Prophylactic Low-Dose Aspirin Therapy

Background. The influence of prophylactic low-dose aspirin on the clinical characteristics of subsequent nonfatal myocardial infarction was examined in the Physicians' Health Study, a randomized, double-blind placebo-controlled trial of alternate-day aspirin (325 mg) among 22,071 US male physicians. Methods and Results. During 60.2 months of follow-up, 342 incident cases of nonfatal myocardial infarction were confirmed (95.2% of all reports): 129 on aspirin and 213 on placebo (p<0.00001). Despite this statistically extreme reduction in occurrence of a first nonfatal infarction attributable to aspirin, there were no significant differences in the size, location, electrocardiographic features, or postinfarction left ventricular ejection fraction between the aspirin and placebo groups. Furthermore, among those undergoing angiography, there were no differences in the distribution or number of coronary vessels obstructed. Conclusions. These data indicate that chronic platelet inhibition with alternate-day aspirin therapy reduces the risk of a first myocardial infarction but does not appear to have a significant effect on the clinical characteristics of events that are survived. This finding may result from a direct effect of aspirin or from an aspirin-induced shift in infarction severity. Regardless of mechanism, these clinical observations suggest that treatment decisions for acute infarction patients should be made independently of a history of aspirin use. (Circulation 1991;84:708-711)