The border zone in acute myocardial ischemia in the dog--a histochemical, biochemical and ultrastructural study.

To identify and characterize the border zone, anesthetized dogs were subjected to 1-hour occlusion of the left anterior descending coronary artery with (Group R) or without (Groups A and B) 2 hours of subsequent reperfusion. Histochemical analysis of glycogen distribution, biochemical determination of lactate and adenosine triphosphate (ATP), and ultrastructural examination were carried out. In Group A, the epicardial edge of cyanosis was clearly visible and the sharply demarcated glycogen-depleted area contained peninsulas of cells with varying amounts of glycogen in its epicardial half, which were suggested to depend on collateral blood flow by intracoronary dye injection. In Group B, the edge of cyanosis was obscure and the glycogen-depleted area contained above-mentioned peninsulas at its lateral edge also. In Group R, although the edge of cynaosis was clear on occlusion, the peninsulas were numerous at the lateral edge as well as in the subepicardium after reperfusion. Lactate accumulation and ATP degradation corresponded well to glycogen decrease in all groups and were reduced significantly by reperfusion (p less than 0.005). Ultrastructural examination confirmed these findings. Therefore epicardial, and in some cases also lateral, salvageable border zones may exist and be composed of peninsulas of normal and intermediately injured cells dependent on collateral blood flow.