Mitral regurgitation in ventricular premature contractions. The role of the papillary muscle.

In view of the possibility that the mechanism of mitral regurgitation following premature ventricular contractions may contribute to the understanding of mitral regurgitation in clinically important causes of nonrheumatic mitral insufficiency, we studied 320 premature ventricular contractions in eight dogs. Since the papillary muscle is an important component of the mitral valvular complex, the extent and course of lengthening and shortening of the papillary muscle was investigated with ultrasonic crystals implanted within the anterolateral papillary muscle. Lengthening and shortening of a segment of the free wall of the left ventricle was measured simultaneously with identical crystals in three dogs. During sinus rhythm, lengthening of the papillary muscle always began well before the onset of isovolumic contraction of the left ventricle and continued throughout isovolumic contraction, indicating that lengthening occurred during closure of the mitral valve. When lengthening was prevented by premature ventricular contractions, left atrial v waves occurred. These observations indicate that lengthening of the papillary muscle during the latter part of diastole is required for proper closure of the mitral valve and that inadequate lengthening can result in mitral regurgitation.