MITRAL-VALVE OPENING IN THE OVINE HEART

To study the three-dimensional size, shape, and motion of the mitral l eaflets and annulus, we surgically attached radiopaque markers to site s on the mitral annulus and leaflets in seven sheep. After 8 days of r ecovery, the animals were sedated, and three-dimensional marker positi ons were measured by computer analysis of biplane videofluorograms (60 /s), We found that the oval mitral annulus became most elliptical in m iddiastole. Both leaflets began to descend into the left ventricle (LV ) during the rapid fall of LV pressure (LVP), before leaflet edge sepa ration. The anterior leaflet exhibited a compound curvature in systole and maintained this shape during opening. The central cusp of the pos terior leaflet was curved slightly concave to the LV during opening. M arkers al the border of the ''rough zone'' were separated by 10 mm dur ing systole. We conclude that coaptation occurs very near the leaflet edges, that the annulus and leaflets move toward their open positions during the rapid fall of LVP, and that leaflet edge separation, the la st event in the opening sequence, occurs near the tints of minimum LVP .