title: Atrial response to ventricular antitachycardia pacing discriminates mechanism of 1:1 atrioventricular tachycardia.
abstract: BACKGROUND
  Inappropriate shocks from implantable cardioverter defibrillators (ICD) remain a significant clinical problem despite device discrimination algorithms. The atrial response to antitachycardia pacing (ATP) may determine the mechanism of 1:1 A:V tachycardia.
  
  
  METHODS
  For this study we refer to sinus tachycardia, atrial tachycardia (AT), atrial fibrillation, and flutter as atrial tachycardia (AT), and all other tachycardia as "non-AT." Three atrial response patterns during the burst of ATP were determined. The atrial cycle length (ACL) may be unchanged (type 1) indicating AT. The ACL may show variation during ATP (type 2) indicating variable VA block and does not discriminate between an AT and a non-AT mechanism, in which case a default diagnosis of non-AT is made. The ACL may accelerate to the ATP cycle length (type 3) indicating entrainment. A VAAV response at the end of ATP was considered diagnostic of AT (type 3A) whereas a VAV or VVA response was considered a non-AT mechanism (type 3B). This algorithm was applied to ICD tracings from 68 episodes of spontaneous 1:1 A:V tachycardia that had 136 sequences of ATP administered. The rhythm "truth" was determined by consensus of two experienced clinicians.
  
  
  RESULTS
  The algorithm correctly identified AT with a sensitivity of 71.9% (95% CI: 67.1-73.6), and specificity of 95% (83.5-99.1). The PPV was 97.2% (90.9-99.5), and NPV 58.5% (51.4-61.0). Kappa was 0.57 (0.43-0.62). If used clinically the algorithm would have aborted 53.3% (8/15) of inappropriate shocks delivered into an AT-mechanism tachycardia and would not have withheld a shock for any episode of VT.
  
  
  CONCLUSIONS
  Analysis of atrial response patterns during and after ventricular ATP can successfully discriminate tachycardia mechanism and may reduce inappropriate ICD shocks.
authors.affiliation: London Health Sciences Centre, London, Ontario N6A 5A5, Canada.
authors.forename: Daryl P
authors.initials: DP
authors.lastname: Ridley
authors.forename: Lorne J
authors.initials: LJ
authors.lastname: Gula
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Krahn
authors.forename: Allan C
authors.initials: AC
authors.lastname: Skanes
authors.forename: Raymond
authors.initials: R
authors.lastname: Yee
authors.forename: Mark L
authors.initials: ML
authors.lastname: Brown
authors.forename: Walter H
authors.initials: WH
authors.lastname: Olson
authors.forename: Jeffrey M
authors.initials: JM
authors.lastname: Gillberg
authors.forename: George J
authors.initials: GJ
authors.lastname: Klein
mesh_terms: D000465:Algorithms; D001281:Atrial Fibrillation / Q000503:physiopathology / Q000628:therapy*; D002304:Cardiac Pacing, Artificial / Q000009:adverse effects*; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D004594:Electrophysiology; D006325:Heart Atria / Q000503:physiopathology*; D006801:Humans; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D013611:Tachycardia, Atrioventricular Nodal Reentry / Q000503:physiopathology / Q000628:therapy*; D017180:Tachycardia, Ventricular / Q000503:physiopathology / Q000628:therapy*