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 infarct 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 survival after acute myocardial infarction is unknown. The purpose of this study was to test the ability of aspirin to enhance the benefits of late coronary artery reperfusion on infarct shape and to examine the mechanism of the benefits of aspirin on infarct shape.

METHODS AND RESULTS

Rats were entered into two different protocols, the morphometric and the histological protocols. In the morphometric protocol, rats were randomized into two groups: the aspirin group, in which rats underwent left coronary artery occlusion followed by treatment with aspirin (12 mg/kg i.v.), and the control group, in which rats underwent left coronary artery occlusion followed by treatment with placebo. Rats in both groups were reperfused 8 hours after coronary occlusion. Rats in the aspirin group received aspirin in the drinking water (12 +/- 2 mg/kg daily). Morphometric analysis was performed 2 weeks after acute myocardial infarction. In the histological protocol, rats underwent the same randomization, coronary occlusion, and reperfusion protocols. Hearts were removed 24 hours after coronary occlusion, and microvessels were assessed for patency. Infarct size expressed as a percent of circumference was 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 aspirin-treated group had thicker infarcts compared with the placebo-treated group (0.8 +/- 0.1 versus 0.5 +/- 0.1 mm, P < .05) and less expanded infarcts (expansion index, 1.2 +/- 0.1 versus 2.0 +/- 0.2, P < .05). Aspirin was associated with increased patency of the microvessels in the infarcted area compared with the placebo group (96% versus 64% of microvessels patent, P < .001).

CONCLUSIONS

Aspirin enhances the benefit of late coronary artery reperfusion on infarct shape after 8 hours of coronary occlusion. The benefits of aspirin on infarct shape after late reperfusion are related to increased patency of the microvessels in the infarcted area.