A Cochrane review (abstract , review [Abstract]) included 14 studies with a total of 4 970 patients. The analysis including four trials which evaluated vitamin K antagonists (VKA) versus no VKA indicate, that oral anticoagulation tendentially favours venous but not artificial graft patency as well as limb salvage and survival (occlusion for venous grafts OR 0.40, 95% CI 0.17 to 0.95 at six months; OR 0.75, 95% CI 0.49 to 1.14 at 12 months; OR 0.80, 95% CI 0.55 to 1.17 at 24 months; and OR 1.00, 95% CI 0.71 to 1.40 at five years). There was a tendency for coumarins to reduce limb loss: five years OR 0.36 (95% CI 0.19 to 0.69; statistical heterogeneity I2 =81%). Two other studies (n=1637) comparing VKA with aspirin or aspirin/dipyridamole supported evidence for a positive effect of VKA on the patency of venous but not artificial grafts (occlusion in venous bypasses OR at three months 0.66, 95% CI 0.46 to 0.93; 24 months 0.59, 95% CI 0.46 to 0.76). Three trials comparing low molecular weight heparin (LMWH) to unfractionated heparin (UFH) failed to demonstrate a significant difference on patency. One trial comparing LMWH with placebo found no significant improvement in graft patency over the first postoperative year in a population receiving aspirin. One trial showed an advantage for LMWH versus aspirin and dipyridamol at one year for patients undergoing limb salvage procedures. Perioperative administration of ancrod showed no greater benefit when compared to unfractionated heparin. Dextran 70 showed similar graft patency rates to LMWH but a significantly higher proportion of patients developed heart failure with dextran.
Adverse effects: VKA was seen to be associated with a higher rate of bleeding complications compared to both no VKA and aspirin.
Comment: The quality of evidence is downgraded imprecise results (limited study size for each comparison) and by inconsistency (heterogeneity in interventions and outcomes; target INR differed between trials).
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