Echocardiographic measurements of cardiac dimensions and indices of cardiac function in normal adult thoroughbred horses.

Cardiac dimensions and indices of cardiac function were measured in 29 clinically normal adult Thoroughbreds (TB) which performed minimal exercise using guided M-mode and two-dimensional (2-D) echocardiography, from a variety of image planes and measurement methods, and standardised imaging planes based on intracardiac anatomical landmarks. The different methods of measuring these variables were compared. The variables which were considered to be most valuable for quantitative echocardiography were measured in a further 9 horses. Comparable measurements of cardiac dimensions can be obtained from a variety of different imaging planes, using either 2-D or guided M-mode echocardiography from the left or right side of the chest, although differences in measurement methods must be taken into account. The results of this study give a useful range of dimensions and indices of cardiac function in normal adult TBs for comparison with those recorded from horses with suspected cardiac disease. Comparisons are only valid if there is meticulous attention to correct orientation of imaging planes with regard to internal landmarks and that comparable measurement locations and timing are used.