The effect of increased cardiac pressure load and volume load on the size of myocardial infarction following coronary artery occlusion.

The size of the myocardial infarction following standardized coronary artery occlusion was studied in rats with myocardial hypertrophy due to increased pressure load (aortic stenosis) and increased volume load (swimming exercise). The infarction was significantly smaller in the latter than in the former group. In normal control rats the infarction was larger than in the swimming-exercised rats and smaller than in the rats with aortic stenosis, but these differences were not statistically significant. The observations support the idea that the myocardial capillary neoformation previously shown to be induced by physical exercise may limit the infarction following coronary artery occlusion, whereas the absence of such a capillary reaction in pressure-induced cardiac hypertrophy renders the myocardium more vulnerable, to damage by a coronary occlusion. The size and distribution of the infarction was highly variable as was the configuration of the infarction in the individual heart. For an accurate determination of the size of the infarction, serial sectioning of the whole heart is necessary, with a distance between the sections examined not exceeding 0.5 mm.