Papillary Muscle Rupture

Papillary muscle rupture is a mechanical complication of acute myocardial infarction. The papillary muscles anchor the mitral valve leaflets through the chordae tendineae; when an infarcted muscle partially or completely tears, the leaflet loses normal support and becomes flail. The result is acute, often severe mitral regurgitation. The posteromedial papillary muscle is affected most often because it usually receives blood from a single coronary artery branch. The anterolateral muscle has a dual blood supply and is therefore less vulnerable to ischemic necrosis. Rupture most commonly occurs during the first week after infarction, particularly after an inferior MI. During systole, blood suddenly moves backward from the left ventricle into the left atrium instead of forward into the aorta. A chronically regurgitant valve allows time for the left atrium and ventricle to enlarge; acute rupture does not. The nonadapted left atrium experiences a rapid pressure rise, which is transmitted to the pulmonary veins and produces flash pulmonary edema. Forward cardiac output falls at the same time, so hypotension, impaired organ perfusion, and cardiogenic shock can develop quickly. A partial rupture may produce...