title: The precise timing of tachycardia entrainment is determined by the postpacing interval, the tachycardia cycle length, and the pacing rate: Theoretical insights and practical applications.
abstract: BACKGROUND
  Previous observations have reported that the number of pacing stimuli required to entrain a tachycardia varies on the basis of arrhythmia type and location, but a quantitative formulation of the number needed to entrain (NNE) that unifies these observations has not been characterized.
  
  
  OBJECTIVE
  We sought to investigate the relationship between the number of pacing stimulations, the tachycardia cycle length (TCL), the overdrive pacing cycle length (PCL), and the postpacing interval (PPI) to accurately estimate the timing of tachycardia entrainment.
  
  
  METHODS
  First, we detailed a mathematical derivation unifying electrophysiological parameters with empirical confirmation in 2 patients undergoing catheter ablation of typical atrial flutter. Second, we validated our formula in 44 patients who underwent various catheter ablation procedures. For accuracy, we corrected for rate-related changes in conduction velocity.
  
  
  RESULTS
  We derived the equations NNE = |(PPI - TCL)/(TCL - PCL)| + 1 and Tachycardia advancement = (NNE - 1) × (TCL - PCL) - (PPI - TCL), which state that the NNE and the amount of tachycardia advancement on the first resetting stimulation are determined using regularly measured intracardiac parameters. In the retrospective cohort, the observed PPI - TCL highly correlated with the predicted PPI - TCL (mean difference 5.8 ms; r = 0.97; P < .001), calculated as PPI - TCL = (NNE - 1) × (TCL - PCL) - tachycardia advancement.
  
  
  CONCLUSIONS
  The number of pacing stimulations required to entrain a reentrant tachycardia is predictable at any PCL after correcting for cycle length-dependent changes in conduction velocity. This relationship unifies established empirically derived diagnostic and mapping criteria for supraventricular tachycardia and ventricular tachycardia. This relationship may help elucidate when antitachycardia pacing episodes are ineffective or proarrhythmic and could potentially serve as a theoretical basis to customize antitachycardia pacing settings for improved safety and effectiveness.
authors.affiliation: Stanford University School of Medicine, Stanford, California; El Camino Hospital, Mountain View, California. Electronic address: dwkaiser@stanford.edu.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Kaiser
authors.affiliation: University of California, San Francisco, California.
authors.forename: Henry H
authors.initials: HH
authors.lastname: Hsia
authors.affiliation: Stanford University School of Medicine, Stanford, California.
authors.forename: Anne M
authors.initials: AM
authors.lastname: Dubin
authors.affiliation: El Camino Hospital, Mountain View, California.
authors.forename: L Bing
authors.initials: LB
authors.lastname: Liem
authors.affiliation: Stanford University School of Medicine, Stanford, California.
authors.forename: Mohan N
authors.initials: MN
authors.lastname: Viswanathan
authors.affiliation: Stanford University School of Medicine, Stanford, California.
authors.forename: Paul C
authors.initials: PC
authors.lastname: Zei
authors.affiliation: Stanford University School of Medicine, Stanford, California.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wang
authors.affiliation: Stanford University School of Medicine, Stanford, California.
authors.forename: Sanjiv M
authors.initials: SM
authors.lastname: Narayan
authors.affiliation: Stanford University School of Medicine, Stanford, California; Veterans Affairs Palo Alto Health Care System, Palo Alto, California.
authors.forename: Mintu P
authors.initials: MP
authors.lastname: Turakhia
mesh_terms: D000328:Adult; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D022062:Electrophysiologic Techniques, Cardiac / Q000379:methods*; D005260:Female; D005500:Follow-Up Studies; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008962:Models, Theoretical; D011379:Prognosis; D012189:Retrospective Studies; D017180:Tachycardia, Ventricular / Q000175:diagnosis* / Q000503:physiopathology / Q000628:therapy
keywords: Antitachycardia pacing; Arrhythmia; Catheter ablation; Entrainment; Number needed to entrain; Right ventricular overdrive pacing