title: Differences in the electrocardiographic QT interval of various breeds of athletic horses during rest and exercise.
abstract: OBJECTIVE
  Quantitative measurements of cardiac repolarization, defined as the electrocardiographic QT interval, have important diagnostic implications in humans, as irregularities can trigger potentially fatal ventricular tachyarrhythmia. In both humans and horses, cardiac repolarization is influenced to some extent by heart rate, age, body weight (BW), sex, autonomic tone, and environment. In horses, there is substantial inter-breed variation in size and training, and the aims of this study were therefore to determine the best model describing the QT to RR relationship in breeds of various athletic horses and to test for differences in the QT interval.
  
  
  METHODS
  Ten Icelandic horses, 10 Arabian horses, 10 Thoroughbreds, 10 Standardbreds, six Coldblood trotters, 10 Warmbloods (dressage) and 10 Warmbloods (show jumping). All horses were geldings.
  
  
  METHODS
  QT intervals were measured from resting to peak exercise level and plotted against RR intervals. Data points were fitted with relevant regression models, and the effect of breed, BW, and estimated exercise intensity was examined.
  
  
  RESULTS
  For all breeds in this study, the QT interval was best described as a function of RR by the piecewise linear regression model. The breed of horse had a significant effect on the model. There was no systematic effect of BW or estimated exercise intensity, but a high inter-horse variability was observed.
  
  
  CONCLUSIONS
  The equine QT interval should preferably be corrected for heart rate according to breed. In addition, the results indicate that equine studies of the QT interval must be designed to eliminate the influence of a large inter-horse variation.
authors.affiliation: Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlaegevej 100, 1870 Frederiksberg C, Denmark.
authors.forename: P J
authors.initials: PJ
authors.lastname: Pedersen
authors.affiliation: Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Agrovej 8, 2630 Taastrup, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Karlsson
authors.affiliation: Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Agrovej 8, 2630 Taastrup, Denmark.
authors.forename: M
authors.initials: M
authors.lastname: Flethøj
authors.affiliation: Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlaegevej 100, 1870 Frederiksberg C, Denmark; Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Agrovej 8, 2630 Taastrup, Denmark. Electronic address: dagmart@sund.ku.dk.
authors.forename: D S
authors.initials: DS
authors.lastname: Trachsel
authors.affiliation: Laboratory of Experimental Cardiology, Department of Biomedical Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Blegdamsvej 3B, 2200 Koebenhavn N, Denmark; Department of Cardiology, Herlev and Gentofte University Hospitals, Niels Andersens Vej, 2900 Hellerup, Denmark.
authors.forename: J K
authors.initials: JK
authors.lastname: Kanters
authors.affiliation: Department of Veterinary Clinical and Animal Science, Faculty of Health and Medical Sciences, University of Copenhagen, Dyrlaegevej 100, 1870 Frederiksberg C, Denmark.
authors.forename: D A
authors.initials: DA
authors.lastname: Klaerke
authors.affiliation: Department of Large Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, Agrovej 8, 2630 Taastrup, Denmark.
authors.forename: R
authors.initials: R
authors.lastname: Buhl
mesh_terms: D000818:Animals; D004562:Electrocardiography / Q000662:veterinary*; D005260:Female; D006321:Heart / Q000502:physiology*; D006339:Heart Rate; D006736:Horses / Q000502:physiology*; D008297:Male; D005082:Physical Exertion / Q000502:physiology*; D012146:Rest / Q000502:physiology*; D013045:Species Specificity
keywords: ECG; Equine; Heart; LQTS; Repolarization