title: Cardiorespiratory fitness and atrial fibrillation: A population-based follow-up study.
abstract: BACKGROUND
  Atrial fibrillation (AF) is the most common arrhythmia worldwide and has a complex association with physical fitness. The relationship of cardiorespiratory fitness (CRF) with the risk for AF has not been previously investigated in population-based studies.
  
  
  OBJECTIVE
  The purpose of this study was to determine the relationship of CRF with incident AF.
  
  
  METHODS
  CRF, as assessed by maximal oxygen uptake (VO2max) during exercise testing, was measured at baseline in 1950 middle-aged men (mean age 52.6 years, SD 5.1) from the Kuopio Ischaemic Heart Disease (KIHD) study.
  
  
  RESULTS
  During average follow-up of 19.5 years, there were 305 incident AF cases (annual AF rate of 65.1/1000 person-years, 95% confidence interval [CI] 58.2-72.8). Overall, a nonlinear association was observed between CRF and incident AF. The rate of incident AF varied from 11.5 (95% CI 9.4-14.0) for the first quartile of CRF, to 9.1 (95% CI 7.4-11.2) for the second quartile, 5.7 (95% CI 4.4-7.4) for the third quartile, and 6.3 (95% CI 5.0-8.0) for the fourth quartile. Age-adjusted hazard ratio comparing top vs bottom fourth of usual CRF levels was 0.67 (95% CI 0.48-0.95), attenuated to 0.98 (95% CI 0.66-1.43) upon further adjustment for risk factors. These findings were comparable across age, body mass index, history of smoking, diabetes, and cardiovascular disease status at baseline.
  
  
  CONCLUSIONS
  Improved fitness as indicated by higher levels of CRF is protective of AF within a certain range, beyond which the risk of AF rises again. These findings warrant further replication.
authors.affiliation: Emory University, Atlanta, Georgia. Electronic address: hassan.khan@emory.edu.
authors.forename: Hassan
authors.initials: H
authors.lastname: Khan
authors.affiliation: Emory University, Atlanta, Georgia.
authors.forename: Danesh
authors.initials: D
authors.lastname: Kella
authors.affiliation: Kuopio Research Institute of Exercise Medicine, Kuopio, Finland.
authors.forename: Rainer
authors.initials: R
authors.lastname: Rauramaa
authors.affiliation: Kuopio Research Institute of Exercise Medicine, Kuopio, Finland.
authors.forename: Kai
authors.initials: K
authors.lastname: Savonen
authors.affiliation: Emory University, Atlanta, Georgia.
authors.forename: Michael S
authors.initials: MS
authors.lastname: Lloyd
authors.affiliation: Institute of Public Health and Clinical Nutrition, University of Eastern Finland, Kuopio, Finland; Lapland Central Hospital, Department of Internal Medicine, Rovaniemi, Finland.
authors.forename: Jari A
authors.initials: JA
authors.lastname: Laukkanen
mesh_terms: D001281:Atrial Fibrillation / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D005080:Exercise Test / Q000379:methods / Q000706:statistics & numerical data; D005387:Finland / Q000453:epidemiology; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption; D010809:Physical Fitness / Q000502:physiology*; D016016:Proportional Hazards Models; D012307:Risk Factors; D013223:Statistics as Topic
keywords: Atrial fibrillation; Cardiorespiratory fitness; Maximal oxygen uptake