Cardiac responses to training in 2-year-old thoroughbreds: an echocardiographic study

Guided M-mode echocardiography was performed in seven 2-year-old Thoroughbreds before commencement of commercial flat-race training, and 18 weeks later, when all horses were either racing regularly (5 horses), or at racing fitness (2 horses). M-mode echocardiography was performed using a 2.5 MHz annular phased array ultrasound transducer and a Vingmed 800 Supervision echocardiograph. Images were obtained from the right hemithorax; a short axis view of the left ventricle (LV) at the level of the chordae tendinae was used to position the M-mode cursor. The following variables were measured: left ventricular (LV) internal diameter in diastole (LVIDd) and systole (LVIDs) and interventricular septal (IVS) and left ventricular free wall thickness (LVFW) in systole and diastole. The following variables were also calculated: LV fractional shortening (%FS), LV ejection fraction (EF), LV relative and mean wall thickness and muscle mass. Values before and after training were compared using a paired Student's t test. Training resulted in significant reductions in %FS and EF. Left ventricular internal diameter increased from 11.38 s.d = 0.58) cm before training to 12.16 (s.d. = 0.7) cm after training (P < 0.001). Calculated left ventricular mass also increased significantly (mean increase of 33% P < 0.001). Bodyweight was unchanged in the present study. Relative wall thickness was significantly increased in all horses, suggesting that eccentric cardiac hypertrophy occurs in response to commercial flat-race training. The mean post training value for relative wall thickness of 0.45 (s.d. = 0.05) for the horses in the present study is similar to that of human athletes in power/endurance disciplines.