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Subcutaneous Implantable Defibrillator

Leading the Charge

The PRAETORIAN Trial1, 9

The PRAETORIAN Trial is an investigator-sponsored study (ISR)* initiated, designed and led by Academic Medical Center in Amsterdam (AMC) and Reinoud E. Knops, MD, PhD. It is the first prospective randomized head-to-head trial comparing the performance of S-ICD and TV-ICD.

The trial hypothesis was that the S-ICD is non-inferior to the TV-ICD with respect to major ICD-related adverse events, including:

  • Inappropriate shocks
  • ICD-related complications that require intervention
  • Lead-related complications

The trial enrolled 849 patients between March 2011 and January 2017 within the EU and US.



Data from the PRAETORIAN trial confirmed that the S-ICD can be the preferred therapy choice over the TV-ICD for protection from sudden cardiac death. The S-ICD offers comparable performance for the majority of ICD-indicated patients who do not have a need for pacing, while avoiding the serious complications associated with TV-ICDs such as serious infections and lead-related complications.

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Primary and Secondary Endpoints**

Mortality Rates

  • No significant difference in overall and arrhythmic mortality rates between the two groups.
  • Mortality rate was low in both groups, even though:
    • Over 90% had ischemic (>68%) or non-ischemic heart failure
    • Secondary prevention for 19% of S-ICD patients and 20% of TV-ICD patients
    • Median EF was 30%
    • Median age was 63 years
  • Arrhythmic deaths were identical in both groups.
  • Numerically, more deaths occurred in the S-ICD group; this difference was due to non-cardiac causes including cancer and gastrointestinal disease.

Lead-Related Complications

  • Data showed a statistical difference in lead-related complications, with TV-ICD patients experiencing more than 4 times as many as S-ICD patients did.1
  • The S-ICD leaves the vasculature untouched, thereby reducing the risk of acute and future complications associated with transvenous leads.
  • Eliminating device leads within the vasculature is particularly important for ICD-indicated patients with co-morbidities such as diabetes and renal disease who often are at an increased risk of infection and may have vascular access issues.2

Infections Requiring Device Extraction

  • Numerically, TV-ICD patients experienced twice as many infections that required device extraction as S-ICD patients did.
  • Data in >91,000 transvenous lead extractions demonstrated that those extracted for infection had significantly higher rates of complications and mortality.3

Device-Related Complications

  • No statistical difference in device-related complications at the median 4-year follow-up.
  • The trial authors have initiated an extended follow-up, PRAETORIAN XL, and anticipate that at 8 years the S-ICD will demonstrate superiority to TV-ICD for all device-related complications.1

Inappropriate Shock Rates

  • No significant difference in inappropriate shock rates between the two groups.
  • The PRAETORIAN trial used mainly devices available prior to 2016. Studies using modern S-ICDs like the EMBLEMTM S-ICD have demonstrated even lower rates of IAS.5

S-ICD: A Smart Alternative to TV-ICD

Because it avoids some of the more major complications associated with the TV-ICD, including serious infection and lead-related complications, data shows that the S-ICD is an appropriate and potentially desirable alternative for primary and secondary ICD-indicated patients who do not require pacing. 

Additional Trial Results9

  • Mean implant time for S-ICD was only 5 minutes more than TV-ICD (55 min vs 50 min implant time).
  • 2-incision technique was utilized in 70% of all S-ICD implants.
  • Appropriate shock rates for the S-ICD group were higher than the TV-ICD group; only one patient with an S-ICD was converted to a CRT-D at two years for slow VT where ATP could potentially benefit.
    • Higher rates in S-ICD group likely due to: (1) devices used prior to 2016 without SMART Pass, (2) conditional programming zone of 180 bpm.4-5***
    • Other contemporary S-ICD studies featured appropriate shock rates of 5.3%4 [1 yr.] in patients with a SMART Pass enabled S-ICD (comparable to 6.5% and 5.9% rates for single chamber TV-ICDs in the PainFree SST and ADVANCE III trials6, 10).

Reducing TV-ICD Infections Can Lower Mortality Rates

When it comes to reducing complications, lowering mortality rates and cutting costs, avoiding infected TV-ICD leads can go a long way.

  • Data in >91,000 transvenous lead extractions found that those extracted for infection had a higher overall complication rate and a higher in-hospital mortality rate compared to those without infection.3
  • In this same study, the median cost of lead extraction was $39,308 for infected devices and $14,916 for non-infected devices.

Contemporary S-ICDs Further Reduce Rates of Inappropriate Shock

SMART PassTM, included in the EMBLEM MRI S-ICD, has been shown to reduce IAS rates by 68%.4

  • In the more recent UNTOUCHED study, the 1-year IAS rate was 3.1%,5 which is comparable to or lower than the rates observed with TV-ICDs in other studies, including the PRAETORIAN trial.1, 6-8
  • In addition, the 1-year IAS rate was 2.4% for those who received an EMBLEM MRI with SMART Pass.5, 9

S-ICD Procedures Are Becoming More Common Than Ever

Optimized implant techniques (such the intermuscular technique) and implant best practices have emerged as experience with S-ICD has increased to over 87,000 patients worldwide—and counting.



The PRAETORIAN trial is being extended to an 8-year follow-up, PRAETORIAN XL, that is due to complete in 2023. PRAETORIAN XL will be completed with the primary objective of establishing superiority of S-ICDs to TV-ICDs for acute and chronic complications.

*Supported by a research grant from Boston Scientific
***Likely resulted in higher appropriate shock rates and total shock burden than featured in S-ICD studies where more contemporary programming and SMART Pass were utilized.4,5


1. Knops R. et al., A Randomized Trial of Subcutaneous versus Transvenous Defibrillator Therapy: The PRAETORIAN Trial. Heart Rhythm Society Late Breaking Clinical Trials LBCT-01 2020.

2. Polyzos KA, Konstantelias AA, Falagas ME. Risk factors for cardiac implantable electronic device infection: a systematic review and meta-analysis. Europace. 2015;17(5):767-777.

3. Deshmukh A, Patel N, Noseworthy PA, et al. Trends in Use and Adverse Outcomes Associated with Transvenous Lead Removal in the United States. Circulation. 2015;132(25):2363-2371.

4. Theuns D, Brouwer TF, Jones PW, et al. Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator. Heart Rhythm. 2018;15(10):1515-1522

5. Gold M. et al., Understanding Outcomes With The S-ICD In Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) Trial Primary Results. Heart Rhythm Society Late Breaking Clinical Trials LBCT-02 2020.

6. Gasparini M, Lunati MG, Proclemer A, et al. Long Detection Programming in Single-Chamber Defibrillators Reduces Unnecessary Therapies and Mortality. JACC: Clinical Electrophysiology. 2017;3:1275–82.

7. Kutyifa V, Daubert JP, Schuger C, 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):e001965.

8. Auricchio A, Hudnall JH, Schloss EJ, et al. Inappropriate shocks in single-chamber and subcutaneous implantable cardioverter-defibrillators: a systematic review and meta-analysis. Europace. 2017;19(12):1973-1980.

9. Knops R. Subcutaneous versus Transvenous Defibrillator Therapy. New England Journal of Medicine. August 6th 2020.

10. Auricchio A, Schloss EJ, Kurita T, et al. Low inappropriate shock rates in patients with single- and dual/triple-chamber implantable cardioverter-defibrillators using a novel suite of detection algorithms: PainFree SST trial primary results. Heart Rhythm. 2015;12(5):926-936.

11. Boston Scientific RM PPR Report, Q4 2020.

EMBLEM Indications, Safety and Warnings