Automaticity of the A-V junctional area after sinus node injury, with special reference to the effects of low rate atrial overdrive and of the autonomic nervous system.

Abstract

It is the purpose of this study to investigate the effects of overdrive suppression and of autonomic nervous system on the A-V junctional rhythm after sinus node injury in the dog in which the A-V junctional area is left intact. The following results were obtained. l) The A-V junctional pacemaker is susceptible to overdrive suppression and significantly suppressed even by atrial overdrive with low rates. 2) Automaticity of the A-V junctional pacemaker is markedly suppressed by the vagal stimulation and the beta-adrenergic blocking. 3) Suppressive effect of low rate atrial overdrive on the A-V junctional pacemaker is markedly enhanced by the vagal stimulation and the beta-adrenergic blocking. On the basis of these results, it was suggested that, in the sick sinus syndrome, overdrive with relatively low rate would sufficiently suppress the automaticity of the already impaired sinus node and of the intact A-V junctional area, which lead to long pauses and consequent cerebral symptoms. Increase in the vagal tone and decrease in the sympathetic tone, alone or in combination, would intensely suppress the automaticity of the sinus node and the A-V junctional area and also enhance the effect of overdrive with relatively low rate on the automaticity of the cardiac pacemakers.