Patients with atrial fibrillation (AF) have a fivefold higher risk of stroke compared with the general population, and women, particularly those over the age of 75, are at greater risk than men in the same age group. Although the reasons for this have remained unclear, one theory that has been put forward is the undertreatment of female patients with the oral anticoagulant warfarin. A recent study, however, appears to refute that explanation.

Researchers conducted a population-based cohort study of patients ages 65 years and older admitted to a hospital from 1998 to 2007 in Quebec, Canada, with recently diagnosed AF. They found that women had a higher risk of stroke than men even after adjusting for baseline comorbid conditions, CHADS₂ (congestive heart failure, hypertension, age 75 years or older, diabetes mellitus, prior stroke or transient ischemic attack) score, and warfarin treatment. Contrary to expectations, more women in the study filled warfarin prescriptions than men, and both sexes adhered well to their treatment.

Although the study doesn't answer the question of why elderly women are at greater risk for stroke, it does make clear that the risk exists even when the standard preventive drug treatment is used. Theories to explain the disparity that still require study include differences in physiologic factors, such as uncontrolled hypertension, vascular biology, genetics, and hormonal makeup, and psychosocial factors. It's imperative for clinicians to be aware that their elderly female patients are at increased risk so that new treatment strategies can be explored and employed. "Elderly women with AF may need to be targeted for more effective stroke prevention therapy," the authors write.-Laura Wallis

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