Two digital electrocardiographs and their computer-based analysis programs produce clinically significant differences...

To compare measured ECG intervals and amplitudes obtained using electrocardiographs adapted for veterinary or human use and to develop ECG reference intervals for endurance-trained dogs.

Standard limb lead ECG recordings were obtained simultaneously in February and early March of 2021 using 2 digital electrocardiographs and a convenience sample of 121 endurance-trained sled adult dogs. Visually verified computer-based ECG measurements for the 2 electrocardiographs were compared using the Wilcoxon signed-rank test, Deming regression, and Bland-Altman plots. We assigned acceptable median values for differences (effect sizes) of < 10 milliseconds for P-wave duration, PQ interval, QRS duration, JT interval, and QT interval and < 10% for P-, Q-, R-, S-, and T-wave amplitudes.

Statistically significant differences between the 2 electrocardiographs existed for the majority (7 of 9) of global ECG indices and the majority (10 of 15) of lead I-, II-, and III-wave amplitudes. Clinically important differences based on assigned effect sizes were identified for lead II and III Q- and R-wave amplitudes, which the veterinary electrocardiograph measured 11% to 23% higher. The veterinary electrocardiograph identified a higher proportion of dogs that may have left or right ventricular enlargement. Reference intervals developed for 7 of 9 global ECG indices were narrower for the veterinary electrocardiograph.

The low-pass filter on the veterinary electrocardiograph attenuates higher frequencies on the canine ECG to a lower extent than the human electrocardiograph.

Reference intervals for dog ECGs depend on the digital electrocardiograph, its high-frequency filtering characteristics, and its computer-based analysis program.