Silent Mitral Insufficiency in Acute Myocardial Infarction

Severe mitral insufficiency in the absence of an audible murmur was diagnosed by left ventricular angiography in three patients with power failure secondary to acute myocardial infarction during evaluation for mechanical circulatory assist and surgery. Mitral valve prolapse was present in two patients. Postmortem examination did not reveal an anatomic basis for the mitral insufficiency: the valve, papillary muscles, and supporting structures were all grossly normal. A single papillary muscle removed at surgery revealed a marked decrease in force development (0.22 g/mm2 vs 0.62 ± 0.22 g/mm2 in eight normal papillary muscles from patients with rheumatic heart disease). During isoproterenol stimulation, force development in this muscle decreased 20%, whereas in the normal muscles force development increased 73 ± 31%. Microscopically, all papillary muscles revealed evidence of extensive necrosis. Silent mitral insufficiency in acute myocardial infarction, therefore, was probably related to diminished flow velocity across the mitral valve secondary to diminished myocardial contractility. Failure to recognize and treat this entity may contribute significantly to the genesis of power failure and ultimate mortality.