Disappearance of echocardiographic mitral valve prolapse during ventricular pacing with retrograde artial activation.

M-mode echocardiography in a 68-year-old man with a permanent transvenous pacemaker revealed intermittent mitral valve prolapse. The mitral valve prolapse was present during normal sinus rhythm as well as during pacemaker beats either preceded by or not associated with any P wave activity. During pacemaker beats followed by retrograde P waves, the mitral valve prolapse was no longer seen. It is postulated that atrial contraction during ventricular systole produced a rise in left atrial pressure and prevented the mitral valve leaflets from prolapsing into the left atrium.