Echocardiographic drag effect index predicts response to mavacamten in obstructive hypertrophic cardiomyopathy

Abstract Background Mavacamten effectively reduces left ventricular outflow tract (LVOT) obstruction in hypertrophic cardiomyopathy (HCM). However, a significant proportion of patients do not achieve meaningful improvements in LVOT obstruction or clinical symptoms. More information is needed to understand the characteristics and to identify predictors of responders vs. non-responders. Systolic anterior motion (SAM), a key contributor to LVOT obstruction in HCM, results from two hemodynamic forces — flow acceleration through a narrowed outflow tract known as the Venturi effect, and forward-directed flow that pushes the mitral leaflet toward the septum, known as the drag effect. The influence of these forces depends on the geometry and orientation of the mitral leaflet. Purpose We aimed to evaluate whether novel echocardiographic parameters reflecting hemodynamic forces involved in systolic anterior motion (SAM) could predict clinical responses to mavacamten. We hypothesized that indices representing drag (sin(α) × residual leaflet length [RL]) and venturi (cos(α) × RL) effects would accurately predict treatment response. Methods We analyzed 45 patients with obstructive HCM who were prospectively enrolled and followed during mavacamten treatment at a single center. Echocardiographic parameters influencing SAM—including anterior leaflet length (AL), posterior leaflet length (PL), residual leaflet length (RL), protrusion height (PH), and the aortomitral angle (α)—were measured. We derived echocardiographic parameters representing the drag effect (sin(α) × RL) and venturi effect (cos(α) × RL) based on leaflet geometry and hemodynamic principles. These simplified indices were used to estimate the relative contribution of perpendicular forces—drag and venturi—acting on the mitral leaflet. Responders were defined by achieving an LVOT gradient