Short-term exercise has a prolonged effect on scar formation after experimental acute myocardial infarction

The effect of early short-term exercise on late scar formation of myocardial infarction is unknown. Therefore, rats anesthetized with ether underwent proximal left coronary artery occlusion. Infarct extent was assessed 24 hours later by electrocardiographic criteria (QRS morphology). Immediately after electrocardiography, the rats were divided into two groups. Group 1 rats (n = 8) were subjected to daily graded swimming (up to 45 minutes a day) starting 24 hours after coronary occlusion for a total of 7 days followed by 2 weeks of nonswimming. Group 2 rats (n = 7) served as a control group and were not subjected to swimming. Twenty-one days after coronary occlusion, the rats were anesthetized, their heart excised and wall thickness determined histologically. Noninfarcted septal wall thickness was similar in both Groups 1 and 2. A ratio for transmural infarcts was obtained from multiple measurements by dividing scar thickness by noninfarcted septal wall thickness. Ratio of scar thickness divided by noninfarcted wall thickness for the control (nonswimming) group was 0.48 +/- 0.05 (mean +/- standard error of the mean); however, in the exercise (swimming) group, there was marked scar thinning with a ratio of 0.25 +/- 0.02 (mean +/- standard error of the mean, p less than 0.001). Infarct extent assessed by planimetry as percent of left ventricular slices was similar in both groups. Thus, early short-term swimming exercise during the first week after experimental myocardial infarction even when followed by 2 weeks without swimming, has long-lasting effects on scar formation.