The effects of chronic ventricular pacing on the human conduction system

Six cardiac patients had His bundle electrograms obtained prior to ventricular pacing. Hours to days after constant pacing, repeat His bundle electrograms were obtained. The H-Q interval increased after pacing in 5 of the 6 patients. The average H-Q interval of 55.8 msec increased to the post pacing value of 67.5 msec (p smaller 0.02). Thus ventricular pacing can produce a conduction delay in the His Purkinje system.