Two-dimensional echocardiographic right heart ratios for assessment of right heart size in dogs: Reference intervals and reproducibility.

Background: Reference intervals for simple body weight-independent measurements of right heart size and function are limited.

Objectives: Generate reference intervals for measurements of right heart size indexed to the long-axis aortic valve diameter (AoD) or corresponding left heart structure (right heart ratios) and describe the reproducibility of these indices.

Animals: Ninety healthy adult dogs of variable body weight.

Methods: Prospective study. All dogs underwent an echocardiogram performed by the same operator. Numerous linear 2-dimensional measurements of right heart size and function from different imaging planes were performed. Eight dogs underwent repeated echocardiograms by the same operator on 3 different days, and 3 different operators performed repeated echocardiograms on the same day. Reference intervals were generated using the Clinical Laboratory Standards Institute method. Reproducibility was quantitated using coefficients of variation (CVs) and reproducibility coefficients.

Results: Reference intervals for right heart ratios were generated and allow simple assessments of right heart size and function that do not require a scaling exponent or body weight table. Right heart ratios did not show clinically relevant associations with body weight. All CVs were <22.6%. In general, CVs for right heart measurements indexed to AoD were lower compared with right heart measurements indexed to the corresponding left heart structure.

Conclusions and clinical importance: Reference intervals for simple body weight-independent right heart ratios are available to help detect abnormalities of right heart size and function. Reproducibility coefficients might be useful to help identify meaningful changes in right heart size during serial evaluations.