Quantitative Analysis of Stress Echocardiograms in Healthy Horses with 2-Dimensional (2D) Echocardiography, Anatomical M-Mode, Tissue Doppler Imaging, and 2D Speckle Tracking

Background Stress echocardiography is used to diagnose myocardial dysfunction in horses, but current methods are not well standardized. The influence of heart rate (HR) on measurements is largely unknown. Objectives To investigate the use of 2-dimensional echocardiography (2DE), anatomical M-mode (AMM), tissue Doppler imaging (TDI), and 2D speckle tracking (2DST) at rest and after exercise for quantification of regional and global left-ventricular (LV) function. Animals Five athletic Warmblood horses; 11.6 +/- 3.6 years; 529 +/- 48 kg. Methods Prospective study. Three separate echocardiographic examinations were performed before (baseline) and over 5 minutes after treadmill exercise with 2DE (1st, short-axis view; 2nd, long-axis view) and pulsed-wave TDI (3rd examination). Offline analyses were performed at baseline and after exercise at HR 120, 110, 100, 90, and 80 minute-1. Global and segmental measurements were compared by analysis of variance. Results Quantitative analyses of stress echocardiograms were feasible in all horses. None of the AMM indices changed significantly after exercise. Stroke volume and ejection fraction by 2DE and strain by 2DST decreased, whereas strain rate by 2DST increased significantly at HR > 100 minute-1. TDI analyses were technically difficult and provided little additional information. Conclusions and Clinical Importance Volumetric indices by 2DE and strain and strain rate by 2DST are applicable for quantitative assessment of stress echocardiograms. In healthy horses, they are significantly altered at a HR > 100 minute-1 and need to be evaluated in view of the instantaneous HR. Further investigations are needed to define the clinical value of stress echocardiography in horses with cardiac disease.