Epinephrine-induced ventricular arrhythmias in dogs anesthetized with halothane: potentiation by thiamylal and thiopental.

Epinephrine-induced ventricular arrhythmias were studied in 8 dogs anesthetized at weekly intervals with halothane (1.09% end-tidal concentration) preceded by thiamylal or thiopental (20 mg/kg of body weight). Lead II, bundle of His and high right atrial electrograms, and femoral artery and airway pressures were recorded. Epinephrine was infused in logarithmically spaced increasing rates (initial rate = 0.25 micrograms/kg/min) for a maximum of 2.5 minutes. The maximal (greater than or equal to 4 ventricular premature depolarizations within 15 s of each other) and minimal (all other ventricular or junctional rhythms) arrhythmogenic doses were calculated (infusion rate X time to arrhythmia). The mean (+/- SD) minimal arrhythmogenic dosages for the thiamylal-halothane, thiopental-halothane, and halothane-only groups were 1.84 +/- 0.66, 1.83 +/- 0.64, and 3.69 +/- 1.32 micrograms/kg, respectively; the mean (+/- SD) maximal arrhythmogenic dosages were 2.32 +/- 0.77, 3.37 +/- 1.30, and 8.86 +/- 4.40 micrograms/kg, respectively, with no change after 4 hours of anesthesia. During infusion of the maximal arrhythmogenic dosages, the mean infusion of the maximal arrhythmogenic dosages, the mean percentage increase in serum K+ for thiamylal-halothane, thiopental-halothane, and halothane-only groups was 33 +/- 14%, 31 +/- 13%, and 38 +/- 18%, respectively.