Electrocardiographic characterization of the p wave and determination of the mean atrial electrical axis in dogs with atrial remodeling

Due to potential alterations in atrial depolarization vectors in canine heart disease, the atrial electrical axis (AEA) may appear altered in patients with atrial remodeling (AR). The aim of this study was to analyze the AEA and P-wave duration in the electrocardiogram of three groups of dogs: healthy patients, cardiac patients without left AR, and cardiac patients with left AR. Of the 56 evaluated dogs, nine were healthy, 27 were cardiac patients without left AR, and 20 were cardiac patients with left AR. The classification of myxomatous mitral valve disease includes stage A, comprising dogs at high risk of developing the condition; stage B, which includes asymptomatic dogs subdivided into B1, with mitral valve regurgitation not yet causing cardiac remodeling, and B2, with sufficient mitral valve regurgitation to cause cardiac remodeling, where treatment is indicated even in the absence of clinical signs; stage C, covering symptomatic dogs; and stage D, including dogs refractory to treatment. Therefore, 27 dogs were in stage B1, two in B2, 15 in C, and three in D. The P-wave duration in the remodeling group (53 milliseconds (ms)) was higher (p=0.0088) than in the group without left AR (46 ms). The P-wave duration in healthy dogs did not differ from that of dogs with and without remodeling. The AEA in healthy animals (43.65±19.79º) was lower (p=0.0015) than in the groups with and without left AR (69.58±18.00º and 63.40±15.89º). Animals without remodeling did not differ from those with remodeling, and despite the difference found in healthy animals, the values were within the normal range for the species, and no cardiac dogs exhibited a deviation of the AEA. Stage D dogs had longer P-wave durations than healthy and stage B1 dogs and did not differ from stage B2 and C groups (p=0.0269). Healthy dogs did not differ from stage B2, C, or D dogs in recording the AEA, only being lower than the B1 dogs (p=0.0120). The AEA and P wave duration are parameters that should not be used to define left AR in dogs with heart disease.