Aficamten in symptomatic obstructive hypertrophic cardiomyopathy: the FOREST-HCM long-term study.

BACKGROUND AND AIMS: Aficamten is a next-in-class, oral selective cardiac myosin inhibitor that ameliorates hypercontractility in hypertrophic cardiomyopathy (HCM). This study assessed the safety and efficacy of extended aficamten treatment in symptomatic obstructive HCM (oHCM).

METHODS

Patients completing a parent aficamten study were eligible to enrol in FOREST-HCM (NCT04848506), an open-label study evaluating long-term aficamten treatment.

RESULTS

Patients with oHCM (N = 296; mean age ±SD 61 ± 12.3 years, 44.3% female) enrolled between May 2021 and August 2024. Cumulative exposure was 352 patient-years; median follow-up 51.6 (IQR 41.5, 70.8) weeks. At Weeks 12 and 96, aficamten reduced Valsalva left ventricular outflow tract gradient by 56 ± 43 and 62 ± 33 mmHg from baseline (both P < 0.0001), with minimal reduction in left ventricular ejection fraction (LVEF) (-3% ± 6% and -5% ± 5%); 69% and 93% of participants had at least one NYHA class improvement; Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score improved by 15 ± 16 and 16 ± 16 points. Treatment-emergent serious adverse events (TESAEs) occurred in 36 (12.2%) patients; no deaths, heart failure, or events considered related to aficamten were reported. One (0.3%) patient terminated therapy due to a TESAE (ischemic colitis). LVEF<50% occurred in 10 (3.4%) patients [exposure-adjusted incidence rate (EAIR): 2.9 per 100 patient-years] with 2 having non-serious mild/moderate dyspnoea. No treatment interruptions for LVEF<50%, and no events of LVEF<40% occurred. New-onset atrial fibrillation occurred in seven (2.4%) patients (EAIR 2.0 per 100 patient-years).

CONCLUSIONS

Extended aficamten treatment in patients with symptomatic oHCM yielded early and sustained hemodynamic and clinical responses with low incidences of new-onset atrial fibrillation and LVEF<50%.