Prevalence and Predictors of Warfarin Use in Patients With Atrial Fibrillation at Low or Intermediate Risk and Relation to Thromboembolic Events

Background: According to the American College of Cardiology/American Heart Association/European Society of Cardiology guidelines, the choice of aspirin or warfarin to prevent thromboembolic events (TEs) in patients with nonrheumatic atrial fibrillation (AF) should be based on the CHADS(2) score. The purpose of this study was to determine the predictors of warfarin use in patients with AF at low (CHADS(2) = 0) or intermediate (CHADS(2) = 1) risk for TEs. Hypothesis: Warfarin use is low in intermediate- and low-risk patients. Methods: Clinical characteristics of 3086 consecutive patients (mean age, 70 +/- 13 years) with nonrheumatic AF from an academic multispecialty practice were determined between 2006 and 2008 through individual chart review. Patients were identified based on an inpatient or outpatient encounter, in which a billing diagnosis code of AF or atrial flutter (AFl) was recorded. The decision for anticoagulation was at the discretion of the primary care physician or cardiologist. No intervention to guide anticoagulant therapy was made. Results: Warfarin was prescribed in 180/497 low-risk patients (36%), and in 646/938 intermediate-risk patients (69%). Among high-risk patients (CHADS(2) >= 2), warfarin was used in 792/968 patients (82%) with a CHADS(2) = 2, in 343/410 patients (84%) with a CHADS(2) = 3, and in 225/273 patients (82%) with a CHADS(2) >= 4. On multivariate analysis, independent predictors of warfarin use in low-risk patients were nonparoxysmal AF (odds ratio [OR]: 5.02, P < 0.0001) and age between 65 and 74 years (OR: 2.21, P < 0.0001). Among intermediate-risk patients, congestive heart failure (OR: 7.34, P < 0.0001), nonparoxysmal AF (OR: 4.04, P < 0.0001), coronary artery disease (OR: 2.53, P < 0.0001), age between 65 and 74 years (OR: 1.68, P = 0.002), and female gender (OR: 1.69, P = 0.002) were independent predictors of warfarin use. Lack of warfarin use (OR: 4.9, P < 0.001) and female gender (OR: 2.0, P = 0.03) were associated with a higher risk of TEs in intermediate-risk patients. None of the CHADS(2) parameters was predictive of TEs. Warfarin was not associated with reduction in TEs in low-risk patients. Warfarin use did not have a significant effect on bleeding. Conclusions: Although either aspirin or warfarin is recommended to prevent TEs in patients with AF at intermediate risk for TEs, warfarin is preferred in the majority of patients in general practice. Lack of warfarin use is associated with a higher risk of TEs in intermediate-risk patients with AF. The adoption of new oral anticoagulants that have lower risk of major hemorrhage than warfarin for low-or intermediate-risk AF patients remains to be determined.