Abstract

Background Disopyramide, used in obstructive hypertrophic cardiomyopathy (oHCM) for its negative inotropic properties mediated by its reduction in cytosolic calcium, has been recommended for decades as an option to relieve resistant obstruction. Aficamten is a selective cardiac myosin inhibitor that reduces hypercontractility directly by reducing myosin-actin interaction. Objectives This study aims to investigate the safety and efficacy of concomitant use and withdrawal of disopyramide in patients with symptomatic oHCM receiving aficamten. Methods Patients with oHCM enrolled in REDWOOD-HCM Cohort 3 (open-label), SEQUOIA-HCM (placebo-controlled), and FOREST-HCM (open-label) were analyzed. The authors identified 4 groups, each with patients symptomatic despite background therapy with disopyramide who received: 1) disopyramide plus aficamten and subsequent aficamten withdrawal per protocol (Diso-Afi Withdrawal); 2) disopyramide plus placebo (Diso-Pbo); 3) aficamten plus disopyramide with subsequent disopyramide withdrawal (Afi-Diso Withdrawal); and 4) continued both disopyramide and aficamten (Diso+Afi Continuous). Assessments were performed at baseline, after aficamten or placebo add-on therapy, and after washout (except at week 24 for Diso+Afi Continuous group). Results Overall, 50 unique patients from 3 trials enrolled, resulting in 93 subjects (segments) across 4 groups: Diso-Afi Withdrawal (n = 29), Diso-Pbo (n = 20), Afi-Diso Withdrawal (n = 17), and Diso+Afi Continuous (n = 27); mean disopyramide dose was 331 ± 146 mg/d. The addition of aficamten to disopyramide alleviated left ventricular outflow tract (LVOT) obstruction (resting: change [Δ] in least squares mean −27.0 ± 3.6, Valsalva: Δ least squares mean −39.2 ± 5.0, both P < 0.0001), symptoms (≥1 NYHA functional class improvement: 77.8% [95% CI: 61.0-94.5]; P < 0.0001; Kansas City Cardiomyopathy Questionnaire–Clinical Summary Score: 12.3 ± 3.3 [P < 0.001]), and reduced N-terminal pro–B-type natriuretic peptide ratio: 0.35 [95% CI: 0.26-0.48]; P < 0.0001, and there was no significant change with placebo. Withdrawal of aficamten while on disopyramide resulted in return of LVOT obstruction, worsening of symptoms, and increase in NT-proBNP to baseline values. Conversely, withdrawal of disopyramide while on aficamten did not impact efficacy. There were no safety events associated with aficamten or disopyramide withdrawal, and no episodes of atrial fibrillation after disopyramide withdrawal. Conclusions In this cohort of patients with symptomatic oHCM with persistent LVOT obstruction, combination therapy with aficamten and disopyramide was safe and well tolerated but did not enhance clinical efficacy vs aficamten alone. For such oHCM patients, aficamten treatment may be considered with an option to discontinue disopyramide. (Dose-finding Study to Evaluate the Safety, Tolerability, PK, and PD of CK-3773274 in Adults With HCM [REDWOOD-HCM]; NCT04219826) (Aficamten vs Placebo in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy [SEQUOIA-HCM]; NCT05186818) (Open-label Extension Study to Evaluate the Long-term Safety and Tolerability of Aficamten in Adults With HCM [FOREST-HCM]; NCT04848506)