title: Long-term reproducibility of ventricular tachycardia induction in patients with implantable cardioverter/defibrillators. Serial noninvasive studies.
abstract: BACKGROUND
  Noninvasive electrophysiological studies (EPSs) can be performed in current implantable antitachycardia pacemaker/cardioverter/defibrillators (ICDs). Thus, these devices may be used as tools to study changes in the electrophysiological substrate and ventricular tachycardia characteristics over time.
  
  
  RESULTS
  Fifty-five patients receiving an ICD for treatment of sustained ventricular tachyarrhythmias underwent serial EPSs after implantation of the ICD. Studies were performed before hospital discharge and 1, 3, 5, 9, 12, 18, 24, and 36 months after ICD implantation. Sustained monomorphic ventricular tachycardia (VT) was induced in 37 patients (group 1) at the predischarge EPS, whereas no sustained arrhythmia could be induced in 18 patients (group 2) at baseline. Group 1 patients underwent 165 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 72% of the follow-up EPSs, ventricular fibrillation (VF) was induced during 11% of follow-up EPSs, and no sustained VT or VF was induced during 17% of follow-up visits. Sustained VT was induced at every follow-up EPS in 23 patients (62%), whereas no sustained VT/VF could be induced at least once during follow-up in 14 patients (38%). Clinical or electrophysiological variables did not predict noninducibility during follow-up. However, the probability that a patient would experience spontaneous VT decreased significantly over time in patients in whom VT was not inducible during at least 1 follow-up EPS (P = .05). Group 2 patients underwent 86 noninvasive EPSs after discharge. Sustained monomorphic VT was induced during 22% of follow-up EPSs, VF was induced during 19% of follow-up EPSs, and no sustained VT/VF could be induced during 68% of follow-up EPSs. No sustained VT/VF could be induced during every follow-up EPS in 9 patients (50%), whereas sustained monomorphic VT was induced at least once during follow-up in 7 patients (34%). Persistent noninducibility of VT during follow-up was associated with low probability of occurrence of spontaneous VT (11%), whereas inducibility of VT at least once during follow-up was associated with the occurrence of spontaneous VT (89%, P = .003).
  
  
  CONCLUSIONS
  Considerable variability of VT induction is observed over a lengthy period in patients presenting with sustained VT/VF. Persistent noninducibility of VT is associated with a reduced probability of spontaneous VT. These observations suggest that the substrates for inducible and spontaneous VT change in parallel over time.
authors.affiliation: Department of Medicine, Foothills Medical Centre, Alberta, Canada.
authors.forename: A M
authors.initials: AM
authors.lastname: Gillis
authors.forename: R S
authors.initials: RS
authors.lastname: Sheldon
authors.forename: D G
authors.initials: DG
authors.lastname: Wyse
authors.forename: J W
authors.initials: JW
authors.lastname: Leitch
authors.forename: R
authors.initials: R
authors.lastname: Yee
authors.forename: G J
authors.initials: GJ
authors.lastname: Klein
authors.forename: H J
authors.initials: HJ
authors.lastname: Duff
authors.forename: L B
authors.initials: LB
authors.lastname: Mitchell
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D004594:Electrophysiology; D005260:Female; D006334:Heart Function Tests; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D017180:Tachycardia, Ventricular / Q000503:physiopathology* / Q000601:surgery*; D013997:Time Factors