His Bundle Rhythm

Traditionally the site of impulse formation in so-called A-V nodal rhythms has been considered to be within the upper, middle, and lower portions of the A-V node. In this study, evidence obtained supports the concept that the His bundle and not the A-V node is the pacemaker site in nodal rhythms. His bundle activity was recorded in clinical cases of nodal rhythms and A-V dissociation by using an electrode catheter positioned at the tricuspid valve. In these studies a single His deflection preceded each QRS com-plex. From the results of this study, it is suggested that in so-called lower and middle nodal rhythms the pacemaker site is within the His bundle. It is further suggested that so-called upper nodal rhythms may represent a coronary sinus or inferior left atrial rhythm. Additional Indexing Words: A-V nodal rhythms Pacemaker site Conduction T RADITIONALLY, A-V nodal rhythms have been described as arising from the upper, middle, or lower portions of the A-V node.1-3 In so-called nodal rhythms the P wave is inverted in leads II, III, and aVF and may precede, follow, or be buried within the QRS complex. The P-R or R-P interval has been thought to be dependent upon the region of the A-V node in which the pacemaker is lo-cated and also upon the speed of antegrade and retrograde conduction. The characteristics of the transmembrane action potential of A-V nodal cells, as recorded by micro-electrode technics, suggest that the A-V node itself does not possess properties of automaticity.46 Accordingly, it has been suggested that the pacemaker in so-called A-V nodal rhythms is located in the N-H region or bundle of His.7 The purpose of this study was to obtain evidence supporting the concept that the pace-maker in so-called nodal rhythms is located in the region of the His bundle and not in th