Optimal oral anticoagulant intensity to prevent secondary ischemic and hemorrhagic events in patients after infrainguinal bypass graft surgery

Objectives: The purpose of this study war; to determine the optimal intensi ty of oral anticoagulation in patients who participated in a randomized tri al of oral anticoagulants or aspirin after infrainguinal bypass graft surge ry Methods: The distribution of patient-time spent in international normalized ratio (INR) classes of 0.5 INR unit was calculated assuming a linear chang e between successive measurements. INR-specific incidence rates of ischemic and hemorrhagic events were calculated as the ratio of the number of event s at a certain INR category and the total patient-time spent in that class. The relationship between INR class and event rates was quantified by rate ratios calculated in a Poisson regression model. Results: In 1326 patients (mean age, 69 gears) 41,928 INR measurements were recorded in 1698 patient-years. Patients spent 50% of the total time withi n th(: target range of 3.0 to 4.5 INR Most of the patient-time (60%) was sp ent between 2.5 and 3.5 INR For each increasing class of 0.5 INR, the incid ence of ischemic events (n = 154, INR data. on event available in 49%) decr eased by a factor of 0.97 (95% CI, 0.87-1.08). The incidence of major bleed ing (n = 123, INR data on event available in 65%) increased significantly b y a factor of 1.27 (95% CI, 1.19-1.34) for each increasing 0.5 INR category The optimal target range was 3.0 to 4.0 INR, with an incidence of 3.8 even ts (0.9 ischemic and 2.9 hemorrhagic) per 100 patient-years. Conclusions: The target range of 3.0 to 4.0 INR is the optimal range of ach ieved anticoagulation intensity and is safe for the prevention of ischemic events in patients after infrainguinal bypass graft surgery.