Comparing Two‐Dimensional Ellipsoid Model Variants in Estimating Three‐Dimensional Echocardiographic Right Ventricular Volume in Dogs

ABSTRACT Background Determining right ventricular (RV) volume typically requires three‐dimensional imaging due to its complex shape. The ellipsoid model offers a two‐dimensional alternative, employing area‐ or linear‐based formulas with further variations depending on the echocardiographic views used for measurements. Hypothesis/Objectives To identify which ellipsoid model variant best agrees with real‐time three‐dimensional echocardiography (RT3D) as a reference standard and to assess within‐day reproducibility. Animals Sixty‐seven client‐owned dogs (23 normal, 44 with right‐sided heart diseases) underwent echocardiograms, with 20 normal dogs receiving a repeat examination. Methods Prospective method comparison study. Body weight‐indexed end‐diastolic (iEDV) and end‐systolic volumes (iESV) were calculated across eight ellipsoid model variants. Agreement was assessed using concordance correlation coefficients (rc) and Bland–Altman analysis, while within‐day reproducibility was evaluated using intraclass correlation coefficients (ICC) and reproducibility coefficients. Results The area‐ and linear‐based variants using RV parameters from the left apical four‐chamber view and perpendicular diameter from the right parasternal short‐axis view (AEMA4C‐RPS and LEMA4C‐RPS, respectively) were the only methods to achieve moderate agreement with RT3D (rc > 0.90). The AEMA4C‐RPS showed no significant systematic bias for iEDV (median of the differences [95% confidence interval]: 0.09 [0.00–0.13]), while LEMA4C‐RPS exhibited no significant systematic bias for iEDV (0.03 [−0.02–0.08]) and iESV (0.04 [−0.01–0.12]), though biases increased at larger volumes. Both methods demonstrated good reproducibility (ICC > 0.75), with iESV reproducibility significantly greater than that of methods using RV parameters from the right parasternal long‐axis four‐chamber view. Conclusions and Clinical Importance The AEMA4C‐RPS and LEMA4C‐RPS offer practical RV volume estimates.