Effect of Body Weight on Echocardiographic Measurements in 19,866 Pure-Bred Cats with or without Heart Disease

Abstract

Background: Echocardiography is a cost-efficient method to screen cats for presence of heart disease. Current reference intervals for feline cardiac dimensions do not account for body weight (BW).

Objective: To study the effect of BW on heart rate (HR), aortic (Ao), left atrial (LA) and ventricular (LV) linear dimensions in cats, and to calculate 95% prediction intervals for these variables in normal adult pure-bred cats.

Animals: 19 866 pure-bred cats.

Methods: Clinical data from heart screens conducted between 1999 and 2014 were included. Associations between BW, HR, and cardiac dimensions were assessed using univariate linear models and allometric scaling, including all cats, and only those considered normal, respectively. Prediction intervals were created using 95% confidence intervals obtained from regression curves.

Results: Associations between BW and echocardiographic dimensions were best described by allometric scaling, and all dimensions increased with increasing BW (all P<0.001). Strongest associations were found between BW and Ao, LV end diastolic, LA dimensions, and thickness of LV free wall. Weak linear associations were found between BW and HR and left atrial to aortic ratio (LA:Ao), for which HR decreased with increasing BW (P<0.001), and LA:Ao increased with increasing BW (P<0.001). Marginal differences were found for prediction formulas and prediction intervals when the dataset included all cats versus only those considered normal.

Conclusions and importance: BW had a clinically relevant effect on echocardiographic dimensions in cats, and BW based 95% prediction intervals may help in screening cats for heart disease.

Keywords: Heart dimensions; M-mode; Prediction intervals; Screening.

Figure 1

Scatter plots and heat maps of diastolic left ventricular wall thicknesses plotted against body weight in 19,866 cats. Figures A–D show plots of diastolic interventricular septal wall thickness; Figures E–H show plots of diastolic free wall thickness. Figures A and E: all cats (n = 19,866). Figures B and F: cats with abnormal echocardiograms (n = 1,406, red dots) and cats with normal echocardiograms (n = 18,460, gray dots). Figures C and G: heat maps of all cats (n = 19,866). Figures D and H: heat maps as in Figures C and G, with superimposed regression line (solid line) and 95% prediction intervals (dotted lines) (n = 19,866). In Figures C, D, G and H, dots are coded according to their density at each point in the plot, from purple (<5% of the observations below) to dark red (95% of the observations below). Each color represents 5% intervals.

Figure 2

Regression lines (bold lines) and 95% prediction intervals (thin lines) for body weight plotted against diastolic interventricular septum in diastole (A), left ventricular internal diameter in diastole (B), left ventricular free wall in diastole (C), interventricular septum in systole (D), left ventricular internal diameter in systole (E), left ventricular free wall in systole (F), aortic (G) and left atrial (H) diameters, fractional shortening (I), and left atrial‐to‐aortic root ratio (J). Red lines indicate regression lines and 95% prediction intervals for all cats (n = 19,866). Black lines indicate regression lines and 95% prediction intervals including only cats with normal echocardiograms (n = 18,460).