Atrial fibrillation developing in the acute phase of myocardial infarction. Prognostic implications.

Atrial fibrillation was observed in 39 (11 percent) of 350 instances of acute myocardial infarction. The mortality among these patients was 41 percent (16/39). Atrial fibrillation was more common in patients with undetermined infarctions and in older people. As opposed to death rates close to 50 percent among patients with anterior, combined, and undetermined infarctions, the presence of atrial fibrillation did not affect the mortality among patients with inferior infarctions (10 percent, 1/10). Ventricular rates higher than 120 beats per minute and duration of the arrhythmia longer than six hours were not associated with increased mortality. Hemodynamic failure was present in almost all of the cases and preceded the arrhythmia in most of them. It is concluded that different mechanisms are responsible for the production of atrial fibrillation in the setting of acute myocardial infarction, and the prognosis of the patient is related to the mechanism of production and not to the arrhythmia itself.