Effect of stimulation of cardiac sympathetic nerves on vagus escape of the heart

Abstract

1. The effect of stimulation of the sympathetic nerves against the background of stimulation of the vagus is determined by which cardiac sympathetic and parasympathetic nerves are stimulated simultaneously, and by the strength of this stimulation. 2. When automatism of the sino-atrial node is predominantly depressed during stimulation of the vagus (usually the right), a more rapid onset of vagus escape is observed during stimulation of sympathetic nerves that increase the automatism of the atrioventricular (AV) node or of the third-order pacemakers. If, on the other hand, during stimulation of the vagus (usually the left) automatism of the AV node is predominantly depressed, a more rapid onset of vagus escape takes place during stimulation of sympathetic nerves that increase the automatism of the sino-strial or of the third-order pacemakers. 3. Stimulation of sympathetic branches influencing predominantly the sino-atrial node, or stimulation of sympathetic branches influencing predominantly the AV node, differs in its effect depending on the degree to which the automatism of these nodes is depressed by vagal stimulation. If depression of automatism is slight, vagus escape develops more rapidly, but if automatism is strongly depressed, this effect is absent. 4. Stimulation of the augmentor nerves has no effect either on the duration of vagal cardiac arrest or on vagus escape.