FREQUENT REOCCLUSION OF PATENT INFARCT-RELATED ARTERIES BETWEEN 4 WEEKS AND 1 YEAR - EFFECTS OF ANTIPLATELET THERAPY

Objectives. This study assessed the effect of the combination of aspirin and dipyridamole on patency of the infarct-related artery between 4 weeks and 1 year after myocardial infarction. Background. Patency of the infarct-related artery is an important determinant of prognosis after myocardial infarction. The incidence of late reocclusion and the effects of antiplatelet therapy are unknown. Methods. To investigate the importance of antiplatelet therapy for the prevention of late reocclusion, 215 patients who had a patent infarct related artery 4 weeks after myocardial infarction were randomized in a double-blind manner to receive either a combination of 25 mg of aspirin and 200 mg of dipyridamole twice daily or placebo. One hundred fifty-four patients underwent further coronary arteriography 1 year later. Results. At 1 year, 38 (25%) of 154 patients had reocclusion of the infarct-related artery; 18 (23%) of 79 patients receiving aspirin and dipyridamole had late reocclusion versus 20 (27%) of 75 who received placebo (p = NS). The rate of reocclusion was related to the severity of the residual coronary artery stenosis at 4 weeks (<50% stenosis 9.2%; 50% to 69% stenosis 11.6%; 70% to 89% stenosis 30.4%; greater than or equal to 90% stenosis 70%, p < 0.01). The majority of reocclusions were silent, and only 17 (45%) of 38 were clinically associated with further infarction. There were no differences for a hierarchic end point of cardiac death, myocardial infarction or revascularization (14.8% aspirin and dipyridamole vs. 17.8% placebo). Conclusions. Late reocclusion of the patent infarct-related artery is a frequent event, occurring in 25% of patients. Antiplatelet therapy with the combination of aspirin and dipyridamole does not alter the overall rate of late reocclusion. Other strategies are required to reduce late reocclusion.