Summary
Intracellular recording studies have been carried out on the effects of methoxyflurane (Penthrane) and halothane (Fluothane) on cardiac pacemaker fibers in the rabbit, cat, and dog. Both compounds are capable of causing arrest of electrical activity of fibers of the sinoatrial node. The concentration of halothane required is higher than that normally employed for clinical anaesthesia, but the effect is seen with methoxyflurane in concentrations as low as 0.5 per cent. The effect is reversible. Some fibers resist the action longer than others. This effect on pacemaker fibers could easily go unnoticed, if only heart rate was being monitored. In the intact animal, and in isolated preparations, it leads to a shift in pacemaker site to thea-v node. Thea-v node resists a concentration of 2 per cent methoxyflurane for some time, but eventually activity ceases. In the case of methoxyflurane, latent pacemakers are stimulated rather than depressed and this effect is quite marked in the presence of adrenaline. It is felt that the incidence of nodal rhythm during anaesthesia with this agent is probably higher than reports would indicate. We are inclined to question the wisdom of using methoxyflurane in concentrations of 2.0 per cent and higher.
Résumé
Nous avons comparé les effets du méthoxyflurane (Penthrane) et de l’halothane (Fluothane) sur les cellules des noeuds isolés sinoauriculaire et atrioventriculaire en employant les techniques de microélectrodes. les deux agents anesthésiques sont capables de causer l’arrêt de l’activité électrique et, dans le cas du méthoxyflurane, cela peut survenir avec des concentrations employées ordinairement pour l’anesthésie clinique. Cet effet entraine un déplacement du site du pacemaker dominant au noeud atrioventriculaire, lequel est quelque peu plus résistant à l’action déprimante. Les cellules de Purkinje dans le système de conduction ventriculaire sont déprimées par l’halothane mais stimulées par le méthoxyflurane. L’action stimulante est plutôt marquée si l’on associe méthoxyflurane et adrénaline. Comme résultat de ces études, nous avons l’impression que la fréquence de la perte de dominance du sinus durant l’anesthésie au méthoxyflurane est beaucoup plus élevée que les rapports semblent l’indiquer Cela peut facilement passer inaperçu si l’on se contente d’enregistrer la fréquence des pulsations. La décision d’employer des concentrations de méthoxyflurane de 2.0 pour cent et plus est d’une sagesse douteuse.
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This investigation was supported by the Medical Research Council of Canada and the Canadian Heart Foundation.
This paper was presented in part at the Canadian Federation of Biological Sciences Meeting, Montreal, June 1970.
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Reynolds, A.K., Chiz, J.F. & Pasquet, A.F. Pacemaker migration and sinus node arrest with methoxyflurane and halothane. Canad. Anaesth. Soc. J. 18, 137–144 (1971). https://doi.org/10.1007/BF03025442
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DOI: https://doi.org/10.1007/BF03025442