Effects of prosthetic valve placement on mitral annular dynamics and the left ventricular base

Insertion of a rigid mitral prosthesis impairs the function of the mitral a nnulus and induces systolic narrowing of the left ventricular outflow tract (LVOT). To study this mechanism, we investigated dynamic changes in the le ft ventricular (LV) base, which consists of the mitral annulus and LVOT ori fice. In seven patients with mechanical mitral valve prostheses and eight n ormal subjects, the image of the LV base was reconstructed three-dimensiona lly and its dynamic change during systole was studied. In the patients, the rigid prosthetic valve (=mitral annulus) tilted toward the left ventricle with a hinge point at the posterior mitral annulus during systole. The left ventricular base exhibited contraction, but the size of the prosthetic val ve was constant. As a consequence, the prosthetic valve occupied more of th e left ventricular base, which resulted in narrowing of the LVOT. In the no rmal subjects, the mitral annulus did not interfere with the region of the LVOT orifice during systole as the mitral annulus underwent both dorsiflexi on and contraction. Thus, fixation of the mitral annulus induces an anti-ph ysiologic motion of the annulus. Conscious preservation of annular flexibil ity in mitral valve surgery is important in avoiding potential dynamic LVOT obstruction.