Coronary hyperperfusion and ventricular function in intact and isovolumic pig hearts

This study characterized the effect of coronary hyperperfusion on left ventricular (LV) geometry and myocardial vascular and tissue volumes in intact hearts, and tested the hypothesis that ventricular function is significantly enhanced only under isovolumic conditions. Randomized 10-min trials of coronary perfusion pressures at approximately 100-110, approximately 150-160, and approximately 180-190 mmHg were performed in extracorporeally perfused pig hearts. First, ultrasonic crystals were used to measure LV wall thickness and major and minor epicardial diameters. LV pressures, maximum dP/dt, and myocardial O2 consumption were not significantly different despite increases in the end-diastolic and end-systolic wall thickness. There were either no changes or small decreases in epicardial major and minor axis dimensions. Second, intramyocardial small vessel vascular and extracellular volumes were measured using radiolabeled dextran and inulin. There was no significant difference in small vessel plasma volume or extracellular space. Finally, pigs were placed on cardiopulmonary bypass and LV volume was fixed with a ventricular balloon. In this isovolumic preparation, coronary hyperperfusion significantly increased peak LV pressure. We conclude that coronary hyperperfusion in hearts with intact peripheral circulations results in small changes in LV geometry but no physiologically significant changes in LV performance. Only under the rigid conditions of an isovolumic preparation is LV function enhanced, and thus the "garden-hose" effect is a model-dependent phenomenon.