title: Sequential dual chamber extrastimulation: a novel pacing maneuver to identify the presence of a slowly conducting concealed accessory pathway.
abstract: BACKGROUND
  Transient VA block can be created in the AV node (AVN) when an atrial extrastimulus is delivered at the AVN effective refractory period (ERP) due to anterograde concealed conduction.
  
  
  OBJECTIVE
  We hypothesized that ventricular stimulation during pacing-induced AVN refractoriness could identify concealed accessory pathways (APs) that remain hidden with standard maneuvers.
  
  
  METHODS
  Patients undergoing electrophysiological study for supraventricular tachycardia were screened for presence of an AP using standard pacing maneuvers and/or V pacing during adenosine infusion. The dual-chamber sequential extrastimulation maneuver consisted of an 8-beat drive train of simultaneous AV pacing at 600 msec, followed by an A2 delivered at AVN ERP, followed by a V2 delivered at the drive train cycle length (600 msec). Repeat drives were then performed with decrements of 10 msec for V2 until VA block was seen. Retrograde AVN and AP ERP were recorded with standard (V1, V2) and dual-chamber extrastimulation (A1/V1, A2, V2). Patients with an AP identified with standard pacing, manifest pre-excitation, or A ERP < AVN ERP were excluded.
  
  
  RESULTS
  Fourteen patients with and 19 patients without an AP were studied. In all patients with an AP, exclusive VA conduction over the AP, without fusion, was seen with the described pacing maneuver. In patients without an AP, retrograde AV nodal ERP was extended by a mean of 138 +/- 46 msec (range 50 to 210 msec) with the A2. Anterograde concealed conduction into the AP was also seen in some patients who showed AP conduction during standard V1V2 pacing (mean retrograde extension of ERP 12 +/- 8 msec, range 0 to 20 msec).
  
  
  CONCLUSIONS
  Dual-chamber sequential extrastimulation is a useful maneuver for identifying slowly conducting APs not revealed with standard pacing maneuvers because of an ERP and conduction time similar to the AVN. The maneuver uses anterograde concealed conduction to prolong AVN refractoriness much more than that of a concealed AP, thereby allowing the AP to become manifest with the V2.
authors.affiliation: University of Colorado Denver, Aurora, Colorado 80045, USA. william.sauer@uchsc.edu
authors.forename: William H
authors.initials: WH
authors.lastname: Sauer
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Lowery
authors.forename: Joshua M
authors.initials: JM
authors.lastname: Cooper
authors.forename: Laurent
authors.initials: L
authors.lastname: Lewkowiez
mesh_terms: D000328:Adult; D054537:Atrioventricular Block / Q000503:physiopathology*; D002304:Cardiac Pacing, Artificial; D017115:Catheter Ablation; D004562:Electrocardiography; D004594:Electrophysiology; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013617:Tachycardia, Supraventricular / Q000503:physiopathology / Q000601:surgery / Q000628:therapy*; D013997:Time Factors