ASPIRIN ENHANCES THE BENEFITS OF LATE REPERFUSION ON INFARCT SHAPE - A POSSIBLE MECHANISM OF THE BENEFICIAL-EFFECTS OF ASPIRIN ON SURVIVAL AFTER ACUTE MYOCARDIAL-INFARCTION

Background The time window of the benefits of late reperfusion on infa rct shape is limited. In rats, these benefits diminish in a wave front over time, with minimal benefits when reperfusion follows 16 hours of coronary occlusion. The mechanism of the benefits of aspirin on survi val after acute myocardial infarction is unknown. The purpose of this study was to test the ability of aspirin to enhance the benefits of la te coronary artery reperfusion on infarct shape and to examine the mec hanism of the benefits of aspirin on infarct shape. Methods and Result s Rats were entered into two different protocols, the morphometric and the histological protocols. In the morphometric protocol, rats were r andomized into two groups: the aspirin group, in which rats underwent left coronary artery occlusion followed by treatment with aspirin (12 mg/kg IV), and the control group, in which rats underwent left coronar y artery occlusion followed by treatment with placebo. Rats in both gr oups were reperfused 8 hours after coronary occlusion. Rats in the asp irin group received aspirin in the drinking water (12+/-2 mg/kg daily) . Morphometric analysis was performed 2 weeks after acute myocardial i nfarction. In the histological protocol, rats underwent the same rando mization, coronary occlusion, and reperfusion protocols. Hearts were r emoved 24 hours after coronary occlusion, and microvessels were assess ed for patency. Infarct size expressed as a percent of circumference w as similar in the aspirin and placebo treatment groups (28+/-2% versus 33+/-3%, P=NS). Septal thickness was also similar in both groups (1.8 +/-0.1 versus 2.1+/-0.1 mm, P=NS for aspirin versus placebo). The aspi rin-treated group had thicker infarcts compared with the placebo-treat ed group (0.8+/-0.1 versus 0.5+/-0.1 mm, P<.05) and less expanded infa rcts (expansion index, 1.2+/-0.1 versus 2.0+/-0.2, P<.05). Aspirin was associated with increased patency of the microvessels in the infarcte d area compared with the placebo group (96% versus 64% of microvessels patent, P<.001). Conclusions Aspirin enhances the benefit of late cor onary artery reperfusion on infarct shape after 8 hours of coronary oc clusion. The benefits of aspirin on infarct shape after late reperfusi on are related to increased patency of the microvessels in the infarct ed area.