Aspirin versus heparin to prevent myocardial infarction during the acute phase of unstable angina

Abstract

Background. Antiplatelet therapy with aspirin and antithrombotic therapy with heparin both prevent the complications of unstable angina; however, no definitive data exist on the relative clinical efficacy of the two drugs. Methods and Results. Aspirin (325 nig bid) or heparin (5000-U intravenous bolus followed by a perfusion titrated to the APTT) were compared in a double-blind randomized trial of 484 patients in two cohorts enrolled sequentially. The study was initiated at admission to hospital at a mean of 8.3±7.8 hours after the last episode of pain. End points were assessed 5.7±3.3 days later, when the decision for long-term management was made. Myocardial infarction occurred in 2 (0.8%) of the 240 patients randomized to heparin and in 9 (3.7%) of the 244 randomized to aspirin (P=.035), an odds ratio of 0.22 and a risk difference of 2.9% (95% confidence limits, 0.3% to 5.6%) with heparin. The only death resulted from a myocardial infarction in an aspirin patient. Survival curves with Cox logistic regression analysis showed that the improvement in survival without myocardial infarction with heparin (P=.035) was independent of other baseline characteristics. Conclusions. This study documents that heparin prevents myocardial infarction better than aspirin during the acute phase of unstable angina.