Evaluation of coagulant activity after mechanical heart valve replacement

Long-term oral anticoagulant therapy is required for recipients of mechanical heart valves. In our hospital, the international normalized ratio of prothrombin time (PT-INR) has been set in the range 1.5-2.5 since October 2001. To evaluate whether coagulant activity is fully suppressed by this target range, coagulant activity was evaluated by measuring thrombin-antithrombin III complex (TAT) levels and valve-related complications were investigated retrospectively. Two hundred twenty-three patients who underwent mechanical valve replacement were enrolled in this study. PT-INR and TAT were measured at our outpatient clinic in March 2005 and valve-related complications since October 2001, when we started to control PT-INR in the range 1.5-2.5, were investigated. Under adequate warfarin control, there was no significant correlation between PT-INR and TAT, however nine patients who exhibited a PT-INR of less than 2.0 had high levels of TAT. And in atrial fibrillation (AF) patients after mitral valve replacement (MVR), the level of TAT was significantly high compared with sinus rhythm patients after atrial valve replacement. Valve-related complications were bleeding events at 2.75% per patient year and thromboembolism at 0.32% per patient year. Attention to complications of thromboembolism is necessary when the PT-INR is less than 2.0, especially in AF patients after MVR and in those with a thrombotic past history or high levels of TAT. The monitoring of TAT is useful in detecting potential coagulation factors and to determine the therapeutic range of warfarin that can normalize coagulant activity.