Influence of Signalment Variables on Body Weight-Normalized Echocardiographic Measurements of Heart Size in 56 169 Adult Unsedated Normal Pure-Bred Cats

BACKGROUND: Echocardiography is widely used to breed-screen cats for the presence of heart disease. Left-sided cardiac dimensions are non-linearly related to body weight (BW), but the association with signalment variables is incompletely evaluated. OBJECTIVE: To validate previously published prediction equations (PE) and 95% prediction intervals (PI) and study the effects of breed, age, sex, and neutering on BW-normalized aortic (Ao), left atrial (LA) and ventricular (LV) dimensions. ANIMALS: 56 169 pure-bred adult cats. METHODS: Data from heart screens conducted between 1999 and 2023 were included. Body-weight-(BW)-based PE and 95% PIs were obtained by allometric scaling including only cats considered normal. The effects of signalment variables on BW-normalized cardiac dimensions were examined using group-wise comparisons and uni- and multivariable analyses. RESULTS: The PE and PI changed marginally from those previously reported. The BW-normalized measurements showed greater variation for LV systolic than diastolic measurements (p < 0.001), and LA showed greater variation than Ao measurements. All signalment variables had small but significant effects on BW-normalized variables (p < 0.001), where the effect of breed was most prominent. None of the breeds had a variable median measurement > 10% above or below the PE, or > 10% of cats outside the PI. Signalment main effects persisted after adjusting for examiner and year of examination. CONCLUSIONS AND CLINICAL RELEVANCE: Breed, age, sex, and neutering status had small and mostly clinically irrelevant effects on BW-normalized Ao, LA, and LV linear dimensions. The PE and PI intervals are valid in adult pure-bred cats across many breeds, different ages, sexes, and neutering status.