THE THIRD HEART SOUND IN MITRAL REGURGITATION

Abstract

In mitral regurgitation and in health the 3rd heart coincides with ascent of the mitral annulus fibrosus. This event is marked in the left atrial pressure pulse by sudden deceleration of "y" descent or by the start of a transient positive wave, the annular ascent wing. It is marked phonocardiographically by the onset of the diastolic murmur of mitral regurgitation. These pressure and sound phenomena are attributed to apposition of the mitral curtains caused by ascent of the annulus fibrosus and abrupt elongation of the ventricle; sudden tensing of the mitral valves and chordae is considered responsible for 3d heart sound vibrations. The loudness of the 3d sound in heart disease is related to stiffening of the fibrous part of the valve which renders it capable of producing more sound, and to diastolic distension of the left ventricle which presumably acts by increasing tension in the valve cusps and chordae. It is considered unlikely that this 3d sound can be caused by vibrations in the relaxing and sound-deadening heart muscle.