M-Mode Echocardiographic Measurements of Interventricular Septum, Left Ventricular Internal Diameter, and Left Ventricular Free-Wall Thickness in Normal Horses—A Meta-Analytical Study

SIMPLE SUMMARY: The current meta-analysis offers a general perspective on the echocardiographic measurements of heart dimensions in sound Thoroughbred and Standardbred horses. The study was performed according to the guidelines of PRISMA. The echocardiographic findings varied from one study to the next due to the fact that there were multiple investigations. The meta-analysis indicates variations in results among different studies. This result should be considered when evaluating a horse for heart disease and each case should be evaluated independently. ABSTRACT: The purpose of this study was to provide a systematic meta-analysis on echocardiographic measurements in normal Thoroughbred and Standardbred horses. The current systematic meta-analysis followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). All the available published papers on the reference values of echocardiographic assessment via M-mode echocardiography were searched, and fifteen studies were finally selected for analysis. In both fixed and random effect, the confidence interval (CI) for the interventricular septum (IVS) was 2.8–3.1 and 4.7–7.5; for the left ventricular free-wall (LVFW) thickness, it was 2.9–3.2 and 4.2–6.7; and for the left ventricular internal diameter (LVID), it was −5.0–4.6 and −10.0–−6.7, respectively. For IVS, the Q statistic, I-squared, and tau-squared were 925.3, 98.1, and 7.9, respectively. Similarly, for LVFW, all the effects were on the positive side of zero, with a range of 1.3–68.1. The CI indicated a significant variation among the studies (fixed, 2.9–3.2; random, 4.2–6.7). The z-values of LVFW for fixed and random effects were, respectively, 41.1 (p < 0.001) and 8.5 (p < 0.001). However, the Q statistic was 886.6 (p < 0.001). Moreover, the I-squared was 98.08, and the tau-squared was 6.6. By contrast, the effects of LVID fell on the negative side of zero, (2.8–83.9). The present meta-analysis provides an overview of the echocardiographic measurements of cardiac diameters in healthy Thoroughbred and Standardbred horses. The meta-analysis indicates variations in results among different studies. This result should be considered when evaluating a horse for heart disease and each case should be evaluated independently.