Antiarrhythmic anesthetic action. II. The effect of methoxyflurane on ventricular automaticity

During the course of surgical anesthesia, the majority of patients experience some arrhythmias, virtually all of which can be attributed to changes in cardiac pacemaker automaticity and/or alterations in cardiac conduction velocity. Therefore, a better understanding of these mechansims is of importance to anesthesiologists. Cardiac automaticity in the intact heart of dogs under methoxyflurane anesthesia was assessed by measuring changes in ventricular escape time (VET) and ventricular escape rate (VER). A slight shortening of VET was noted, while there was virtually no change from control in VER. Unexpectedly, however, a nonsinus supraventricular escape focus became prominent in many animals at a low anesthetic dose and in all animals at a higher anesthetic concentration. This effect was shown to be preventable by pretreatment with reserpine or a beta-blocking agent. It is concluded that methoxyflurane increases the automaticity of parts of the atrial conducting system, other than the sinus, either by a direct effect or by increasing the sensitivity to prevailing background adrenergic levels.