Figure 50-19 Left, Proposed mechanism of mitral leaflet systolic anterior motion (SAM) in early systole in hypertrophic cardiomyopathy. Ventricular septal hypertrophy causes a narrowed outflow tract, as result of which ejection velocity is rapid and the path of ejection (dashed line) is closer to the mitral leaflets (MV) than normal. This results in Venturi forces (three short oblique arrows in the outflow tract) drawing the anterior or posterior mitral leaflets, or both, toward the septum. Subsequent mitral leaflet-septal contact results in obstruction to left ventricular (LV) outflow and concomitant mitral regurgitation as seen in the right panel. By midsystole, SAM-septal contact is well established and is causing marked narrowing of the LV outflow tract with obstruction to outflow. LA, left atrium; AO, aorta. Right, Proximal to the level of SAM-septal contact, converging lines indicate acceleration of the jet just proximal to the obstruction and narrowing of the jet width. Distal to the obstruction, the arrow and diverging lines indicate a high-velocity flow that emanates from the site of SAM-septal contact and is directed posterolaterally at a considerable angle from the normal path of aortic outflow. In late systole, although forward flow continues into the outflow tract and aorta, the volume of flow is much less than in the early nonobstructed systole. Typical Doppler flow patterns are shown. A, integrated Doppler flow signal in the ascending aorta; B, high outflow tract velocity recorded by continuous-wave (CW) Doppler at the site of SAM-septal contact; C, presence of mitral regurgitation recorded by CW Doppler; D, late systolic velocity peak that can be recorded in the apical region of the left ventricle. (Redrawn from Wigle ED: Hypertrophic cardiomyopathy: A 1987 viewpoint. Circulation 75:312, 1987.)