title: Repolarization dynamics during exercise discriminate between LQT1 and LQT2 genotypes.
abstract: Genotype and Exercise in LQTS.
  
  
  BACKGROUND
  Repolarization dynamics during exercise in patients with long-QT Syndrome (LQTS) may be influenced by various factors such as a patient's genotype. We sought to systematically characterize the repolarization dynamics during exercise in patients with LQTS with a particular focus on the influence of genotype.
  
  
  METHODS
  Three groups of patients were studied on the basis of clinical status and genotype: LQT1, LQT2, and normal controls. Twenty-five age- and gender-matched patients were selected for each group. The QTc was measured during bicycle exercise testing and its dynamics were compared between the 3 groups.
  
  
  RESULTS
  The degree of QTc prolongation during exercise was greater in LQTS patients (LQT1 80 ± 47 ms, LQT2 64 ± 41 ms, Control 46 ± 20 ms, P = 0.02), with significant differences between LQT1 and LQT2 patients observed at heart rates ≥ 60% of the predicted maximum (P < 0.05). LQT1 patients demonstrated progressive or persistent QTc prolongation at higher heart rates, whereas LQT2 patients demonstrated maximum QTc prolongation at submaximal heart rates (50% of the predicted maximum) with subsequent QTc correction toward baseline values at higher heart rates. Importantly, these observations were consistent regardless of age, gender, or exercise type in subgroup analyses.
  
  
  CONCLUSIONS
  Reduced repolarization reserve in LQTS is genotype and heart rate specific.
authors.affiliation: Division of Cardiology, University of Western Ontario, London, Ontario, Canada.
authors.forename: Raymond W
authors.initials: RW
authors.lastname: Sy
authors.forename: Ishvinder S
authors.initials: IS
authors.lastname: Chattha
authors.forename: George J
authors.initials: GJ
authors.lastname: Klein
authors.forename: Lorne J
authors.initials: LJ
authors.lastname: Gula
authors.forename: Allan C
authors.initials: AC
authors.lastname: Skanes
authors.forename: Raymond
authors.initials: R
authors.lastname: Yee
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Bennett
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Krahn
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods*; D005080:Exercise Test; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D005838:Genotype; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000235:genetics*; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology*; D008297:Male; D005082:Physical Exertion; D015221:Potassium Channels / Q000235:genetics*
chemical_list: D015221:Potassium Channels