title: Aerobic Fitness and Risk of Ventricular Arrhythmia Following Physical Exertion.
abstract: BACKGROUND
  Brief episodes of physical exertion are associated with an immediately greater risk of cardiovascular events. Previous studies on the risk of ventricular arrhythmia (VA) shortly after exertion have not assessed if this risk differs according to the level of aerobic fitness or sedentary behaviour. Therefore, we conducted a prospective cohort study of patients with implantable cardioverter-defibrillators (ICDs) with a nested case-crossover analysis to examine the risk of VA shortly after exertion and whether this risk is modified by aerobic fitness and sedentary behaviour.
  
  
  METHODS
  Ninety-seven consecutive patients were recruited at the time of ICD implantation and 30 confirmed events occurred among patients who completed interviews about physical exertion preceding ICD therapy. We compared the frequency of exertion within an hour of ICD discharge to each patient's usual frequency of exertion reported at the time of ICD implantation.
  
  
  RESULTS
  Within an hour of episodes of exertion, the risk of VA was 5.3 (95% confidence interval [CI], 2.7-10.6) times greater compared with periods of rest. The association was higher among patients with aerobic fitness below the median (relative risk [RR] = 17.5; 95% CI, 5.2-58.5) than for patients with aerobic fitness above the median (RR, 1.2; 95% CI, 0.4-4.2; P homogeneity = 0.002) and higher among patients who were sedentary (RR, 52.8; 95% CI, 10.1-277) compared with individuals who were not sedentary (RR, 3.2; 95% CI, 1.3-7.6; P homogeneity = 0.0002).
  
  
  CONCLUSIONS
  Within 1 hour of episodes of exertion, there is an increased risk of VA, especially among individuals with lower levels of aerobic fitness and with sedentary behaviour.
authors.affiliation: Department of Epidemiology and Biostatistics, Schulich Medicine and Dentistry, Western University, London, Ontario, Canada; Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA.
authors.forename: Harpreet S
authors.initials: HS
authors.lastname: Chahal
authors.affiliation: Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA; Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Mostofsky
authors.affiliation: Cardiovascular Epidemiology Research Unit, Department of Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA; Department of Epidemiology, Harvard School of Public Health, Boston, Massachusetts, USA.
authors.forename: Murray A
authors.initials: MA
authors.lastname: Mittleman
authors.affiliation: Department of Epidemiology and Biostatistics, Schulich Medicine and Dentistry, Western University, London, Ontario, Canada; Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: Neville
authors.initials: N
authors.lastname: Suskin
authors.affiliation: Department of Epidemiology and Biostatistics, Schulich Medicine and Dentistry, Western University, London, Ontario, Canada.
authors.forename: Mark
authors.initials: M
authors.lastname: Speechley
authors.affiliation: Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: Allan C
authors.initials: AC
authors.lastname: Skanes
authors.affiliation: Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Leong-Sit
authors.affiliation: Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: Jaimie
authors.initials: J
authors.lastname: Manlucu
authors.affiliation: Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: Raymond
authors.initials: R
authors.lastname: Yee
authors.affiliation: Division of Cardiology, Western University, London, Ontario, Canada.
authors.forename: George J
authors.initials: GJ
authors.lastname: Klein
authors.affiliation: Department of Epidemiology and Biostatistics, Schulich Medicine and Dentistry, Western University, London, Ontario, Canada; Division of Cardiology, Western University, London, Ontario, Canada. Electronic address: lgula@uwo.ca.
authors.forename: Lorne J
authors.initials: LJ
authors.lastname: Gula
mesh_terms: D018592:Cross-Over Studies; D017147:Defibrillators, Implantable; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009864:Ontario / Q000453:epidemiology; D005082:Physical Exertion / Q000502:physiology*; D010809:Physical Fitness; D011446:Prospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D017180:Tachycardia, Ventricular / Q000453:epidemiology / Q000209:etiology* / Q000628:therapy