In the two decades since mitral valve prolapse was described, the syndrome was thought to be a frequently diagnosed valvular deformity, more common in women. This assessment was based on studies that had patient selection bias and diagnostic criteria that were less specific than those used today. In a community population study, with false-positive results, false-negative results, and selection bias greatly minimized, the picture looks quite different.39 The Framingham Study reports that prevalence is no more than 1 to 2 percent, no more common in women than in men, and diagnosis of associated cardiovascular sequelae is low. This assessment also has its limitations. Study results are based on a white population only, confidence limits around the prevalence estimates are large, results are subject to a survival bias, and patients with mitral valve prolapse that resulted in sudden death may not have been included in the cohort. The major importance of mitral valve prolapse may be the threat of endocarditis, which must be rare, and arrhythmias, which may be common (see Chap. 65).
Little information is available on the prevalence of valvular heart disease in the general population. Most prevalence estimates come from surgical studies and small numbers of patients referred for diagnosis. The Framingham Study has estimated prevalence of mitral, tricuspid, and aortic regurgitation in their population sample using color Doppler echocardiography routinely obtained on all participants.40 Some degree of mitral and tricuspid regurgitation was seen in 19 and 15 percent of men and 19 and 18 percent of women, respectively. Aortic regurgitation was found in 13 percent of men and 8.5 percent of women.
Rheumatic heart disease is no longer the most frequent cause of valve disease. Mitral valve prolapse and degeneration of congenital aortic valve lesions are now the most common causes.41 Aortic stenosis also may result from atherosclerotic degeneration of the valve in diabetes with dyslipidemia. It is the most common valve lesion in the elderly having valve replacement.42 Aortic root or annular dilatation is responsible for most aortic regurgitation, of which 40 to 60 percent is of unknown cause.
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