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. 2012 May 30:344:e3522.
doi: 10.1136/bmj.e3522.

Assessment of female sex as a risk factor in atrial fibrillation in Sweden: nationwide retrospective cohort study

Leif Friberg  1 , Lina Benson, Mårten Rosenqvist, Gregory Y H Lip
Affiliations

Assessment of female sex as a risk factor in atrial fibrillation in Sweden: nationwide retrospective cohort study

Leif Friberg et al. BMJ. .

Abstract

Objective: To determine whether women with atrial fibrillation have a higher risk of stroke than men.

Design: Nationwide retrospective cohort study.

Setting: Patients with a diagnosis of atrial fibrillation in the Swedish hospital discharge register between 1 July 2005 and 31 December 2008. Information about drug treatment taken from the Swedish drug register.

Participants: 100,802 patients with atrial fibrillation at any Swedish hospital or hospital affiliated outpatient clinic with a total follow-up of 139,504 years at risk (median 1.2 years). We excluded patients with warfarin at baseline, mitral stenosis, previous valvular surgery, or who died within 14 days from baseline.

Main outcome measure: Incidence of ischaemic stroke.

Results: Ischaemic strokes were more common in women than in men (6.2% v 4.2% per year, P<0.0001). The univariable hazard ratio for women compared with men was 1.47 (95% confidence 1.40 to 1.54), indicating a 47% higher incidence of ischaemic stroke in women than in men. Stratification according to the CHADS(2) scheme showed increased stroke rates for women in all strata. After multivariable adjustment for 35 cofactors for stroke, an increased risk of stroke in women remained (1.18, 1.12 to 1.24). Among patients with "lone atrial fibrillation" (age <65 years and no vascular disease), the annual stroke rate tended to be higher in women than in men, although this difference was not significant (0.7% v 0.5%, P=0.09). When low risk patients with CHADS(2) scores of 0-1 were stratified according to their CHA(2)DS(2)-VASc scores, women did not have higher stroke incidence than men at CHA(2)DS(2)-VASc scores of 2 or less.

Conclusion: 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 anticoagulation treatment. However, women younger than 65 years and without other risk factors have a low risk for stroke, and do not need anticoagulant treatment.

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Conflict of interest statement

Competing interests: All authors have completed the Unified Competing Interest form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: the study received support from the Swedish Heart and Lung Foundation, Stockholm County Council and Board of Benevolence of the Swedish Order of Freemasons for the submitted work; LF is a consultant to Sanofi-Aventis, Boehringer-Ingelheim, and Bristol-Myers Squibb; LB has nothing to declare; MR is a consultant to Sanofi-Aventis and Nycomed, Sweden, and has been national coordinator for the RECORD, REALISE, and ARISTOTLE study; GYHL has received funding for research, educational symposia, consultancy, and lecturing from different manufacturers of drugs used for the treatment of atrial fibrillation and thrombosis; no other relationships or activities that could appear to have influenced the submitted work.

Figures

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Fig 1 Unadjusted incidence of stroke in relation to age. Cox regression with main and interaction terms for sex and age group
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Fig 2 Stroke rate in relation to CHADS2 score
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Fig 3 Stroke rate in patients with CHADS2 score 0-1 in relation to CHA2DS2-VASc score
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Fig 4 Risk of ischaemic stroke in women compared with men in relation to risk factors in CHADS2 and CHA2DS2-VASc schemes. All interactions modelled within the multivariable primary Cox regression, except CHADS2 (in which only sex and CHADS2 were included in the model). Interaction between sex and age was significant when age was included as a continuous variable in the model
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