By Emma Ross
The Associated Press

VIENNA, Austria - An irregular heartbeat is more common among men but much more hazardous when it occurs in women, according to the first major study to examine gender differences in the ailment.

The study found that women who have atrial fibrillation were more than four times more likely to suffer a stroke than were men with the disorder.

The findings by scientists at Bispebjerg University Hospital in Copenhagen were presented Monday to the European Society of Cardiology in Vienna.

Atrial fibrillation is the most common type of heart rhythm abnormality. It is estimated to affect up to 2 percent of all people, and up to 14 percent of the elderly.

Symptoms include palpitations, breathlessness and tiredness; the major hazard is an increased risk of stroke. It is about three times more common among men than women.

The study involved 29,310 Danes over age 40 who had never had a stroke. They were followed for about five years. Among them, 166 men and 110 women had atrial fibrillation.

During the study, there were 635 strokes, with 35 of them in people with the irregular heartbeat.

Women with the disorder were nearly eight times more likely to have a stroke than those with a normal heartbeat and four times more likely than men with the disorder. Men with the problem were twice as likely as other men to have a stroke.

Researchers also found women with the disorder were more than twice as likely to die from heart or blood vessel problems than men with an irregular heartbeat. The disorder was far more likely to lead to stroke in women than other factors, such as diabetes or high blood pressure.

The study's leader, Dr. Jens Friberg, said it is unclear why women with irregular heartbeats fare worse than men.

However, he said that since atrial fibrillation is more common in men, it might be that women who develop the problem have sicker hearts.

Dr. Robert Hatala, a professor of the Slovak Cardiovascular Institute in Bratislava, said Friberg's study means that doctors probably need to treat women much more vigorously than they have been.