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Subcutaneous Implantable Defibrillator

S-ICD Clinical Data

Explore clinical study and real-world data on inappropriate shock rates, complication rates and more. Plus, learn about the first prospective, randomized, head-to-head, non-inferiority clinical trial comparing S-ICD to TV-ICD.

ATLAS Randomized Controlled Trial: S-ICD Superior to TV-ICD1

Study overview

The ATLAS Trial is an investigator-sponsored research study (ISR) initiated, designed and led by Population Health Research Institute (PHRI), Jeff S. Healey MD, MSc, FHRS, and the ATLAS Steering Committee. It is the first prospective randomized controlled trial where the primary objective was to evaluate lead-related complication rates between the S-ICD and single chamber TV-ICD devices at six months after implant.


The trial hypothesis is that S-ICD is superior to TV-ICD with respect to serious lead-related complications*, including:

  • Moderate-severe or severe tricuspid regurgitation,
  • Hemothorax or pneumothorax
  • Cardiac perforation, tamponade, or pericardial effusion or pericarditis
  • Ipsilateral upper extremity deep vein thrombosis
  • Lead dislodgement or loss of sensing or pacing requiring revision


Sample Size and Timing

The trial randomized 503 patients, who passed electrocardiographic screening, from clinical centers across Canada between February 2017 and July 2021.


Primary Outcomes

Patients in the S-ICD group showed significantly fewer serious lead-related complications* than patients implanted with a single-chamber TV-ICD.

The ATLAS trial met its primary superiority endpoint demonstrating a highly significant 92% reduction in serious lead-related complications* at six months for the EMBLEM™ S-ICD compared to any manufacturers single chamber TV-ICD devices. p=0.0031
Serious lead-related complication* occurred in 12 times as many patients in the single chamber TV-ICD arm (4.8%) at six months compared to 1 patient (0.4%) in the S-ICD arm.1


PRAETORIAN is the first prospective, randomized, head-to-head, non-inferiority clinical trial that compares S-ICD to TV-ICD. The trial followed 850 patients at 40 centers across Europe and the United States. Full results were published in 2020.

Analysis of the UNTOUCHED Study


The incidence of inappropriate shocks in primary prevention, LVEF ≤ 35% patients will be non-inferior to the rate in transvenous ICD patients with similar programming observed in MADIT-RIT Arms B and C.

Study Design

  • Follow-up for 18 months
  • Device programming with a conditional zone of 200 bpm and a shock zone of 250 bpm
  • Primary endpoint of inappropriate shock-free rate at 18 months
  • Secondary endpoints of all cause shock-free rate at 18 months and system and procedure complications at 30 days

Key Takeaways

1. The inappropriate shock rate of 2.4% at 1 year for EMBLEM™ MRI S-ICDs is the lowest reported for S-ICD, despite a cohort with more left ventricular dysfunction and heart failure.2

acute outcomes
2. The appropriate shock rate of 5.7% over 18 months was low with a high conversion success of 98.4%, similar to that reported with TV-ICD trials.2
S-ICD-Conversion Rates
3. Complication rates remain very low (95.8% complication free rate at 30 days, 92.7% at 18 months, and no systemic infections), despite enrolling a sicker patient population.2
EMBLEM complication rates

TV-ICD Lead Complications in the Real World

The transvenous lead is the most common source of complications in a TV-ICD system. Data from over 40,000 patients from the OptumLabs Data Warehouse demonstrated that the incidence of mechanical and infectious complications of transvenous leads over long-term follow-up is much higher in the real world than in clinical studies. 
3-4% of patients with TV-ICD suffer lead malfunctions in the first year of implant15
About 25% mechanical failure rate for TV-ICD at 10 years15
4% infection rate for TV-ICD at 10 years15
freedom from complication
 Kaplan-Meier plot of lead revision associated with a diagnosis of infection or mechanical complication for patients with an implantable cardioverter-defibrillator or cardiac resynchronization therapy defibrillator. 

S-ICD is Guideline Recommended

The S-ICD is now guideline recommended for patients at high risk of infection, inadequate venous access, and any patient without a pacing indication – the majority of ICD indicated patients.16

75% of ICD-Indicated Patients Have ≥1 Comorbidity Associated with Device Infection17-19
70% of DR & VR ICD Patients Under 75 Have No Pacing Indication at Implant7, 20
61% of Patients May Have Venous Stenosis Following Initial Device Implantation21

Analysis of MADIT RIT Data22

A new analysis of data from MADIT RIT demonstrates patients are more likely to develop complications from transvenous leads than they are to benefit from ATP.

  • There is a statistically significant reduction in ATP with contemporary programming, suggesting that many VTs are self-terminating and earlier interventions may lead to an overestimation of the value of ATP. 
  • Despite the use of significantly more ATP in the conventional programming arm of MADIT RIT, there was no reduction in the final shock rate when compared to the contemporary programming arms.

SMART Pass Significantly Reduces IAS

Real-world LATITUDE data for 1,984 patients demonstrated the annual rate of inappropriate shocks (IAS) went down to 4.3% when SMART Pass was enabled. This is a reduction of over 67% compared to the IAS rate seen in the original IDE study.23

Clinical Data Resources

Dr. Michael Gold Discusses the UNTOUCHED Study at HRS 2020

EFFORTLESS Midterm Outcomes

The Impact of SMART Pass on IAS

S-ICD and Patients at High Risk for Infection


Bradycardia Pacing Need in ICD Patients

Real-World Longevity Projections


Training & Education

Explore continuing education courses, best practices modules and other training and resources for S-ICD.



Why S-ICD?

See how S-ICD helps protect patients at risk for sudden cardiac death while also eliminating the risk of TV-ICD lead complications.

Implant Procedure

Implant Procedure

Learn about advancements in the S-ICD implant procedure, including the 2-incision and intermuscular implant techniques.

Videos & Resources

Videos & Resources

Hear physician perspectives about S-ICD, find media information, and download product images, patient videos and more.



  1. Healey JS et al. Subcutaneous Versus Transvenous Defibrillators: The Atlas Trial. Heart Rhythm Society Late Breaking Clinical Trials LB-733 Randomized Clinical Trials. 2022
  2. Gold, MR, et al. The UNTOUCHED Study. Circulation. 2020.
  3. Weiss, et al. The Safety and Efficacy of a Totally Subcutaneous Implantable-Defibrillator. CIRCULATION. Vol. 128, no. 9. (August 2013.): 944-953.
  4. Boersma, L, Barr, C, Knops, R, et al., Implant and Midterm Outcomes of the Subcutaneous Implantable Cardioverter-Defibrillator Registry: The EFFORTLESS Study. J Am Coll Cardiol, 2017. 70(7): p. 830-841.
  5. Knops R. et al., The PRAETORIAN Trial. Heart Rhythm Society Late Breaking Clinical Trials LBCT-01 2020.
  6. Theuns, et al. Prospective Blinded Evaluation of a Novel Sensing Methodology Designed to Reduce Inappropriate Shocks by S-ICD. Heart Rhythm. 2018.
  7. Gasparini, M, Lunati, MG, Proclemer, A, et al., Long Detection Programming in Single-Chamber Defibrillators Reduces Unnecessary Therapies and Mortality. JACC: Clinical Electrophysiology, 2017.
  8. Kutyifa, et al., Novel ICD Programming and Inappropriate ICD Therapy in CRT-D Versus ICD Patients: A MADIT-RIT Sub-Study. Circ Arrhythm Electrophysiol, 2016. 9(1): p. e001965.
  9. Burke MC, et al. 1-Year Prospective Evaluation of Clinical Outcomes and Shocks. JACC: Clinical Electrophysiology. 2020.
  10. Healey, J, et al. Cardioverter defibrillator implantation without induction of ventricular fibrillation: a single-blind, non-inferiority, randomised controlled trial (SIMPLE). The Lancet. 2015.
  11. Blatt, JA, Poole, JE, Johnson, GW, et al., No benefit from defibrillation threshold testing in the SCD-HeFT. J Am Coll Cardiol, 2008. 52(7): p. 551-6.
  12. Swerdlow CD et al. The Dilemma of ICD Implant Testing. PACE 2007; 30:675–700
  13. Kutyifa V, et al. Clinical Impact, Safety, and Efficacy of Single- versus Dual-Coil ICD Leads in MADIT-CRT J Cardiovasc Electrophysiol 2013;24:1246-52
  14. Gold MR et al. Efficacy and Temporal Stability of Reduced Safety Margins for Ventricular Defibrillation: Primary Results From the Low Energy Safety Study (LESS)Circulation 2002.
  15. Koneru, JN, Jones, PW, Hammill, EF, Wold, N, and Ellenbogen, KA, Risk Factors and Temporal Trends of Complications Associated With Transvenous Implantable Cardiac Defibrillator Leads. J Am Heart Assoc, 2018. 7(10).
  16. Al-Khatib SM, Stevenson WG, Ackerman MJ, Bryant WJ, Callans DJ, et al., 2017 AHA/ACC/HRS Guideline for Management of Patients With Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death, Heart Rhythm (2017), doi: 10.1016/j.hrthm.2017.10.036.
  17. Polyzos, KA, Konstantelias, AA, and Falagas, ME, Risk factors for cardiac implantable electronic device infection: a systematic review and meta-analysis. Europace, 2015. 17(5): p. 767-777.
  18. Greenspon, AJ, Patel, JD, Lau, E, et al., 16-Year Trends in the Infection Burden for Pacemakers and Implantable Cardioverter-Defibrillators in the United States. Journal of the American College of Cardiology, 2011. 58(10): p. 1001-1006.
  19. Friedman, DJ, Parzynski, CS, Varosy, PD, et al., Trends and In-Hospital Outcomes Associated With Adoption of the Subcutaneous Implantable Cardioverter Defibrillator in the United States. JAMA Cardiol, 2016. 1(8): p. 900-911.
  20. LATITUDE data on file. Boston Scientific 2017.
  21. Kusumoto, FM, Schoenfeld, MH, Wilkoff, BL, et al., 2017 HRS expert consensus statement on cardiovascular implantable electronic device lead management and extraction. Heart Rhythm, 2017.
  22. Schuger, et al. Avoiding Unnecessary Therapy for Ventricular Arrhythmias ≥ 200 bpm: Results from MADIT-RIT. S-PO03 at HRS 2019, San Francisco, CA.
  23. Theuns, et al. Evaluation of a Novel Algorithm Designed to Reduce Oversensing in the S-ICD. HRS 2016; AB05-01.

*In the ATLAS trial, serious complications were defined as moderate-severe or severe tricuspid regurgitation, hemothorax/pneumothorax, cardiac perforation, tamponade, pericardial effusion or pericarditis, ipsilateral upper extremity deep vein thrombosis and lead dislodgement or loss of sensing or pacing requiring revision.