Effect of Acute Sympathectomy by Epidural Anesthesia on the Canine Coronary Circulation

Abstract

The effects of reversible sympathetic neural blockade of the canine myocardium under control conditions and in the presence of decreased coronary blood flow and after myocardial infarction were investigated in 17 dogs. A multiple-microsphere technique was used to measure distribution of blood flow in the myocardium. Epidural blockade was associated with the following changes in the ratio of endocardial to epicardial blood flow: under control conditions, no change; after 50% decrease in coronary flow, 18% increase in endocardial/epicardial ratio; after myocardial infarction at unrestricted coronary flow, 43% ratio increase; after myocardial infarction and 50% decrease in coronary flow, 76% increase of endocardial/epicardial ratio. These effects appear to be independent of systemic factors, and may result from alterations in tone of transmural resistance vessels. Cervicothoracic epidural blockade resulted in a decrease in systemic pressure and an increase in coronary vascular resistance as myocardial O2 demand decreased. When systemic pressure was restored, these effects were abolished. In the presence of myocardial infarction, epidural blockade had less effect on systemic pressure and left ventricular filling pressure was decreased. With decreased coronary flow, sympathetic blockade redistributed coronary blood flow, favoring the endocardium in the normal and infarcted heart.