Studies on Subendocardial Vulnerability to Underperfusion using a Needle-probe CCD microscope

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Subendocardium is most vulnerable to underperfusion and ischemia in the myocardium. Growing experimental and clinical evidence suggests that abnormal phasic coronary flow patterns, especially to-and-fro flow motion or coronary slosh phenomenon, are associated with coronary underperfusion. It is conceivable that diameter change of coronary arterioles is associated with the coronary underperfusion and phasic flow pattern. During the past several years, important observations have been made regarding the differences in arteriolar behaviors between subepicardium and subendocardium. Most striking difference is the greater arteriolar pulsation in subendocardium than in subepicardium. Therefore, to understand the cause and effect of abnormal phasic coronary flow pattern in relation to subendocardial underperfusion, it is crucial to evaluate behaviors of both subepicardial and subendocardial arterioles during coronary underperfusion. In the present study, in open-chest anesthetized dogs, a nee … More dle-probe CCD video-microscope was employed to visualize subendocardial microcirculation. In response to a transient cessation of coronary arterial flow and reperfusion (reactive hyperemia) , the percent increase in end-diastolic diameter of subendocardial arterioles was greater than that of subepicardial arterioles. The diastolic-to-systolic vascular pulsation amplitude at the peak flow was greater in the subendocardium than subepicardium. To produce a stable condition of coronary underperfusion, which is known to enhance coronary slosh phenomenon, a newly developed coronary perfusion system was connected to the left main coronary artery. The coronary perfusion pressure could be changed to a preset level. With coronary underperfusion, both subepicardial and subendocardial arterioles showed rapid changes of their diameters, suggesting the presence of quick vascular regulation. Since vasodilation is associated with a greater pulsation in the coronary arterioles, the vasodilatory response of subendocardial arterioles to a coronary underperfusion may contribute to enhance slosh phenomenon and the process of subendocardial ischemia. Less