Impact of Time in Therapeutic Range on Adverse Events in Atrial Fibrillation Patients in an Ambulatory Care Setting

Purpose: This study examines the correlation between time-in-therapeutic range (TTR) and anticoagulation-related adverse events (AEs) in patients with atrial fibrillation (Afib) in a pharmacist-managed ambulatory care clinic. Methods: A single-center, retrospective cohort study was conducted at a community hospital-based outpatient anticoagulation clinic to investigate the predictive value of suboptimal TTR percentages for hemorrhagic or thromboembolic events in Afib patients. Eligible participants were aged 18 years or older, diagnosed with Afib, and receiving warfarin therapy as current or past enrollees in the anticoagulation management program. Patients seen at the clinic between April 2017 and June 2023 were included and categorized into 2 groups based on their TTR: TTR < 65% or TTR ≥ 65%. The primary outcome assessed was the TTR achieved by clinic patients. Secondary outcomes included the duration of warfarin therapy, percentage of thromboembolic events, percentage of hemorrhagic events, CHADs-VASc score, HAS-BLED score, and reasons documented for suboptimal TTR. Results: A total of 193 patients were included, with an average TTR of 66.17%. Baseline characteristics were similar between groups. Five patients in the TTR < 65% group and 3 in the TTR ≥ 65% group (P = .391) experienced thromboembolic events; 19 and 15 patients (P = .291) experienced hemorrhagic events, respectively. Those with TTR ≥ 65% had longer warfarin durations and lower HAS-BLED scores. CHADs-VASc scores were comparable. Main reasons for suboptimal TTR included drug-drug interactions, missed warfarin doses, dietary vitamin K intake changes, held warfarin doses, and incorrect warfarin dosing. Conclusion: This study found that at an outpatient pharmacist-managed anticoagulation clinic, the average TTR for atrial fibrillation patients with an INR goal range of 2 to 3 was greater than 65%. Additionally, there were no differences in bleeding or stroke events for patients whose TTR < 65% when compared to those patients whose TTR was  ≥ 65%.