Effects of Cardiac Contraction and Increased Coronary Sinus Pressure on the Coronary Arterial Pressure-flow Relationship

Abstract

Increased coronary sinus (CS) pressure and cardiac contraction impair coronary inflow independently. However, it has not been determined how the coronary pressure-flow relationship is strongly affected by changes in CS pressure in the beating heart compared to the non-beating heart. The purpose of this study was to evaluate the combined mechanical effects of cardiac contraction and increased CS pressure. Using isolated, perfused canine hearts, coronary perfusion pressure in the left anterior descending coronary artery (LAD) was gradually reduced in beating and non-beating conditions. Measurements were obtained with and without elevation of CS pressure to determine the mean LAD pressure-flow relationships. At normal and elevated CS pressures, the corresponding zero-flow pressures were not significantly different between the beating and non-beating hearts. A rightward shift of the mean coronary perfusion pressure-coronary flow curve for the beating heart compared to the non-beating heart was observed when CS pressure was not elevated. In contrast, the slopes for both beating and non-beating hearts were similar if the CS pressure was increased. There was a smaller increase in the mean intramyocardial pressure (IMP) at elevated CS pressures in the beating heart as compared to the non-beating heart. Moreover, the increase in diastolic IMP with increased CS pressures in the beating heart was significantly less than that in the non-beating heart. These results indicate that cardiac contraction attenuates the inhibitory effects of increased CS pressure on coronary inflow.