P-wave duration in a clinically normal hound population

Electrocardiogram (ECG) analysis is a common noninvasive technique used for diagnosis of cardiac disease in the clinical and research branches of veterinary medicine. Accurate analysis of P-wave duration, amplitude, and morphology is crucial to identification of morphologic and functional changes of the atria. The published accepted maximal normal value for P-wave duration in the dog is < or = 40 milliseconds. We looked at P-wave duration in ECG obtained as part of routine quarantine health screening over a period of 1 year in 364 clinically normal hounds weighing 13 to 35 kg. The dogs were neither anesthetized nor sedated and were placed in standard position. P-wave duration was classically determined from the lead-II recording. Mean P-wave duration for all dogs (44.9 +/- 6.1 milliseconds) was greater than published accepted normal values for the dog. There was a significant difference in mean P-wave duration by body weight (P < 0.001); dogs weighing > or = 20 kg had longer mean P-wave durations than dogs weighing < 20 kg (45.3 and 41.6 milliseconds respectively). There were also significant differences in mean P-wave duration by sex (P < 0.01), with a greater mean duration for females (45.4 milliseconds) than for males (43.8 milliseconds). All other ECG parameters were within published accepted normal values. A P-wave of prolonged duration leads to a diagnosis of abnormalities in cardiac morphology and/or function. Published accepted normal values for P-wave duration, at least for a clinically normal hound population, appear to be shorter than the true normal values. An error in published accepted normal standards may lead to overdiagnosis of cardiac abnormalities, as well as to erroneous results in cardiovascular studies. Therefore we recommend that the standard for P-wave duration be increased above the currently accepted standard of < or = 40 milliseconds.