The Net Clinical Benefit of Warfarin Anticoagulation in Atrial Fibrillation

Potential Conflicts of Interest: None disclosed.

TO THE EDITOR:

Current guidelines from the American College of Cardiology/American Heart Association recommend that warfarin be given to patients with atrial fibrillation on the basis of stroke risk. This strategy maximizes stroke reduction only if the effect of warfarin is uniform across all risk factors. Singer and colleagues (1) present data that suggest otherwise. Their subgroup analysis found that men and women with atrial fibrillation have markedly different relative risk reductions when treated with warfarin (adjusted relative risk reduction, about 34% in men vs. 55% in women). Formal testing for treatment by covariate interaction (not reported by the authors) might confirm that the benefit of warfarin varies substantially in different subgroups of patients. Although female sex is not currently considered an indication for warfarin, the data suggest that certain patient subgroups may reap greater benefit from warfarin therapy than others. The presence of hypertension supports the use of warfarin according to current guidelines, but subgroup analysis shows little, if any, additional benefit in patients with hypertension compared with those without hypertension (absolute stroke reduction with warfarin, 1.11 per 100 person-years in patients with hypertension vs. 0.95 per 100 person-years in patients without hypertension). An optimum strategy for stroke reduction in patients with atrial fibrillation should be based not on factors that imply a high risk for stroke (as recommended by current guidelines), but rather on factors that imply a greater benefit of treatment.