Murmurs of mitral regurgitation are common (55-80%), especially in the early phase of myocardial infarction (MI). However, they are transient and are related to the dynamic nature of the ischemic process. A more serious form of ischemic mitral regurgitation may develop post-MI, though fortunately with a low incidence ranging from 0.9-5%. This complication may lead to severe mitral regurgitation frequently associated with pulmonary edema, hypotension, and death.
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Three etiologies have been described: (1) papillary muscle dysfunction. (2) generalized left ventricular dilatation, and (3) papillary muscle rupture.
Complete transection of a left ventricular papillary muscle is uniformly fatal because of sudden massive mitral regurgitation that is usually hemodynamically intolerable. Mitral regurgitation post-MI has a wide clinical spectrum, ranging from minimal hemodynamic consequences to a catastrophic syndrome, frequently fatal unless aggressive medical and surgical management is rapidly implemented.
Why does severe mitral regurgitation occur following myocardial infarction?
Blood supply to the anterolateral papillary muscle is dual, with branches from both the left anterior descending and circumflex arteries. In contrast, the posteromedial papillary muscle has a single blood supply, either the posterior branches of the dominant right coronary artery or the dominant circumflex artery. Therefore, inferoposterior and posterolateral Mis are the ones most commonly associated with severe mitral regurgitation. Ischemic mitral regurgitation is seen mostly in women and the elderly. Its prognosis depends on the degree of rupture, severity of mitral regurgitation, and previous left ventricular function.
How often does rupture of the interventricular septum occur?
This complication occurs in 1-3% of all infarctions and accounts for approximately 12% of all cardiac ruptures. It usually occurs early, 2-6 days after MI, with 66% occurring in the first 3 days. It is commonly seen in patients with hypertension and those with anteroseptal MI (60%), the rest occurring usually in patients with inferior wall MI with rupture of the posterobasilar septum.