Antiplatelet therapy after bioprosthetic aortic valve replacement is unnecessary in patients without thromboembolic risk☆

We read with interest the article titled ‘Antiplatelet therapy early after bioprosthetic aortic valve replacement is unnecessary in patients without thromboembolic risk factors’ [1]. The authors conducted a retrospective non-randomised observational study to examine antiplatelet therapy after bioprosthetic aortic valve replacement in 288 patients without thromboembolic risk factors. They conclude that there is no apparent benefit to early antiplatelet therapy in this cohort of patients. We concur with the authors that guidelines are confusing and the evidence is weak. We have recently reviewed the literature on antithrombotic therapy following bioprosthetic aortic valve replacement [2]. There are only two prospective randomised trials comparing an antiplatelet agent with a vitamin K antagonist [3,4] and both showed equivalence. The incidence of thromboembolism following bioprosthetic AVR is between 0.9% and 2.2% per patient year. For an event rate of 2% and a risk ratio of 1.2, approximately 28,000 patients will be required and for a risk ratio of 2.0, 1527 patients will be required to identify a significant difference between the groups. Therefore, it is not surprising that Brueck and colleagues did not find a reduction in cerebral thromboembolism comparing their groups over a 12-month period. We agree that a three-arm trial comparing aspirin, warfarin and no antithrombotic treatment is desirable. However, our own survey of UK cardiothoracic consultants showed that most were in favour of a two-arm trial. Surgeons appeared reluctant to offer no treatment since there are no guidelines advocating this approach. Similarly, there are no studies specifically examining the safety of omitting warfarin and for this reason guidelines remain weighted in favour of early anticoagulation, albeit for 3 months. There are also no studies supporting aspirin therapy to prevent pannus formation. Therefore, it is timely to carry out a randomised controlled trial of patients undergoing tissue aortic valve replacement, comparing warfarin, aspirin and no treatment.