Comparing Echocardiographic Estimates of Stroke Volume in Healthy Dogs

Abstract:

Background: Differences in echocardiographic estimates of stroke volume (SV) calculated from different anatomic sites should theoretically be zero in a healthy dog but might vary due to technical issues, physiologic variability, or measurement error. Hypothesis/

Objectives: We sought to compare SV at different anatomic sites that are used to calculate clinically important indices including, shunt volume (ShuntVol) or regurgitant volume (RegVol) in a large sample of healthy dogs. Animals: Ninety healthy adult dogs.

Methods: Prospective study. All dogs underwent an echocardiogram. Stroke volume was derived from the product of stroke distance and cross-sectional area at the pulmonary valve (SVPV), aortic valve (SVAV), and mitral valve (SVMV) levels. Stroke volume was also derived from the difference of left ventricular end-diastolic volume and end-systolic volume using Simpson’s method from a right parasternal long-axis (SVLV_RPLx) and an apical 4-chamber (SVLV_Ap4Ch) view. Bland-Altman plots and 95% reference intervals (Clinical Laboratory Standards Institute methodology) were generated.

Results: Mean difference (95% limits of agreement) for ShuntVol (SVPV-SVAV), RegVolLV_RPLx (SVLV_RPLx-SVAV), RegVolLV_Ap4Ch (SVLV_Ap4Ch-SVAV), and RegVolMV (SVMV-SVAV) were: -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, with all but RegVolLV_RPLx showing significant (P< 0.01) fixed bias. Reference intervals for ShuntVol, RegVolLV_RPLx, RegVolLV_Ap4Ch, and RegVolMV were: -0.85-0.64, -0.65-0.58, -0.77-0.52, and -0.91-1.06 mL/kg, respectively. Conclusions and clinical importance: Echocardiographic estimates of SV are not interchangeable and exhibit relatively wide limits of agreement. Reference intervals provide a frame of reference when quantitating lesion severity for dogs with a congenital shunt (ShuntVol) and mitral regurgitation (RegVol).