The effect of an isovolumic left ventricle on the coronary vascular competence during reflow after global ischemia in the rat heart.

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Abstract
During global ischemia in isolated rat hearts, the development of contracture, due to irreversible myofilament sliding, causes reduction of left ventricle luminal volume. Also, a considerable area of the myocardium cannot be reperfused after 1 hour's global ischemia. The purpose of this study was to reduce myofilament sliding by placing a fluid-filled isovolumic balloon in the left ventricular cavity of isolated rat hearts and assess the extent of reflow, after 60 minutes' ischemia, by perfusion of a 1% fluorescein tracer solution. Light and electron microscopy was used to determine the state of the vasculature and myofibrillar apparatus. In hearts without the left ventricular balloon (control) the ischemia produced a no-reflow zone comprising 45% of the myocardial wall. In contrast, if an isovolumic balloon was in place during the ischemic period, only 6% of the wall was involved. The volume of the capillary bed in the subendocardium of the control hearts was about 60% of that in th isovolumic hearts. In the isovolumic ("isometric") mode, ischemic contracture was associated with more severe myocardial cell injury than in the corresponding control ("isotonic") mode. Our results support the concept that intramyocardial pressure generated by ischemic contracture plays a major role in the production of the no-reflow phenomenon in globally ischemic rat hearts, and indicate that it is the series elastic component of cardiac muscle which imparts the stiffness necessary to prevent reopening of coronary vessels after a severe ischemic insult.