Systolic Murmurs - Mitral Valve Prolapse

     You are listening to a typical example of the murmur caused by mitral valve prolapse. The pathophysiology of mitral valve prolapse is varied, but can be thought of as an inability of the papillary muscles or chordae tendineae to completely tether the mitral valve during the late stages of systole. As the left ventricle chamber decreases in size, the papillary muscles and/or the chordae fail to maintain tension on the mitral valve, and it prolapses with a brief regurgitant period into the left atrium. This is a common syndrome which frequently is associated with young adult women, and can present as attacks of palpitations, anxiety, or light-headedness. Although it is usually a mild symptom, patients with mitral valve prolapse with evidence of regurgitation by echo should be given antibiotic prophylaxis during invasive procedures to help prevent bacterial endocarditis.

     The murmur of mitral valve prolapse is somewhat complex. Following a normal S1 and briefly quiet systole, the valve suddenly prolapses, resulting in a mid-systolic click. The click is so characteristic of MVP that even without a subsequent murmur, its presence alone is enough for the diagnosis. Immediately after the click, a brief crescendo-decrescendo murmur is heard, usually best at the apex. In stark contrast to most other murmurs, MVP is enhanced by Valsalva maneuvers and decreased by squatting. This is because those maneuvers which decrease the volume of the left ventricle (Valsalva, standing) will cause the prolapse to occur sooner and more severely, while those that increase venous return and diastolic filling (squatting) and thereby enhance the ventricular volume, help to maintain tension along the chordae and to keep the valve shut. The only other murmur which, for similar reasons, responds in this paradoxical way to these common maneuvers is hypertrophic cardiomyopathy, also known as idiopathic hypertrophic subaortic stenosis.