Selective In Situ Parasympathetic Control of the Canine Sinoatrial and Atrioventricular Nodes

Methods were devised for the selective alteration of parasympathetic control over the sinoatrial (SA) or the atrioventricular (AV) node in anesthetized, thoracotomized mongrel dogs. Two epicardial sites were located at which parasympathetic nerve fibers enroute to the SA or the AV node could be stimulated or blocked. Selective nerve stimulation was accomplished with brief pulses (0.05 msec), and blockade was accomplished with topically applied lidocaine. At the intercaval site, only the SA node was affected. At the site near the coronary sinus ostium, only the AV node was affected in terms of parasympathetic control, but sometimes there were modest sympathetic effects on the SA node. The effects of stimulation at these sites, except for the SA speeding produced by stimulation at the site near the coronary sinus, were blocked by atropine. The effects were also blocked by ganglionic blockade. Probably, preganglionic parasympathetic fibers to the nodes are concentrated at these sites.