A. Mitral valve endocarditis
B. Dilated cardiomyopathy
C. Mitral valve prolapse
D. Rheumatic mitral valve disease
The etiologies of MR are diverse since the MV apparatus is complex. MR can occur when the MV apparatus is itself diseased (organic MR) or in the absence of any abnormality of the MV apparatus (functional MR). The causes of functional and organic MR are listed in the table below.
Myxomatous changes (MVP)
Rheumatic heart disease (RHD)
Collagen vascular disease
Papillary muscle dysfunction
Mitral annular calcification (MAC)
Spontaneous chordal rupture
Left atrial dilation
Functional MR occurs when the LA or LV dilates causing the MV annulus to also dilate thus preventing the MV leaflets from properly coapting. There are many causes of LA or LV dilation and the treatment of this type of MR is directed at the primary cause. For example, if a patient develops systolic heart failure with a dilated LV resulting in MR, treatment would be directed at reversal of the heart failure.
Organic MR results from actual disease of the MV apparatus. The MV leaflets, annulus, papillary muscles and chordae tendinae must interact properly for the MV to function properly. Thus, disruption of any of these structures can result in organic MR.
The most common cause of chronic MR in the United States is due to the myxomatous changes seen in mitral valve prolapse (MVP). In this condition, the middle layer of the valve leaflets become thickened frequently causing leaflet redundancy making it difficult for them to coapt properly. The chordae tendinae may also be affected disrupting support of the MV apparatus.