Effect of Mavacamten on Echocardiographic Features in Chinese Patients with Obstructive Hypertrophic Cardiomyopathy: Results from the EXPLORER-CN Study.

Background: Mavacamten, a cardiac myosin inhibitor, has demonstrated positive outcomes in left ventricular outflow tract (LVOT) gradient reduction and improvements of symptoms and function in Chinese patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM) in EXPLORER-CN. This exploratory analysis aimed to evaluate the effect of mavacamten on echocardiographic measures of cardiac structure and function and its relationship with other clinical biomarkers.

Methods: Key echocardiographic parameters acquired over 30 weeks from 81 patients (n = 54 on mavacamten and n = 27 on placebo) were assessed in a central laboratory.

Results: At 30 weeks, greater improvements in measures of diastolic function were observed with mavacamten versus placebo, including lateral E/e' (least-squares mean [LSM] change from baseline [CFB] - 5.1 vs. 0.6; between-group LSM difference - 5.7; 95% confidence interval [CI] - 7.6 to - 3.7), septal E/e' (LSM CFB - 6.0 vs. - 0.3; between-group LSM difference - 5.7; 95% CI - 7.8 to - 3.7), and left atrial volume index (LAVI) (LSM CFB - 11.7 vs. - 3.5 ml/m2; between-group LSM difference - 8.2; 95% CI - 12.0 to - 4.4) (nominal p < 0.001 for all). Twelve patients (23.1%) treated with mavacamten had complete resolution of mitral valve systolic anterior motion (SAM) versus two patients (7.4%) receiving placebo. Among mavacamten-treated patients, reductions in resting and Valsalva LVOT gradients, left ventricular (LV) mass index, LAVI, and lateral and septal E/e' were associated with reduced N-terminal pro-B-type natriuretic peptide levels (nominal p < 0.0001 for all). In the mavacamten group, reductions in LVOT gradients and LV end-diastolic interventricular septal thickness were associated with improved patient-reported Kansas City Cardiomyopathy Questionnaire Overall Summary Score (nominal p < 0.05 for all).

Conclusions: Clinically meaningful improvements were evident in Chinese patients treated with mavacamten compared with placebo in several hallmarks of obstructive HCM, including measures of LV diastolic function, SAM, and LVOT gradient. These results add further evidence to support the positive effects of mavacamten in cardiac remodeling. Background: ClinicalTrials.gov identifier: NCT05174416.