Local epicardial chemical ablation of vagal input to sino-atrial and atrioventricular regions of the canine heart

Abstract

In open-chest, pentobarbitalized dogs, right and left cervical vagi were electrically stimulated (20 Hz, 5.0 ms, 4–6 volts) before and after carefully painting phenol (90%) over each of 6–8 narrow strips (2–3 mm width) and over restricted portions of the superior and inferior right atrium. Successive phenol strips were applied until the sino-atrial nodal (SAN) region had been completely surrounded, and also applied over a triangular fat pad at the junction of the inferior vena cava (IVC) and inferior left atrium (ILA). Electrical excitation of the autonomic trunks following each sequential epicardial phenol blockade resulted in successive deletion of cardio-inhibitory responses, a majority of sympathetic excitatory responses remaining intact. We conclude that most vagal fibers reach the SAN region via the superior-posterior right atrium (SVC and superior pulmonary veins) and these can be ablated leaving most vagal fibers to the atrioventricular nodal AVN region unimpaired. Phenol painting at the junction of IVC and ILA abolished vagal inhibition of conduction across the A-V junction. These studies illustrate distinct vagal distributions to the SAN and AVN regions of the canine heart. After all responses to vagal stimulation have been abolished, sympathetic alterations in heart rate and A-V conduction remain, thus revealing important differentiation in sympathetic fiber distribution to these key regions of automaticity and conduction.