Absence of a cumulative deterioration of regional function during three repeated 5 or 15 minute coronary occlusions

Recurrent myocardial ischemia is commonly seen in patients with coronary artery disease, in patients undergoing cardiac surgery with intermittent cross-clamping, and experimentally when multiple occlusion preparations are used to test drugs. Our study was designed to investigate whether myocardial injury is cumulative after three sequential ischemic episodes. Sixteen dogs were instrumented with ultrasonic crystals to assess percentage of segmental shortening and percentage of wall thickening in ischemic and nonischemic regions. The left anterior descending coronary artery was occluded three times for 5 min in one group (n = 8) and three times for 15 min in another group of dogs (n = 8) and each occlusion was followed by 30 min of reflow. Blood flow was determined with microspheres before coronary artery occlusion in the 5-min group and during occlusion in the 15-min group and in all dogs 25 min into the first and third reperfusion periods. During the three reperfusion periods mean segmental shortening in the ischemic zone recovered to only 60.5 ± 8.7% (± SEM) of the preocclusion level (p < .003) in the 5-min occlusion group and to 36.9 ± 17.7% in the 15-min occlusion group (p < .01). Mean wall thickening recovered to 61.3 ± 16.6% (p < .06) in the 5-min group and to 48.6 ± 11.8% in the 15-min group (p < .004). There were no significant differences during the reperfusion phase when mean values for the ischemic segment after the second and third occlusion were compared with the data obtained after the first occlusion in either group. The degree and pattern of postischemic recovery was similar after each occlusion. In both groups during reperfusion blood flow in the previously ischemic zone tended to be lower than flow in the nonischemic zone. Infarction was absent, as assessed by tetrazolium staining, in both groups. The results show that a coronary artery occlusion as brief as 5 or 15 min leads to depression of endocardial contractile function in the reperfused zone, but that these alterations are not cumulative after three repetitive coronary artery occlusions.