Ask the doctors: Why do I need to take blood thinners after a valve replacement?

Q. I thought one of the reasons to receive a heart valve made from cow tissue was that you don't have to take blood thinners. Now my doctor is telling me that I will need to take warfarin [Coumadin] for several months after I have my aortic valve replaced. Has the thinking changed?

A. You're right—thinking is evolving on whether people who receive a bioprosthetic (natural-tissue) valve benefit from warfarin therapy. The trend is toward using this treatment for three to six months unless the person has a history of bleeding that would make anticoagulation dangerous. Bioprosthetic valves are used more often than mechanical valves in older people undergoing aortic valve replacement, because they are often frail and have conditions that predispose them to bleeding complications. However, recent research shows that three to six months of warfarin seems to lead to lower rates of blood clots than bleeding complications. The risk of blood clots—and thus the benefit of taking warfarin—is greatest in the first three months, and then declines. After six months, the benefits and risks seem too close to recommend the medication. So unless you have a high risk of bleeding, I would make the same recommendation. Make sure you are followed closely after surgery to be sure that your blood is thinned to an appropriate level.