Electrocardiographic findings in healthy Cavalier King Charles Spaniels, Pugs, and English Bulldogs

Objective: To describe the ECG findings in 3 different canine brachycephalic breeds: the Cavalier King Charles Spaniel, the Pug, and the English Bulldog (EB). Animals: 135 healthy dogs (50 Cavalier King Charles Spaniels, 50 Pugs, and 35 EBs). Procedures: Medical records were retrospectively reviewed to identify healthy dogs ≥ 1 year old that had undergone an ECG. The Mann-Whitney U test or the Student t test were used to compare continuous variables between male and female dogs, whereas the χ2 test was used for categorical variables. Spearman correlation coefficients between ECG measurements and age and body weight were also calculated in the case of continuous variables, whereas the Kruskal-Wallis test was used for categorical ones. Results: Electrocardiographic parameters of healthy Cavalier King Charles Spaniels overall fitted with traditional reference intervals cited in textbooks; in contrast, 28% of Pugs and 20% of EBs showed a shift of the QRS-complex mean electrical axis (QRS-MEA). In Pugs and EBs, the mean/median QRS-MEA value was 56° (from 0° to 100°) and 59° (from 20° to 100°), respectively. All axis shifts were left shifts (in Pugs, from 0° to 34°; in EBs, 20° to 39°). Only a few meaningful differences were found when comparing ECG variables between males and females. Similarly, only 1 statistically significant correlation was found between ECG parameters and age and body weight. Clinical relevance: Healthy Pugs and EBs present a trend to a left shift of the QRS-MEA. This should be considered when interpreting ECG tracings in these breeds.