Antiplatelet agents for preventing thrombosis after peripheral arterial bypass surgery
Abstract
Background
Peripheral arterial disease (PAD) may cause occlusions (blockages) in the main arteries of lower limbs. One treatment option is bypass surgery using autologous (the patient's own tissue) vein graft or artificial graft. A number of factors influence occlusion rates, including the material used. To prevent graft occlusion patients are usually treated with antiplatelet, antithrombotic drugs, or a combination of both.
Objectives
To evaluate whether antiplatelet treatment in patients with symptomatic PAD undergoing infrainguinal bypass surgery improves graft patency, limb salvage and survival.
Search methods
The authors searched the Cochrane Peripheral Vascular Diseases Group Specialised Register (January 2008) and the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2007, Issue 4). Additional trials were sought through reference lists of papers and proceedings from the vascular surgical society meetings.
Selection criteria
For this update the methodological quality of each original trial was assessed independently by review authors (JB, HM, AW) with emphasis on concealment of allocation.
Data collection and analysis
Details of the selected studies were extracted independently by JB and HM for the update. The treatment and control groups were compared for important prognostic factors and differences described. If any data were unavailable, further information was sought from authors. Data were synthesised by comparing group results. Unit of analysis issues were addressed by subgroup analysis.
Main results
The administration of a variety of platelet inhibitors resulted in improved venous and artificial graft patency when compared to no treatment. However, analysing patients for graft‐type indicated that those patients receiving a prosthetic graft were more likely to benefit from administration of platelet inhibitors than patients treated with venous grafts.
Authors' conclusions
Antiplatelet therapy with aspirin had a slight beneficial effect on the patency of peripheral bypass grafts but seemed to have an inferior effect on venous graft patency compared with artificial grafts. The effect of aspirin on cardiovascular outcomes and survival was small and not statistically significant. This might be due to the fact that the majority of patients receiving a peripheral graft have an advanced stage of PAD with critical ischaemia. They are usually seriously ill as a result of cardiovascular disease and have high mortality rates, of 20% per year. Additionally, the number of patients included in this analysis might be too small to reach a statistically significant effect for mortality and cardiovascular morbidity.
PICOs
Plain language summary
Antiplatelet agents for preventing failure of peripheral arterial grafts
Symptomatic peripheral arterial disease in people with atherosclerosis can present as intermittent claudication, disabling pain on walking, or as critical limb ischaemia with pain at rest, ulceration, gangrene and the risk of losing a leg. One treatment option is to implant a graft or makeshift blood vessel to bypass a blockage in the main artery of the thigh. Using a section of the vein from the patient's calf is often better than artificial materials such as Dacron or polytetrafluoroethylene, which take up platelets. Other factors affecting the patency of the graft, how long the bypass remains open, include length of the bypass, site where the graft connects to the existing artery and blood flow out of the graft. Narrowing (stenosis) of the graft most frequently occurs at the surgical connections because of smooth muscle cells often followed by the formation of a thrombosis (clot) at the stenotic site. Fifteen randomised controlled studies were included in the review.
The long‐term (6 weeks to 2 years) administration of antiplatelet agents, started prior to surgery, resulted in improved graft patency. People who received aspirin alone or with dipyridamol showed reduced occlusion of grafts at one year (odds ratio 0.6, range 0.45 to 0.8) compared with no treatment (6 trials, 966 participants). People receiving an artificial graft were more likely to benefit than those treated with a venous graft. There was no clear beneficial effect of aspirin on cardiovascular outcomes or survival (4 trials, 811 participants). Gastrointestinal side effects and major bleeding tended to be more frequent with aspirin. Aspirin alone or in combination with dipyridamol was no different than anticoagulant vitamin K antagonist coumarin drugs on overall graft patency (2 trials, 2741 participants). For venous graft patency (1637 participants) coumarins had a more favourable effect but not for artificial grafts (1 trial, 1104 participants) where the findings favoured low dose aspirin over coumarin (OR 1.33, range 1.02 to 1.74 at 12 months). Haemorrhage necessitating hospitalisation was more evident with coumarin (9% of people) than with aspirin (4.5% of people) in one of the trials.
