Aspirin usage and its influence on femoro-popliteal vein graft patency

As part of the Femoro-popliteal Bypass Trial patients undergoing femoro-popliteal vein bypass were randomised to aspirin 300 mg and dipyridamole 150 mg twice daily or identical placebo tablets. Blood was taken from a subgroup of 145 patients (mean age 66.3 years) with patent grafts at 6 months. Serum salicylate analysis revealed that of the 65 randomised to receive placebo 18 (28%) had evidence of salicylate in their sample (>50 ng ml −1 ). Similarly, in those randomised to active treatment and considered to be good compliers 16/61 (26%) had no evidence of salicylate in their serum sample ( −1 ). Analysis of primary graft patency by “intention to treat” failed to detect a difference by life table, the risk being slightly higher in the group assigned to placebo (RR = 1.33, 95% confidence internal C.I. 0.64–2.78, p = 0.438). When comparing patients with no detectable serum concentration ( −1 ) with patients with serum salicylate over 50 ng ml −1 there was a significant difference in graft patency at 66 versus 83% respectively at 3 years (RR = 2.38, 95%C.I.1.08–5.26, p = 0.024). When corrected for a number of possible risk factors this significant difference was maintained (RR = 2.78, 95%C.I. 1.15–6.67, p = 0.017). Although these findings are based on observational data they provide indirect evidence of an improvement in graft patency with aspirin. This result combined with the finding of a significant reduction in cardiovascular events in the main trial results support the use of aspirin and dipyridamole in patients undergoing femoro-popliteal vein bypass.