Myocardial Injury in Rats Exposed to High-Intensity Exercise Evaluated by 2-D Speckle Tracking Imaging

The aim of the work described here was to evaluate strain and morphological change of the left ventricle in Sprague Dawley (SD) rats at different exercise intensities by 2-D speckle tracking imaging (STI).

Seventy-two 8-wk-old SD rats were divided into four groups on the basis of exercise intensity: sedentary (SED), low-intensity running, medium-intensity running (MIR) and high-intensity running (HIR). Each group was further sub-divided into three groups of different exercise lengths: 1, 4 and 8 wk. The structural measurements of the left ventricle and left ventricular ejection fraction (LVEF) were obtained by echocardiography. Systolic peak values of global longitudinal, circumferential and radial strains (GLS, GCS and GRS) were obtained. Histopathological results of the cross-sectional area (CSA) of myocardial cells, collagen volume fraction (CVF) of the myocardium and perivascular collagen area (PVCA) were also observed.

Structural measurements of the left ventricle and LVEF did not change with different exercise intensities or lengths. GLS of the HIR_{8 wk} sub-group was significantly lower than those of the SED_{8 wk} and MIR_{8 wk} sub-groups. Conversely, the GLS and GCS of the HIR_{8 wk} sub-group were lower than those of the HIR_{1 wk} and HIR_{4 wk} sub-groups. Histopathologically, the CSA of myocardial cells significantly increased across all HIR sub-groups and the MIR_{4 wk} and MIR_{8 wk} sub-groups. CVF_endo and PVCA were also significantly increased in the HIR_{4 wk} and HIR_{8 wk} sub-groups. The HIR_{8 wk} group also had regional swelling and ill-defined boundaries of myocardial cells.

Prolonged, high-intensity exercise may lead to exercise-induced injury of the myocardium. Two-dimensional STI can be used as a non-invasive early detection method for exercise-induced injury of myocardial function, compared with LVEF.