Transient negative dromotropic effects of catecholamines on canine Purkinje fibers exposed to halothane and isoflurane.

The time-dependent effects of catecholamines in combination with volatile anesthetics on conduction velocity of canine Purkinje fibers were investigated to evaluate a controversial older hypothesis that the arrhythmogenic interaction between epinephrine and halothane may involve abnormal conduction. Two groups of 12 in vitro preparations were stimulated at 150 beats/min. In the first group, 5 microM epinephrine by itself did not alter conduction velocity over a 10-min period from a control mean value of 1.97 +/- 0.08 m/s. However, 5 microM epinephrine, in the presence of either 0.4 mM halothane or 0.4 mM isoflurane, reduced conduction velocity (P < or = 0.01) by about 10-15% within 3-5 min, with recovery toward control by 10 min. The mean conduction velocity at the 4th minute of exposure, in the presence of halothane and epinephrine (1.65 +/- 0.11 m/s), was lower (P < or = 0.01) than that obtained in the presence of isoflurane and epinephrine (1.74 +/- 0.07 m/s). In the second group, both 5 microM norepinephrine and 5 microM epinephrine, in the presence of either anesthetic, depressed conduction velocity (P < or = 0.01) with a similar time course. The reduction of conduction velocity with norepinephrine was less (P < or = 0.01) than that with epinephrine, and again the decreases of conduction velocity were larger (P < or = 0.01) with 0.4 mM halothane than 0.4 mM isoflurane.(ABSTRACT TRUNCATED AT 250 WORDS)