Reproducibility of echocardiographic indices of left atrial size in dogs with subclinical myxomatous mitral valve disease

Background Reliability of echocardiographic measurements of left atrial (LA) size, an important marker of disease severity, has not been reported in dogs with myxomatous mitral valve disease (MMVD). Objectives To define and compare reliability of left atrial dimension/diameter (LAD), LAD indexed to aortic valve diameter (LAD/AoD), left atrium-to-aortic root ratio (LA/Ao), left atrial volume acquired from a right parasternal long-axis (LAVRPLx), and left apical view (LAVLAP) in dogs with subclinical MMVD. Animals Nine dogs with subclinical MMVD. Methods Prospective reproducibility study. Dogs underwent 12 echocardiographic examinations by 2 operators on the mornings and afternoons of 3 nonconsecutive days within 1 week. Reliability (measurement variability) was quantified using coefficients of variation (CV) and 95% repeatability/reproducibility coefficients (95% RC). A mixed-model analysis of variance (ANOVA) was used to determine if time of day, day, and operator were significant sources of variability for each index. Results Linear measurements (LAD, LAD/AoD, and LA/Ao) exhibited less within-day, between-day, and interoperator variability (CVs, 3.9%-12.5%) than did volume estimate measurements (LAVRPLx and LAVLAP; CVs, 11.8%-17.9%). Of the linear measurements, LA/Ao exhibited greater variability (CVs, 9.9%-12.5%) compared to LAD and LAD/AoD (CVs, 3.9%-4.9%). Operator was a significant (P = .005) source of variability for LA/Ao. Conclusions and Clinical Importance Compared to other linear measurements, LA/Ao was the least reproducible and most dependent on operator. The 95% RC for each LA size index are provided to help identify clinically relevant changes (beyond intraoperator or interoperator variability) during serial echocardiographic examinations of dogs with subclinical MMVD.