Three to six months of warfarin associated with better survival after bioprosthetic aortic valve replacement

Warfarin therapy after bioprosthetic aortic valve replacement was associated with reduced rates of thromboembolic events and mortality, a new study found.

Researchers used data on more than 4,000 patients from the Danish National Patient Registry who had surgical aortic valve replacement (AVR) with biological prostheses in 1997-2009. The study looked at whether warfarin was prescribed, and if so, when the prescription was discontinued. The mean follow-up was 6.57 years. Results were published in the Nov. 28 Journal of the American Medical Association.

Patients who took warfarin had significantly lower risk of stroke (2.69 per 100 person-years vs. 7 per 100 person-years; adjusted incidence rate ratio [IRR], 2.46) and thromboembolic events (3.97 vs. 13.07 per 100 person-years; IRR, 2.93) than those who were not taking it. The warfarin group also had fewer cardiovascular deaths: The comparison was 3.83 versus 31.74 per 100 person-years (IRR, 7.61) for deaths 30 to 89 days after surgery and 2.08 versus 6.50 per 100 person-years (IRR, 3.51) for deaths 90 to 179 days after surgery.

The results suggest a benefit to using warfarin during the initial three months after surgery which may extend to six months, the study authors concluded. They noted that their study was limited by lack of data about achieved international normalized ratios and potential confounding by comorbidities, but given these results and the lack of randomized data, they called for review of existing guidelines to consider the extension of warfarin treatment for patients receiving bioprosthetic AVR.

Current guidelines on this question are conflicting, noted an accompanying editorial. The American College of Cardiology/American Heart Association (ACC/AHA) and European Society of Cardiology recommend three months of warfarin, and the ACC/AHA recommends adding aspirin. The American College of Chest Physicians recommends aspirin alone.

This study does not resolve the dilemma of whether to use aspirin (or the emerging option of novel oral anticoagulants), but it should change warfarin prescribing practices, the editorialist concluded, noting that “the optimal duration of therapy appears to be 6 months.”