Limitation of myocardial infarct size after surgical reperfusion for acute coronary occlusion

We investigated the effect of different forms of myocardial protection on infarct size and on the necrotic myocardial process after reperfusion for acute occlusion of the left anterior descending coronary artery (LAD) in dogs. Three control groups were formed: a 1 hour, 2 hour, and 6 hour locally ischemic control. Three experimental groups were locally ischemic for 1 hour and then reperfused after an additional hour of local ischemia on cardiopulmonary bypass with the heart protected by intermittent ischemia, cold potassium cardioplegia, or blood cardioplegia. To delineate the area at risk, the LAD was temporarily occluded 30 seconds before the 6 hour sacrifice time, and monastral blue dye was injected through a polyvinyl catheter placed in the left atrial appendage. The LAD area at risk (AR) was not stained. After 6 hours the heart was excised and treated with triphenyltetrazolium chloride (TTC) to define the area of myocardial necrosis (AN). The AN/AR ratio was determined for each animal by planimetry. Mean values were then computed in each of the six groups and evaluated by the Student's t test for paired data. The 1 hour control group had an AN/AR ratio of 64% +/- 5%; the 2 hour control group, 80% +/- 6%; and the 6 hour control group, 92% +/- 1%. The intermittent ischemia group had an AN/AR ratio of 83% +/- 2%; the crystalloid cardioplegic group (2 hours of ischemia) had a ratio of 69% +/- 4%, similar to the 1 hour control but significantly smaller than the 2 hour control (p less than 0.05); and the blood cardioplegia group had an AN/AR ratio of 48% +/- 8%, significantly better than any other group. These data demonstrate that myocardial necrosis after coronary occlusion is a time-related phenomenon and will increase to encompass a large fraction of the area at risk unless there is physical or pharmacologic modification during reperfusion, such as crystalloid or blood cardioplegia.