Quantitative two-dimensional echocardiography in the horse: a review

Quantitative two-dimensional echocardiography (2DE) was introduced into equine cardiology in the early 1990s. At first, linear and area dimensions and left ventricular volume were validated by the comparison of parameters determined during in vitro 2DE and autopsy measurements. Based on these studies, tomographic planes and intracardiac reference points for in vivo measurements were established and 2DE values have been determined for healthy adult horses by various authors. These data were similar to each other and proved to be comparable with M-mode echocardiography measurements. However, differences in the measured parameters are due to breed and body weight variations of the examined populations, as well as to technical differences between M-mode and 2DE measurement methods. Currently, little information is available on 2DE values in equine cardiac diseases. In one report, 23 horses with aortic insufficiency had significant increases in the mean values of left ventricular chamber size, aortic root diameter and shortening fraction, and left ventricular thickness was also increased. These values were measured by M-mode echocardiography, but diastolic left ventricular enlargement was also measured and illustrated by the use of 2DE. In another study, 38 horses with mitral insufficiency had increased diastolic values of left ventricular and atrial cross-sectional internal diameter.