Impact of Baseline Stroke Risk and Bleeding Risk on Warfarin International Normalized Ratio Control in Atrial Fibrillation (from the TREAT-AF Study)

Warfarin prevents stroke and prolongs survival in patients with atrial fibrillation and flutter (AF, collectively) but can cause hemorrhage. The time in international normalized ratio (INR) therapeutic range (TTR) mediates stroke reduction and bleeding risk. This study sought to determine the relation between baseline stroke, bleeding risk, and TTR. Using data from The Retrospective Evaluation and Assessment of Therapies in Atrial Fibrillation (TREAT-AF) retrospective cohort study, national Veterans Health Administration records were used to identify patients with newly diagnosed AF from 2003 to 2012 and subsequent initiation of warfarin. Baseline stroke and bleeding risk was determined by calculating CHA2DS2-VASc and HAS-BLED scores, respectively. Main outcomes were first-year and long-term TTR and INR monitoring rate. In 167,190 patients, the proportion of patients with TTR (>65%) decreased across increasing strata of CHA2DS2-VASc and HAS-BLED. After covariate adjustment, odds of achieving TTR >65% were significantly associated with high CHA2DS2-VASc or HAS-BLED score. INR monitoring rate was similar across risk strata. In conclusion, increased baseline stroke and bleeding risk is associated with poor INR control, despite similar rates of INR monitoring. These findings may paradoxically limit warfarin's efficacy and safety in high-risk patients and may explain observed increased bleeding and stroke rates in this cohort.