Body Weight Affects Echocardiographic Measurements in Cats

Body weight has a clinically relevant effect on echocardiographic measurements in cats, according to the results of a study published in the Journal of Veterinary Internal Medicine. The authors suggest that standard fixed reference intervals are not appropriate for all cats. The article includes 95% prediction intervals for feline cardiac dimensions based on body weight.

Previously reported reference intervals for cardiac measurements in cats often used outdated ultrasound equipment or small sample sizes, say the authors. Body size is known to affect cardiac dimensions in dogs, and canine cardiac measurements are often scaled to body weight. “Given that, in the absence of obesity, adult purebred cats range in body size from 2.5 kg to >10 kg, it is important to identify equations that accurately describe the associations between body size and cardiac dimensions in cats,” they write.

The investigators reviewed data from 19,866 purebred cats in a pedigree database. The cats received screening echocardiograms in North America, Europe, Australia, or New Zealand between 1999 and 2014. The breeds with the largest representation were Maine coon (5274 cats), Norwegian forest (3301 cats), and British shorthair (2663 cats). Cats included in the database appeared to be healthy at the time of screening. Their median age was 1.8 years and median body weight was 4.2 kg. The vast majority of the cats with recorded sexual status were intact (11,496 intact, 1872 neutered).

Echocardiogram results were normal in 18,460 cats, consistent with hypertrophic cardiomyopathy in 686, equivocal in 529, indicative of other cardiac diseases in 183, and indicative of restrictive cardiomyopathy in 8. Cats with abnormal or equivocal findings were significantly older (median age, 4.5 years) and heavier (median body weight, 4.6 kg) than those with normal results.

All echocardiographic measurements except fractional shortening increased as body weight increased. The investigators created a table of 95% prediction intervals for echocardiographic measurements by body weight using data from cats with normal findings. Higher body weight was also associated with lower heart rate and higher left atrial to aortic root diameter ratio, although these findings were not clinically significant.

Statistical analysis showed that allometric scaling, as opposed to linear regression, most accurately described the associations between echocardiographic measurements and body weight. This is also the case with other mammalian species, say the authors. Linear regression best described the relationships between body weight and heart rate, fractional shortening, and left atrial to aortic root diameter ratio.

One study limitation was that the clinical data did not include body condition score, so the effect of obesity on cardiac measurements could not be examined. The data were also collected by ultrasonographers using many different systems. The authors note that the relatively young median age of the cats in the study may have affected the results; including more data from older cats might have increased the variation.

The authors conclude that prediction intervals for echocardiographic measurements in cats must take into account the effect of body weight. “Body weight—based 95% prediction intervals determined in the present study may help in screening cats for heart disease,” they write.

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.