Comparison of two methods for electrocardiographic analysis in Gallega sheep

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The basal electrocardiographic parameters in 37 adult Gallega breed ewes were studied by comparing two electrode placing systems; the classical system (applying the Einthoven's triangle in the frontal plane) and the experimental system in which the electrodes are placed on the back of the neck (red electrode), in the sacrum area (yellow electrode), in the area beneath the breastbone (green electrode) and on the skin fold of the knee joint of the rear right leg (black electrode). The second derivation (DII with both systems was chosen in order to measure and study the amplitude and duration of P and T waves, QRS complex, P-R, Q-T, and R-R intervals and S-T segment as well as the frequency, axis (using Derivations I and III) and the heart rhythms. With regard to duration in seconds of the waves, complexes, segments and intervals we found no significant differences between the two methods. Significant differences in P-wave amplitude, which was bigger in the experimental method, were seen. There was a greater variability in the morphology of the QRS complex in the classical method than in the experimental method. The heart rhythms found in Gallega ewes in the classical and experimental methods were as follows: sinus rhythm was the most common followed by phasic sinus arrhythmia, and finally sinus tachycardia. The average value obtained for the cardiac frequency using the classical method was 119.7 beats per min and 116.2 beats per min using the experimental method. As for the heart axis, the average values were −165 ° and −137 ° with the classic and the experimental layout, respectively. Despite the subcutaneous fixing of the electrodes in the experimental system, their application points are appropriately related to the position of the heart. This, together with there being points subject to fewer variations related to position, to layout regularity and to the amplitude needed for the correct measurement of all parameters as well as the fulfilment of the Einthoven law, makes the experimental method ideal for electrocardiograms in sheep.