title: Patient alert in implantable cardioverter defibrillators: toy or tool?
abstract: OBJECTIVE
  The purpose of this study was to analyze the utility of patient-alert features in implantable cardioverter defibrillators (ICDs).
  
  
  BACKGROUND
  Various alert features producing acoustic warning signals have been implemented in newer generation ICDs, but their role in early detection of system-related complications has not been systematically evaluated.
  
  
  METHODS
  In 240 patients implanted with Medtronic ICD devices, the following alert features were routinely activated: pacing lead impedance <200 or >2,000 Omega, high-voltage lead impedance <10 or >200 Omega, low battery voltage (elective replacement indicator), long charge time (>18 s), >3 shocks delivered per episode, and all therapies in a zone delivered. Alert events occurring during follow-up were assessed in relation to actual findings (hospital charts, chest X-rays, ICD printouts including sensing/pacing/defibrillation threshold tests, episode data) to determine incidence, sensitivity, and specificity of the alert function.
  
  
  RESULTS
  During 12.2 +/- 8.9 months, 24 alert events occurred in the 240 patients (pacing lead impedance, n = 4; high-voltage lead impedance, n = 7; low battery voltage, n = 1; >3 shocks, n = 6; all therapies, n = 6). A total of 22 serious complications (necessitating reprogramming or device/lead replacement) were observed, 14 of which were primarily identified through a patient alert (lead fracture, n = 11; connector defect, n = 1; T-wave oversensing, n = 1; battery depletion, n = 1). This reflects a sensitivity of 64% and a specificity of 96% of the alert function for serious complications. With 14 of 24 patient alerts being caused by serious complications, the positive predictive value reached 58%.
  
  
  CONCLUSIONS
  Patient-alert features are a useful additional tool facilitating early detection of serious ICD complications, but they do not substitute for regular ICD follow-up, because of their low sensitivity.
authors.affiliation: University of Heidelberg/Cardiology, Heidelberg, Germany. ruediger_becker@med.uni-heidelberg.de
authors.forename: Ruediger
authors.initials: R
authors.lastname: Becker
authors.forename: Jutta
authors.initials: J
authors.lastname: Ruf-Richter
authors.forename: Julia C
authors.initials: JC
authors.lastname: Senges-Becker
authors.forename: Alexander
authors.initials: A
authors.lastname: Bauer
authors.forename: Slawomir
authors.initials: S
authors.lastname: Weretka
authors.forename: Frederik
authors.initials: F
authors.lastname: Voss
authors.forename: Hugo A
authors.initials: HA
authors.lastname: Katus
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schoels
mesh_terms: D000368:Aged; D002304:Cardiac Pacing, Artificial; D017147:Defibrillators, Implantable; D020878:Device Removal; D004869:Equipment Safety; D005500:Follow-Up Studies; D006329:Heart Conduction System / Q000503:physiopathology / Q000601:surgery; D006801:Humans; D008875:Middle Aged; D010138:Pacemaker, Artificial; D011183:Postoperative Complications / Q000209:etiology / Q000503:physiopathology; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013223:Statistics as Topic; D014693:Ventricular Fibrillation / Q000503:physiopathology / Q000628:therapy