New insights into the reduction of mitral valve systolic anterior motion after ventricular septal myectomy in hypertrophic obstructive cardiomyopathy

To determine the mechanism of reduction of mitral valve systolic anterior motion by myectomy, we examined 33 patients with hypertrophic obstructive cardiomyopathy echocardiographically before and after myectomy. Measurements included outflow tract diameter, the direction of ejection streamline (the angle between the ejection flow and the mitral valve), midventricular fractional area change, and papillary muscle inward excursion in the short-axis image. After myectomy, the outflow tract was enlarged (from 1.2 ± 0.3 cm to 2.1 ± 0.4 cm; p < 0.001), and the ejection flow became more parallel to mitral leaflets (from 51 ± 10 degrees to 28 ± 8 degrees; p < 0.001), whereas hyperdynamic midventricular fractional area change was reduced (81% ± 14% to 62% ± 14%; p < 0.001), and papillary muscle excursion decreased (1.3 ± 0.3 cm to 0.8 ± 0.3 cm; p < 0.001). Outflow enlargement and reduced ventricular contraction would decrease the Venturi force. Change of ejection streamline and reduced contraction would decrease the drag force onto the mitral leaflets. Blunted papillary motion would increase the mitral leaflet tension and decrease the effect of drag force on both leaflets. Thus myectomy decreases Venturi and drag forces and appears to reduce systolic anterior motion of the mitral valve.