Key result
Halothane did not show a synergistic interaction with epinephrine on myocardial conduction, but epinephrine depressed conduction at 8 mM potassium (P<0.05).
Why the study?
Does halothane interact synergistically with epinephrine or isoproterenol to depress myocardial conduction velocity in canine epicardial muscle at normal and elevated potassium levels?
Does halothane interact synergistically with epinephrine or isoproterenol to depress myocardial conduction velocity in canine epicardial muscle at normal and elevated potassium levels?
Halothane does not synergistically interact with epinephrine to depress myocardial conduction, although epinephrine alone depresses conduction at elevated potassium levels.
Answers are grounded in this paper and cite their sources.
No synergistic conduction effect seen in canine model; leaves open clinical relevance at hyperkalemia.
BACKGROUND: Halothane is known to potentiate catecholamine-induced depression of conduction velocity in Purkinje fibers but not endocardial muscle fibers. The purpose of this study was to examine the interactions of halothane with epinephrine and isoproterenol on canine epicardial conduction velocity at moderately elevated extracellular potassium concentration ([K]0). METHODS: Epicardial muscle strips (10x10x2 mm) were superfused with Tyrode's solution containing 4 or 8 mM [K]0 in the presence of 5 microM epinephrine or 1 microM isoproterenol with or without 0.8 mM halothane. Conduction velocity in the longitudinal and transverse directions relative to epicardial fiber orientation was recorded during alternate stimulation in each direction. RESULTS: In the presence of halothane, a change from 4 to 8 mM [K]0 decreased (P< or =0.05) longitudinal and transverse conduction velocities by 26% and 21%, respectively. Isoproterenol alone at 4 and 8 mM [K]0 depressed (P<0.05) both longitudinal and transverse conduction velocities. However, the depression of longitudinal conduction velocity by isoproterenol at 4 mM [K]0 was attenuated by halothane. Epinephrine with or without halothane depressed (P<0.05) both longitudinal and transverse conduction velocities at 8 but not at 4 mM [K]0. CONCLUSION: The results do not support a synergistic interaction between halothane and epinephrine on myocardial conduction but do demonstrate depression of conduction by epinephrine at 8 mM [K+]0, a potassium ion concentration comparable to those reported following epinephrine infusions.
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Camara et al. (2001) studied this question. Halothane with epinephrine or isoproterenol vs. Without halothane / different potassium levels was evaluated on Longitudinal and transverse conduction velocities (p=<0.05). Halothane did not show a synergistic interaction with epinephrine on myocardial conduction, but epinephrine depressed conduction at 8 mM potassium (P<0.05).
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