Effects of exercise on dynamic cardiac function and survival after myocardial infarction

Objective To study the effects of exercise after myocardial infarction on the survival rate and the dynamic functioning of the left ventricle (LV). Methods Ninety-six male Sprague-Dawley rats were randomly assigned to a sedentary sham operation group (Sed-Sh), a previous exercise and sham operation group (PreE-Sh), a sedentary myocardial infarction (MI) group (Sed-MI), a previous exercise MI group (PreE-MI), a post exercise MI group (PostE-MI) and a combined exercise MI group (ComE-MI), each of 16.All of the rats underwent either MI induction or a sham MI operation, the PreE groups after exercising for 5 weeks on a treadmill. The Sed groups did not exercise. The Post E-MI group did not exercise before the operation, but performed treadmill exercises for 4 weeks beginning 8 weeks after the operation. The ComE-MI group exercised for 5 weeks before and 4 weeks after the operation. All the exercising rats ran on the treadmill for 60 minutes daily, 5 d/wk. Life situation and spontaneous mortality were recorded, and echocardiographic measurements were performed on the4thday and 2, 4, 8 and 12weeks after the operation. All of the rats were sacrificed at the end of the experiment. Results Compared with the Sed-Sh group, the Sed-MI group had significantly larger average LV dimensions at the end of both the diastol (LVEDd) and the systol (LVEDs, but it had lower average fractional shortening (FS) and a smaller average ejection fraction(EF) at all of the different measuring times. The PreE-MI group had significantly lower average LVEDd and LVEDs, but a significantly higher FS and EF than the Sed-MI group on the 4th day. However, 2 weeks after the intervention the difference in LVEDd between the two groups was no longer significant. Significantly higher FS and EF were observed in the PostE-MI group at 12 weeks compared to the Sed-MI group. The ComE-MI group had significantly lower average LVEDd and LVEDs, but significantly higher FS and EF at all the time points than the Sed-MI group. The ComE-MI group had a significantly lower average LVEDs but a higher average FS and EF than the PreE-MI group at 12 weeks after the intervention. Conclusion Pre-MI exercise improves LV function significantly at the early stage, though the difference is temporary. Post-MI exercise improves LV function in the longer term. Combined exercise improves LV function the most effectively. Key words: Exercise; Myocardial infarction; Left ventricular function; Survival rate