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British Medical Journal

Clinical Articles, Featured

Women with AF at higher risk of stroke than men

Women with atrial fibrillation (AF) have a moderately increased risk of stroke compared with men, suggesting that female gender should be considered when making decisions about anti-clotting treatment, according to a study1 by Scandinavian workers (pictured) published recently on bmj.com.

Several studies have suggested that women with AF are at higher risk for ischaemic stroke 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.

Researchers based at the Karolinska Institute in Sweden and the University of Birmingham in the UK investigated 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).

Dr Leif Friberg

Dr Leif Friberg

In this period there were 7,221 patients who had thromboembolic strokes due to clots, while ischaemic strokes 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 AF) 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.

Speaking to BJC Arrhythmia Watch, lead author Dr Leif Friberg said: “Women with atrial fibrillation have an increased risk of stroke compared with men acrross all ages. We found an  excess risk of 18%, which makes female sex as important a risk factor as diabetes (18%) and hypertension (19%)”.

“It is important to consider female sex when decisions are made regarding anticoagulation, but this should not make us overzealous… Women aged <65 years without other risk factors have low absolute risk of stroke, and do not require anticoagulant therapy.”

Professor Eva Prescott

Professor Eva Prescott

The authors conclude that: “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.”

In an accompanying editorial,2 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.”

References

1. Friberg L, Benson L, Rosenqvist M, Lip GHY.  Assessment of female sex as a risk factor in atrial fibrillation in Sweden: nationwide retrospective cohort study. BMJ 2012;344:e3522. doi: 10.1136/bmj.e3522.

2. Prescott E, Sørensen R. Female sex as a risk factor for stroke in atrial fibrillation. BMJ 2012;344:e3789. doi: 10.1136/bmj.e3789.

Published on: June 25, 2012

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