal Ca2+ waves in E46K-cardiomyocytes. CONCLUSIONS: We, for the first time, established a CaM-related CPVT iPSC-CM model which recapitulated severe arrhythmogenic features resulting from E46K-CaM dominantly binding and facilitating RyR2. In addition, the findings in iPSC-based drug testing will contribute to precision medicine.

Matched comparison of catheter ablation versus conservative management for atrial fibrillation.

It is still controversial whether catheter ablation for atrial fibrillation (AF) could improve clinical outcomes in general AF population. Among 4398 patients with diagnosis of AF in the outpatient department of Kyoto University Hospital between January 2005 and March 2015, we identified 537 pairs of patients who received first-time catheter ablation (ablation group) or conservative management (conservative group), matched for age, gender, AF duration, AF type, AF symptoms, and previous heart failure (HF). The primary outcome measure was a composite of cardiovascular death, HF hospitalization, ischemic stroke, or major bleeding. Most baseline characteristics were well balanced between the 2 groups, except for the higher prevalence of low body weight, history of malignancy, and severe chronic kidney disease in the conservative group. Median follow-up duration was 5.3 years. The cumulative 5-year incidence of the primary outcome measure was significantly lower in the ablation group than in the conservative group (5.2% versus 15.6%, log-rank P < 0.001). Even after adjusting for the imbalances in the baseline characteristics, the lower risk of the ablation group relative to the conservative group for the primary outcome measure remained highly significant (HR 0.32, 95% CI 0.21-0.47, P < 0.001). Ablation compared with conservative management was also associated with significantly lower risks for the individual components of the primary outcome. In this matched analysis in AF patients, ablation as compared with conservative management was associated with better long-term clinical outcomes, although we could not deny the possibility of selection bias and unmeasured confounding.