Changes in cardiac dimensions and indices of cardiac function during deconditioning in horses

To investigate the effects of deconditioning on cardiac dimensions and indices of cardiac function in horses. Thirteen 3-to 4-year-old Standardbred geldings. All horses had echocardiographic measurements performed at the conclusion of 9 months of intense training and at weeks 1.5, 4, 8, and 12 of deconditioning. Direct echocardiographic measurements included interventricular septal thickness, left ventricular internal dimensions, left ventricular freewall thickness, left atrial dimension, aortic diameter, diameter of the pulmonary artery, slopes of the mitral valve, heart rate, preejection period, and ejection time. Derived indices of cardiac function included fractional shortening, fractional area change, and cardiac output. Cardiac dimensions did not change significantly for the first 4 weeks of deconditioning but decreased significantly by week 8 and continued to decrease until week 12. Indices of cardiac function increased significantly during the first 10 days of deconditioning, remaining stable until week 4 of deconditioning. After week 4, indices of cardiac function decreased significantly until week 12. Deconditioning resulted in a general reduction in cardiac dimensions and indices of cardiac function over 12 weeks. However, results of the study reported here indicate that following an intense period of training, cardiac function may be maintained during the first 4 weeks of deconditioning. Results indicate that trained horses may rest for up to 4 weeks without a substantial reduction in cardiac capacity as reflected by echocardiographic indices.