Abstract
BACKGROUND: Mavacamten, a first-in-class cardiac myosin inhibitor and the only approved cardiac myosin inhibitor worldwide, improved clinical symptoms and health status in patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM) in phase 3 EXPLORER-HCM (Clinical Study to Evaluate Mavacamten [MYK-461] in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy; NCT03470545) and EXPLORER-CN (A Study to Evaluate the Efficacy and Safety of Mavacamten in Chinese Adults With Symptomatic Obstructive HCM; NCT05174416). OBJECTIVES: The purpose of this work was to study the effect of mavacamten on cardiac structure and function by cardiac magnetic resonance (CMR) imaging in Chinese participants in EXPLORER-CN. METHODS: Eligible patients with obstructive HCM underwent CMR imaging at screening and week 30. Change from baseline to week 30 in left ventricular (LV) mass index was analyzed as a prespecified secondary outcome. Prespecified exploratory outcomes included changes in cellular hypertrophy, cardiac structure and function, and myocardial fibrosis by CMR. RESULTS: Among 81 patients randomized, 58 patients (mean age 51.2 years, 74.1% men) with CMR data available were analyzed (mavacamten, n = 39; placebo, n = 19). After 30 weeks, greater reductions from baseline were observed (mean between-group difference) with mavacamten vs placebo in LV mass index (-30.8 g/m(2) [95% CI: -41.5 to -20.1 g/m(2)]), maximal LV wall thickness (-3.5 mm [95% CI: -4.7 to -2.4 mm]), and maximal left atrial volume index (-18.3 mL/m(2) [95% CI: -26.7 to -9.8 mL/m(2)]); all nominal P < 0.001. Reduction from baseline to week 30 in global mass of late gadolinium enhancement by 6 SDs was also observed with mavacamten vs placebo (mean between-group difference, -2.0 g [95% CI: -11.9 to 8.0 g]; nominal P = 0.007). CONCLUSIONS: At 30 weeks, improvements were observed in measures of cardiac structure and function, with reductions in indicators of myocardial fibrosis, in the mavacamten vs the placebo group. (A Study to Evaluate the Efficacy and Safety of Mavacamten in Chinese Adults With Symptomatic Obstructive HCM; NCT05174416).