Altered systolic left ventricular function in horses completing a long distance endurance race

Reasons for performing the study: It is unknown whether exercise-induced cardiac fatigue (EICF), as demonstrated in athletes performing long duration exercise, occurs in endurance horses. Objective: To examine the effects of a long distance endurance race on left ventricular systolic function in horses. Methods: Echocardiography was performed before and after a 2 or 3 star international endurance race (106 to 132 km) in 11 horses. Systolic (s) and diastolic (d) interventricular and left ventricular free wall thickness (IVS and LVFW, respectively), left ventricular, left atrial and aortic internal diameter (LVID, LA and Ao, respectively), fractional shortening (FS) and ejection fraction (EF) were measured by echocardiography. Heart rate (HR), peak flow velocity (Vmax), flow velocity integral (FVI), ejection time (ET), pre-ejection period (PEP), velocity of circumferential fiber shortening (Vcf), stroke volume (SV) and cardiac output (CO) were measured from aortic Doppler wave recordings. Results: After the race, LVIDd, Ao, LA, EF, FS, FVI, SV, ET and ET indexed for HR were significantly lower and IVSd, LVFWd, HR, PEP, PEP/ET, and Vcf were significantly higher as compared with pre-race values. Pre- to post-exercise changes in those parameters were not significantly correlated with changes in HR or in LVIDd. Conclusions: Results suggest that EICF, with a decrease in left ventricular systolic function, could occur post-exercise in horses performing long duration endurance races. However, a confounding effect of altered preload and heart rate on the studied variables cannot be discounted.