Incidence of Atrial Tachyarrhythmias in Patients With Early Repolarization Syndrome

Clinical and Functional Genetic Characterization of the Role of Cardiac Calcium Channel Variants in the Early Repolarization Syndrome

Background: Early repolarization syndrome (ERS) is an inherited sudden cardiac death (SCD) syndrome. The present study investigates the role of genetic variants in cardiac calcium-channel genes in the pathogenesis of ERS and probes the underlying mechanisms. Methods: Polymerase chain reaction-based next-generation sequencing was carried out using a targeted gene approach. Unrelated ERS probands carrying calcium-channel variants were evaluated clinically and compared with matched healthy controls. Wild-type (WT) and mutant CACNA1C genes were coexpressed with CACNB2b and CACNA2D1 in HEK293 cells and studied using whole-cell patch-clamp techniques and confocal fluorescence microscope. Results: Among 104 ERS probands, 16 carried pathogenic variants in calcium-channel genes (32.2 ± 14.6 years old, 87.5% male). The symptoms at diagnosis included syncope (56.3%), ventricular tachycardia/fibrillation (62.5%), and SCD (56.3%). Three cases (18.8%) had a family history of SCD or syncope. Eight patients (50.0%) had a single calcium gene rare variant. The other half carried rare variants in other ERS-susceptible genes. Compared with controls, the heart rate was slower (72.7 ± 8.9 vs. 65.6 ± 16.1 beats/min, * p < 0.05), QTc interval was shorter (408.2 ± 21.4 vs. 386.8 ± 16.9 ms, ** p < 0.01), and Tp-e/QT was longer (0.22 ± 0.05 vs. 0.28 ± 0.04, *** p < 0.001) in single calcium mutation carriers. Electrophysiological analysis of one mutation, CACNA1C-P817S (c.2449C>T), revealed that the density of whole-cell calcium current (I Ca) was reduced by ~84.61% compared to WT (-3.17 ± 2.53 vs. -20.59 ± 3.60 pA/pF, n = 11 and 15, respectively, ** p < 0.01). Heterozygous expression of mutant channels was associated with a 51.35% reduction of I Ca. Steady-state inactivation was shifted to more negative potentials and significantly accelerated as well. Confocal microscopy revealed trafficking impairment of CACNA1C-P817S (peripheral/central intensity: 0.94 ± 0.10 in WT vs. 0.33 ± 0.12 in P817S, n = 10 and 9, respectively, ** p < 0.01). Conclusions: ERS associated with loss-of-function (LOF) genetic defects in genes encoding the cardiac calcium channel represents a unique clinical entity characterized by decreased heart rate and QTc, as well as increased transmural dispersion of repolarization. In the case of CACNA1C-P817S, impaired trafficking of the channel to the membrane contributes to the LOF.

Atrial Fibrillation in Inherited Channelopathies

Atrial fibrillation (AF), the common sustained arrhythmia in clinical practice, has major public health implications due to its associated morbidity and increased mortality. The AF epidemic is due to the burgeoning elderly population and the identification of novel risk factors, for example, genetics. Since the diagnosis of AF has a major impact on the clinical assessment and management of patients with inherited arrhythmia syndromes, improved understanding of the cause and pathogenesis of AF has provided important insights into the underlying pathophysiological mechanisms of this common arrhythmia and identified potential mechanism-based therapies.

Additional Value of Early Repolarization Pattern in Prediction of Obstructive Coronary Artery Disease as Assessed by Coronary Angiography

Recent reports show that an early repolarization pattern (ERP) is associated with a higher incidence of sudden cardiac death in patients with obstructive coronary artery disease (CAD). Sporadic case studies have pointed out that ERP might be related to obstructive CAD.In consecutive patients who had undergone coronary angiography, we investigated the relationship between ERP and obstructive CAD by evaluating its association with coronary artery stenosis.The study population consisted of 3785 patients (59.9% men; mean age 63.1 years) with or without obstructive CAD. Adjusting for major cardiovascular risk factors, ERP was significantly associated with obstructive CAD (adjusted odds ratio (OR): 2.24 [95% CI 1.70-2.95]) with an incremental predictive value (ROC AUC 0.76 versus 0.71, P = 0.02; NRI 55.3%, P < 0.001; IDI = 0.05, P = 0.008), specifically in subjects with low risk and intermediate risk. ERP also significantly improved the predictive value for multi-vessel disease (AUC: 0.77 versus 0.72, P = 0.02 for two-vessel disease; 0.79 versus 0.73, P = 0.04 for three-vessel disease). ERP was consistently associated with stenoses of 3 main coronary arteries.ERP is associated with significant increased risk for obstructive CAD.Further studies are warranted to confirm our results and to elucidate the specific pathogenic mechanisms.

A Slower Heart Rate and Therapeutic Hypothermia Unmasked Early Repolarization Syndrome in a Ventricular Fibrillation Survivor

Patients presenting with aborted cardiac arrest who display early repolarization generally are diagnosed with early repolarization syndrome. Therapeutic hypothermia is a standard strategy to improve neurological outcome in comatose patients after cardiac arrest. We present here a patient in whom therapeutic hypothermia exacerbated the J-wave amplitude and morphology, which resulted in episodes of refractory ventricular fibrillation.