Endogenous and exogenous catecholamines can accentuate myocardial ischemia only when coronary blood flow is below a critical level

Seventy-eight dogs with graded constriction of the left main coronary artery were studied to determine the coronary blood flow at which the heart is vulnerable to catecholamine induced ischemia. The left main coronary artery was cannulated with a Griggs' type selfperfusing cannula. The coronary blood flow (CBF) was reduced by graded constriction of the extra-corporeal circuit connected with this cannula. Blood flow rates between 12 and 117 ml/min/100g were studied. Cardiac activation was achieved by either intracoronary administration of a physiological dose of catecholamine (noradrenaline ; 0.4 μg/kg/min or adrenaline ; 0.2μ/kg/min), or by electrical stimulation of the left stellate ganglion (4 Hz, 2 msec, 10 V for 5 min). When CBF was below 30 ml/min/100g, accentuated myocardial ischemia was always indicated by lactate production, myocardial creatine phosphate depletion, ischemic ST segment changes, and elevated left ventricular end diastolic pressure (LVEDP) during these simulations. When CBF was above 50 ml/min/100g, catecholamine clearly accelerated the cardiac function and myocardial metabolism with no sign of ischemia. When CBF was between 30 and 50 ml/min/100g signs of accelerated myocardial ischemia appeared during catecholamine activation in only 1/2 of the dogs. This study indicated that the critical level for CBF at which endogenenous or exogenous catecholamine can produce ischemia is between 30 and 50 ml/min/100g.