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Mitral valve prolapse (MVP) is a valvular heart disease characterized by the displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. In its nonclassic form, MVP carries a low risk of complications.[1] In severe cases of classic MVP, complications include mitral regurgitation, infective endocarditis, and — in rare circumstances — cardiac arrest, usually resulting in sudden death.
The mitral valve, so named because of its resemblance to a bishop’s mitre, is the heart valve that prevents the backflow of blood from the left ventricle into the left atrium. It is composed of two leaflets (one anterior, one posterior) that close when the left ventricle contracts.[2]
Each leaflet is composed of three layers of tissue: the atrialis, fibrosa, and spongiosa. Patients with classic 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 dermatan sulfate, a glycosaminoglycan. This weakens the leaflets and adjacent tissue, resulting in increased leaflet area and elongation of the chordae tendineae. Elongation of the chordae tendineae often causes rupture, commonly to the chordae attached to the posterior leaflet. Advanced lesions — also commonly involving the posterior leaflet — lead to leaflet folding, inversion, and displacement toward the left atrium.
The term mitral valve prolapse was coined by J. Michael Criley in 1966 and gained acceptance over the other descriptor of “billowing” of the mitral valve, as described by JB Barlow.[3]
For many years, mitral valve prolapse was a poorly understood anomaly associated with a wide variety of both related and seemingly unrelated signs and symptoms, including late systolic murmurs, inexplicable panic attacks, and polythelia (extra nipples). Recent studies suggest that these symptoms were incorrectly linked to MVP because the disorder was simply over-diagnosed at the time. Continuously-evolving criteria for diagnosis of MVP with echocardiography made proper diagnosis difficult, and hence many subjects without MVP were included in studies of the disorder and its prevalence. In fact, some modern studies report that as many as 55% of the population would be diagnosed with MVP if older, less reliable methods of MVP diagnosis—notably M-mode echocardiography—were used today.
In recent years, new criteria have been proposed as an objective measure for diagnosis of MVP using more reliable two- and three-dimensional echocardiography. The disorder has also been classified into a number of subtypes with respect to these criteria.
Prolapsed mitral valves are classified into several subtypes, based on leaflet thickness, concavity, and type of connection to the mitral annulus. Subtypes can be described as classic, nonclassic, symmetric, asymmetric, flail, or non-flail.
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