Mechanism of abnormal motion of the posterior leaflet in mitral stenosis.
Echocardiographic visualization of diastolic anterior motion of the posterior leaflet has proven to be diagnostic of mitral stenosis. In order to elucidate the mechanisms which underlie this finding and to explain why it is absent in some proven instances of mitral stenosis, we analyzed leaflet motion as a function of torque and derived a theoretic expression which permitted us to predict the direction of leaflet motion in mitral stenosis in terms of degree of commissural fusion and leaflet dimensions. The analysis was tested in an experimental model consisting of an isolated, perfused pig heart. Dimensions and degree of fusion of mitral valve leaflets were varied surgically in 5 specimens. Corresponding values proportional to torque were computed for each leaflet and the associated modifications of valve motion recorded cinematographically through a fiberscope inserted into the left ventricular cavity. The theoretical considerations indicated that, when leaflet commissures are fused, diastolic movement of the posterior leaflet is determined by the torques on both leaflets and that the relative length (base to free edge) of the leaflets is the major determinant of the direction of the resultant displacing force. The posterior leaflet may move posteriorly early in diastole until this motion is restricted by the fusion, but anterior motion of both leaflets results when the anteriorly directing force becomes dominant. Anterior motion of the posterior leaflet therefore occurs when leaflet fusion is extensive and the anterior leaflet remains longer than the posterior. Posterior motion of the posterior leaflet tends to occur with leaflet fusion, even in severe or moderate mitral stenosis, when the ratio of anterior to posterior leaflet length approximates unity. Direct observations of leaflet motion in the perfused porcine hearts confirmed these relationships.
D000818:Animals; D003971:Diastole; D004452:Echocardiography; D008943:Mitral Valve / Q000503:physiopathology; D008946:Mitral Valve Stenosis / Q000503:physiopathology*; D008955:Models, Cardiovascular; D013552:Swine