Older Women Less Likely than Men to Get Warfarin

FOR RELEASE: 4 p.m. EDT, Monday May 14, 2001

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American Heart Association journal report:Older women less likely than men to get warfarin for irregular heartbeat

DALLAS, May 15 -- Elderly women -- those older than 75 -- were half as likely as elderly men to receive the drug warfarin, which treats irregular heartbeats that can increase stroke risk, researchers report in today's Circulation: Journal of the American Heart Association.

"We found that warfarin -- an effective therapy for the prevention of stroke caused by atrial fibrillation -- remains underused, particularly in elderly women," says Karin H. Humphries, D.Sc., lead author of the study. "Gender differences in coronary artery disease have received considerable attention but few studies have dealt with gender differences in arrhythmias."

Atrial fibrillation (AF) is triggered when the electrical impulses that regulate heart rhythm become disorganized, causing the upper chambers of the heart (the atria) to quiver, rather than contract normally. Thus, blood flow in the atria is slower, allowing blood clots to form.

Although changes in heart rhythm caused by AF are not themselves life-threatening, the condition increases the potential for blood clots to form in the circulatory system, thereby heightening the risk of stroke.

AF is the most common sustained cardiac arrhythmia in the general population and its incidence increases with age. Compared with women, men have a higher incidence, however because there are more women than men in the over 75 age group, the absolute number of men and women with AF is about equal, according to Humphries.

To determine if there were gender differences in diagnosis, treatment and outcome of AF, investigators at the Canadian Registry of Atrial Fibrillation centers and the Centre for Health Evaluation and Outcome Sciences (HEOS) in Vancouver, British Columbia, studied 339 women and 560 men who had cases of new-onset atrial fibrillation.

Researchers gathered data on symptoms -- dizziness, fatigue, nausea, chest pain -- and performed standard heart function tests such as electrocardiograms. Women were more likely to be older and to seek medical advice because of symptoms.

Although the overall prevalence of antithrombotic therapy (warfarin or aspirin) did not vary by gender, the choice of therapy did. Women ages 75 and older were 54 percent less likely to receive warfarin, but twice as likely to receive aspirin than were men ages 75 and older.

"Current evidence clearly indicates that warfarin is the most effective medication for preventing strokes in patients with AF and that it offers far greater benefits than aspirin, the most widely used blood-thinning agent," says Humphries, an epidemiologist at HEOS.

To determine if the lower use of warfarin was related to a lower perceived risk of stroke in women, researchers compared warfarin and aspirin use in a subgroup of individuals with one or more stroke risk factors. In this subgroup, men were still more likely to be on warfarin than were women: 44.9 percent of men received warfarin versus 24.5 percent of women.

The study is also the first to show that women are more likely than men to have bleeding problems from taking the drug. Women experienced major bleeds at a rate of 9.2 percent compared to 2.8 percent for men.

Nine of the 10 women who experienced a major bleed were younger than age 75.

"Women receiving warfarin also have a significantly higher risk than men of major bleeding -- meaning either external or internal hemorrhaging that is severe enough to require medical intervention," Humphries adds. "So when warfarin is prescribed for women, special attention is needed in choosing the appropriate dosage and monitoring the anti-clotting effect."

This risk of bleeding should not deter physicians from prescribing warfarin for women, she adds. "The complications resulting from a major bleed, other than one in the brain, are far less serious than the potential complications from a stroke."

Risk factors for AF include existing heart disease, high blood pressure, lung disease and excessive alcohol use. "Not all the causes of AF are amenable to prevention," she says, "but reducing overall risk of heart disease and early detection and control of high blood pressure are important ways of minimizing a person's chances of developing AF."

The researchers were unable to pinpoint specific reasons why female patients have received warfarin less frequently than males in the past. "Since our paper is the first to document a greater likelihood of bleeding in women, it seems unlikely that physicians would have previously factored this into their decision making," Humphries says.

"This finding requires further investigation and implies a need for careful monitoring of anticoagulant treatment in women," says Humphries.

Other researchers participating in the study include Charles R. Kerr, M.D.; Stuart J. Connolly, M.D.; George Klein, M.D.; John A. Boone, M.D.; Martin Green, M.D.; Robert Sheldon, M.D., Ph.D.; Mario Talajic, M.D.; Paul Dorian, M.D.; and David Newman, M.D.

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NR01-1288 (Circ/Humphries)