Site of conduction delay during functional block in the His-Purkinje system in man.

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Abstract
Using recordings from the His bundle (H) and right bundle (RB), the site of functional conduction delay and/or block along the H-RB axis was analyzed in 14 patients with normal intraventricular conduction. During sinus rhythm, the HV and RB-V intervals had a mean value of 46.4 .+-. 3.6 ms (range 40-50 ms) and 22.8 .+-. 7.5 ms (range 5-30 ms), respectively, with an average H-RB interval of 23.6 .+-. 9.1 ms. In response to single atrial premature beats, all 14 patients developed right bundle branch block (RBBB), while 9 of 14 also developed left bundle branch block (LBBB) and bilateral block within the His-Purkinje system (HPS). During RBBB, the RB potential disappeared in 13 of 14 patients with and without concomitant increase in the HV interval, suggesting an increase in the H-RB interval due to conduction delay distal to the H but proximal to the RB recording site. In 2 of these 13 patients and the remaining patient, RBBB also occurred without a corresponding increase in the H-RB interval, indicating conduction delay and/or block distal to the RB recording. An increase of 40-325 ms in the H-RB interval was noted during LBBB. During bilateral block within the HPS, a clearly recorded H potential was not followed by RB deflection. When either RBBB (6 patients) or LBBB (3 patients) persisted for 2 or more successive premature beats, the H-RB interval lengthened preceding the 1st beat but normalized during subsequent beats. The site of functional conduction delay and/or block along the H-RB axis is generally proximal (i.e., distal H or proximal RB), but could vary in the same patient, and can quickly shift from a proximal to a distal location with successive short cycles.