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 anter ior motion by myectomy, we examined 33 patients with hypertrophic obst ructive cardiomyopathy echocardiographically before and after myectomy . Measurements included outflow tract diameter, the direction of eject ion streamline (the angle between the ejection flow and the mitral val ve), midventricular fractional area change, and papillary muscle inwar d 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 midv entricular 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 ven tricular contraction would decrease the Venturi force. Change of eject ion streamline and reduced contraction would decrease the drag force o nto the mitral leaflets. Blunted papillary motion would increase the m itral leaflet tension and decrease the effect of drag force on both le aflets. Thus myectomy decreases Venturi and drag forces and appears to reduce systolic anterior motion of the mitral valve.