Reperfusion injury in dog hearts with permanent occlusion of a coronary artery, probably due to reperfusion via collateral vessels

To clarify whether or not reperfusion injury occurs in the permanent occlusion of a coronary artery, we analyzed quantitatively contraction band necrosis as an indicator of early recanalization, coagulation necrosis, infarct size and measured regional blood flow in dog hearts with collateral circulation. Fifty mongrel dogs were divided into four groups: 15 dogs with a 24-hour occlusion of the left anterior descending coronary artery just distal to the first diagonal branch (permanent occlusion group): 15 dogs a with 3-hour occlusion followed by 24-hour recanalization (recanalization group); 10 dogs with a 2-hour occlusion without recanalization (transient occlusion group); 10 dogs with a 4-hour occlusion without recanalization (transient occlusion group).

The regional blood flow in the subepicardium and subendocardium determined by the generated hydrogen gas clearance method was greatly decreased 30 minutes after occlusion (14 + 8%/12 ± 9%) and was relatively restored from 180 minutes (31 ± 21%/21 ± 14%) to 24 hours later (41 + 19%/26 + 16%) in spite of complete occlusion of the coronary artery. The percentage infarct area in the risk area was significantly greater in the permanent occlusion group (60 ± 26%) than in the recanalization group (35 ± 31%). Although most of the infarct was occupied by contraction band necrosis in the recanalization group (86 ± 12%), contraction band necrosis was diffusely seen even in the permanent occlusion group (54 ± 27%). In both the permanent and recanalization groups, contraction band necrosis was the main histological feature of small infarcts occupying less than 30% of the risk area, while coagulation necrosis was the main feature in very large infarcts occupying more than 80% of the risk area. In the occlusion groups without recanalization, the percentage area of contraction band necrosis in the risk area was 6 ± 8% after the 2-hour occlusion, 23 ± 17% after the 4-hour occlusion and 31 ± 21% after permanent occlusion; the difference between the 4-hour and permanent occlusion groups was not significant. In the permanent occlusion group, the percentage infarct area in the risk area was inversely correlated with regional blood flow during occlusion, an indicator of collateral flow. It was concluded that reperfusion injury occurs even in hearts without recanalization. The pathogenesis may involve reperfusion in the risk area via collateral circulation. Protection against reperfusion injury is important to minimize the infarct size even in hearts with permanent occlusion, although the presence of collateral flow is an important factor in limiting infarct size.