Functional His-Purkinje system behavior during sudden ventricular rate acceleration in man.

Abstract

During sudden rate acceleration the assessment of human His-Purkinje system (HPS) behavior in the antegrade direction is generally limited by the maximal attainable input frequency due to atrioventricular nodal (AVN) refractoriness. With incremental ventricular pacing, however, faster rates of input into the HPS are achievable. In seven patients with normal HPS function, the HPS response to an abrupt increase in ventricular rate was systematically evaluated with a pacing protocol in which rapid ventricular pacing at any constant cycle length (CL; range 280 to 400 msec) could be initiated at a programmed interval after the last beat of a paced ventricular or atrial basic drive. The following four patterns of HPS behavior accompanying sudden ventricular rate acceleration were observed: (I) 1:1 response without conduction delay, (II) 1:1 response with initial conduction delay but subsequent accommodation, (III) occurrence initially of 2:1 or 3:2 Wenckebach block followed by either subsequent accommodation or repetitive block, and (IV) sustained conduction delay with persistent appearance of the His deflection beyond the ventricular electrogram. The three latter patterns were found to be functional in nature, i.e., dependent on the CL just before rate acceleration, with improved conduction and ability to accommodate facilitated at shorter preceding CLs. Furthermore, with the availability of additional recordings from the right bundle branch, it could be postulated that pattern IV represented retrograde right bundle branch block that was sustained because of repetitive antegrade concealment by impulses conducted retrogradely via the left bundle branch (“linking” phenomenon). We conclude that functional delay and/or block in the HPS is relatively common during constant CL ventricular pacing at rapid rates (i.e., greater than 160/min) and recognition of this fact is important for accurate interpretation of electrophysiologic phenomena.