Acute coronary occlusion: oxygen pressure in the border zone studied in the pig

The area between ischemic and normal myocardium after acute coronary occlusion-the border zone-is of great interest. It has been proposed that this area contains reversibly damaged myocardium subjectable to myocardial salvage. Twenty Swedish land race pigs were studied, 13 after acute occlusion of the left anterior descending coronary artery (LAD), while seven served as controls. We measured tissue oxygen pressures (ptO2) subepicardially with the MDO electrode. This is a multiwire surface electrode measuring ptO2 with eight individual platinum wires. Hundred and twenty values were collected in each measuring situation. The electrode was positioned on the lateral border zone, measurements were performed before and 5, 30 and 120 min after LAD occlusion. In five cases successful measurements were performed across the border zone. A mixture of normal and ischemic ptO2 values was found 5 min after occlusion. After 30 min of occlusion the number of ischemic values decreased and this was particularly the case after two hours of occlusion. The results support the view that the border zone was very narrow. The reduced number of ischemic values after two hours of permanent LAD occlusion also indicated that the border zone may be narrow but not necessarily fixed but instead dynamic. In this case there was a spontaneous decrease of the ischemic area.