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 7 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 40 ms) could be initiated at a programmed interval after the last beat of a paced ventricular or atrial basic drive. The following 4 patterns of HPS behavior accompanying sudden ventricular rate acceleration were observed: 1:1 response without conduction delay, 1:1 response with initial conduction delay but subsequent accommodation, occurrence initially of 2:1 or 3:2 Wenckebach block followed by either subsequent accommodation or repetitive block and sustained conduction delay with persistent appearance of the His deflection beyond the ventricular electrogram. The 3 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 CL. 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). Functional delay and/or block in the HPS evidently is relatively common during constant CL ventricular pacing at rapid rates (i.e., > 160/min) and recognition of this fact is important for accurate interpretation of electrophysiologic phenomena.