Unique Features

Implantable Cardiac Devices

Importance of Shock Reduction

Clinical Need

Data from published studies reveal that up to 21% of ICD patients receive inappropriate shocks.1-4

Incidence of inappropriate shocks

Detail Incidence of inappropriate shocks in ICD patients

Reducing shocks has been shown to improve ICD patients’ quality of life and increased ICD acceptance.

  • For patients, simply the fear of shocks can be disruptive to a normal, active life5,6
  • The Canadian ICD Study (CIDS) found that patients randomized to ICD therapy (versus those given amiodarone) had better quality of life until they received five shocks7
  • Some studies have demonstrated that experiencing just one shock causes temporary reductions in patients’ quality of life7

Avoiding shocks is important for:

  • Reducing pain and anxiety, and increasing patients’ acceptance of ICDs8,9
  • Reducing healthcare burden and improving patient quality of life8
  • Improving survival/heart failure10


  1. Kadish A, Dyer A, Daubert JP, et al., for the Defibrillators in Non-Ischemic Cardiomyopathy Treatment Evaluation (DEFINITE) Investigators. Prophylactic defibrillator implantation in patients with nonischemic dilated cardiomyopathy. N Engl J Med. 2004;350:2151-2158.
  2. Daubert JP, Zareba W, Cannom DS, et al., for the MADIT II Investigators. Inappropriate implantable cardioverter-defibrillator shocks in MADIT-II: frequency, mechanisms, predictors, and survival impact. J Am Coll Cardiol. 2008;5:1357-1365.
  3. Poole JE, Johnson GW, Hellkamp AS, et al. Prognostic importance of defibrillator shocks in patients with heart failure. N Engl J Med. September 4, 2008;359:1009-1017.
  4. Mitka M. New study supports lifesaving benefits of implantable defibrillation devices. JAMA. 2009;302:134-135.
  5. Sears SF JR, Todaro JF, Lewis TS, et al. Examining the psychosocial impact of implantable cardioverter defibrillators: a literature review. Clin Cardiol. 1999;22:481-489.
  6. Sears SF Jr, Conti JB. Understanding implantable cardioverter defibrillator shocks and storms: medical and psychosocial considerations for research and clinical care. Clin Cardiol. 2003;26:107-111.
  7. Irvine J, Dorian P, Baker B, et al. Quality of life in the Canadian Implantable Defibrillator Study (CIDS). Am Heart J. 2002;144:282-289.
  8. Wathen MS, DeGroot PJ, Sweeney MO, et al, for the PainFREE RX II Investigators. Prospective randomized multicenter trial of empirical antitachycardia pacing versus shocks for spontaneous rapid ventricular tachycardia in patients with implantable cardioverter-defibrillators. Circulation. 2004;110:2591-2596.
  9. Ahmad M, Bloomstein L, Roelke M, et al. Patients’ attitudes toward implantable defibrillator shocks. PACE. 2000;23:934-938.
  10. Sweeney MO, Sherfesee L, DeGroot PJ, et al. Differences in effects of electrical therapy type for ventricular arrhythmias on mortality in implantable cardioverter-defibrillator patients. Heart Rhythm. 2010;7:353-360.

SmartShock Technology

Medtronic developed its exclusive SmartShock Technology based on more than 20 years of experience in shock reduction. Consisting of six exclusive algorithms that discriminate true lethal arrhythmias from other arrhythmic and non-arrhythmic events, SmartShock Technology dramatically reduces the incidence of inappropriate shocks while maintaining sensitivity.1,2

Fewer inappropriate shocks

Detail Fewer inappropriate shocks

With SmartShock Technology, 98% of ICD patients are free of inappropriate shocks at 1 year1 and 92% remain free of inappropriate shocks at 5 years.1


Detail Time to first in appropriate shock


Detail SmartShock Techology algorithms

How SmartShock Technology Works

The six algorithms in SmartShock Technology address all major causes of inappropriate shocks1:


T Wave Discrimination

Identifies T Wave oversensing and provides ability to withhold therapy delivery without compromising VT/VF detection sensitivity.

  • New approach to T Wave oversensing (TWOS)
  • Frequency analysis versus manual sensitivity adjustment
  • Fully automatic
  • Does not require an initial shock for TWOS
  • No compromise on VF detection sensitivity


View animationt-wave-discrimination

T Wave Discrimination algorithm

Lead Integrity Suite

Combines two algorithms that detect, alert, and withhold inappropriate therapy for lead failure.

Lead Integrity Alert

Provides advance warning for lead fracture and extends the VF detection time

Lead Noise Discriminator + Alert

Identifies oversensing due to noise artifacts and provides ability to withhold therapy

  • No compromise of VT/VF detection sensitivity
  • Notifies clinician to potential lead noise


View animationLead Integrity Suite

Lead Integrity Suite algorithm

PR Logic + Wavelet

Combines morphology and A-V pattern recognition to better discriminate against all types of SVTs – even the very fast ones.

PR Logic

Effectively discriminates sinus tachycardia and most atrial fibrillation/atrial flutter



Uses EGM morphology to improve SVT discrimination (i.e., conducted AF and sudden onset SVT)

Discrimination in the VF Zone (Nominal)

  • SVT limit = 260 ms
  • VF high-rate timeout


View animationpr-logic-wavelet

PR Logic + Wavelet algorithm

Confirmation +

  • Better identifies that a tachycardia has been terminated with ATP or spontaneously during the charge and aborts the shock
  • Avoids inappropriate shocks for single PVCs or single fast events at the end of the charge

View animationconfirmation-algorithm

Confirmation + algorithm


  1. Volosin KJ, Exner DV, Wathen MS, Sherfesee L, Scinicariello A, Gillberg JM. Combining shock reduction strategies to enhance ICD therapy: A role for computer modeling. J Cardiovas Electrophysiol. Published online October 11, 2010.
  2. Protecta Clinical Study, Medtronic data on file.


SmartShock 2.0

SmartShock 2.0 includes the following enhancements to improve long-term shock reduction, while simplifying device programming:

  • New nominal settings for number of intervals to detect (NID); now at 24/32
  • T wave discrimination is now applied when even sensed events are ≥ 32 mV, which improves algorithm recognition of T wave oversensing (TWOs) with very large R waves
  • An interaction between TWOs and lead noise discrimination (LND) algorithms has been removed to improve recognition of lead noise episodes

Important Safety Information

Changes in a patient’s disease and/or medications may alter the efficacy of a device’s programmed parameters or related features.

Reducing shocks by NID extension can benefit both primary and secondary prevention patients.1,2

  • In primary prevention patients:
    – The PREPARE study showed a 63% reduction in shocks for patients programmed with strategically chosen programming, including an NID of 30/40, as compared to historical trials.1
  • In secondary prevention patients:
    – The ADVANCE III study showed a 37% reduction in shock and ATP therapies for patients programmed to 30/40 as compared to 18/24 with no difference in syncopal events.3

According to data from the US CareLink® Network, more than 60% of devices are left at nominal settings of 18/24.4 The new nominal settings are designed to simplify clinician workflow and help reduce inappropriate shocks by allowing more rhythms to self-terminate.


  1. Wilkoff BL, Williamson BD, Stern RS, et al. Strategic programming of detection and therapy parameters in implantable cardioverter-defibrillators reduces shocks in primary prevention patients: results from the PREPARE (Primary Prevention Parameters Evaluation) study. J Am Coll Cardiol. August 12, 2008;52(7):541-550.
  2. Sweeney MO, Wathen MS, Volosin K, et al. Appropriate and inappropriate ventricular therapies, quality of life, and mortality among primary and secondary prevention implantable cardioverter defibrillator patients: results from the Pacing Fast VT REduces Shock ThErapies (PainFREE Rx II) trial. Circulation. June 7, 2005;111(22):2898-2905.
  3. Gasparini M, et al. ADVANCE III: Longer detection window effective in reducing unnecessary ICD therapy. Late-Breaking Trial Session,LB01-4. Presented at the Heart Rhythm Society 33rd Annual Scientific Sessions, May 9-12, 2012, Boston, Mass.
  4. Medtronic CareLink Database. July 2012.
Last updated: 19 Apr 2016

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