Myocardial oxygen pressure across the border zone during acute coronary artery occlusion in the pig heart.

An experimental model for studies of local myocardial ischemia is described. During coronary artery occlusion of various durations, from two to sixty minutes, tissue oxygen pressure (ptO2) was measured across the "border zone" i.e., the tissue between normal and ischemic myocardium. PtO2 was measured with a surface oxygen electrode with eight measuring points arranged in an array. In fourteen pigs a total of forty coronary artery occlusions were studied. During occlusion one single pattern of ptO2 values was found; the measurements from the first point, closest to the core of ischemia, dropped rapidly to zero while the second, third and fourth measuring points showed a stepwise slower decrease in ptO2. In four animals we found a spontaneous increase in ptO2 during coronary artery occlusion. Upon reopening of the occluded artery there was a rapid rise in ptO2 as well as an "overshoot". Our findings support the hypothesis of a narrow "border zone" with a small residual blood flow thus subjectable to treatment aiming at reduction in the size of the infarct.