MITRAL VALVE PROLAPSE
Mitral valve prolapse is a condition in which the two flaps of the mitral valve do not close smoothly or evenly. When the heart contracts, part of one or both flaps can collapse back into the left atrium. In some cases, the prolapsed valve causes regurgitation, or the flow of a small amount of blood back through the valve and can be heard as a murmur. In most cases, a mitral valve prolapse is harmless.
The most common cause of mitral valve prolapse is myxomatous change, or the presence of small collagenous growths on the valve. Patients with mitral valve prolapse have excess connective tissue that thickens the spongiosa and separates collagen bundles in the fibrosa. This is due to an excess of a glycosaminoglycan called dermatan sulfate. MVP may occur with greater frequency in individuals with Ehler-Danlos syndrome, Marfan syndrome, polycystic kidney disease and chest wall deformities such a pectus excavatum. Rheumatic fever can also damage the heart valves. Chronic rheumatic fever is characterized by repeated inflammation with fibrinous resolution. This causes thickened leaflets, commissural fusion and shortening and thickening of the tendinous chords.
MVP may be identified by a characteristic heart sound. A mid-systolic click followed by a late systolic murmur is heard at the apex. The murmur is accentuated by standing and valsalva and diminished by squatting. Both valsalva and standing decrease the venous return to the heart, thereby decreasing left ventricular diastolic filling and causing more laxity of the chordate tendinae. This allows the mitral valve to prolapsed earlier in systole, leading to an earlier systolic click and a longer murmur.
MVP without associated symptoms tends to be benign. MVP patients with a murmur (as opposed to an isolated click) have an increased mortality rate of 15-20%. The major predictors of mortality are the severity of mitral regurgitation and the ejection fraction.
Most patients with MVP, especially those without symptoms, often require no treatment. Those with palpitations and chest pain may benefit from beta-blockers. Patients with a history of stroke or atrial fibrillation may require blood thinners such as aspirin and warfarin. If MVP is associated with severe mitral regurgitation, mitral valve repair or surgical replacement may be necessary. Repair is preferred to replacement. The current American Heart Association guidelines promote repair of mitral valve in patients before symptoms of heart failure develop.