Effect of Vagal Stimulation on Cardiac Excitability

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Abstract
Twenty maximal shocks per sec. (duration 0.05 to 12.0 m. sec.) do not change the diastolic threshold of a dog''s auricle when applied to the vagus. Auricular conduction rates were increased (latency unchanged), absolute refractory period shortened and thresholds lowered during the relative refractory period by strong vagal stimulation. Vagal stimulation made the auricle much more likely to fibrillation after single shocks. Repolariza-tion is accelerated by vagal stimulation. Monopolar and bipolar bioelectric currents are decreased in amplitude. Vagal excitation did not change ventricular excitability or conduction velocities. Similarities in these experiments to those seen when concentration of extracellular Na+ is low are pointed out.