Morphology and amplitude values of the electrocardiogram of Spanish-bred horses of different ages in the Dubois leads system

The aim of this work was to record the modifications of the form and amplit ude of the electrocardiographic tracings during growth using the Dubois sys tem and to study its sensibility to these physiological changes. This work was carried out on 179 healthy, young and adult Spanish-bred horses (98 fem ales and 81 males). One electrocardiogram (ECG) was obtained from each hors e using the Dubois leads system. The bifid shape deflection of the P wave w as generally more frequent than the simple one in animals at 4 months of ag e or older. Amplitudes of the P-2 component and of the simple positive wave presented significant differences (p < 0.01) between the age groups studie d: animals up to 3 months in age and older than 2 years of age (highest amp litudes), and the rest of the animals (lowest amplitudes). Significant vari ations (p < 0.05) were found for the QS amplitude between :animals: of I mo nth of age, and all the other groups. The multiple range analysis did not d efine a clear distribution of age groups for the amplitude of the T wave. I t may therefore be concluded, that in the Spanish-bred horse up to 4 month of age, the form and amplitude of the QRS complex in the Dubois leads syste m differ from those of older animals. Thus, this study shows the sensibilit y of the Dubois leads system for detecting the electrocardiographic changes related to the growing process in the Spanish-bred horse. In addition, it provides standard values of electrocardiographic parameters in the Spanish- bred horse at different stages of growth.