The border zone of the early myocardial infarction in dogs; its characteristics and viability.

In open-chest dogs, the left anterior descending coronary artery was ligated for 150 min. The heart was semiserially cut on a cryomicrotome and areas of ischemic damage were visualized by means of glycogen depletion (PAS reaction) and tissue acidosis (a "sandwich" technique with pH indicator dispersed in a layer of gel). The extent of myocardial damage was determined morphometrically. The mass of the glycogen-depleted heart muscle was greater than the mass of the ischemic tissue detected by means of decreased pH (p less than 0.01). The border zone was characterized by glycogen depletion without acidosis. Circulation studies using intravital fluorescein staining have shown that perfusion is partially retained in the border zone; it is assumed that the hypoperfusion triggers glycogenolysis. Nevertheless, the level of perfusion suffices to wash out the acidic end products. Comparison of contrapulsation-treated dogs and untreated dogs shows that the amount of damaged tissue comprising the border zone can be reduced by this therapeutic intervention (p less than 0.02) - in contrast to the acidotic tissue, the amount of which is not significantly influenced. Therefore the border zone contains damaged but still viable muscle cells.