One- and two-year structural changes of mavacamten therapy in hypertrophic obstructive cardiomyopathy: a case report with serial comprehensive CMR demonstrating continuous reverse remodelling.

Background: Hypertrophic obstructive cardiomyopathy (HOCM) is characterized by dynamic left ventricular outflow tract (LVOT) obstruction and impaired quality of life. Mavacamten, a first-in-class myosin inhibitor, offers a novel therapeutic approach for HOCM, which improves clinical symptoms and exercise capacity while leading to reduction of LVOT gradient and favourable cardiac remodelling in echocardiography and cardiovascular magnetic resonance (CMR). However, data on CMR-derived treatment effects remain limited to short follow-up studies. Case summary: A 39-year-old male with symptomatic HOCM refractory to bisoprolol and disopyramide was initiated on mavacamten therapy. Serial CMR after one and two years demonstrated progressive reverse remodelling over the follow-up period, including ongoing reduction of LV ejection fraction and LV mass index. While late gadolinium enhancement mass remained unchanged, there were divergent changes to measures of interstitial fibrosis: While native T1 relaxation times steadily decreased, extracellular volume (ECV) fraction initially increased but normalized at two-year follow-up. Discussion: This case indicates that mavacamten leads to longer-term cardiac remodelling up to two years after initiation of treatment, beyond early haemodynamic improvement and reduction of LVOT obstruction. These observations nurture additional studies to investigate longer-term effects on myocardial structure, function, and interstitial fibrosis.