Post‐MI Exercise, Cardiac Remodeling and Function

Abstract

We studied the timing effect of exercise (EX) training on Post-MI (myocardial infarction) myocardial remodeling and function in rats. Rats were surgically induced MI (~40% infarct of left ventricle) and assigned to 6 groups (n=5/group): 1. MI-EX starting at 1wk post-MI (MI-EX1), 2. MI-Sedentary (Sed) at 1wk (MI-Sed1), 3. Sham-Sed at 1wk (Sham1), 4. MI-EX starting at 4wk (MI-EX4), 5. MI-Sed at 4wk (MI-Sed4), and 6. Sham-Sed at 4 wk (Sham4). The EX groups started running on a treadmill at 1or 4 wk after MI at 16m/min, 50min/d, and 5d/wk for 8 wk. Cardiac function and left ventricle (LV) dimensions were measured prior to and after 8 wk of EX. The results showed that both LV internal diameter diastole (LVIDD) and systole (LVIDS) were dilated in all of the MI rats after 8 wk (LVIDD: MI-EX1=11.6±0.01mm, MI-Sed1=11.7±0.04, MI-EX4=11.1±0.01, MI-Sed4=11.8±0.04; LVIDS: MI-EX1=10.0±0.01mm, MI-Sed1=10.3±0.03, MI-EX4=9.72±0.04, MI-Sed4=10.0±0.05). Fractional shortening (FS) was not changed in MI-EX1 (pre vs post: 15.8±0.95% vs 14.1±0.92), decreased in MI-Sed1 (17.2±1.95% vs 11.61±1.25, p<0.01) and in MI-EX4 (14.1±1.45% vs 12.6±1.23, p<0.02) after 8 wk. Stroke volume (SV) was increased in MI-EX1 (313±15.5ul vs 589±43.7, p<0.001) but unchanged in MI-EX4 (424±25.1 vs 439±20.2ul). Ejection fraction (EF) was unchanged in MI-EX1(40.1±0.02% vs 36.3±0.02), but decreased in MI-EX4 (38.1±0.03% vs 32.5±0.02, p<0.005) and in MI-Sed groups. These parameters remained unchanged in Sham groups over 8 wk of period. The data suggest that starting EX 1wk after MI may improve cardiac function but did not prevent LV dilation.