S. Vodanovic et al., TRANSIENT NEGATIVE DROMOTROPIC EFFECTS OF CATECHOLAMINES ON CANINE PURKINJE-FIBERS EXPOSED TO HALOTHANE AND ISOFLURANE, Anesthesia and analgesia, 76(3), 1993, pp. 592-597
The time-dependent effects of catecholamines in combination with volat
ile anesthetics on conduction velocity of canine Purkinje fibers were
investigated to evaluate a controversial older hypothesis that the arr
hythmogenic interaction between epinephrine and halothane may involve
abnormal conduction. Two groups of 12 in vitro preparations were stimu
lated at 150 beats/min. In the first group, 5 muM epinephrine by itsel
f did not alter conduction velocity over a 10-min period from a contro
l mean value of 1.97 +/- 0.08 m/s. However, 5 muM epinephrine, in the
presence of either 0.4 mM halothane or 0.4 mM isoflurane, reduced cond
uction velocity (P less-than-or-equal-to 0.01) by about 10-15% within
3-5 min, with recovery toward control by 10 min. The mean conduction v
elocity at the 4th minute of exposure, in the presence of halothane an
d epinephrine (1.65 +/- 0.11 m/s), was lower (P less-than-or-equal-to
0.01) than that obtained in the presence of isoflurane and epinephrine
(1.74 +/- 0.07 m/s). In the second group, both 5 muM norepinephrine a
nd 5 muM epinephrine, in the presence of either anesthetic, depressed
conduction velocity (P less-than-or-equal-to 0.01) with a similar time
course. The reduction of conduction velocity with norepinephrine was
less (P less-than-or-equal-to 0.01) than that with epinephrine, and ag
ain the decreases of conduction velocity were larger (P less-than-or-e
qual-to 0.01) with 0.4 mM halothane than 0.4 mM isoflurane. The negati
ve dromotropic interaction between epinephrine and halothane was not a
ssociated with reduction of the action potential amplitude or rate of
phase 0 depolarization, which suggests that the catecholamine effect m
ay involve modulation of passive membrane properties, such as cell-to-
cell coupling, rather than changes of the peak inward current during t
he action potential upstroke. These results confirm an earlier report
that epinephrine potentiates the modest slowing of conduction produced
by halothane in Purkinje fibers and indicate that catecholamines' abn
ormally slow conduction with halothane is greater than with the ''less
sensitizing'' anesthetic isoflurane.