Optimal level of oral anticoagulant therapy for the prevention of arterial thrombosis in patients with mechanical heart valve prostheses, atrial fibrillation, or myocardial infarction: a prospective study of 4202 patients.

BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSION: 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.

Risks of oral anticoagulant therapy with increasing age.

BACKGROUND: Oral anticoagulation in the elderly is a dilemma. Although many elderly patients have strict indications for treatment with coumarin derivatives, the tendency toward an increased bleeding risk with age is a matter of concern. We investigated the risk of hemorrhage and thromboembolism according to age in patients who were treated with oral anticoagulants in the routine setting of an anticoagulation clinic. METHODS: All patients of the Leiden Anticoagulation Clinic (Leiden, the Netherlands) who were treated because of mechanical heart valve prostheses (target, international normalized ratio [INR] of 3.5), atrial fibrillation (target, INR of 3.0), or after a myocardial infarction (target, INR of 3.0) between 1994 and 1998 were included in the study and grouped by age at the start of follow-up. We calculated incidence rates of major hemorrhage and thromboembolism per age group. RESULTS: We included 4202 patients: 842 patients younger than 60 years; 1200 patients aged between 60 and 70 years; 1464 patients aged between 71 and 80 years; and 696 patients older than 80 years. The incidence rate of major hemorrhage rose gradually with age from 1.5 per 100 patient-years for patients younger than 60 years to 4.2 per 100 patient-years for patients older than 80 years, yielding a hazard ratio of 2.7 (95% confidence interval, 1.7-4.4). The incidence rate of major thromboembolism rose from 1.0 per 100 patient-years for patients younger than 60 years to 2.4 per 100 patient-years for patients older than 80 years (hazard ratio, 2.2; 95% confidence interval, 1.2-4.2). CONCLUSIONS: The incidence of both bleeding and thromboembolic events increases sharply with advanced age. Because higher thromboembolic risk with age often makes it unfeasible to withhold oral anticoagulation from elderly patients, future studies should focus on ways to lower the bleeding risk.