Faculty Bibliography

BACKGROUND:Pathogenic variants in plakophilin-2 (PKP2) cause arrhythmogenic cardiomyopathy (ACM) with intracellular calcium dysregulation as a major component of its arrhythmia phenotype. Recent adeno-associated viral (AAV) based Pkp2 (AAV-PKP2) gene therapy has shown promising results in a few different PKP2-associated ACM models. Fibroblast growth factor 21 (FGF21) has multiple cardioprotective effects and has recently emerged as a promising therapeutic agent for cardiovascular disease. OBJECTIVES/OBJECTIVE:To assess the efficacy and impact on calcium regulation of a novel AAV8-based FGF21 gene therapy on adult cardiac-specific, tamoxifen-activated PKP2 knockout (PKP2-cKO) mice. METHODS:Experiments were performed using a PKP2-cKO murine model. AAV8-FGF21 was delivered to adult mice by a single tail vein injection 7 days before tamoxifen-activated PKP2-cKO. Cardiac functions were monitored by echocardiography and electrocardiography. Intracellular calcium transients were investigated in acute isolated adult mouse cardiomyocytes and calcium fluorescent signals were acquired with the IonOptix system. RESULTS:Loss of PKP2 expression caused cardiac mechanical dysfunction and pro-arrhythmic phenotype in adult mouse models. AAV-mediated delivery of FGF21 mitigated the progression of biventricular structural changes, decreased the occurrence of adrenergic arrhythmias, and rescued intracellular calcium imbalance in the setting of PKP2 haploinsufficiency. In contrast, acute in vitro FGF21 treatment for 1 hour had no effect on intracellular calcium transients. CONCLUSIONS:These beneficial effects of AAV8-FGF21 on the PKP2-ACM phenotype suggest a therapeutic landscape for various targeted cardiomyopathies.

Arrhythmogenic cardiomyopathy (ACM) is a genetically heterogeneous inherited cardiomyopathy with an estimated prevalence of 1:5000-10 000 that predisposes patients to life-threatening ventricular arrhythmias (VA) and sudden cardiac death (SCD). ACM diagnostic criteria and risk prediction models, particularly for arrhythmogenic right ventricular cardiomyopathy (ARVC), the most common form of ACM, are typically genotype-agnostic, but numerous studies have established clinically meaningful genotype-phenotype associations. Early signs of ACM onset differ by genotype indicating the need for genotype-specific diagnostic criteria and family screening paradigms. Likewise, risk factors for SCD vary by genetic subtype, indicating that genotype-specific guidelines for management are also warranted. Of particular importance, genotype-specific therapeutic approaches are being developed. Results from a randomized controlled trial for flecainide use in ARVC patients are currently pending. Research in a plakophilin-2-deficient mouse model suggests this antiarrhythmic drug may be particularly useful for patients with likely pathogenic or pathogenic (LP/P) PKP2 variants. Additionally, the first gene therapy clinical trials in ARVC patients harboring LP/P PKP2 variants are currently underway. This review aims to provide clinicians caring for ACM patients with an up-to-date overview of the current literature in genotype-specific natural history of disease and management of ACM patients and describe scientific advances that have led to upcoming clinical trials.

BACKGROUND:Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy associated with a high risk of ventricular arrhythmia (VA). Several animal models have been used to postulate a therapeutic role of the inhibition of the ryanodine 2 receptor via the use of flecainide for this disease. Clinical data describing its use are scarce, however, especially in patients without implantable cardioverter-defibrillators or with left ventricular (LV) involvement. OBJECTIVES/OBJECTIVE:This study sought to report safety and effectiveness long-term, multicenter data on the impact of flecainide therapy on arrhythmic outcomes in patients with a definite diagnosis of ARVC. METHODS:Patients with definite ARVC receiving flecainide at 12 academic institutions were enrolled in the study. Baseline was defined as the time of flecainide initiation. Premature ventricular complex burdens, nonsustained ventricular tachycardia (NSVT) rates, and sustained VA yearly/rates were collected and compared while on and off flecainide. Side effects and flecainide discontinuation were tracked. Analyses were performed in the overall cohort as well as stratifying for genotype (gene positive vs negative; plakohpillin-2 [PKP-2] vs non PKP-2) and for LV involvement. RESULTS:; LV ejection fraction 55.9 ± 7.3%; right ventricular ejection fraction 44.5 ± 10.5% at baseline) were enrolled, with 66 patients (34.6%) showing LV involvement. The median dose of flecainide was 200 mg/d [150-200 mg/d], with 166 patients (86.9%) also taking a beta-blocker. The median follow-up time on flecainide was 4.2 years [1.9-6.3 years]. Flecainide was well tolerated, with a low (7.9%) discontinuation rate. After flecainide initiation, a significant reduction in the 24-hour premature ventricular complex burden and in the rate of nonsustained ventricular tachycardia was observed (2,190 vs 418; P < 0.001; 35.1% vs 21.5%; P = 0.003). For patients with prior VA events, a significant reduction in the amount of VA episodes/y (1.1 [0.4-1.6] episodes/y vs 0 [0-0.3] episodes/y; P < 0.001) was observed. These safety and effectiveness findings were consistent across genotype subgroups, as well as in patients with and without LV involvement. CONCLUSIONS:Flecainide use had a favorable safety profile and was associated with an observed to a significant reduction in arrhythmic burden in patients with ARVC, irrespective of the underlying genotype or LV involvement.

BACKGROUND:Genetic testing is a cornerstone in the assessment of many cardiac diseases. However, variants are frequently classified as variants of unknown significance, limiting the utility of testing. Recently, the DeepMind group (Google) developed AlphaMissense, a unique artificial intelligence-based model, based on language model principles, for the prediction of missense variant pathogenicity. We aimed to report on the performance of AlphaMissense, accessed by VarCardio, an open web-based variant annotation engine, in a real-world cardiovascular genetics center. METHODS AND RESULTS/RESULTS:<0.001). Genotype-phenotype concordance was highly aligned using VarCard.io predictions, at 95.9% (95% CI, 92.8-97.9) concordance rate. For 109 variants classified as pathogenic, likely pathogenic, benign, or likely benign by ClinVar, concordance with VarCard.io was high (90.5%). CONCLUSIONS:AlphaMissense, accessed via VarCard.io, may be a highly efficient tool for cardiac genetic variant interpretation. The engine's notable performance in assessing variants that are classified as variants of unknown significance in ClinVar demonstrates its potential to enhance cardiac genetic testing.

BACKGROUND/UNASSIGNED:Whether vigorous exercise increases risk of ventricular arrhythmias for individuals diagnosed and treated for congenital long QT syndrome (LQTS) remains unknown. METHODS/UNASSIGNED:The National Institutes of Health-funded LIVE-LQTS study (Lifestyle and Exercise in the Long QT Syndrome) prospectively enrolled individuals 8 to 60 years of age with phenotypic and/or genotypic LQTS from 37 sites in 5 countries from May 2015 to February 2019. Participants (or parents) answered physical activity and clinical events surveys every 6 months for 3 years with follow-up completed in February 2022. Vigorous exercise was defined as ≥6 metabolic equivalents for >60 hours per year. A blinded Clinical Events Committee adjudicated the composite end point of sudden death, sudden cardiac arrest, ventricular arrhythmia treated by an implantable cardioverter defibrillator, and likely arrhythmic syncope. A National Death Index search ascertained vital status for those with incomplete follow-up. A noninferiority hypothesis (boundary of 1.5) between vigorous exercisers and others was tested with multivariable Cox regression analysis. RESULTS/UNASSIGNED:Among the 1413 participants (13% <18 years of age, 35% 18-25 years of age, 67% female, 25% with implantable cardioverter defibrillators, 90% genotype positive, 49% with LQT1, 91% were treated with beta-blockers, left cardiac sympathetic denervation, and/or implantable cardioverter defibrillator), 52% participated in vigorous exercise (55% of these competitively). Thirty-seven individuals experienced the composite end point (including one sudden cardiac arrest and one sudden death in the nonvigorous group, one sudden cardiac arrest in the vigorous group) with overall event rates at 3 years of 2.6% in the vigorous and 2.7% in the nonvigorous exercise groups. The unadjusted hazard ratio for experience of events for the vigorous group compared with the nonvigorous group was 0.97 (90% CI, 0.57-1.67), with an adjusted hazard ratio of 1.17 (90% CI, 0.67-2.04). The upper 95% one-sided confidence level extended beyond the 1.5 boundary. Neither vigorous or nonvigorous exercise was found to be superior in any group or subgroup. CONCLUSIONS/UNASSIGNED:Among individuals diagnosed with phenotypic and/or genotypic LQTS who were risk assessed and treated in experienced centers, LQTS-associated cardiac event rates were low and similar between those exercising vigorously and those not exercising vigorously. Consistent with the low event rate, CIs are wide, and noninferiority was not demonstrated. These data further inform shared decision-making discussions between patient and physician about exercise and competitive sports participation. REGISTRATION/UNASSIGNED:URL: https://www.clinicaltrials.gov; Unique identifier: NCT02549664.

BACKGROUND/UNASSIGNED:gene to an adult mammalian heart deficient in PKP2 can arrest disease progression and significantly prolong survival. METHODS/UNASSIGNED:Experiments were performed using a PKP2-cKO (cardiac-specific, tamoxifen-activated deletion of plakophilin-2). The potential therapeutic, adeno-associated virus vector of serotype rh.74 (AAVrh.74)-PKP2a (PKP2 variant A; RP-A601) is a recombinant AAVrh.74 gene therapy viral vector encoding the human PKP2a. AAVrh.74-PKP2a was delivered to adult mice by a single tail vein injection either before or after tamoxifen-activated PKP2-cKO. PKP2 expression was confirmed by molecular and histopathologic analyses. Cardiac function and disease progression were monitored by survival analyses, echocardiography, and electrocardiography. RESULTS/UNASSIGNED:Consistent with prior findings, loss of PKP2 expression caused 100% mortality within 50 days after tamoxifen injection. In contrast, AAVrh.74-PKP2a-mediated PKP2a expression resulted in 100% survival for >5 months (at study termination). Echocardiographic analysis revealed that AAVrh.74-PKP2a prevented right ventricle dilation, arrested left ventricle functional decline, and mitigated arrhythmia burden. Molecular and histological analyses showed AAVrh.74-PKP2a-mediated transgene mRNA and protein expression and appropriate PKP2 localization at the cardiomyocyte intercalated disc. Importantly, the therapeutic benefit was shown in mice receiving AAVrh.74-PKP2a after disease onset. CONCLUSIONS/UNASSIGNED:These preclinical data demonstrate the potential for AAVrh.74-PKP2a (RP-A601) as a therapeutic for PKP2-related arrhythmogenic right ventricular cardiomyopathy in both early and more advanced stages of the disease.