Echocardiographic estimates of stroke volume in healthy dogs: comparability, reference intervals, and reproducibility

This study aimed to compare estimates of stroke volume (SV) from different anatomic sites and to generate reference intervals for indices such as shunt volume (ShuntVol) or regurgitant volume (RegVol) in a large sample of healthy dogs.

Ninety healthy dogs underwent an echocardiogram, where SV was assessed at the level of the pulmonary valve (SV_PV), aortic valve (SV_AV), mitral valve (SV_MV), and left ventricle using the difference in end-diastolic volume and end-systolic volume from a right parasternal long-axis four-chamber view (SV_{LV_RPLx}) and left apical four-chamber view (SV_{LV_Ap4Ch}). Eight dogs underwent repeated echocardiograms by the same operator on three different days and by three different operators on the same day. Bland-Altman plots and 95% reference intervals were generated. Reproducibility was described using coefficients of variation and reproducibility coefficients.

Mean differences (95% limits of agreement) for ShuntVol (SV_PV-SV_AV), RegVol_{LV_RPLx} (SV_{LV_RPLx}-SV_AV), RegVol_{LV_Ap4Ch} (SV_{LV_Ap4Ch}-SV_AV), and RegVol_MV (SV_MV-SV_AV) were as follows: -0.14 (-0.72, 0.44), -0.05 (-0.59, 0.48), -0.16 (-0.71, 0.39), and 0.12 (-0.76, 1.00) mL/kg, respectively. All but RegVol_{LV_RPLx} showed significant (P<0.01) fixed bias. Reference intervals for ShuntVol, RegVol_{LV_RPLx}, RegVol_{LV_Ap4Ch}, and RegVol_MV were as follows: -0.85-0.64, -0.65-0.58, -0.77-0.52, and -0.91-1.06 mL/kg, respectively. Intra-operator and interoperator coefficients of variation were lowest for SV_AV and highest for SV_MV and SV_{LV_AP4Ch}.

Echocardiographic estimates of SV are not interchangeable and can exhibit wide limits of agreement. Reference intervals help provide a frame of reference to assess disease severity in dogs with a shunting lesion (ShuntVol) and mitral regurgitation (RegVol).