To the Editor.
—Dr Gage and colleagues1 presented a thorough and well-done analysis of warfarin vs aspirin for nonvalvular atrial fibrillation. However, we disagree with their conclusions for low-risk patients. The authors conclude, "In 65-year-old patients with NVAF [nonvalvular atrial fibrillation] but no other risk factors for stroke, prescribing warfarin instead of aspirin would affect quality-adjusted survival minimally but increase costs significantly." They argue that, in these patients, "prescribing warfarin... is prohibitively expensive relative to other health interventions." A close examination of their results and data from the randomized NVAF trials suggests that this conclusion is questionable.The marginal effectiveness of warfarin vs aspirin in the group at low risk for stroke was 0.01 quality-adjusted life year (QALY). A marginal effectiveness value in this range is not robust and is generally considered a clinical "toss-up."2 Because the cost-effectiveness ratio is calculated by placing the effectiveness value in the
Kan BD, Katz DA. Cost-effectiveness of Stroke Prophylaxis for Nonvalvular Atrial Fibrillation. JAMA. 1996;275(12):909. doi:10.1001/jama.1996.03530360019023
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