Older women who have been diagnosed with an irregular heartbeat are at higher risk of stroke than men. A new study led by the Research Institute of the McGill University Health Centre (RI MUHC) shows that warfarin, the most common anticoagulant therapy used to prevent stroke in patients with Atrial fibrillation (AF) may not be as effective in women, 75 years or older, as in men. The results of the study are published in the Journal of the American Medical Association (JAMA).

"Our results suggest that elderly women with AF may need to be targeted for more effective stroke prevention therapy," says Dr. Louise Pilote, corresponding author of the study, researcher in epidemiology at the RI MUHC and Professor at McGill University's Department of Medicine. "Knowing the stroke risk is higher in women is something that both physicians and patients should be focusing on."

Atrial fibrillation (AF) affects approximately 350,000 Canadians and is the most common cardiac arrhythmia, a condition involving an irregular heart rhythm. Generally, the risk of developing AF increases with age and with other risk factors such as diabetes, high blood pressure, and underlying heart disease. People with AF have a risk of stroke that is 5 times greater than those in the general population

"We found that women had a 14 % higher risk of stroke then men," says Dr. Meytal Avgil Tsadok, first author of the study and Post-Doctoral Fellow funded by the Canadian Institutes of Health Research (CIHR) in the Division of Clinical Epidemiology at the MUHC. "Even though the adherence to warfarin was the same in both sexes the follow up and the level of anticoagulation may not be as high in women compared to men. Other reasons could be a combination of uncontrolled hypertension and some other vascular factors."

Researchers compared the incidence of stroke and warfarin use among 39,398 men and 44,115 women with AF in Quebec between 1998 and 2007. They used administrative data with linkage between hospital discharge, physicians and prescriptions drug claims databases.

"Physicians should put more emphasis on female sex as a risk factor in deciding to start anti coagulation treatment for stroke," says Dr. Pilote who is also director of the Division of General Internal Medicine at McGill and the MUHC. "Because study results in men do not always apply to women, we need women to participate in our studies in order to develop new strategies to effectively prevent stroke equally in both sexes."