Can patients at elevated risk of stroke treated with anticoagulants be further risk stratified?

Patients with atrial fibrillation have a varied risk of stroke, depending on age and comorbid conditions. The objective of this study was to assess the predictive value of stroke risk classification schemes and to identify patients with atrial fibrillation who are at substantial risk of stroke despite optimal anticoagulant therapy.

Seven recognized classification schemes-the American College of Chest Physicians 2001, American College of Chest Physicians 2004, Stroke Prevention in Atrial Fibrillation (SPAF), Atrial Fibrillation Investigators, Framingham, van Walraven, and CHADS(2)-were compared for their ability to predict ischemic stroke in patients receiving anticoagulant therapy. Data came from the Stroke Prevention using an ORal Thrombin Inhibitor in atrial Fibrillation III and V trials, which compared the efficacy of adjusted-dose warfarin and the direct thrombin inhibitor ximelagatran (36 mg twice daily) in preventing thromboembolic events in 7329 patients with chronic or paroxysmal nonvalvular atrial fibrillation who were at moderate or high risk of ischemic stroke. The main outcome measure was ischemic stroke, as determined by a central event adjudication committee.

During 11 245 patient-years of follow-up, 159 patients had an ischemic stroke (1.4%/year). As indicated by c statistics and hazard ratios, 3 of the classification schemes predicted stroke significantly better than chance: Framingham (c=0.64), CHADS(2) (c=0.65), and SPAF (c=0.61).

In a large cohort of atrial fibrillation patients at moderate or high risk of ischemic stroke treated with warfarin or ximelagatran, the CHADS(2), SPAF, and Framingham schemes had greater predictive accuracy than chance. This predictive ability may allow clinicians to target high-risk patients for more aggressive intervention.