Effect of coronary artery reperfusion on infarct size in swine

Several authors have reported a low mortality and salvage of ischemic myocardium in patients undergoing coronary revascularization after recent myocardial infarction. In this study, 20 surviving pigs with a coronary circulation similar to that of man were divided into two groups of 10 animals each. In the first group, the left anterior descending coronary artery (LAD) was ligated just beyond the first diagonal branch. Five animals were put to death at 24 hours and the remaining five animals, at 7 days. In the other group of 10 animals, the LAD was occluded just beyond the first diagonal branch and reperfused 3 hours after occlusion. Five of these animals were put to death at 24 hours and the remaining five animals, at 7 days. The left atrial pressure (LAP), heart rate, mean arterial pressure (MAP), and cardiac output were continuously monitored. Myocardial infarct size was determined planimetrically after the myocardium was sliced and stained with nitroblue tetrazolium. In five animals subjected to ligation for 24 hours, myocardial infarct size was 20.3 +/- 0.53 standard error mean (SEM) grams infarct per 100 gm left ventricular and septal mass (gm/100 gm LVS). In five animals subjected to occlusion, reperfusion in 3 hours, and death at 24 hours, the infarct size was 22.9 +/- 1.7 SEM gm/100 gm LVS. At 1 week in the ligated animals the infarction decreased to 15.5 +/- 1.7 SEM gm/100 gm LVS. In the reperfused animals at 1 week the infarction size was 14.5 +/- 1.7 SEM gm/100gm LVS. There was no significant difference in these values (Student's t test). Light and electron micrographs demonstrated hemorrhagic necrosis in every instance with reperfusion. Cardiac output, LAP, and MAP remained unchanged after reperfusion. These data suggest that in human beings without well-developed inherent collaterals sustaining myocardial infarction with coronary occlusion, that reperfusion as early as 3 hours after infarction would not be beneficial.