Controversies in antithrombotic therapy for patients with mechanical heart valves

Current anticoagulation guidelines for patients with mechanical heart valves are based on studies that are seriously flawed in that they used prothrombin time ratios rather than the international normalized ratio (INR) and failed to consider the level of anticoagulation actually achieved. Available data suggest that the appropriate INR range varies according to risk factors and that "tight control" of the INR is of critical importance in reducing thromboembolic and hemorrhagic events. Whether antiplatelet therapy adds benefit to an appropriately controlled level of anticoagulation is not clear. During pregnancy, warfarin is contraindicated; adjusted-dose heparin is recommended by published American and European guidelines. Even so, one small study suggests that this may be inadequate. Topical antifibrinolytic agents can negate the need to alter systemic anticoagulation during dental surgery.