Abstract 325: Paradoxical Relationship Between Bleeding Risk, Stroke Risk, and Time in Therapeutic Range for Atrial Fibrillation Patients on Warfarin: Data from ORBIT-AF

Abstract

Objective: Time in the therapeutic range (TTR) of INR 2.0-3.0 is an important measurement of warfarin anticoagulation quality. There are few reports on TTR in United States (US) clinical practice. Methods: Using the US ORBIT AF registry, we analyzed TTR for patients on warfarin with at least 5 recorded INR measurements. The Rosendaal method of linear interpolation was used between each pair of measured INR values. Patients were stratified into quartiles based on TTR. Results: We studied 5,451 patients treated at 169 US sites with 48% of patients being followed at an anticoagulation clinic. Patients had a median age of 76 years [interquartile range (IQR) 68-82 years] and median follow-up was 18.9 months [IQR 12.7-23.3 months], and patients were 42% women. The median number of INR draws was 21 [IQR 12-30]. Patients had an overall median TTR of 68% [IQR 52-80%]. The median TTR by quartile was 40%, 60%, 73%, and 87%. Patients were more likely to be subtherapeutic (median time of 17%) than supratherapeutic (median time of 10%). Patients age 61-80 years and those with a college education had the highest TTRs. Patients with their INR followed at an anticoagulation clinic were more likely to be in the highest TTR quartile than in the lowest (27% vs 23%, p=0.0002). Patients with worsening renal function and higher risk for bleeding (ATRIA) or stroke (CHADS2 score) had lower TTR (p<0.0001 for all) (Figure). Conclusions: In US clinical practices, warfarin patients have therapeutic INR levels about 2/3 of the time. Those at highest risk for stroke and bleeding paradoxically were the least likely to be in the therapeutic range.