Women with irregular heart rhythm (known as atrial fibrillation) have a moderately increased risk of stroke compared with men, suggesting that female sex should be considered when making decisions about anti-clotting treatment, finds a study published on BMJ today.
Several studies have suggested that women with atrial fibrillation are at higher risk for ischaemic stroke (caused by an interruption of the blood supply to the brain) than men, but other studies found no such difference.
If few or no other stroke risk factors exist, doctors need to know whether female sex is important in making decisions about anti-clotting treatment.
So researchers based at the Karolinska Institute in Sweden and the University of Birmingham in the UK decided to investigate whether women with atrial fibrillation have higher risk of stroke than men.
The study involved over 100,000 patients with a diagnosis of atrial fibrillation at any Swedish hospital or hospital affiliated outpatient clinic. Participants were tracked for an average of 1.2 years (a total of 139,504 years at risk - a term that adds up the time each person in the study was at risk).
In this period there were 7,221 patients who had thromboembolic strokes due to clots, while ischaemic strokes (due to lack of blood supply to the brain) were more common: there were 4,264 strokes during 69,005 years at risk in women, and 2,957 strokes during 70,594 years at risk in men, corresponding to overall annual stroke rates of 6.2% and 4.2% respectively.
Even after adjusting for 35 factors that could have influenced the results, women still had an 18% higher risk of stroke than men. The absolute risks were low for both sexes, however: the annual rate of stroke was 1.9% for women aged 65-74 and was lower for men.
Furthermore, women younger than 65 years and without any other risk factors (apart from atrial fibrillation) did not have a higher risk of stroke than men. There were 31 strokes in women (during 4,626 years at risk) and 53 strokes in men (during 11,677) and this difference was not statistically significant.
The authors conclude that women with atrial fibrillation have a moderately increased risk of stroke compared with men, and thus, female sex should be considered when making decisions about anti-clotting treatment. They add: "In borderline situations, in which a decision about whether to give anticoagulation treatment weighs in the balance, we suggest that female sex should probably tip the scale towards initiating treatment."
However, they say that women younger than 65 years and without other risk factors have a low risk for stroke, and do not need anticoagulation treatment.
In an accompanying editorial, Professor Eva Prescott from the University Hospital, Bispebjerg in Denmark says, despite some inherent weaknesses, this and other registry studies provide reassurance to clinicians. "The registry data confirm overall that women are at higher risk of stroke than men, but when differences in age and risk factor profile are taken into account the excess risk is low," she writes. "More importantly, the absolute risk in younger women with no other risk factors is low and does not merit treatment with oral anticoagulants."