Echocardiographic quantitation of left heart size and function in 122 healthy dogs: A prospective study proposing reference intervals and assessing repeatability

Abstract

Background: Broadly applicable reference intervals (RIs) for measurements of left atrial (LA) and left ventricular (LV) size and function generated prospectively using statistically appropriate methods are limited.

Objectives: To generate body size-independent RIs for linear, area, and volume measurements of LA size and LV size and function.

Animals: Healthy adult dogs (n = 122) of variable size and somatotype.

Methods: Prospective study. All dogs underwent an echocardiogram performed by the same examiner. Effects of body weight, sex, age, and heart rate were evaluated by regression and correlation analyses. Scaling exponents and prediction intervals were generated for linear measurements using the allometric equation. After normalization to body weight, 95% RIs were determined using nonparametric methods with 2.5 and 97.5 percentiles serving as the lower and upper limits (each with 90% confidence intervals), respectively.

Results: Linear LA and LV measurements were strongly correlated (R² ≥ 0.79) with body weight. Scaling exponents were close to the expected 1/3 (0.299-0.392). Prediction intervals for linear measurements of LV chamber size were considerably narrower than previously reported. Weak correlations (r = -0.42 to -0.50) among LV fractional shortening, fractional area change, and ejection fraction and body weight were identified. No other meaningful relationships were identified between the measurements and sex, age, and heart rate.

Conclusions and clinical importance: Body size-independent RIs for several linear, area, and volume measurements of LA and LV size and function were generated prospectively from a large and diverse reference population and are available for clinical use.

Keywords: ejection fraction; fractional shortening; left atrium; left ventricle; reference range; reproducibility.

Figure 1

Representative measurements of maximum left atrial (LA) volume (LAV) (A), left ventricular (LV) volume at end‐diastole (LVVd) (B), and end‐systole (LVVs) (C) from the right parasternal long‐axis tomographic planes used in this study. For all measurements, the internal border (blood‐tissue interface) was manually traced. The echocardiography software calculated estimates of chamber volume from a series of stacked discs using a monoplane Simpson's method. The height of the stacked discs was always selected to be perpendicular to the midpoint of the mitral valve annulus, bisecting the chamber area in the long (major)‐axis. For LAV (A), a straight line was drawn from hinge point to hinge point across the mitral valve annulus and defined the boundary of the LA and LV. The confluence of the pulmonary vein was excluded. For LVVd and LVVs, a straight line was drawn from hinge point to hinge point (ventricular side) across the mitral valve annulus to define the boundary between the LV and LA. If encountered, the papillary muscles were excluded. RA, right atrium; RV, right ventricle