Objective: To determine the effect of body size on various echocardiographic measurements in dogs of widely differing size, but identical body conformation.
Design: A randomised echocardiographic study of healthy sighthounds.
Animals: 60 dogs comprising an equal number (20) of racing Greyhounds, Whippets and Italian Greyhounds.
Procedure: Following sedation with acepromazine and morphine, and acclimatization, a thorough echocardiographic examination was performed on each dog using standard methods.
Results: Dimensions measured echocardiographically were highly correlated with body size. These data were subsequently examined using analyses of variance and regression. Body surface area was the best overall predictor of dimensional measurements. In comparison to previous studies using dogs of differing size and conformation, the spread of values for measurements plotted against body surface area showed substantially narrower ranges. Thus, the relationship between echocardiographic measurements and body surface area was much closer for dogs with an identical somatotype than for dogs of differing size and conformation. Commonly used ejection phase indices (fractional shortening, ejection fraction and velocity of circumferential fibre shortening) were negatively correlated with body size. In contrast, the thickening fraction of the left ventricular posterior wall, another ejection phase index, was independent of body weight and body surface area for all three breeds and when the data were pooled.
Conclusion: Taken in consideration with previous work, this study demonstrates that body conformation and body size both influence canine echocardiographic measurements. Commonly used ejection phase indices are significantly affected by body size, with larger sighthounds having lower values. A more appropriate method of quantitating left ventricular function may be the determination of the thickening fraction of the left ventricular posterior wall.