SINOVENTRICULAR TRANSMISSION IN 10 MM K+ BY CANINE ATRIOVENTRICULAR NODAL INPUTS - SUPERIOR ATRIONODAL BUNDLE AND PROXIMAL ATRIOVENTRICULAR BUNDLE

Background. This study was done to determine the electrical properties of the superior atrionodal bundle (SAB) and the proximal atrioventricular bundle (PAVB). Methods and Results. Extracellular potentials associated with electrical activity in the SAB and PAVB were identified in electrograms using adult canine atrial preparations in which the AV node (AVN) and distal AV (His) bundle (DAVB) had been exposed. Intracellular potentials and/or electrograms of the sinoatrial node (SAN), SAB, PAVB, AVN, DAVB, and atrial contractions from a pectinate muscle bundle in the high right atrial wall were recorded. The electrograms contained deflections representing discharge of the specific tissues and atrial potentials from the adjacent or overlying atrial contractile myocardium. In superfusates containing 2.7 mM K+, sequential discharge of the tissues resulted in brief SAN-SAB, PAVB-DAVB, and AVN-DAVB intervals and a major delay after discharge of the SAB. The delay was attributed to activation of the PAVB, as reflected in extracellular PAVB potentials of long duration. Atrial potentials and the onset of the contractile event followed discharge of the SAN and SAB but preceded activation of the PAVB, AVN, and DAVB. After transection of the PAVB-AVN connections, the AVN exhibited automaticity, but the SAB, PAVB, atrial potentials in all of the electrograms, and atrial contractions persisted at the sinus rate. During exposure to 10 mM K+, atrial potentials in all of the electrograms and atrial contractions ceased, indicating electrical quiescence of the contractile myocardium; however, the unique pattern of discharge of the SAB, PAVB, AVN, and DAVB persisted at the SA nodal rate. Conclusions. Thus, the SAB and PAVB can be classified as specialized conducting tissues and are intrinsic components of the internodal conductile pathway.