Mitral leaflet billowing and prolapse: its prevalence around the world.

Primary mitral leaflet billowing, or so-called mitral valve prolapse, has become the most common valve anomaly in the United States and is also frequently found throughout the world. Its prevalence varies from less than 1% to 38%, differing not only between countries but also within the same country. The prevalence depends on whether the study is clinical or echocardiographic, based on autopsy or surgical material, or of hospital or non-care-seeking population. Other explanations for the varying prevalence are the age, sex and weight differences of the study population, imprecise terminology, the care with which auscultation and/or echocardiography are carried out and interpreted, and some selection biases. Although prevalent throughout the world, the condition is generally benign and can often be regarded as a normal variant. Among the complications of mitral valve prolapse, progressive mitral regurgitation and infective endocarditis are particularly noteworthy. Primary mitral valve prolapse is currently a leading cause of mitral regurgitation and also of infective endocarditis.