Collaborative overview of randomised trials of antiplatelet therapy - II: Maintenance of vascular graft or arterial patency by antiplatelet therapy

Abstract

Objective : To determine the efficacy of antiplatelet therapy in maintaining vascular patency in various categories of patients. Design : Overviews of 46 randomised trials of antiplatelet therapy versus control and 14 randomised trials comparing one antiplatelet regimen with another. Setting : Randomised trials that could have been available by March 1990 and in which vascular graft or arterial patency was to be studied systematically. Subjects : About 8000 patients at varying degrees of risk of vascular occlusion (by virtue of disease or of having some vascular procedure) were in trials of antiplatelet therapy versus control and 4000 such patients were in trials directly comparing different antiplatelet regimens. Results : Overall, antiplatelet therapy produced a highly significant (2P<0.00001) reduction in vascular occlusion, with similar proportional reductions in several different types of patient. Hence the absolute reductions tended to be largest among patients at highest risk of occlusion, with smaller but still significant absolute reductions among lower risk patients. The proportions of patients with confirmed occlusion among those allocated antiplatelet therapy versus appropriately adjusted control proportions (and mean scheduled treatment durations and net absolute benefits) were: (a) among about 4000 patients with coronary artery grafts, 21% antiplatelet therapy v 30% control (seven month benefit about 90 patients protected per 1000 allocated antiplatelet therapy (2P<0.00001); (b) among about 800 patients after coronary angioplasty, 4% antiplatelet therapy upsilion 8% control (six month benefit about 40/1000 (2P = 0.02)); (c) among about 3000 patients with peripheral artery procedures or disease, 16% antiplatelet therapy v 25% control (19 month benefit about 90/1000 (2P<0.00001); (d) among about 400 renal patients with a shunt or fistula placed for haemodialysis access, 17% antiplatelet therapy v 39% control (two month benefit about 200/1000 (2P<0.00001)). Conclusion : Antiplatelet therapy (chiefly aspirin alone or aspirin plus dipyridamole) greatly reduces the risk of vascular occlusion in a wide range of patients at high risk of this complication. Further studies are required to determine exactly when treatment should start (to limit any perioperative bleeding while still preventing most early occlusion) and for how long it should be continued.