Myosin Inhibition and Left Ventricular Diastolic Function in Patients With Obstructive Hypertrophic Cardiomyopathy Referred for Septal Reduction Therapy: Insights From the VALOR-HCM Study.

BACKGROUND: In the randomized phase 3 VALOR-HCM study (A Study to Evaluate Mavacamten in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy Who Are Eligible for Septal Reduction Therapy) of patients with obstructive hypertrophic cardiomyopathy, mavacamten reduced the need for septal reduction therapy. Because mavacamten improves ventricular compliance, this sub-study examined the effects of treatment with this cardiac myosin inhibitor on diastolic function. METHODS: Symptomatic obstructive hypertrophic cardiomyopathy patients on maximally tolerated medical therapy referred for septal reduction therapy were randomized 1:1 to mavacamten or placebo. At baseline and week 16, a resting and stress echocardiogram was performed with interpretation by a core laboratory. In this exploratory substudy, the principal end point was the change in parameters used to define the grade of diastolic function in patients treated with mavacamten and placebo. A related objective was to assess the proportion of patients with an improvement in diastolic function grade. A secondary aim was to assess for correlation between diastolic function parameters and the secondary end points from VALOR-HCM: New York Heart Association class, quality of life, and cardiac biomarkers. RESULTS: Diastolic dysfunction grade was evaluable in 98 patients at baseline and week 16. Among patients treated with mavacamten, 29.4% (15 of 51) demonstrated improvement in diastolic function grade compared with 12.8% (6 of 47) patients with placebo (P=0.05). Average E/e' ratio decreased significantly in patients treated with mavacamten (-3.4±5.3) compared with placebo (0.57±3.5; P<0.001). Indexed left atrial volumes (mL/m2) also decreased significantly in patients who received mavacamten (-5.2±7.8) compared with placebo (-0.51±8.1; P=0.005). After adjustment for change in left ventricular outflow tract gradient and mitral regurgitation, mavacamten was significantly associated with a decrease in average E/e' ratio and indexed left atrial volumes. Change in average E/e' ratio was significantly correlated with the secondary end points from VALOR-HCM. CONCLUSIONS: In this exploratory substudy, after 16 weeks of therapy, mavacamten improved diastolic function, and this change correlated with improvement in clinical and biomarker end points. REGISTRATION: URL: https://www. CLINICALTRIALS: gov; Unique identifier: NCT04349072.