Twenty eight studies were included in the review (n=11,667 patients who had tissue aortic valve replacement only). Sample size of included studies ranged from 121 to 2,943 patients. Three were prospective randomised controlled trials (RCTs, n=640 patients) and the rest were prospective or retrospective case series, although the design of some included studies was unclear.
Three studies provided evidence in favour of early anticoagulation; one prospective study (n=209 patients) and two retrospective studies (n=985 patients). The prospective study found that ticlopidine statistically significantly reduced the risk of thromboembolic events compared to oral anticoagulant (p=0.002) but bleeding related episodes were not statistically significantly reduced.
Five studies provided evidence against early anticoagulation: one prospective (n=249) and four retrospective (n=1,218). The prospective study found no statistically significant difference between warfarin and low dose aspirin in frequency of cerebral ischaemic events or in rates of bleeding.
Risk factors associated with bioprosthetic aortic valve replacement, incidence of thromboembolism and bleeding complications due to anticoagulation were reported in the review.