[Clinical problems in mitral valve prolapse: an echocardiographic review]

Several unsolved problems in the echocardiographic diagnosis of mitral valve prolapse were reviewed. At present, two-dimensional echocardiography is the most reliable method for assessing mitral valve prolapse. However, basic knowledge on the anatomical orientation of the mitral annulus, hitherto not sufficiently studied, is indispensable before making adequate echocardiographic diagnosis. The annulus is not like a geometrical plane and occupies certain millimeters' width between the left atrium and the ventricle. Therefore, assuming the left atrial margin of the annulus as the reference, many unmistakable prolapse with mitral regurgitation are overlooked, while assuming the left ventricular margins as the reference, some false positive diagnoses will be inevitable. Consulting several autopsy specimens, the author noticed that the central fibrous body, the site of the anterior mitral valve insertion to the interventricular septum, forms the most inferior part of the mitral annulus. This fact could explain a higher sensitivity of the apical four-chamber view for detecting anterior mitral valve prolapse reported by several investigators, and also more frequent over-diagnosis according to our experience. Although the author prefers the left ventricular margin of the mitral annulus defined by the long-axis view as the reference for echocardiographic diagnosis of mitral prolapse, further investigation should be made in relation to the clinical significance of this abnormality diagnosed by echocardiography.