Anterior mitral leaflet mobility is limited by the basal stay chords

Background-We hypothesize that 2 tendon-like anterior basal stay chords, which remain taut during the entire cardiac cycle, limit the motion of the anterior mitral leaflet. Methods and Results-Sonomicrometric crystals were implanted in 6 sheep at the insertion of stay chords at anterior mitral leaflet (S1 and S2), papillary muscle tips, fibrous trigones, mitral annulus, and the tip of the anterior leaflet (AL). Distances between crystals were recorded before and after section of stay chords. During the cardiac cycle, the angle alpha between mitral annulus and AL changed by +54.2 +/- 12.4 degrees; the angles between mitral annulus and S1 (beta1) changed by +25.7 +/- 14.6 degrees, and between mitral annulus and S2 (beta2) by +20.4 +/- 7.8 degrees. During diastole, AL twice crossed the virtual plane formed by the stay chords: during E-wave by a maximum of 6.5 mm (mean, 2.5 +/- 2.2 mm) and during A-wave by a maximum of 3.2 mm (mean, 1.7 +/- 0.9 mm). After section of both stay chords, total anterior mitral leaflet motion increased as follows: AL, +6.9 +/- 3.4 degrees; S1, +13.1 +/- 4.4 degrees; and S2, +30.9 +/- 11.7 degrees (P < 0.05). Conclusions-Although the lateral movement of anterior mitral leaflet is limited by stay chords, the midportion moves unimpaired toward the septum, like a sail, between the 2 stay chords during diastole. A diastolic left ventricular-inflow and systolic left ventricular-outflow funnel mechanism is created. Stay chord section increased lateral anterior mitral leaflet movement.