Electrocardiographic parameters of 20 Thoroughbred Arabian horses were established at rest and after prolonged endurance exercise. The mean heart rate was 35.85bpm at rest with predominant sinus rhythm, and 53.78bpm with sinus tachycardia after exercise. As physiological variation, wandering pacemaker was observed, and as non physiological, premature ventricular complex was noted. At post-exercise there was an increase of the amplitude of waves P, R, S and T, with P wave tending to become single in 35% of the animals and bifid positive in 65%, and with monophase positive T wave. There was a reduction in the duration of the waves, intervals and segments, and elongation of QTc, but the QRS complex hardly changed. The electrical axis in the frontal plane showed deviations to the right and to the left at rest, suggesting chamber enlargement and hypertrophy secondary to training, while after the exercise it showed extreme deviation to the right, indicating electrolyte imbalances. The average heart score was 128.45ms, which features the animals as athletes, being reduced to 118.60ms after exercise.
electrocardiogram; equine; physiology of stress; endurance
