Poor Time in Therapeutic Range Control is Associated with Adverse Clinical Outcomes in Patients with Non-Valvular Atrial Fibrillation: A Report from the Nationwide COOL-AF Registry

Background: Warfarin remains the most commonly used oral anticoagulant (OAC) in Thailand for stroke prevention among patients with non-valvular atrial fibrillation (NVAF). The aim of this study was to investigate the relationship between time in therapeutic range (TTR) after warfarin initiation and clinical outcomes of NVAF. Methods: TTR was calculated by the Rosendaal method from international normalized ratio (INR) data acquired from a nationwide NVAF registry in Thailand. Patients were followed-up every six months. The association between TTR and clinical outcomes was analyzed. Results: There was a total of 2233 patients from 27 hospitals. The average age was 68.4 +/- 10.6 years. The average TTR was 53.56 +/- 26.37%. Rates of ischemic stroke/TIA, major bleeding, ICH, and death were 1.33, 2.48, 0.76, and 3.3 per 100 person-years, respectively. When patients with a TTR < 65% were compared with those with TTR >= 65%, the adjusted hazard ratios (aHR) for the increased risks of ischemic stroke/TIA, major bleeding, ICH, and death were 3.07, 1.90, 2.34, and 2.11, respectively. Conclusion: Poor TTR control is associated with adverse clinical outcomes in patients with NVAF who were on warfarin. Efforts to ensure good TTR (>= 65%) after initiation of warfarin are mandatory to minimize the risk of adverse clinical outcomes.