Are atrial fibrillation patients receiving warfarin in accordance with stroke risk?

Clinical guidelines for the management of atrial fibrillation and atrial flutter provide recommendations for anticoagulation based on patients' overall risk of stroke. To determine the real-world compliance of physicians with these recommendations, we conducted a retrospective cohort study examining the utilization of warfarin in atrial fibrillation/flutter patients by stroke risk level.

Patients with a qualifying atrial fibrillation/flutter diagnosis during > or =18 months' continuous enrollment between January 2003 and September 2007, and with > or =6 months' eligibility after the first atrial fibrillation/flutter diagnosis, were identified from the US MarketScan database (Thomson Reuters, New York, NY). Warfarin use within 30 days of the first diagnosis was assessed according to stroke risk, estimated using the Congestive heart failure, Hypertension, Age >75 years, Diabetes, Stroke (CHADS(2)) score.

Of 171,393 patients included in the analysis, 20.0% had a CHADS(2) score of 0 (low risk), 61.6% a score of 1-2 (moderate risk), and 18.4% a score of 3-6 (high risk). Warfarin, recommended for high stroke-risk patients, was given to only 42.1% of those with a CHADS(2) score of 3-6. A similar percentage of patients with moderate (43.5%) or low stroke risk (40.1%) received warfarin. Only 29.6% of high-risk, 33.3% of moderate-risk, and 34.1% of low-risk patients who were started on warfarin received uninterrupted therapy for 6 months following their initial prescription.

These data suggest that guideline recommendations that anticoagulation should be provided in accordance with stroke risk in atrial fibrillation patients are not routinely followed in clinical practice. The causes and clinical implications of under-utilization of anticoagulation in atrial fibrillation patients with high stroke risk warrant further study.