Background: There are several clinical situations in which large epicardial coronary arteries are deprived of blood flow, such as occurs when an obstructing thrombus or embolus lodges within a vessel or during coronary dissection. There is little information concerning the effect of flow deprivation on large epicardial coronary arteries.
Methods and results: We studied a model in which a segment of a large epicardial coronary artery was deprived of blood flow using both proximal and distal clamps for 3 hours followed by reperfusion. On examination by light microscopy of cross sections of the arteries, 19 +/- 6 neutrophils were present in the intima of ischemic/reperfused vessels, whereas only a mean of 4 +/- 3 (SEM) were present in the intima of nonischemic vessels (p less than 0.02). On average, there were 17 +/- 9 neutrophils just under the elastic lamina in ischemic/reperfused vessels versus none in the nonischemic vessels (p less than 0.05); there were 16 +/- 10 neutrophils present within the media of ischemic/reperfused vessels, and none (p less than 0.05) in the nonischemic vessels. Electron microscopic analysis revealed that neutrophils in the ischemic/reperfused vessels were often "sandwiched" between the endothelial cells and the elastic lamina. Ultrastructural abnormalities within the myocardium also revealed damage to the microvasculature, including the presence of neutrophils within the vessels and erythrocyte stasis. To rule out the possibility that findings in the large epicardial arteries were due to toxic substances from static blood within the isolated arterial segment, a protocol was performed in which blood was removed from the isolated segment. Again, neutrophil infiltration into the vessel was observed. Resting mean epicardial coronary artery blood flow before coronary occlusion was 19 +/- 3 ml/min; mean coronary blood flow 2.5 hours after reperfusion was identical at 19 +/- 3 ml/min. Response to both endothelial-dependent vasodilation (acetylcholine) and endothelial-independent vasodilation (nitroglycerin) challenges was normal early after reperfusion but was depressed late after reperfusion, suggesting progressive vascular dysfunction and hence a form of vascular reperfusion injury in this model.
Conclusions: When large epicardial coronary arteries are deprived of blood flow, followed by reperfusion in this model, neutrophils migrate into the vessel wall as well as into the microvasculature. These abnormalities are associated with reduced endothelial-dependent and endothelial-independent coronary vasodilator reserve.