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Heart Rhythm. 2014 Aug;11(8):1352-8. doi: 10.1016/j.hrthm.2014.04.012. Epub 2014 Apr 13.

Use of a discrimination algorithm to reduce inappropriate shocks with a subcutaneous implantable cardioverter-defibrillator.

Author information

  • 1Medical University of South Carolina, Charleston, South Carolina. Electronic address: goldmr@musc.edu.
  • 2Ohio State University, Columbus, Ohio.
  • 3Erasmus Medical Center, Rotterdam, The Netherlands.
  • 4Auckland City Hospital, Auckland, New Zealand.
  • 5Emory University School of Medicine, Atlanta, Georgia.
  • 6Northwestern University, Chicago, Illinois.
  • 7Boston Scientific Corporation, Natick, Massachusetts.
  • 8University of Chicago, Chicago, Illinois.



The subcutaneous implantable cardioverter-defibrillator system (S-ICD) uses a novel detection algorithm previously shown to discriminate induced tachyarrhythmias (ventricular vs supraventricular) effectively.


The purpose of this study was to evaluate the role of the S-ICD discrimination algorithm in reducing the incidence of spontaneous inappropriate shocks.


A total of 314 subjects underwent implantation with an S-ICD system as part of the S-ICD Clinical Investigation (IDE Trial). Subjects were grouped according to programming at discharge to either a single shock zone or 2 shock zones, with a discrimination algorithm in the lower rate zone.


This cohort had 226 subjects (72%) with dual zone programming and 88 subjects (28%) with single zone programming. Over a mean follow-up period of 661 ± 174 days, inappropriate shocks occurred in 23 subjects from the dual zone subgroup (10.2%) and 23 subjects from the single zone subgroup (26.1%, P < .001), with 2-year inappropriate shock-free rates of 89.7% vs. 73.6%;,respectively (hazard ratio 0.38, P = .001). Freedom from appropriate shocks did not differ between subgroups (92.2% vs. 90.3%, hazard ratio 0.82, P = .64). Moreover, mean time to appropriate therapy did not differ between subgroups, and there was only 1 episode of arrhythmic syncope in the cohort.


The addition of a second shock zone with an active discrimination algorithm was strongly associated with a reduction in inappropriate shocks with the S-ICD system and did not result in prolongation of detection times or increased syncope. These data support the use of dual zone programming as a standard setting for S-ICD patients.

Copyright © 2014 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.


Inappropriate shock; Inappropriate therapy; Oversensing; Rhythm discrimination; Subcutaneous implantable-defibrillator; Supraventricular tachyarrhythmia

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