Effect of serial brief ischemic episodes on extracellular K+, pH, and activation in the pig

This study was performed to determine the reproducibility of the ionic and electrical changes associated with serial ischemic episodes. We used ion-selective and bipolar plunge electrodes to determine the changes in left ventricular extracellular potassium ([K+]e), extracellular pH (pHe), and local activation during sequential 10 min occlusions of the left anterior descending coronary artery separated by 50 min of reperfusion in open-chest anesthetized pigs. We found that uniformly during the initial occlusion, and in approximately 50% of animals during the second occlusion, [K+]e rose more rapidly but to a lower level than in subsequent occlusions. By the third occlusion the changes in [K+]e were reproducible. Extracellular acidosis was greatest in the first occlusion and decreased progressively with each subsequent occlusion. Local activation was characterized by a decrease in spontaneous improvement and increase in block with each successive occlusion. The occurrence of ventricular fibrillation could not be directly attributed to the magnitude of the change in [K+]e or pHe. Moreover, the occurrence of ventricular fibrillation in one occlusion did not necessarily predict its occurrence thereafter. Our results indicate that serial episodes of ischemia are associated with different but predictable changes in ionic and electrical events that may be clinically relevant and that must be appreciated before the results from similar protocols with serial ischemic episodes can be interpreted meaningfully.