SCOUT‑HCM: Mavacamten Benefits Adolescents With HCM

The SCOUT‑HCM trial, presented at ACC.26 and simultaneously published in the New England Journal of Medicine, shows that mavacamten, a first‑in‑class cardiac myosin inhibitor, significantly improves left ventricular outflow tract (LVOT) gradient in adolescents with obstructive hypertrophic cardiomyopathy (oHCM). 

In this first mavacamten trial in pediatric patients, 43 symptomatic adolescents (ages 12–17, NYHA II–III, peak LVOT gradient >50 mm Hg, LVEF >60%) were randomized to 28 weeks of daily mavacamten or placebo.

At week 28, the mavacamten group had an average drop in Valsalva LVOT gradient of 48.5 mm Hg versus only 0.5 mm Hg with placebo (p < 0.001). 

The treatment arm also showed larger reductions in resting LVOT gradient and maximal LV wall thickness, along with improved peak oxygen consumption and fewer symptoms such as fatigue and shortness of breath. 

Biomarkers like troponin and natriuretic peptides declined in the mavacamten group but rose in the placebo group.

Adverse events were modest, with syncope and an inappropriate ICD shock in the treatment arm and chest pain and suicidal ideation in the placebo group; no patient developed an LVEF below 50% and there were no deaths. 

The authors suggest that early treatment with mavacamten could remodel the heart and potentially alter the long‑term course of oHCM. 

Limitations include the trial’s small size, short duration, and predominantly White population, with follow‑up planned out to 50 weeks and plans to study the drug in children under 12 and in other HCM subtypes.