Oral anticoagulant therapy is effective for the prevention of arterial thromboembolism in various patient groups. The increased risk of hemorrhage remains the major drawback to this therapy and is associated with the intensity of anticoagulation. Finding the optimal intensity at which the overall incidence rate of both bleeding and thromboembolic events is minimized represents a way to improve the safety of oral anticoagulant treatment.
We evaluated all patients visiting the Leiden Anticoagulation Clinic with mechanical heart valve prostheses, atrial fibrillation, or myocardial infarction from 1994 to 1998. Untoward events were major thromboembolism and major hemorrhage. We calculated intensity-specific incidence rates of untoward events to assess the optimal intensity per indication of treatment. We enrolled 4202 patients for a total of 7788 patient-years.
A total of 3226 hospital admissions were reported, 306 owing to an untoward event. Incidence rates of untoward events were around 4% per year for all indications: 4.3 (95% confidence interval [CI], 3.1-5.6) for patients with mechanical heart valve prostheses, 4.3 (95% CI, 3.7-5.1) for patients with atrial fibrillation, and 3.6 per year (95% CI, 3.0-4.4) for patients treated after a myocardial infarction. The optimal intensity of anticoagulation for patients with mechanical heart valve prostheses was an international normalized ratio (INR) of 2.5 to 2.9; for patients with atrial fibrillation, an INR of 3.0 to 3.4; and for patients after myocardial infarction, an INR of 3.5 to 3.9.
Our study suggests target INRs of 3.0 for patients with mechanical heart valve prostheses and atrial fibrillation and 3.5 after myocardial infarction as a starting point in future clinical trials.