EFFECTS OF LOW-DOSE ASPIRIN (50-MG DAY), LOW-DOSE ASPIRIN PLUS DIPYRIDAMOLE, AND ORAL ANTICOAGULANT AGENTS AFTER INTERNAL MAMMARY ARTERY BYPASS-GRAFTING - PATENCY AND CLINICAL OUTCOME AT 1 YEAR/

Objectives. This study was performed to compare the efficacy and safet y of aspirin, aspirin plus dipyridamole, and oral anti coagulant agent s in the prevention of internal mammary artery graft occlusion. Backgr ound. Antithrombotic drugs increase vein graft patency after coronary artery bypass surgery. Their benefit after internal mammary artery gra fting has not been established. Methods. Angiographic internal mammary artery graft patency at 1 year was assessed in 494 patients who recei ved both internal mammary artery and vein grafts. These patients were a subgroup of a prospective, randomized vein graft patency study in 94 8 patients assigned to treatment with aspirin, aspirin plus dipyri- da mole, or oral anticoagulant agents. The design was double blind for bo th aspirin groups and open for oral anticoagulant treatment. Dipyridam ole (5 mg/kg body weight per 24 h intravenously, followed by 200 mg tw ice daily) and oral anticoagulant agents (prothrombin time target rang e 2.8 to 4.8 international normalized ratio) were started before opera tion, and low dose aspirin (50 mg/day) after operation. Clinical outco me was assessed by the incidence of myocardial infarction, thrombosis, major bleeding or death. Results. Occlusion rates of distal anastomos es were 4.6% in the aspirin plus dipyridamole group and 6.8% in the or al anticoagulant group versus 5.3% in the aspirin group (p = NS). Over all clinical event rates were 23.3% and 13.3% in the aspirin plus dipy ridamole group and the aspirin group, respectively (relative risk 1.75 , 95% confidence interval 1.09 to 2.81, p = 0.025), and 17.1% in the o ral anticoagulant group. Conclusions. Internal mammary artery graft pa tency at 1 year is not improved by aspirin plus dipyridamole or oral a nticoagulant agents over that obtained with low dose aspirin alone. Ho wever, there is evidence that the overall clinical event rate increase s if dipyridamole is added to aspirin.