title: Inappropriate implantable cardioverter-defibrillator discharges unrelated to supraventricular tachyarrhythmias.
abstract: OBJECTIVE
  The development of implantable cardioverter-defibrillators (ICDs) with QRS morphology discrimination and dual-chamber sensing capabilities has improved the differentiation of supraventricular from ventricular tachycardias (VTs). Inappropriate ICD discharges may result from extracardiac signals caused by electromagnetic interference (EMI), because of electric fields and leakage currents from domestic or medical electrical devices, damaged sensing leads, and various cardiac and extracardiac signals that mimic VT and/or ventricular fibrillation. The aim of our study was to determine retrospectively the incidence and clinical relevance of these ICD behaviours and offer possible therapeutic solutions.
  
  
  RESULTS
  We have observed inappropriate discharges unrelated to supraventricular arrhythmias in 13 (3.9%) of the 336 patients implanted with ICDs in our centre from 1989 to 2005. Seven patients received inappropriate shocks following exposure to external EMI: improperly grounded electric stove, electrically powered watering system, hydro-massage bath, electrical pruner, electrocautery current during cardiac surgery, transcutaneous electric nerve stimulation. In four patients, spurious discharges were related to internal noise of the ICD system from inappropriate lead connections. In two cases, erroneous antitachycardia therapy was delivered following different body signals oversensing (T-wave oversensing, wide QRS double-counting and myopotentials). In nine patients, non-invasive solutions prevented further inappropriate therapies (avoidance of EMI, malfunctioning atrial lead exclusion, ventricular sensing reprogramming). In four patients, surgical revision of the system was required (lead connections or position revision).
  
  
  CONCLUSIONS
  In our experience, inappropriate ICD discharges unrelated to supraventricular arrhythmias occurred in about 4% of ICD patients. A careful evaluation of clinical data and telemetric information (lead impedance, sensed R-wave, stored electrograms) is essential in order to understand the nature of inappropriate ICD discharges and to select the most appropriate solution.
authors.affiliation: Divisione Clinicizzata di Cardiologia, Facoltà di Medicina e Chirurgia di Novara, Università degli Studi del Piemonte Orientale, Azienda Ospedaliera Maggiore della Carità, Corso Mazzini 18, 28100 Novara, Italy. occhetta@r-j.it
authors.forename: Eraldo
authors.initials: E
authors.lastname: Occhetta
authors.forename: Miriam
authors.initials: M
authors.lastname: Bortnik
authors.forename: Andrea
authors.initials: A
authors.lastname: Magnani
authors.forename: Gabriella
authors.initials: G
authors.lastname: Francalacci
authors.forename: Paolo
authors.initials: P
authors.lastname: Marino
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable / Q000009:adverse effects*; D055590:Electromagnetic Phenomena; D004868:Equipment Failure; D005260:Female; D006801:Humans; D008297:Male; D012189:Retrospective Studies; D013617:Tachycardia, Supraventricular / Q000209:etiology*