Subendocardial versus transmural myocardial infarction: relationship to the collateral circulation in canine and porcine hearts.

In the present study, the relationship between transmural perfusion gradients and myocardial infarct size and distribution in canine and porcine hearts was characterized. Anesthetized pigs (N = 6) and dogs (N = 7) underwent a 2-h occlusion and 5-h reperfusion of the distal third of the left anterior descending coronary artery. The area at risk for infarction and ultimate infarct size were determined by fluorescein dye infused intracoronary and nitro blue tetrazolium stain, respectively. Myocardial perfusion within normal, ischemic, and infarcted regions was determined by the radioactive microsphere technique in each species. In dogs, infarction was subendocardial and comprised 29.9 +/- 5.5% of the area at risk, while in pigs infarction was transmural and comprised 50.1 +/- 4.2% (p less than 0.05). Collateral perfusion of the subendocardium of infarcted regions in pig and dog hearts was similar (0.05 mL X min-1 X g-1), while flow to the subepicardium was significantly (p less than 0.05) higher in dogs than in pigs (0.25 versus 0.05 mL X min-1 X g-1). The data demonstrate that species differences in myocardial infarct size and shape are related to differences in coronary collateral blood flow. The smaller subendocardial infarction in dog hearts is related to a relatively high subepicardial perfusion and transmural infarction in pig hearts owing to the lack of collateral perfusion in subepicardium as well as subendocardium.