Interactions of halothane with isoproterenol and epinephrine on canine epicardial conduction velocity at normal and elevated potassium levels

Background: Halothane is known to potentiate catecholamine-induced depressi on of conduction velocity in Purkinje fibers but not endocardial muscle fib ers. The purpose of this study was to examine the interactions of halothane with epinephrine and isoproterenol on canine epicardial conduction velocit y at moderately elevated extracellular potassium concentration ([K](0)). Methods: Epicardial muscle strips (10x10x2 nun) were superfused with Tyrode 's solution containing 4 or 8 mM [K](0) in the presence of 5 muM epinephrin e or I muM isoproterenol with or without 0.8 mM halothane. Conduction veloc ity in the longitudinal and transverse directions relative to epicardial fi ber orientation was recorded during alternate stimulation in each direction . Results: In the presence of halothane, a change from 4 to 8 mM [K](0) decre ased (P less than or equal to0.05) longitudinal and transverse conduction v elocities by 26% and 21%, respectively. Isoproterenol alone at 4 and 8 mM [ K](0) depressed (P <0.05) both longitudinal and transverse conduction veloc ities. However, the depression of longitudinal conduction velocity by isopr oterenol at 4 mM [K](0) was attenuated by halothane. Epinephrine with or wi thout halothane depressed (P <0.05) both longitudinal and transverse conduc tion velocities at 8 but not at 4 mM [K](0). Conclusion: The results do not support a synergistic interaction between ha lothane and epinephrine on myocardial conduction but do demonstrate depress ion of conduction by epinephrine at 8 mM [K+](0), a potassium ion concentra tion comparable to those reported following epinephrine infusions.