EFFECTS OF THORACIC EPIDURAL-ANESTHESIA ON CHANGES IN ISCHEMIC MYOCARDIAL-METABOLISM INDUCED BY INTRACORONARY INJECTION OF ENDOTHELIN IN DOGS

Objective: Thoracic epidural anesthesia (TEA) has been reported to all eviate ischemic damage to the myocardium. Endothelin, an endothelium-d erived peptide and a potent coronary vasoconstrictor, may contribute t o poor cardiac perfusion and ischemia. The objective was to examine re gional myocardial metabolism during ischemia caused by intracoronary i njection of endothelin with and without TEA. Design: The three experim ental groups and three treatments were randomized. Setting: All studie s were conducted in a university research laboratory. Participants: Th irty anesthetized dogs comprised the study groups. Interventions: Stud y animals were divided into three groups of la animals each identified as normal saline (Ns); TEA; and TEA + blood pressure controlled (TEA + BPC). The NS group had 0.5 mL/kg of normal saline injected into the T-4-5 epidural space. The TEA group had 0.5 mL/kg of saline containing 1% lidocaine injected into the T-4-5 epidural space. The TEA + BPC gr oup had blood pressure and heart rate maintained at pre-epidural injec tion values by partially occluding the descending aorta and by atrial pacing. Endothelin (15 pmol/kg) was bolus injected into the left anter ior descending (LAD) artery of each heart. Systolic and diastolic bloo d pressure, heart rate, and LAD coronary blood flow (CBF) were monitor ed. Three minutes after injection of endothelin, myocardial tissue was sampled from the distribution of the LAD artery and from the control, left circumflex (LCx) artery. ATP, ADP, AMP, lactate, and pyruvate we re measured by enzymatic methods. Measurements and Main Results: It wa s found that in each group endothelin consistently decreased LAD CBF, but the decrease was less in the TEA + BPC group. In the tissue distri bution of the LAD, the levels of ATP and energy charge potential were lower, and the level bf lactate was higher in the NS group than in the TEA or the TEA + BPC groups (p < 0.01). Conclusions: These results co nfirm that (1) endothelin injected into the LAD artery decreases CBF a nd causes selective myocardial ischemia in a fashion similar to intrav ascular stenosis of the LAD rather than to mechanical occlusion and (2 ) TEA, with or without pressure support, lessens the degree of regiona l ischemia induced by injection of endothelin in the LAD. Copyright (C ) 1996 by W.B. Saunders Company