Automaticity of the SN and A-V junctional tissue before and after chemical denervation in the dog

Automaticity of SN and A-V junctional tissue was studied in 40 dogs in which a stable junctional rhythm was obtained following thermal ablation of the SN and sulcus terminalis. Atrial overdrive pacing studies were performed both before and after chemical denervation of the heart. Control sinus cycle and junctional CL were 438 ± 13 ms and 751 ±23 ms, respectively. Chemical denervation resulted in significant prolongation of both junctional CL and maximal corrected junctional recovery time; junctional rate was down to 46 percent of the sinus rate observed before suppression of SN activity. Neither sinus CL nor maximal corrected SN recovery time changed significantly after administration of drugs. The basal autonomic nervous system has a relatively greater influence on the junctional pacemaker than on the normal SN in the dog and, when SN was suppressed, chemical denervation prolonged the junctional CL by 23 percent and junctional recovery time by 63 percent.