Faculty Bibliography

Background and Rationale: Mutations in Plakophilin-2 (PKP2) are the most common cause of ARVC, an inherited disease characterized by fibro- or fibrofatty infiltration of RV predominance, ventricular arrhythmias and sudden death in the young. The relation between PKP2 expression and the heart transcriptome in vivo, is unknown. Furthermore, while splicing misregulation has been associated with other inherited diseases, PKP2-dependent exon usage differences remain unexplored. We generated a murine line of cardiac-restricted, tamoxifen activated PKP2 deficiency ("PKP2-cKO") and defined PKP2- dependent exon usage in adult non-failing hearts. Methods and Results: The first disease manifestation was an increase in RV area, detected by echocardiography 14 days after tamoxifen injection (14 days post-injection or "dpi"), followed by marked RV dilation and reparative fibrosis (21 dpi), then bi-ventricular dilated cardiomyopathy (28 dpi), heart failure and death (30-50 dpi). To capture the earliest molecular events, hearts 14 dpi were used for RNAseq and exon usage. Comparing RV vs LV revealed minor changes in transcript abundance, but significant differences in alternative splicing (AS) program. We found ~75% of differentially spliced exons flanked by sequences that bind RBFox2, an RNA-binding protein that acts as central AS regulator of the adult heart, and that is necessary to maintain cardiac structure. Western blot analysis at 14 dpi and thereafter showed reduced abundance of RBFox2. RNAseq at 21 dpi showed that in addition to RBFox2, transcripts were reduced for RBFox1, MBNL1, MBNL2 and RBM20 (also molecules that control the AS program). Exon usage analysis at 21 dpi identified massive AS misregulation, similar to that of a failing heart, even though ejection fraction at this stage was ~50%. Misregulated genes included several involved in electrical rhythm and intracellular calcium homeostasis. Conclusion: We generated a model of PKP2-dependent ARVC. Our studies point to a previously unrecognized association between a desmosomal molecule, a splicing regulator, and the control of electrical and mechanical function. AS misregulation may be a substrate for sudden unexpected arrhythmic death in the young

Importance: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal genetic arrhythmia syndrome characterized by polymorphic ventricular tachycardia with physical or emotional stress, for which current therapy with beta-blockers is incompletely effective. Flecainide acetate directly suppresses sarcoplasmic reticulum calcium release-the cellular mechanism responsible for triggering ventricular arrhythmias in CPVT-but has never been assessed prospectively. Objective: To determine whether flecainide dosed to therapeutic levels and added to beta-blocker therapy is superior to beta-blocker therapy alone for the prevention of exercise-induced arrhythmias in CPVT. Design, Setting, and Participants: This investigator-initiated, multicenter, single-blind, placebo-controlled crossover clinical trial was conducted from December 19, 2011, through December 29, 2015, with a midtrial protocol change at 10 US sites. Patients with a clinical diagnosis of CPVT and an implantable cardioverter-defibrillator underwent a baseline exercise test while receiving maximally tolerated beta-blocker therapy that was continued throughout the trial. Patients were then randomized to treatment A (flecainide or placebo) for 3 months, followed by exercise testing. After a 1-week washout period, patients crossed over to treatment B (placebo or flecainide) for 3 months, followed by exercise testing. Interventions: Patients received oral flecainide or placebo twice daily, with the dosage guided by trough serum levels. Main Outcomes and Measures: The primary end point of ventricular arrhythmias during exercise was compared between the flecainide and placebo arms. Exercise tests were scored on an ordinal scale of worst ventricular arrhythmia observed (0 indicates no ectopy; 1, isolated premature ventricular beats; 2, bigeminy; 3, couplets; and 4, nonsustained ventricular tachycardia). Results: Of 14 patients (7 males and 7 females; median age, 16 years [interquartile range, 15.0-22.5 years]) randomized, 13 completed the study. The median baseline exercise test score was 3.0 (range, 0-4), with no difference noted between the baseline and placebo (median, 2.5; range, 0-4) exercise scores. The median ventricular arrhythmia score during exercise was significantly reduced by flecainide (0 [range, 0-2] vs 2.5 [range, 0-4] for placebo; P < .01), with complete suppression observed in 11 of 13 patients (85%). Overall and serious adverse events did not differ between the flecainide and placebo arms. Conclusions and Relevance: In this randomized clinical trial of patients with CPVT, flecainide plus beta-blocker significantly reduced ventricular ectopy during exercise compared with placebo plus beta-blocker and beta-blocker alone. Trial Registration: clinicaltrials.gov Identifier: NCT01117454.

AIMS: Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy (ARVD/C) is often associated with desmosomal mutations. Recent studies suggest an interaction between the desmosome and sodium channel protein Nav1.5. We aimed to determine the prevalence and biophysical properties of mutations in SCN5A (the gene encoding Nav1.5) in ARVD/C. METHODS AND RESULTS: We performed whole-exome sequencing in six ARVD/C patients (33% male, 38.2 +/- 12.1 years) without a desmosomal mutation. We found a rare missense variant (p.Arg1898His; R1898H) in SCN5A in one patient. We generated induced pluripotent stem cell-derived cardiomyocytes (hIPSC-CMs) from the patient's peripheral blood mononuclear cells. The variant was then corrected (R1898R) using Clustered Regularly Interspaced Short Palindromic Repeats/Cas9 technology, allowing us to study the impact of the R1898H substitution in the same cellular background. Whole-cell patch clamping revealed a 36% reduction in peak sodium current (P = 0.002); super-resolution fluorescence microscopy showed reduced abundance of NaV1.5 (P = 0.005) and N-Cadherin (P = 0.026) clusters at the intercalated disc. Subsequently, we sequenced SCN5A in an additional 281 ARVD/C patients (60% male, 34.8 +/- 13.7 years, 52% desmosomal mutation-carriers). Five (1.8%) subjects harboured a putatively pathogenic SCN5A variant (p.Tyr416Cys, p.Leu729del, p.Arg1623Ter, p.Ser1787Asn, and p.Val2016Met). SCN5A variants were associated with prolonged QRS duration (119 +/- 15 vs. 94 +/- 14 ms, P < 0.01) and all SCN5A variant carriers had major structural abnormalities on cardiac imaging. CONCLUSIONS: Almost 2% of ARVD/C patients harbour rare SCN5A variants. For one of these variants, we demonstrated reduced sodium current, Nav1.5 and N-Cadherin clusters at junctional sites. This suggests that Nav1.5 is in a functional complex with adhesion molecules, and reveals potential non-canonical mechanisms by which Nav1.5 dysfunction causes cardiomyopathy.

OBJECTIVES: Cardiovascular disease (CVD) is a leading cause of death in systemic lupus erythematosus (SLE) and in rheumatoid arthritis (RA). Although only explored in one study, ECG non-specific ST-T abnormalities, in addition to corrected QT-interval (QTc) prolongation, were recently reported in an SLE inception cohort. Importantly, these ECG abnormalities are known predictors of CVD mortality in the general population, yet their prevalence in patients with established SLE has not been evaluated. METHODS: We cross-sectionally investigated the presence of non-specific ST-T and QTc abnormalities in 50 patients with SLE, predominantly Hispanic and black, without CVD or SLE-related cardiac involvement and compared them with 139 patients with RA without CVD. Demographics, disease-specific characteristics and CVD risk factors were ascertained and adjusted for. RESULTS: Patients with SLE (mean age 36+/-13 years, 92% women, 6 years median disease duration, 96% Hispanics and blacks) had a 3.3-fold higher adjusted prevalence of non-specific ST-T abnormalities (56% vs 17%; p <0.0001) compared with RA, despite the older age and higher percentage of men in the RA group. The QTc was 26 ms longer in SLE compared with RA (p=0.002) in the setting of a higher percentage of women, blacks, Hispanics and higher C reactive protein levels in the SLE group. CONCLUSIONS: This study demonstrates a high prevalence of ECG abnormalities in predominantly Hispanic and black patients with SLE. Longitudinal evaluation of the progression to potentially life-threatening arrhythmias and/or cardiovascular events is warranted.

Studies have demonstrated non-myocytes, including fibroblasts, can electrically couple to myocytes in culture. However, evidence demonstrating current can passively spread across scar tissue in the intact heart remains elusive. We hypothesize electrotonic conduction occurs across non-myocyte gaps in the heart and is partly mediated by Connexin43 (Cx43). We investigated whether non-myocytes in ventricular scar tissue are electrically connected to surrounding myocardial tissue in wild type and fibroblast-specific protein-1 driven conditional Cx43 knock-out mice (Cx43fsp1KO). Electrical coupling between the scar and uninjured myocardium was demonstrated by injecting current into the myocardium and recording depolarization in the scar through optical mapping. Coupling was significantly reduced in Cx43fsp1KO hearts. Voltage signals were recorded using microelectrodes from control scars but no signals were obtained from Cx43fsp1KO hearts. Recordings showed significantly decreased amplitude, depolarized resting membrane potential, increased duration and reduced upstroke velocity compared to surrounding myocytes, suggesting that the non-excitable cells in the scar closely follow myocyte action potentials. These results were further validated by mathematical simulations. Optical mapping demonstrated that current delivered within the scar could induce activation of the surrounding myocardium. These data demonstrate non-myocytes in the scar are electrically coupled to myocytes, and coupling depends on Cx43 expression.

Sudden unexpected death in epilepsy (SUDEP) is the most common cause of epilepsy-related mortality. We hypothesized that electrocardiography (ECG) features may distinguish SUDEP cases from living subjects with epilepsy. Using a matched case-control design, we compared ECG studies of 12 consecutive cases of SUDEP over 10 years and 22 epilepsy controls matched for age, sex, epilepsy type (focal, generalized, or unknown/mixed type), concomitant antiepileptic, and psychotropic drug classes. Conduction intervals and prevalence of abnormal ventricular conduction diagnosis (QRS >/=110 msec), abnormal ventricular conduction pattern (QRS <110 msec, morphology of incomplete right or left bundle branch block or intraventricular conduction delay), early repolarization, and features of inherited cardiac channelopathies were assessed. Abnormal ventricular conduction diagnosis and pattern distinguished SUDEP cases from matched controls. Abnormal ventricular conduction diagnosis was present in two cases and no controls. Abnormal ventricular conduction pattern was more common in cases than controls (58% vs. 18%, p = 0.04). Early repolarization was similarly prevalent in cases and controls, but the overall prevalence exceeded that of published community-based cohorts.