Comparison of Dubois and Base - Apex Lead Methods to Calculate QRS Angle ( Mean Electrical Axis ) in Thoroughbreds

This study evaluated electrocardiographic profile of 53 Thoroughbreds, clinically healthy, with ages ranging 2-7 years old, 38 males and 15 females, all reared at the São Paulo Jockey Club, Brazil. Two electrocardiograms were recorded in each horse, and the results of mean electrical axis in frontal plane, obtained by measuring QRS complexes amplitude, were compared using two electrode positioning methods, Dubois and the baseapex methodology. QRS axis in both methods was calculated using 2 different formulas. First, from Tilley’s table and second, from  tangent. Values obtained through Dubois lead-system, over 2 different formulas, did not show any statistical difference between them. Additionally, this was the best method of ECG acquisition. In conclusion, base apex is not adequate for horses because of the influence of body limb positioning and because of inadequate relationship between electrode positioning and the heart.