Myocardial surface oxygen pressure across the border zone in the pig during acute coronary artery occlusion. A comparison of pretreatment with metoprolol or isoprenaline.

Tissue oxygen pressure was measured in the pig heart during repeated coronary artery occlusions. ptO2 was measured with an array-multiwire-electrode across the border zone, i.e. the transition zone between normal and ischaemic myocardium. The LAD was occluded three times, each lasting 5 min and with 55 min of reperfusion between the occlusions. Three groups of animals were studied: Group 1 served as controls; Group 2 were given metoprolol 0.3 mg/kg i.v. after the first LAD occlusion; Group 3 were given isoprenaline in a continuous infusion, started after the first LAD occlusion and continued throughout the rest of the experiment. Heart rate differed as expected between the two treated groups. The pattern of ptO2 values across the border zone repeated itself for each animal. No change in the pattern of ptO2 values was seen in either treatment group. In conclusion, there were no indications that it was possible to change the ptO2 of the border zone in the pig heart either with metoprolol or isoprenaline in the doses used.