Complete left bundle branch block resolution during treatment with Mavacamten: a case report of a first-in-class scenario.

Background: Hypertrophic cardiomyopathy is a common form of genetic heart disease and in two-thirds of cases is associated with left ventricular outflow tract obstruction. Mavacamten, a selective cardiac myosin ATPase inhibitor, has emerged as the first disease-specific approach able to target the molecular mechanism responsible for this clinical phenotype. Case summary: A 69-year-old woman, admitted for a presyncopal episode, was diagnosed with obstructive hypertrophic cardiomyopathy and treated with beta-blockers at maximal tolerated dose. At follow-up, she was still symptomatic with clinically relevant left ventricular outflow tract obstruction despite treatment and mavacamten was started. After 4 weeks, she reported improved exercise tolerance, with substantial reduction in left ventricular outflow tract gradients and no decline in left ventricular systolic function. Surprisingly, her electrocardiogram (ECG) showed resolution of a pre-existing complete left bundle branch block. Discussion: To our knowledge, this is the first reported case of complete left bundle branch block resolution during treatment with mavacamten. This finding contributes to the growing evidence on the positive electrical and structural remodelling deriving from mavacamten use.