Abstract 13411: Outcomes Associated With Warfarin Time in Therapeutic Range among Veterans With Nonvalvular Atrial Fibrillation in the US, 2005-2015

Abstract

Introduction: This study evaluated the relationship between quality of warfarin control and clinical outcomes among US veterans with nonvalvular atrial fibrillation (NVAF). Hypothesis: Poor quality of warfarin control (time in therapeutic range (TTR) <65%) is associated with reduced effectiveness and safety. Methods: Using the US Veterans Affairs electronic medical records database, patients with NVAF who newly initiated warfarin from 1/1/2005-12/31/2015 were grouped into two cohorts based on TTR <65% or ≥65%. TTR was computed from international normalized ratio test results comprehensively recorded in the database. Clinical outcomes assessed in the study were stroke/systemic embolism (SE), hemorrhagic stroke, ischemic stroke, and major bleeding, defined based on hospitalization with those conditions as primary diagnosis, as well as all-cause mortality. Patients were followed from warfarin initiation to the first occurrence of an outcome or censoring. For each outcome, unadjusted and adjusted hazard ratios (HR and aHR) between two cohorts were estimated, with the latter from propensity score weighting-adjusted time-varying Cox proportional hazard regression stratified by CHA 2 DS 2 -VAS C score (≥2 or not), controlling for setting of warfarin initiation, baseline patient demographic and clinical characteristics, and use of co-medications. Results: A total of 127,385 patients with NVAF (mean age (SD): 71.3 (9.8) years, 99% male) with a median of 1.4 follow-up years (IQR: 3.3) were included. Mean TTR was 51%. TTR<65% was observed in 65% of patients. Mean CHA 2 DS 2 -VAS C score (SD) was 2.9 (1.5) in low TTR cohort and 2.7 (1.4) in high TTR cohort. Low TTR cohort (with mean TTR as 38%) had significantly higher risk for assessed outcomes compared with high TTR cohort (with mean TTR as 77%) (Table). Conclusions: In the study, the observed quality of warfarin control among US veterans with NVAF was suboptimal and associated with elevated risk of adverse clinical outcomes.