Long-term safety and efficacy of mavacamten in obstructive hypertrophic cardiomyopathy: up to 3.5-year follow-up results of the EXPLORER cohort of MAVA-Long-Term Extension study

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Abstract Introduction Mavacamten safety and efficacy in patients with obstructive hypertrophic cardiomyopathy (HCM) was demonstrated in the phase 3 EXPLORER-HCM trial. Long-term safety and efficacy of mavacamten in patients with obstructive HCM is being studied in the MAVA-Long-Term Extension (LTE) study (NCT03723655). Purpose To present long-term safety and efficacy data from the EXPLORER cohort of MAVA-LTE up to week 180 (data cutoff: August 31, 2023). Methods Patients who completed EXPLORER-HCM could enroll in MAVA-LTE following washout. All patients received mavacamten 5 mg at baseline; dose titration to 2.5, 10, or 15 mg was based on site-read echocardiographic evaluation of Valsalva left ventricular outflow tract (LVOT) gradient and left ventricular ejection fraction (LVEF). Following titration, patients were assessed at 12-week intervals between weeks 24 to 156; week 180 was the first visit following a 24-week interval. Results At the data cutoff, 211 of 231 patients who enrolled in MAVA-LTE were on treatment; 185 and 99 patients had reached week 156 and 180, respectively (median [interquartile range (IQR)] time on study: 166 [160–189] weeks; total exposure: 739 patient-years). Sustained improvements from baseline to weeks 156 and 180 were observed in mean (standard deviation [SD]) resting LVOT gradient (−40.2 [32.8] mmHg, n=187; and −40.3 [32.7] mmHg, n=94; respectively), Valsalva LVOT gradient (−55.3 [37.3] mmHg, n=184; and −55.3 [33.7] mmHg, n=91) (Figure 1), and median (IQR) N-terminal pro B-type natriuretic peptide levels (−504 [−1160, −143] ng/L, n=179; and −562 [−1162.5, −209] ng/L, n=88). Improvements from baseline to weeks 144 and 180 were sustained in mean (SD) left atrial volume index (−3.5 [10.4] mL/m2, n=193; and −5.5 [9.7] mL/m2, n=62; respectively). At week 156 and 180, 53.5% and 66.3% of patients, respectively, were in New York Heart Association class I. Mean (SD) LVEF decreased from baseline to week 180 (−11.0% [8.9%]; n=93) but the mean (63.9%) remained within normal range. Overall, 33 patients (14.3%) experienced atrial fibrillation, 14 patients (6.1%) experienced cardiac failure episodes, 13 patients (5.6%) permanently discontinued treatment owing to adverse events and 20 patients (8.7%) experienced transient reductions in LVEF < 50% (range: 30–48%), of whom 6 (2.6%) experienced LVEF < 40% (Figure 2). Of these 20 patients (13 from the placebo group in EXPLORER-HCM), all recovered LVEF ≥ 50% following treatment interruption and 14 reinitiated medication. In total, 5 patients died during the study (all deaths unrelated to mavacamten). Conclusions Long-term mavacamten treatment in patients with obstructive HCM resulted in sustained improvements in echocardiographic measures, symptoms, and biomarkers. Treatment was well-tolerated; no new safety signals were observed. Transient and reversible reductions in LVEF were observed in a small proportion of patients during long-term therapy.