The Journal of Thoracic and Cardiovascular Surgery, Vol 77, 436-447, Copyright © 1979 by The American Association for Thoracic Surgery and The Western Thoracic Surgical Association
Cardiac rhythm following exclusion of the sinoatrial node and most of the right atrium from the remainder of the heart
WC Sealy and AV Seaber
In this study two surgical interventions on the right atrium were followed
by long-term observation of their effect on the cardiac rhythm. In the
first, the sinoatrial (SA) node and a small area of surrounding atrium were
excluded from the heart by a circumferential incision. This was followed
immediately by an unstable junctional rhythm accompanied by periods of
pacemaker arrest. After 14 days a rhythm, indistinguishable from sinus
rhythm, became permanently established. On atrial mapping the area of
earliest epicardial breakthrough was the low right atrium, indicating that
the pacemaker was in this area. In the second procedure, most of the right
atrium including the SA node was excluded by an incision from the remainder
of the heart, but left in continuity were the left atrium, right atrium in
the area about the coronary sinus and inferior vena caval ostium and the
atrial septum (areas where the low atrial pacemakers are known to occur),
and the ventricles. A permanent junctional rhythm associated with periods
of pacemaker arrest was produced. In two dogs permanent atrial fibrillation
eventually developed. The area of earliest breakthrough found on epicardial
mapping was to the right of the right inferior pulmonary vein, close to the
atrial septum. One of the differences between the two interventions was the
amount of right atrium remaining between the potential low atrial
pacemakers and the atrioventricular (AV) node. It is suggested that
summation, a factor needed for the atrial excitation wave to penetrate the
AV node, was inadequate in the more extensive intervention. This may
explain the failure of a potential low atrial pacemaker to become dominant
in the second intervention. The clinical implications of these findings are
discussed.
