title: Rate stabilization by right ventricular apex or His bundle pacing in patients with atrial fibrillation.
abstract: OBJECTIVE
  In patients with atrial fibrillation right ventricular pacing can block antegrade conduction at pacing intervals longer than the shortest spontaneous R-R interval, causing the stabilization of ventricular rhythm. In this study the effects of pacing at two sites were compared in order to evaluate the role of conduction times in determining the stabilization of ventricular rhythm.
  
  
  METHODS
  In eight patients with permanent atrial fibrillation, the ventricular rate was recorded before and during pacing at the right ventricular apex and the His bundle with different cycle lengths.
  
  
  RESULTS
  In all patients, we obtained a reduction in spontaneous QRS complexes with respect to those anticipated at pacing rates slightly above the spontaneous mean rate, and the ventricular rhythm stabilized at pacing intervals longer than the spontaneous shortest R-R intervals. Between pacing sites we did not observe any difference in the reduction in spontaneous beats and the cycle stabilizing the rhythm. Moreover, simulation of the interaction between antegrade and retrograde impulses in a computer model confirmed that results obtained by pacing at the His bundle cannot be readily explained as a consequence of conduction delays.
  
  
  CONCLUSIONS
  This study suggests that the lag introduced by the His-Purkinje conduction cannot explain, as proposed, the stabilization of ventricular rhythm observed in patients with atrial fibrillation and right ventricular pacing.
authors.affiliation: Institute of Internal Medicine and Cardiology, University of Florence, Italy. elettrofisiologia@dfc.unifi.it
authors.forename: Luigi
authors.initials: L
authors.lastname: Padeletti
authors.forename: Fabio
authors.initials: F
authors.lastname: Fantini
authors.forename: Antonio
authors.initials: A
authors.lastname: Michelucci
authors.forename: Paolo
authors.initials: P
authors.lastname: Pieragnoli
authors.forename: Andrea
authors.initials: A
authors.lastname: Colella
authors.forename: Nicola
authors.initials: N
authors.lastname: Musilli
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Ricciardi
authors.forename: Trina A
authors.initials: TA
authors.lastname: Buhr
authors.forename: Sergio
authors.initials: S
authors.lastname: Valsecchi
mesh_terms: D000368:Aged; D001281:Atrial Fibrillation / Q000503:physiopathology* / Q000628:therapy*; D002036:Bundle of His / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D016896:Treatment Outcome