ELECTROPHYSIOLOGIC DEMONSTRATION OF ANTEROGRADE FAST AND SLOW PATHWAYS WITHIN THE HIS-BUNDLE IN PATIENTS WITH NORMAL INTRAVENTRICULAR-CONDUCTION

Electrophysiological evidence of functional longitudinal dissociation has been shown in different structures of the normal conduction system of the heart and in anomalous atrioventricular (AV) pathways. The typ ical sudden fast-to-slow jump phenomenon, which is commonly observed i n patients with dual AV nodal pathways, has not been demonstrated so f ar within the normal His bundle. Herein we report unusual electrophysi ological properties of the His bundle in two patients with normal intr aventricular conduction. Of 86 patients with discontinuous anterograde AV function curves, programmed atrial stimulation revealed dual anter ograde His bundle pathways in only 2 (2.3%) patients. Extrastimuli int roduced at critically timed coupling intervals produced a sudden marke d increase in H-2-V-2 interval suggesting failure of fast pathway with conduction proceeding through a slower pathway with shorter refractor y period. With further decreasing coupling intervals, the second H-2-V -2 curve showed decremental conduction which allowed a type II gap phe nomenon in the right bundle branch to occur in one of the patients. No echo beats were observed. These results provide the first electrophys iological demonstration, in patients with normal intraventricular cond uction, of anterograde failure of a fast His bundle pathway with subse quent conduction through a slow His bundle pathway. His bundle duality was manifested by dual conduction times and refractory periods. These observations further expand our knowledge on the electrophysiologic p roperties of the His bundle.