Associated changes Chordae tendineae are often primarily involved in the pathologic process and may be shortened preventing closure, lengthened permitting the free edge of the valve to displace toward the atrium, or ruptured permitting upward dis-placement of the free edge of the valve with varying severity of regurgitation. The posterior mitral valve leaflet is drawn dorsally and posteriorly with atrial dilatation and regurgitant flow is directed especially to the caudal wall where jet lesions, atrial myocardial degenerative changes and in severe atrial tears or rupture can occur. Mitral annular ring dilatation secondary to atrial and ventricular dilatation occurs and adds to the severity of valvular incompetence. Intramural coronary arteriosclerosis and focal areas of myocardial necrosis and fibrosis involving the papillary muscles and left ventricle are commonly associated with advanced chronic valvular disease. The cause is not known.
Most investigators regard the change as a dystrophic process.
It has been suggested the disease is a genetically influenced degenerative disease of connective tissue, particularly collagen. No murmur is heard as long as the valves are competent. Some have suggested that systolic clicks may sometimes be associated with early stages of the disease. The intensity of the band shaped murmur varies with severity of the valve disease. The first heart sound may be accentuated.