THE INFLUENCE OF THE VAGUS NERVES ON THE FARADIZED AURICLES IN THE DOG'S HEART

An abnormal auricular activity is produced by faradization of the right auricle of the dog, which frequently becomes established and continues for varying periods of time after faradization is discontinued. This auricular activity consists of a rapid auricular tachycardia coexisting with true auricular fibrillation. In some dogs the auricles are thrown into this abnormal activity more readily by faradization after the vagi have been cut than before. Cutting the nerves has little or no effect on the abnormal auricular activity, but the ventricular rate may be much increased if the vagi are cut after the abnormal auricular activity has been established, apparently because of an improvement in the auriculoventricular conductivity. Stimulation of the right vagus nerve changes the character of the activity of the faradized auricles by inhibiting the auricular tachycardia while the fibrillation is uninfluenced. Stimulation of the left vagus nerve has little or no apparent inhibitory effect on the auricular tachycardia, but has possibly an inhibitory effect on the auricular fibrillation. Vagus stimulation increases the susceptibility of the auricles to faradization. The abnormal activity set up by faradization may be established in hearts otherwise refractory by vagus stimulation of short duration following the faradization. Vagus stimulation usually holds the auricles in the abnormal activity set up by faradization as long as it is continued in hearts in which, without vagus stimulation, the sequential beat always returns as soon as faradization is stopped. The right vagus is more effectual in this respect than the left. In some hearts vagus stimulation alone is capable of initiating the same abnormal auricular activity which is caused by auricular faradization. The normal sequential beat is often restored by vagus stimulation. It replaces the abnormal auricular activity not during, but a few seconds after, the termination of vagus stimulation. Left vagus stimulation is somewhat more effectual in producing this result than right vagus stimulation.