Temporal and spatial development of myocardial infarcts in porcine hearts without significant collateral blood flow.

To evaluate the time-dependent beneficial effect of reperfusion on infarct size, we investigated the temporal and spatial development of infarcts in porcine hearts. The left anterior descending coronary artery was occluded in 17 pigs for different periods of time. Ischemia was always followed by 4 hours of reperfusion. After 60 minutes of ischemia, transmural needle biopsies subdivided into subendocardial and subepicardial halves were removed from the ischemic apex to determine the tissue concentrations of adenosine triphosphate and nicotinamide adenine dinucleotide. The myocardium at risk was determined with a fluorescent dye, and the infarcted tissue with nitroblue tetrazolium stain. Infarct size was expressed as the ratio of the infarcted myocardium over the risk region. Ischemic cell death began in the jeopardized left ventricular subendocardial septum after about 30 minutes of ischemia. Further progress involved the right subendocardial septum and the subendocardium of the left anterior free wall. After 75 minutes of ischemia, most of the myocytes were already irreversibly injured. Tissue damage from the infarctions was complete after 90 to 120 minutes of ischemia. These results indicate that in hearts without a significant collateral blood flow, reperfusion can only reduce infarct size if initiated within 60 to 75 minutes of ischemia. As in canine hearts, infarctions in porcine hearts progress from the ischemic subendocardium toward the outer layers.