Surgical isolation of the atrial septum from the atria: Identification of an atrial septal pacemaker

Abstract

This is a report of the third in a series of experiments carried out to identify and to determine the reliability of atrial pacemakers below the sinoatrial (SA) node. This information could be useful to the surgeon in planning both corrective atrial operations and direct operations for atrial arrhythmias. In this study, done in dogs, the atrial septum containing the atrioventricular (AV) node was completely separated from the remaining atria. Seven dogs survived for 35 to 116 days. Serial electrocardiograms (ECGs) after operation showed that four of the seven dogs developed a regular junctional rhythm with a rate of 85 beats/min, whereas three of seven developed an irregular junctional rhythm with pauses and bigeminy. In a control study, in which the AV node was disconnected from the His bundle, a slow regular junctional rhythm was produced in all three of the dogs. Thus, in the series of three experiments, this being the report of the last one, a hierarchy of pacemakers below the SA node was identified. The first one, a pacemaker in the low right atrium in the region of the coronary sinus, was the most reliable and was associated with a normal ECG. A second, in the atrial septum, did not develop dominance in all dogs. However, the junctional pacemaker in the His bundle always became dominant after the AV node was disconnected from the His bundle and was associated with a regular but slow rhythm.