Atrial fibrillation (AF) patients have a five-fold increase in the risk of stroke; however, older women diagnosed with AF may fare worse than men, despite warfarin use, according to a study published in the May 9 issue of the Journal of the American Medical Association.

“Sex-based differences related to AF have been identified, the most concerning being that women with AF have an increased risk for cardiovascular events, including stroke,” wrote Meytal Avgil Tsadok, PhD, of McGill University Health Center in Montreal, and colleagues. “Previous studies have indicated that the annualized rate of stroke is 3 percent in women compared with 1.6 percent in men.”

To better understand these previously reported sex-based differences in AF patients and evaluate warfarin use trends, Tsadok et al conducted a population-based study of AF patients age 65 years or older who were recently diagnosed with AF in Quebec between 1998 and 2007. The authors used risk of stroke as the study's primary endpoint.

The study enrolled 39,398 men and 44,115 women. Of this cohort, 74.2 percent of women were over the age of 75 compared with 61.4 percent of men.

The researchers reported women to have higher CHADS2 scores, an older age, prior stroke and transient ischemic attack when compared with men. However, men had a greater prevalence of heart failure and diabetes when compared with women.

Thirty days after hospital discharge 58.2 percent of men and 60.6 percent of women filled warfarin prescriptions. While women were more likely than men to fill prescriptions for the drug, the researchers reported adherence to warfarin to be good in both sexes.

Stroke incidence rates were reported to be 2.02 per 100 person-years in women and 1.61 per 100 person years in men. Crude stroke rates were also reportedly higher in women when compared with men, 5.8 percent vs. 4.3 percent, respectively. The authors said that these differences in males and females were mainly in the population of patients who were 75 years or older.

“A history of stroke was the strongest independent risk factor for stroke,” the authors wrote.

“These results suggest that current anticoagulant therapy to prevent stroke might not be sufficient for older women, and new strategies are needed to further reduce stroke risk in women with AF,” the authors wrote. Previous studies like the Framingham Heart Study, SPAF and SPORTIF have also found stroke rates to be higher in women with AF. Some studies have shown women to have a 40 percent to 70 percent increased risk of stroke compared with men. These differences were seen whether or not patients received anticoagulants.

However, the researchers called previously reported discrepancies outlining warfarin treatment between the sexes “inconsistent.” While some studied have alluded to the fact that women may be less likely to receive warfarin compared with men, others have concluded that use among the two sexes was similar.

“In our current study, we found that women had a higher chance of filling a prescription for warfarin; therefore, it appears unlikely that differences in warfarin prescription between the sexes are the main explanation for the higher stroke rates in women,” the authors wrote.

“It is not yet known why women with AF are more susceptible to stroke,” they added. They said that more studies are necessary to evaluate this further. The authors speculated that the increased risk of stroke in women could be associated with physiology, vascular biology, and genetic factors or hormonal differences between men and women.

“Clinicians should be aware of the elevated stroke risk in older women with AF, and new strategies should be applied to effectively prevent stroke equally in men and women,” the authors summed.