Coronary Microcirculation Changes during Myocardial Stunning in Dogs

OBJECTIVE: To investigate changes in the coronary microcirculation during myocardial stunning in dogs. METHODS: Male mongrel dogs underwent a 15- or 60-min occlusion of the left anterior descending coronary artery, followed by a 120-min reperfusion. Myocardial contrast echocardiography was performed before and after treatment with acetylcholine (ACH) or nitroglycerin (NG). Peak videointensity (PVI) in the myocardial zone was measured, and myocardial samples were examined using transmission electron microscopy. RESULTS: In the 15-min group, the ratio of the PVI between the stunned and intact myocardial zone (PVIR) before and after treatment with NG (NG-PVIR) or ACH (ACH-PVIR) declined markedly in the early period of reperfusion and then returned to preligation levels. In the 60-min group, NG-PVIR was reduced in the early period of reperfusion and then returned to its preligation level. A low level of ACH-PVIR lasted during the entire 120-min reperfusion. Similar changes in the ratio of the PVIR before and after treatment with NG or ACH were observed. In the 60-min group, capillary endothelial edema and widening of intercellular linking gaps were observed. CONCLUSIONS: We observed microvascular endothelial damage and endothelium-dependent dilatation impairments in stunned myocardium, and their severity and recovery rate are affected by the duration of ischemia.