Warfarin use in atrial fibrillation patients at low risk for stroke: analysis of the Michigan Anticoagulation Quality Improvement Initiative (MAQI²)

To more accurately quantify the proportion of anticoagulated patients with atrial fibrillation (AF) that may be inappropriately treated with warfarin for stroke prevention. Patients with AF have an increased risk of stroke, which is lowered by the use of warfarin. However there is likely more potential harm than benefit in patients that do not have additional stroke risk factors. Studies have described overuse of warfarin for stroke prophylaxis in lowest risk patients. However, many of those studies did not assess for electrical cardioversion (ECV) or radiofrequency ablation (RFA) as indications for warfarin therapy. Data from 1852 non-valvular AF patients treated with warfarin between October 2009 and October 2011 at seven anticoagulation centers participating in the Michigan Anticoagulation Quality Improvement Initiative registry were analyzed. Low risk AF patients were risk stratified using the CHADS₂ scoring systems, with a score of zero representing lowest risk. 193 (10.4 %) of AF patients receiving warfarin were identified as having the lowest risk of stroke by the CHADS₂ score. Of the patients with CHADS₂ = 0, 130 (67.4 %) had undergone a recent ECV and/or RFA. Of all AF patients, only 63 (3.4 %) had a CHADS₂ score of 0 and no recent ECV or RFA. The vast majority of AF patients receiving anticoagulation in this multi-center registry are doing so in accordance with national and international guidelines. In contrast to prior population-based studies, very few low risk patients are receiving inappropriate warfarin therapy for stroke prophylaxis in AF, when procedure-based indications are also considered.