title: Effects of endurance training on standard and signal-averaged electrocardiograms of sled dogs.
abstract: OBJECTIVE
  To determine the effect of endurance training on QRS duration, QRS-wave amplitude, and QT interval.
  
  
  METHODS
  100 sled dogs in Alaska.
  
  
  METHODS
  Dogs were examined in early September (before training) and late March (after training). During the interim, dogs trained by pulling a sled with a musher (mean, 20 km/d). Standard and signal-averaged ECG were obtained before and after training.
  
  
  RESULTS
  Endurance training significantly increased mean QRS duration by 4.4 milliseconds for standard ECG (mean +/- SEM; 62.3 +/- 0.7 to 66.7 +/- 0.6 milliseconds) and 4.3 milliseconds for signal-averaged ECG (51.5 +/- 0.7 to 55.8 +/- 0.6 milliseconds) without changing body weight. Increase in QRS duration corresponded to a calculated increase in heart weight (standard ECG, 23%; signal-averaged ECG, 27%). Signal-averaged QRS duration was correlated with echocardiographically determined left ventricular diastolic diameter for the X orthogonal lead (r = +0.41), Y orthogonal lead (r = +0.33), and vector (r = +0.35). Training also increased QT interval (234 +/- 2 to 249 +/- 2 milliseconds) and R-wave amplitude in leads II and rV2, increased peak-to-peak voltage and S-wave amplitude in the Y orthogonal lead, and decreased Q-wave amplitude in the Y orthogonal lead.
  
  
  CONCLUSIONS
  Electrocardiographic changes reflected physiologic cardiac hypertrophy in these canine athletes in response to repetitive endurance exercise. The QRS duration increases in response to endurance exercise training and, therefore, may be of use in predicting performance in endurance activities.
authors.affiliation: Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana 61802, USA.
authors.forename: P D
authors.initials: PD
authors.lastname: Constable
authors.forename: K W
authors.initials: KW
authors.lastname: Hinchcliff
authors.forename: J L
authors.initials: JL
authors.lastname: Olson
authors.forename: R L
authors.initials: RL
authors.lastname: Stepien
mesh_terms: D000818:Animals; D004285:Dogs / Q000502:physiology*; D004452:Echocardiography / Q000662:veterinary; D004562:Electrocardiography / Q000662:veterinary*; D006339:Heart Rate; D017379:Hypertrophy, Left Ventricular / Q000503:physiopathology / Q000662:veterinary; D008137:Longitudinal Studies; D010805:Physical Conditioning, Animal / Q000502:physiology*; D018709:Statistics, Nonparametric