title: Atrial fibrillation and risk of stroke: a nationwide cohort study.
abstract: OBJECTIVE
  Although the relation between stroke risk factors and stroke in patients with atrial fibrillation (AF) has been extensively examined, only few studies have explored the association of AF and the risk of ischaemic stroke/systemic thromboembolism/transient ischaemic attack (stroke/TE/TIA) in the presence of concomitant stroke risk factors.
  
  
  RESULTS
  From nationwide registries, all persons who turned 50, 60, 70, or 80 from 1997 to 2011 were identified. Persons receiving warfarin were excluded. The absolute risk of stroke/TE/TIA was reported for a 5-year period, as was the absolute risk ratios for AF vs. no AF according to prior stroke and the number of additional risk factors. The study cohort comprised of 3 076 355 persons without AF and 48 189 with AF. For men aged 50 years, with no risk factors, the 5-year risk of stroke was 1.1% (95% confidence interval 1.1-1.1); with AF alone 2.5% (1.8-3.2); with one risk factor and no prior stroke or AF 2.5% (2.3-2.7); and with one factor, no prior stroke and AF 2.9% (1.4-4.3). In men aged 50 years with prior stroke as the only risk factor, 5-year risk was 10.2% (9.1-11.3). In men aged 70 years, the corresponding risks were 4.8% (4.7-4.9), 6.8% (5.7-7.9), 6.6% (6.3-6.8), 8.7 (7.4-9.9), and 19.1% (18.1-20.1), respectively. In women aged 50 years, the risk was of 0.7% (0.7-0.7), 2.1% (0.9-3.2), 1.6% (1.4-1.8), 4.1% (0.6-7.6), and 7.2% (6.3-8.2), respectively, and in women aged 70 years 3.4% (3.3-3.5), 8.2% (7.0-9.5), 4.6% (4.4-4.8), 9.1% (7.5-10.6), and 15.4% (14.5-16.4), respectively.
  
  
  CONCLUSIONS
  Stroke/TE/TIA risk was particularly increased when prior stroke/TE/TIA was present. Atrial fibrillation is associated with an increase in risk of stroke/TE/TIA in the absence of other risk factors but only a moderate increase in risk when other risk factors are present.
authors.affiliation: Aalborg University Hospital, Forskningens Hus, Sdr. Skovvej 15, Aalborg 9000, Denmark christinebenn@hotmail.com.
authors.forename: Christine Benn
authors.initials: CB
authors.lastname: Christiansen
authors.affiliation: Department of Public Health, Section of Biostatistics, University of Copenhagen, Øster Farimagsgade 5, Copenhagen, Denmark.
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Gerds
authors.affiliation: Department of Cardiology, Gentofte Hospital, Niels Andersens Vej 65, Hellerup 2900, Denmark.
authors.forename: Jonas Bjerring
authors.initials: JB
authors.lastname: Olesen
authors.affiliation: Department of Cardiology, Gentofte Hospital, Niels Andersens Vej 65, Hellerup 2900, Denmark.
authors.forename: Søren Lund
authors.initials: SL
authors.lastname: Kristensen
authors.affiliation: Department of Cardiology, Gentofte Hospital, Niels Andersens Vej 65, Hellerup 2900, Denmark.
authors.forename: Morten
authors.initials: M
authors.lastname: Lamberts
authors.affiliation: University of Birmingham Centre for Cardiovascular Sciences, Birmingham City Hospital, Dudley Road, Birmingham B18 7QH, UK.
authors.forename: Gregory Y H
authors.initials: GY
authors.lastname: Lip
authors.affiliation: Department of Public Health, Section of Biostatistics, University of Copenhagen, Øster Farimagsgade 5, Copenhagen, Denmark.|Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, Copenhagen N 2200, Denmark.|National Institute of Public Health, University of Southern Denmark, Øster Farimagsgade 5 A, Copenhagen, Denmark.
authors.forename: Gunnar H
authors.initials: GH
authors.lastname: Gislason
authors.affiliation: Department of Cardiology, Rigshospitalet, Blegdamsvej 9, Copenhagen 2100, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Køber
authors.affiliation: Department of Health Science and Technology, Aalborg University, Fredrik Bajers Vej 7D2, Aalborg DK-9220, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Torp-Pedersen
mesh_terms: D017677:Age Distribution; D000368:Aged; D000369:Aged, 80 and over; D001281:Atrial Fibrillation / Q000150:complications*; D015331:Cohort Studies; D003718:Denmark; D005260:Female; D006801:Humans; D002546:Ischemic Attack, Transient / Q000453:epidemiology* / Q000209:etiology; D008297:Male; D008875:Middle Aged; D012042:Registries; D012307:Risk Factors; D017678:Sex Distribution; D020521:Stroke / Q000453:epidemiology* / Q000209:etiology; D013923:Thromboembolism / Q000453:epidemiology* / Q000209:etiology
keywords: Atrial fibrillation; Epidemiology; Risk factors; Stroke