Antiarrhythmic Anesthetic Action I

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Abstract
The effect of halothane on intracardiac impulse conduction was assessed in dogs before and after pharmacologic vagotomy. Impulse conduction was measured by anesthetic-related changes in the A-H and H-V intervals of the His bundle electrogram. Prior to vagotomy, both "light" and "deep" halothane prolonged the A-H interval significantly. Maximal A-H interval prolongations corresponded to the maximal decrease in heart rate with either dose of anesthetic. Following vagotomy, the A-H prolongation produced by light halothane was abolished and the prolongation produced by the deep level greatly reduced. Neither dose of halothane had a measurable effect on the H-V interval before or after vagotomy. In one animal in which the effects of increasing rates of atrial pacing were measured without the addition of halothane, the A-H interval lengthened with no measurable change in the H-V interval. In two dogs in which the heart rate was held near pre-halothane levels by atrial pacing, the A-H interval was slightly prolonged and the H-V interval unchanged during the administration of deep halothane. These studies indicate that during sinus rhythm: (1) halothane prolongs A-V impulse conduction, (2) that this effect is correlated with a concomitant decrease in heart rate, and (3) that these effects are largely dependent upon intact vagal innervation of the heart. During atrial pacing, A-V conduction is prolonged by increased heart rate or by deep halothane when the heart rate is held constant. Thus, in addition to the known effects of halothane on pacemaker automaticity, concomitant changes in conduction may contribute to the antiarrhythmic action of this anesthetic.

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