Comparisons of 2- and 3-Dimensional Echocardiographic Methods for Estimation of Left Atrial Size in Dogs with and without Myxomatous Mitral Valve Disease

Background: Two-dimensional (2D) and real-time three-dimensional (RT3D) echocardiography can be used to assess left atrial (LA) size, but their correlation in dogs remains unknown. Hypothesis: Estimations of LA size differ depending on the echocardiographic technique. Animals: Privately owned dogs; 70 with myxomatous mitral valve disease and 32 healthy control dogs. Methods: Prospective observational study comparing RT3D volume at atrial end-diastole (RT3DLAd) with 4 different 2D methods of estimating LA size: LA diameter and area in short-axis (LA(sax) and LA(area)) and LA diameter in long-axis (LAlax), both as indexed variables and as predictors of LA volume indexed to body weight (BW) using allometric scaling and geometric assumption of sphericity. Furthermore, agreement between indexed 2D based methods was studied using concordance correlation coefficient (rho(c)) and Bland-Altman plots. Results: None of the indexed 2D methods of estimating LA size showed good correlation with BW-indexed RT3DLAd volumes. Estimates of LA volumes from 2D measurements using allometric scaling showed better correlation with RT3D volumes than corresponding calculated volume approximations. The best correlation was found between RT3DLAd and estimated LA volumes based on allometric scaling of LA(lax) (rho(c) = 0.89) followed by LA(area) (rho(c) = 0.86) measurements. Comparing indexed 2D-based measurements of LA size, best agreement was found between LAsax to aortic diameter and LA(sax) to expected LA diameter, based on allometric scaling. Conclusions and Clinical Importance: Allometric scaling of 2D-based measurements of LA showed good correlation with RT3DLAd, whereas corresponding indexed measurements or calculated volume approximations did not.