Improved Aortocoronary Bypass Patency by Low-dose Aspirin (100 Mg Daily). Effects on Platelet Aggregation and Thromboxane Formation

Prevention of aortocoronary bypass occlusion by aspirin (ASA, 1 X 100 mg per day) was studied in a prospective double-blind trial of 83 patients. 60 (72%) were randomly allocated to ASA or placebo starting 24 h after operation. 90% of grafts in the ASA group and 68% in the placebo group were patent at four months. At least one anastomosis was occluded in 62% of the patients on placebo and in 27% of those on aspirin. Ventricular arrhythmias increased after surgery in more patients on placebo (12/18) than in patients on ASA (5/17). Platelet thromboxane formation on collagen tested before operation was significantly higher in patients in whom bypass occlusion developed (occlusion: 40 +/- 19, no occlusion: 25 +/- 13 ng/ml). A 100 mg dose of ASA per day effectively blocked platelet thromboxane formation and thromboxane-supported aggregation on collagen and was safe in the postoperative phase. No side effects were reported throughout the trial. The reduced toxicity with full efficacy favours a low and infrequent dosage of aspirin.