Infective endocarditis or myocardial infarction can cause acute rupture of the chordae tendineae or papillary muscles or cause perforation of the valve leaflets. Inferior myocardial infarction due to right coronary occlusion is the most common cause of ischemic mitral valve incompetence. Rarely, trauma may cause acute mitral incompetence. Patients with acute mitral valve rupture deteriorate rapidly. Intermittent mitral incompetence can be due to ischemia, which causes papillary muscle dysfunction. Rheumatic heart disease is the most common cause of chronic mitral incompetence. Recently, an association has been found between the use of appetite suppressant drugs (fenfluramine and phentermine, or dexfenfluramine) and cardiac valve incompetence, 1 although this has been questioned.2
Acute regurgitation into a noncompliant left atrium quickly elevates pressures and causes pulmonary edema. In contrast, in the chronic state the left atrium dilates so that left atrial pressure rises little, even with a large regurgitant flow. As an adaptation, the total stroke volume of the left ventricle increases so that effective forward flow into the aorta is maintained despite the large regurgitant volume across the mitral valve.
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