Warfarin may fail women with atrial fibrillation
MedWire News: The risk for stroke in elderly patients with atrial fibrillation (AF) is higher in women than men, irrespective of whether they are using warfarin, show findings published in JAMA.
"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," say Louise Pilote (McGill University Health Center, Montreal, Quebec, Canada) and co-workers.
The 44,115 female AF patients in their study had a crude stroke rate of 2.02 per 100 person-years, while the 39,398 male patients had a rate of 1.61 per 100 person-years, which was significantly lower.
The gender differences in stroke risk were not caused by less aggressive treatment in women than men, or lower treatment adherence. In all, 60.6% of women and 58.2% of men were prescribed warfarin, women filled slightly but significantly more warfarin prescriptions than men did, and both genders had good treatment adherence.
However, the researchers were unable to judge the quality of anticoagulation, as the administrative data used for the study did not contain international normalized ratios.
Women had a higher baseline stroke risk than men, with CHADS2 scores of 1.99 versus 1.74. However, the effect of gender on stroke risk persisted after accounting for CHADS2 scores and other confounders.
The gender difference was most marked among patients aged at least 75 years, with rates of 2.38 versus 1.95 per 100 person-years in women and men, and age significantly modified the effect of gender on stroke risk in interaction analysis.
This indicates that women older than 75 years represent a specific population with increased stroke risk, say Pilote et al. They point out that increasing life expectancy, particularly in women, means that the burden of stroke will fall predominantly on this subgroup, and that "the effectiveness of novel anticoagulants in this population in real-world practice will need to be closely monitored."
However, they note that warfarin will likely remain in use, given the scarcity of data for novel anticoagulants in elderly women and their current high expense.
"Therefore, the results from our current study on warfarin treatment in real-world practice has essential value, because they emphasize patients' sex as a major risk factor for stroke within the currently accessible and existing treatment protocols," conclude the researchers.
By Eleanor McDermid