Effect of repetitive brief episodes of ischemia on cell volume, electrolytes and ultrastructure

The effects of repeated brief episodes of ischemia on myocardial cell volume, electrolytes and ultrastructure were studied in dogs. Seventeen animals were divided into five groups. Group 1 underwent a single 10 minute occlusion of the circumflex coronary artery, with no subsequent reperfusion. Group 2 was similarly subjected to a 10 minute coronary occlusion, but was allowed a 20 minute reperfusion period. Group 3 underwent two 10 minute occlusions separated by 20 minutes of reperfusion and Group 4 underwent four 10 minute occlusions, each separated from the next by 20 minutes of reperfusion. Group 5 was subjected to a single, uninterrupted 40 minute occlusion. The anterior and posterior papillary muscles in each heart were sampled to compare nonischemic versus ischemic myocardium. No changes in myocardial water or electrolytes occurred during ischemia. However, reperfusion was associated with slight increases in tissue water and potassium, loss of magnesium and minimal changes in sodium or calcium ions. Electron microscopic analysis revealed signs of mild ischemic injury (absence of normal intramitochondrial granules, partial loss of glycogen and slight clumping of the nuclear chromatin) in posterior papillary muscle from Groups 1, 3 and 4. Group 2 showed complete recovery with 20 minutes of reperfusion, whereas Group 5 showed evidence of irreversible injury. There was no difference in the appearance of myocardium that had been subjected to one, two or four 10 minute occlusions. It is concluded that intermittent periods of reperfusion between brief episodes of coronary ischemia have a protective effect and prevent a cumulative deterioration of myocardial ultrastructure.