Mitral Regurgitation - Cause

Cause

The mitral valve is composed of two valve leaflets, the mitral valve annulus (which forms a ring around the valve leaflets), the papillary muscles (which tether the valve leaflets to the left ventricle, preventing them from prolapsing into the left atrium), and the chordae tendineae (which connect the valve leaflets to the papillary muscles). A dysfunction of any of these portions of the mitral valve apparatus can cause mitral regurgitation.

The most common cause of mitral regurgitation is mitral valve prolapse (MVP), which in turn is caused by myxomatous degeneration. The most common cause of primary mitral regurgitation in the United States (causing about 50% of primary mitral regurgitation) is myxomatous degeneration of the valve. Myxomatous degeneration of the mitral valve is more common in females, and is more common in advancing age. This causes a stretching out of the leaflets of the valve and the chordae tendineae. The elongation of the valve leaflets and the chordae tendineae prevent the valve leaflets from fully coapting when the valve is closed, causing the valve leaflets to prolapse into the left atrium, thereby causing mitral regurgitation.

Ischemic heart disease causes mitral regurgitation by the combination of ischemic dysfunction of the papillary muscles, and the dilatation of the left ventricle that is present in ischemic heart disease, with the subsequent displacement of the papillary muscles and the dilatation of the mitral valve annulus.

Rheumatic fever and Marfan's syndrome are other typical causes of mitral regurgitation. It should be noted that mitral regurgitation is common, as is mitral valve prolapse, in Ehlers Danlos Syndrome

Secondary mitral regurgitation is due to the dilatation of the left ventricle, causing stretching of the mitral valve annulus and displacement of the papillary muscles. This dilatation of the left ventricle can be due to any cause of dilated cardiomyopathy, including aortic insufficiency, nonischemic dilated cardiomyopathy and Noncompaction Cardiomyopathy. It is also called functional mitral regurgitation, because the papillary muscles, chordae, and valve leaflets are usually normal.

Acute mitral regurgitation is most often caused by endocarditis, mainly S. aureus. Papillary muscle rupture or dysfunction, including mitral valve prolapse, are also common causes in acute cases.