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 complex. 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.