title: Utilization of retrograde right bundle branch block to differentiate atrioventricular nodal from accessory pathway conduction.
abstract: BACKGROUND
  Defining whether retrograde ventriculoatrial (V-A) conduction is via the AV node (AVN) or an accessory pathway (AP) is important during ablation procedures for supraventricular tachycardia (SVT). With the introduction of ventricular extrastimuli (VEST), retrograde right bundle branch block (RBBB) may occur, prolonging the V-H interval, but only when AV node conduction is present. We hypothesized that when AP conduction was present, the V-A interval would increase less than the V-H interval, whereas with retrograde nodal conduction, the V-A interval would increase at least as much as the V-H interval.
  
  
  RESULTS
  We retrospectively reviewed the electrophysiological studies of patients undergoing ablation for AVN reentrant tachycardia (AVNRT) (55) or AVRT (50), for induction of retrograde RBBB during the introduction of VEST, and the change in the measured V-H and V-A intervals. Results were found to be reproducible between independent observers. Out of 105 patients, 84 had evidence of induced retrograde RBBB. The average V-H interval increase with induction of RBBB was 53.7 ms for patients with AVRT and 54.4 ms for patients with AVNRT (P = NS). The average V-A interval increase with induction of RBBB was 13.6 ms with AVRT and 70.1 ms with AVNRT (P < 0.001). All patients with a greater V-H than V-A interval change had AVRT, and those with a smaller had AVNRT.
  
  
  CONCLUSIONS
  Induction of retrograde RBBB during VEST is common during an electrophysiological study for SVT. The relative change in the intervals during induction of RBBB accurately differentiates between retrograde AVN and AP conduction.
authors.affiliation: Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Suraj
authors.initials: S
authors.lastname: Kapa
authors.forename: Benhur D
authors.initials: BD
authors.lastname: Henz
authors.forename: Chadi
authors.initials: C
authors.lastname: Dib
authors.forename: Yong-Mei
authors.initials: YM
authors.lastname: Cha
authors.forename: Paul A
authors.initials: PA
authors.lastname: Friedman
authors.forename: Thomas M
authors.initials: TM
authors.lastname: Munger
authors.forename: Dorothy J
authors.initials: DJ
authors.lastname: Ladewig
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Hammill
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Packer
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Asirvatham
mesh_terms: D001283:Atrioventricular Node / Q000503:physiopathology*; D002037:Bundle-Branch Block / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D002304:Cardiac Pacing, Artificial; D017115:Catheter Ablation; D003937:Diagnosis, Differential; D022062:Electrophysiologic Techniques, Cardiac; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D015588:Observer Variation; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012189:Retrospective Studies; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D054139:Tachycardia, Reciprocating / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D013617:Tachycardia, Supraventricular / Q000175:diagnosis* / Q000503:physiopathology / Q000601:surgery; D013997:Time Factors