Warfarin use among ambulatory patients with nonvalvular atrial fibrillation: The AnTicoagulation and Risk Factors in Atrial Fibrillation (ATRIA) study

Background: Warfarin dramatically reduces the risk for ischemic stroke in n onvalvular atrial fibrillation, but its use among ambulatory patients with atrial fibrillation has not been widely studied. Objective: To assess the rates and predictors of warfarin use in ambulatory patients with nonvalvular atrial fibrillation. Design: Cross-sectional study. Setting: Large health maintenance organization. Patients: 13428 patients with a confirmed ambulatory diagnosis of nonvalvul ar atrial fibrillation and known warfarin status between 1 July 1996 and 31 December 1997. Measurements: Data from automated pharmacy, laboratory, and clinical-admini strative databases were used to determine the prevalence and determinants o f warfarin use in the 3 months before or after the identified diagnosis of atrial fibrillation. Results: Of 11082 patients with nonvalvular atrial fibrillation and no know n contraindications, 55% received warfarin. Warfarin use was substantially lower in patients who were younger than 55 years of age (44.3%) and those w ho were 85 years of age or older (35.4%). Only 59.3% of patients with one o r more risk factors for stroke and no contraindications were receiving warf arin. Among a subset of "ideal" candidates to receive warfarin (persons 65 to 74 years of age who had no contraindications and had previous stroke, hy pertension, or both), 62.1% had evidence of warfarin use. Among our entire cohort, the strongest predictors of receiving warfarin were previous stroke (adjusted odds ratio, 2.55 [95% CI, 2.23 to 2.92]), heart failure (odds ra tio, 1.63 [CI, 1.51 to 1.77]), previous intracranial hemorrhage (odds ratio , 0.33 [CI, 0.21 to 0.52]), age 85 years or older (odds ratio, 0.35 [CI, 0. 31 to 0.40]), and previous gastrointestinal hemorrhage (odds ratio, 0.47 [C I, 0.40 to 0.57]). Conclusions: In a large, contemporary cohort of ambulatory patients with at rial fibrillation who received care within a health maintenance organizatio n, warfarin use was considerably higher than in other reported studies. Alt hough the reasons why physicians did not prescribe warfarin could not be el ucidated, many apparently eligible patients with atrial fibrillation and at least one additional risk factor for stroke, especially hypertension, did not receive anticoagulation. Interventions are needed to increase the use o f warfarin for stroke prevention among appropriate candidates.