Connolly SJ et al. (2008) Benefit of oral anticoagulant over antiplatelet therapy in atrial fibrillation depends on the quality of international normalized ratio control achieved by centers and countries as measured by time in therapeutic range. Circluation 118: 2029–2037

The efficacy of oral anticoagulation therapy for atrial fibrillation depends on preservation of the international normalized ratio within the established therapeutic range (2.0–3.0). Wide variation in the mean time in therapeutic range (TTR) of oral anticoagulation therapy has been reported, and a low TTR is associated with an increase in adverse events. In a multicenter, multinational study, Connolly et al. evaluated the benefit of oral anticoagulation versus clopidogrel plus aspirin according to the achieved TTR, and determined the minimum TTR required to confer a clinical benefit.

Data from ACTIVE (Atrial fibrillation Clopidogrel Trial with Irbesartan for prevention of Vascular Events) W were used to calculate the TTR of oral anticoagulation compared with that of clopidogrel plus aspirin therapy. The mean TTR for all patients was 63.4% (median 65%); the mean TTR for patients in individual countries ranged from 46% to 78%. Each study centre was assessed in terms of mean TTR and likelihood of a positive response to oral anticoagulation. Patients in centers with a mean TTR >65% benefited from oral anticoagulation therapy, whereas counterparts in centers with a mean TTR <65% experienced no such benefit. Connolly and colleagues suggest that medical centers unable to achieve a TTR >65% should consider treating patients with atrial fibrillation with therapies other than oral anticoagulation, such as antiplatelet therapy.