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Improving Internal Mammary Artery Bypass Graft Patency

Improved survival and fewer cardiac events have been observed in CABG patients who receive internal mammary artery grafts rather than only saphenous vein grafts. This is explained in part by two findings: poorer early and late patency of saphenous vein grafts and evidence of occlusion by thrombosis, shown by the benefits of antithrombotic drug treatment after one year. This study was performed to compare aspirin, aspirin plus dipyridamole, and warfarin in preventing early internal mammary artery graft occlusion.

Patients from 10 European hospitals participated in this study of coronary bypass surgery; 494 received internal mammary artery grafts and were randomly assigned to receive either low-dose aspirin (50 mg daily via nasogastric tube beginning at midnight after the operation), dipyridamole (started as 5 mg/kg intravenously preoperatively and continued postoperatively as 200 mg orally twice a day) plus aspirin, or warfarin (started one day preoperatively and adjusted to International Normalized Ratio between 2.8 and 4.8). Clinical endpoints and one-year angiography (87% follow-up) were obtained.

There were no significant differences between the three groups in the rates of distal graft anastomosis occlusion (5.3% aspirin alone, 4.6% aspirin plus dipyridamole, 6.8% oral anticoagulant). There were also no differences in numbers of patent grafts, occluded grafts, or in subgroups based on type of graft, location of anastomosis, and recipient artery lumen diameter. However, the aspirin plus dipyridamole group had greater blood loss and need for transfusion and reoperation. Similarly, major bleeding was more common in the oral anticoagulant group compared with aspirin alone. Sequential graft patency was improved by oral anticoagulation.

Comment: This study demonstrates that a higher rate of internal mammary artery graft patency at one year can be achieved with low dose aspirin started shortly after surgery. Oral anticoagulant agents provide no benefit over aspirin. The combination of aspirin and dipyridamole was associated with similar patency rates, but with more adverse clinical events, including thrombosis and major bleeding, probably due to dipyridamole's vasodilator properties. Without a placebo group this study does not establish the need for aspirin in patients with internal mammary artery grafts. However, since most patients receive saphenous vein grafts in addition to internal mammary grafts, aspirin remains the preferred treatment.

— HC Herrmann

Published in Journal Watch Cardiology January 1, 1995

Citation(s):

van Der Meer J et al. 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. J Am Coll Cardiol 1994 Nov 1 24 1181-1188.

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