A new study published in the May 9 issue of JAMA reveals that older women, especially those aged 75+, who receive the anticoagulant therapy warfarin after diagnosis of atrial fibrillation are more likely to suffer a stroke than men.

The researchers explained:

“Atrial fibrillation (AF) is the most common cardiac arrhythmia, accounting for approximately one-third of hospitalizations for cardiac rhythm disturbances. It has been estimated that 2.2 million people in the United States and 4.5 million in the European Union have paroxysmal or persistent AF.

Patients with AF have a five-fold increase in the risk of stroke compared with the general population; therefore, antithrombotic agents are prescribed to reduce this risk. 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.”

According to the researchers, underutilization of oral anticoagulant treatment among women may contribute to this increased risk.

In order to compare usage patterns of warfarin and subsequent stroke incidence, Meytal Avgil Tsadok, Ph.D., of the McGill University Health Center, Montreal and colleagues examined 39,398 men and 44,115 women aged 65+ diagnosed with AF in the province of Quebec, Canada, from 1998-2007.

The researchers used administrative data with linkage between physicians, hospital discharge, and prescription drug claims databases.

According to the authors, the women were older at admission (74.2% were older than 75 years) than men (61.4%). In addition, the women had a higher CHADS2 (congestive heart failure, hypertension, diabetes mellitus, age 75+, prior stroke or transient ischemic attack) score than men.

Furthermore, they found that 60.6% of women were prescribed warfarin compared with 58.2% of men, and that the women were also more likely to have more prescriptions filled for the medication within 30 days post-discharge.

When the team evaluated prescription rates within 1 year after discharge, they found that the proportions of prescriptions filled were slightly increased to 68% in both men and women. Generally, adherence to the treatment was relatively high and comparable in both women and men.

In addition, stroke rates were considerably higher in women (5.8%) than men (4.3%). The difference between sexes was primarily driven by the rates in patients aged 75+.

The researchers explained:

“Furthermore, older women had significantly higher rates of stroke than older men, regardless of warfarin use, and women had higher rates of stroke compared with men, regardless of adherence level.”

After adjusting for various factors, the team found that women were 14% more likely to suffer a stroke than men.

The authors stressed that exactly why women have a higher risk of stroke than men, in such cases, is still unknown.

“The increased risk may be attributable to physiology (such as uncontrolled hypertension), vascular biology, genetic factors, hormonal or thromboembolic factors, or psychosocial factors that differ between men and women. We were not able to identify these factors with our database.”

They concluded:

“Although epidemiologic studies have investigated sex differences in stroke occurrence, little is known about warfarin effectiveness between men and women in the real-world clinical setting.

Our results suggest that elderly women with AF may need to be targeted for more effective stroke prevention therapy. 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.

Written by Christian Nordqvist