Autonomic interactions among subsidiary atrial foci

Although the existence of a specific pacemaker hierarchy outside of the sinus node but within the atrium has been documented, little evidence regarding mechanisms controlling activity of these sites has been gathered. This investigation utilized an autologous perfusion of the sinus nodal artery, by way of the femoral artery, in order to suppress the sinus node cholinergically while unmasking latent atrial sites. Electrograms were recorded from the region of the sinus node and several atrial sites. Perfusion with small doses of acetylcholine and physostigmine unmasked pacemakers outside of the sinus and atrioventricular nodes, but within the atrium. Either vagal stimulation or topical acetylcholine on the area of the presumed pacemaker returned dominance gradually toward the sinus node. Stimulation of the right stellate ganglion accelerated the latent pacemaker but did not shift activation toward the sinus node. These results are consistent with the existence of subsidiary atrial pacemakers that appear to be highly sensitive to the effects of acetylcholine. This may represent one mechanism, in addition to overdrive suppression, that maintains pacemaker hierarchy within the right atrium.