Two-dimensional, long-axis echocardiographic ratios for assessment of left atrial and ventricular size in dogs.

INTRODUCTION: Left ventricular (LV) and left atrial (LA) enlargement affect management and outcome of dogs with cardiac disease. Short-axis, two-dimensional echocardiographic (2DE) images, indexed to the aorta (Ao), are frequently used to identify cardiomegaly. Long-axis images offer complementary views of the left heart.

ANIMALS: Eighty healthy dogs and 25 dogs with MMVD.

METHODS: Healthy dogs were prospectively recruited to determine reference intervals (Clinical Laboratory Standards Institute methodology) for long-axis ratios. Measurement variability and repeatability were quantified by intraclass correlation coefficient and coefficient of variation. Mean long-axis ratios from dogs with MMVD were compared with healthy dogs (unpaired t-test). In addition, the proportion of MMVD dogs exceeding the 97.5 percentile by LV/Ao and a conventional, allometric method were compared (McNemar's test).

RESULTS: Two-dimensional echocardiographic long-axis reference intervals were as follows: left ventricular to aortic dimension (LV/Ao) 1.8-2.5; left atrial to aortic dimension (LA/Ao) 1.8-2.4, and left atrial to left ventricular dimension (LA/LV) 0.9-1.1. Intraobserver and interobserver measurement agreement was good-to-excellent (intraclass correlation coefficients ≥0.84), and day-to-day variability was low (coefficient of variations <4%). Left ventricular to aortic dimension, LA/Ao, and LA/LV were significantly greater in canine MMVD compared with healthy dogs (p<0.001). The percentages of MMVD dogs demonstrating LV dilatation by LV/Ao and conventional method were 68% and 36%, respectively (p=0.043, 95% confidence interval for difference 7.9%, 56.1%).

CONCLUSIONS: Simple 2DE long-axis ratios of LV/Ao, LA/Ao, and LA/LV are repeatable and demonstrate clinical utility for identifying LV and LA enlargement in dogs with MMVD.