title: Cardiac Mean Electrical Axis in Thoroughbreds-Standardization by the Dubois Lead Positioning System.
abstract: BACKGROUND
  Different methodologies for electrocardiographic acquisition in horses have been used since the first ECG recordings in equines were reported early in the last century. This study aimed to determine the best ECG electrodes positioning method and the most reliable calculation of mean cardiac axis (MEA) in equines.
  
  
  METHODS
  We evaluated the electrocardiographic profile of 53 clinically healthy Thoroughbreds, 38 males and 15 females, with ages ranging 2-7 years old, all reared at the São Paulo Jockey Club, in Brazil. Two ECG tracings were recorded from each animal, one using the Dubois lead positioning system, the second using the base-apex method. QRS complex amplitudes were analyzed to obtain MEA values in the frontal plane for each of the two electrode positioning methods mentioned above, using two calculation approaches, the first by Tilley tables and the second by trigonometric calculation. Results were compared between the two methods.
  
  
  RESULTS
  There was significant difference in cardiac axis values: MEA obtained by the Tilley tables was +135.1° ± 90.9° vs. -81.1° ± 3.6° (p<0.0001), and by trigonometric calculation it was -15.0° ± 11.3° vs. -79.9° ± 7.4° (p<0.0001), base-apex and Dubois, respectively. Furthermore, Dubois method presented small range of variation without statistical or clinical difference by either calculation mode, while there was a wide variation in the base-apex method.
  
  
  CONCLUSIONS
  Dubois improved centralization of the Thoroughbreds' hearts, engendering what seems to be the real frontal plane. By either calculation mode, it was the most reliable methodology to obtain cardiac mean electrical axis in equines.
authors.affiliation: Clinical Unit of Electrocardiography, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Cássia Fré
authors.initials: CF
authors.lastname: da Costa
authors.affiliation: Clinical Unit of Electrocardiography, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Nelson
authors.initials: N
authors.lastname: Samesima
authors.affiliation: Clinical Unit of Electrocardiography, Heart Institute (InCor), Hospital das Clínicas da Faculdade de Medicina, Universidade de São Paulo, São Paulo, Brazil.
authors.forename: Carlos Alberto
authors.initials: CA
authors.lastname: Pastore
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004562:Electrocardiography / Q000295:instrumentation / Q000379:methods / Q000662:veterinary*; D004566:Electrodes; D005260:Female; D006321:Heart / Q000502:physiology*; D006736:Horses; D008297:Male; D010805:Physical Conditioning, Animal / Q000592:standards*