Investigation of the atrial pacemaker site and rate of the dog heart by the multi-electrodes mapping system

Abstract

The site of impulse origin in the right atrium is generally considered to be a single static locus within the sinoatrial (SA) node. However, it has been recognized that the pacemaker site may shift as a consequence of changes in physiological and pathological conditions. To determine the role of the atrial pacemaker complex including the superior pacemaker site, SA node and inferior pacemaker site quantitatively, we investigated atrial rate and the earliest activation region (EAR) from the isochronal activation sequence map by 48 unipolar electrodes and the mapping system. The epicardial activation sequence of the right atrium including the SA node region was obtained from the 48 electrodes, which were fixed to two flexible templates made of soft plastic plates. Using the mapping system, we found that (1) the EAR was shifted by the sympathetic or parasympathetic neural activity, (2) parasympathetic activity predominates over the sympathetic activity not only on heart rate, but also on the location of the EAR, and (3) the role of the inward Ca2+ current, hyperpolarization inward current and delayed rectifier K+ current, of the pacemaker cells distributed in the atrial pacemaker complex is different in the dog heart in situ.