No effect of coronary perfusion on regional myocardial function within the autoregulatory range in pigs. Evidence against the Gregg phenomenon.

Abstract

The hypothesis that increases in coronary perfusion increase ventricular performance independently from providing enhanced oxygen supply ("Gregg phenomenon") remains controversial. To study the physiological significance of changes in coronary perfusion on global and regional myocardial function in situ, the left anterior descending coronary artery of isoflurane-anesthetized swine was cannulated, and perfusion was varied. In one group of swine (n = 5), coronary arterial pressure was increased in four steps from 88 +/- 11 to 186 +/- 11 mm Hg by increasing the speed of the pump circuit providing coronary blood flow. No changes in left ventricular end-diastolic pressure, peak pressure, or maximum left ventricular dP/dt were observed. Subendocardial blood flow (by radiolabeled microspheres) increased from 0.96 +/- 0.27 to 2.04 +/- 0.73 ml/min/g without any increase in systolic wall thickening (by sonomicrometry) or myocardial oxygen consumption of the anterior myocardium. In a second group of swine (n = 8), coronary arterial pressure was kept constant and coronary blood flow was increased stepwise by intracoronary adenosine infusion. End-diastolic pressure, peak pressure, and maximum left ventricular dP/dt remained unchanged when coronary blood flow increased from 21.7 +/- 9.8 to 93.8 +/- 34.1 ml/min. Subendocardial blood flow increased from 0.89 +/- 0.26 to 3.28 +/- 1.02 ml/min/g, again without any increase in systolic wall thickening (45.6 +/- 8.6 versus 42.6 +/- 9.8%) and myocardial oxygen consumption (5.75 +/- 1.18 versus 5.87 +/- 1.67 ml/min/100 g). In a third group of swine (n = 10), coronary arterial pressure was lowered by intracoronary adenosine infusion during constant coronary inflow. Left ventricular hemodynamics remained unchanged. With a decrease in coronary arterial pressure from 130 +/- 25 to 71 +/- 14 mm Hg, no decreases in subendocardial blood flow and systolic wall thickening were observed. Only when coronary arterial pressure was further reduced to 57 +/- 13 mm Hg did systolic wall thickening fall to 25.7 +/- 9.9% (control, 31.1 +/- 11.1%), associated with a decrease in subendocardial blood flow from 1.17 +/- 0.39 to 0.87 +/- 0.52 ml/min/g. Thus, the Gregg phenomenon plays no significant role within or above the autoregulatory pressure-flow range normally seen in anesthetized swine in situ.