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The subcutaneous implantable cardioverter-defibrillator should be considered for all patients with an implantable cardioverter-defibrillator indication

  • Jian Liang Tan
    Affiliations
    From the Division of Cardiovascular Disease, Cooper Medical School of Rowan University/Cooper University Health System, Camden, New Jersey
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  • Andrea M. Russo
    Correspondence
    Address reprint requests and correspondence: Dr Andrea M. Russo, Cooper Medical School of Rowan University, Cooper University Hospital, 1 Cooper Plaza, Camden, NJ 08103.
    Affiliations
    From the Division of Cardiovascular Disease, Cooper Medical School of Rowan University/Cooper University Health System, Camden, New Jersey
    Search for articles by this author

      Keywords

      Key Findings
      • The subcutaneous implantable cardioverter-defibrillator (S-ICD) has been shown to have comparable efficacy, reliability, and safety outcomes compared to the transvenous implantable cardioverter-defibrillator (TV-ICD) for the prevention of sudden cardiac death (SCD) in patients who do not have pacing indications.
      • When recommending an implantable cardioverter-defibrillator (ICD) for the primary or secondary prevention of SCD, patients should be given the option of an S-ICD with a high level of recommendation in the absence of pacing indications.
      • The S-ICD may be preferred over the TV-ICD in patients at high risk for cardiac implantable electronic device infection, those with limited vascular access, and patients on dialysis in the absence of pacing indications.
      • The S-ICD also may be preferred in younger patients, who may need multiple devices and leads throughout their lifetime, and in women, who are at higher risk for TV-ICD complications, in the absence of pacing indications.
      • It is important to emphasize that the S-ICD should be included in the shared decision-making process, in addition to discussion about the TV-ICD, when offering ICD therapy for the primary or secondary prevention of SCD in patients who meet implantation criteria without pacing indications.
      The implantable cardioverter-defibrillator (ICD) is an essential lifesaving device implanted worldwide for the prevention of sudden cardiac death (SCD). Several clinical trials have demonstrated the efficacy of ICDs in both primary and secondary prevention cohorts over the last two and a half decades.
      Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators
      A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias.
      • Bardy G.H.
      • Lee K.L.
      • Mark D.B.
      • et al.
      Amiodarone or an implantable cardioverter-defibrillator for congestive heart failure.
      • Connolly S.J.
      • Hallstrom A.P.
      • Cappato R.
      • et al.
      Meta-analysis of the implantable cardioverter defibrillator secondary prevention trials. AVID, CASH and CIDS studies. Antiarrhythmics vs Implantable Defibrillator study. Cardiac Arrest Study Hamburg. Canadian Implantable Defibrillator Study.
      • Buxton A.E.
      • Lee K.L.
      • Fisher J.D.
      • Josephson M.E.
      • Prystowsky E.N.
      • Hafley G.
      A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial Investigators.
      • Kadish A.
      • Dyer A.
      • Daubert J.P.
      • et al.
      Prophylactic defibrillator implantation in patients with nonischemic dilated cardiomyopathy.
      Transvenous implantable cardioverter-defibrillators (TV-ICDs) have traditionally been implanted for such purposes. However, the TV-ICD system has considerable limitations and is associated with short- and long-term adverse events related to the endovascular lead.

      Concerns related to the TV-ICD system

      Evidence has demonstrated that 2%–11% of new TV-ICD implantation procedures result in early complications, such as pocket-related complications, device-related infection, procedure-related complications (pneumothorax, pericardial effusion/cardiac tamponade), device malfunction, and lead-related issues (lead dislodgment, lead fracture requiring revision) within 45–90 days postoperatively.
      • Lee D.S.
      • Krahn A.D.
      • Healey J.S.
      • et al.
      Evaluation of early complications related to De Novo cardioverter defibrillator implantation insights from the Ontario ICD database.
      • Reynolds M.R.
      • Cohen D.J.
      • Kugelmass A.D.
      • et al.
      The frequency and incremental cost of major complications among medicare beneficiaries receiving implantable cardioverter-defibrillators.
      • Steckman D.A.
      • Varosy P.D.
      • Parzynski C.S.
      • et al.
      In-hospital complications associated with reoperations of implantable cardioverter defibrillators.
      • Koneru J.N.
      • Jones P.W.
      • Hammill E.F.
      • Wold N.
      • Ellenbogen K.A.
      Risk factors and temporal trends of complications associated with transvenous implantable cardiac defibrillator leads.
      Several other studies also demonstrated that the long-term risk (up to 10 years) of TV-ICD systems for any complications leading to reoperation or hospitalization remain significantly elevated at 8%–33%.
      • Koneru J.N.
      • Jones P.W.
      • Hammill E.F.
      • Wold N.
      • Ellenbogen K.A.
      Risk factors and temporal trends of complications associated with transvenous implantable cardiac defibrillator leads.
      • Ranasinghe I.
      • Parzynski C.S.
      • Freeman J.V.
      • et al.
      Long-term risk for device-related complications and reoperations after implantable cardioverter-defibrillator implantation: an observational cohort study.
      • Kleemann T.
      • Becker T.
      • Doenges K.
      • et al.
      Annual rate of transvenous defibrillation lead defects in implantable cardioverter-defibrillators over a period of >10 years.
      • Duray G.Z.
      • Schmitt J.
      • Cicek-Hartvig S.
      • Hohnloser S.H.
      • Israel C.W.
      Complications leading to surgical revision in implantable cardioverter defibrillator patients: comparison of patients with single-chamber, dual-chamber, and biventricular devices.
      • Brouwer T.F.
      • Yilmaz D.
      • Lindeboom R.
      • et al.
      Long-term clinical outcomes of subcutaneous versus transvenous implantable defibrillator therapy.
      • Ezzat V.A.
      • Lee V.
      • Ahsan S.
      • et al.
      A systematic review of ICD complications in randomised controlled trials versus registries: is our 'real-world' data an underestimation?.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      • Olde Nordkamp L.R.
      • Postema P.G.
      • Knops R.E.
      • et al.
      Implantable cardioverter-defibrillator harm in young patients with inherited arrhythmia syndromes: a systematic review and meta-analysis of inappropriate shocks and complications.
      Interestingly, the National Cardiovascular Data Registry (NCDR) ICD registry reported that women with a TV-ICD system have a higher risk than men for any device-related complications postimplantation (adjusted odds ratio [OR] 1.39; P <.001); 6-month heart failure readmission (adjusted OR 1.32; P <.001); and 6-month all-cause readmission (adjusted OR 1.22; P <.001).
      • Russo A.M.
      • Daugherty S.L.
      • Masoudi F.A.
      • Wang Y.
      • Curtis J.
      • Lampert R.
      Gender and outcomes after primary prevention implantable cardioverter-defibrillator implantation: findings from the National Cardiovascular Data Registry (NCDR).
      Acute procedural complications include a higher risk of pneumothorax and cardiac perforation. Another NCDR ICD registry study reported that dialysis patients seemed to be at greatest risk for developing cardiac implantable electronic device (CIED) infection (OR 1.34; P = .0012) within 6 months of TV-ICD implantation.
      • Prutkin J.M.
      • Reynolds M.R.
      • Bao H.
      • et al.
      Rates of and factors associated with infection in 200 909 Medicare implantable cardioverter-defibrillator implants: results from the National Cardiovascular Data Registry.
      A totally subcutaneous defibrillator system was developed to overcome these complications related to the TV-ICD system.

      Overview of the S-ICD system

      The subcutaneous implantable cardioverter-defibrillator (S-ICD) was first approved by the U.S. Food & Drug Administration (FDA) in 2012 for prevention of SCD. A summary of the differences and similarities between the S-ICD and the TV-ICD system are listed in Table 1. Similar to the single-chamber TV-ICD system, the S-ICD system consists of a defibrillator lead and a pulse generator (PG). The S-ICD is designed to eliminate the need to insert the lead into the vasculature and into the heart, minimizing potential lead-related complications. Before S-ICD implantation, patients are screened with an electrocardiogram (ECG) to evaluate QRS–T-wave morphologies to assure appropriate sensing and reduce the risk of T-wave oversensing, hence minimizing the risk of inappropriate shocks (IAS) or undersensing of ventricular tachyarrhythmias.
      • Olde Nordkamp L.R.A.
      • Warnaars J.L.F.
      • Kooiman K.M.
      • et al.
      Which patients are not suitable for a subcutaneous ICD: incidence and predictors of failed QRS-T-wave morphology screening.
      • Groh C.A.
      • Sharma S.
      • Pelchovitz D.J.
      • et al.
      Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator.
      • Randles D.A.
      • Hawkins N.M.
      • Shaw M.
      • Patwala A.Y.
      • Pettit S.J.
      • Wright D.J.
      How many patients fulfil the surface electrocardiogram criteria for subcutaneous implantable cardioverter-defibrillator implantation?.
      Table 1Summary of S-ICD
      S-ICD generation 3.
      and TV-ICD (single-chamber) systems
      S-ICD
      S-ICD generation 3.
      TV-ICD
      PreimplantationRequires ECG screeningNo prescreening
      Pulse generator implantationSubcutaneous, subfascial, or submuscularSubcutaneous or submuscular
      Lead implantationSubcutaneous, 2-incision vs 3-incision techniquesTransvenous, requires patent vascular access
      Battery life7.3–8.7 y
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      Boston Scientific Corporation
      User’s Manual EMBLEM S-ICD, EMBLEM MRI S-ICD.
      11–12 y,
      Single-chamber transvenous Boston Scientific Model D140 Extended Longevity, Technical Manual (https://www.bostonscientific.com/content/dam/Manuals/au/current-rev-en/359499-004_ICD_PTM_en-AUS_S.pdf).62
      up to 13 yr
      Longevity estimates for Boston Scientific single-chamber TV-ICD device.
      • Boriani G.
      • Ritter P.
      • Biffi M.
      • et al.
      Battery drain in daily practice and medium-term projections on longevity of cardioverter-defibrillators: an analysis from a remote monitoring database.
      Pulse generator sizeLarger (59.5 cc, 130 g)
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      Smaller (30 cc, 68.9 g)
      Single-chamber transvenous Boston Scientific Model D140 Extended Longevity, Technical Manual (https://www.bostonscientific.com/content/dam/Manuals/au/current-rev-en/359499-004_ICD_PTM_en-AUS_S.pdf).62
      CostHigherLower
      Delivered energy
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      • Biffi M.
      • Bongiorni M.G.
      • D'Onofrio A.
      • et al.
      Is 40 Joules enough to successfully defibrillate with subcutaneous implantable cardioverter-defibrillators?.
      80 J
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      41 J
      Energy required to defibrillate (J)HigherLower
      Capacitor charge time
      • Rav Acha M.
      • Milan D.
      Who should receive the subcutaneous implanted defibrillator?: timing is not right to replace the transvenous implantable cardioverter defibrillator.
      Longer (14.6 ± 2.9 s)Shorter (7.1 ± 1.8 s)
      Shock waveform
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      Boston Scientific Corporation
      User’s Manual EMBLEM S-ICD, EMBLEM MRI S-ICD.
      BiphasicBiphasic
      Shock tilt
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      Boston Scientific Corporation
      User’s Manual EMBLEM S-ICD, EMBLEM MRI S-ICD.
      Fixed, 50%Fixed, 50%
      Pacing capability (ATP/brady/CRT)Not available
      Programmable on-demand bradycardia pacing at 50 bpm for up to 30 seconds.
      Available
      Lead removalLess complexMore complex
      Infection risk (4-y follow-up
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      )
      Lower (0.9%)Higher (1.9%)
      Lead failure/complications
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      Lower (1.4%)Higher (6.6%)
      MRI compatibleYesYes
      Atrial arrhythmia monitoringYes (AF detection algorithm)Yes (Various options
      Single-lead ICD with atrial sensing algorithm in single-chamber ICD or atrial lead recording in dual-chamber ICD.
      )
      Remote patient monitoringYesYes
      AF = atrial fibrillation; ATP = antitachycardia pacing; brady = bradyarrhythmia; CRT = cardiac resynchronization therapy; ECG = electrocardiogram; ICD = implantable cardioverter-defibrillator; MRI = magnetic resonance imaging; S-ICD = subcutaneous implantable cardioverter-defibrillator; TV-ICD = transvenous implantable cardioverter-defibrillator.
      S-ICD generation 3.
      Data on file with manufacturer. Based on analysis of >2900 Emblem patients followed on LATITUDE June 2017 (https://www.bostonscientific.com/content/dam/bostonscientific/Rhythm%20Management/portfolio-group/EMBLEM_S-ICD/Download_Center/EMBLEM-S-ICD-Spec-Sheet.pdf) and EMBLEM MRI S-ICD Model A209 & A219 User’s Manual 359480-001 EN US 2015-11. (https://www.bostonscientific.com/content/dam/Manuals/us/current-rev-en/359480-004_EMBLEM_S-ICD_UM_en-US_S.pdf).
      Single-chamber transvenous Boston Scientific Model D140 Extended Longevity, Technical Manual (https://www.bostonscientific.com/content/dam/Manuals/au/current-rev-en/359499-004_ICD_PTM_en-AUS_S.pdf).
      § Longevity estimates for Boston Scientific single-chamber TV-ICD device.
      Programmable on-demand bradycardia pacing at 50 bpm for up to 30 seconds.
      Single-lead ICD with atrial sensing algorithm in single-chamber ICD or atrial lead recording in dual-chamber ICD.

      Different techniques of PG and lead implantation with the S-ICD system

      There are vast differences between the S-ICD and the TV-ICD related to implantation techniques. The PG of the TV-ICD system is traditionally implanted in the left infraclavicular region (less commonly in the right infraclavicular region), and placement of the defibrillator lead requires venous access to the right ventricle through the subclavian, axillary, or cephalic vein. In contrast, the PG of the S-ICD system is implanted subcutaneously in the midaxillary line at the level of the fifth and sixth intercostal spaces, and the defibrillator lead is tunneled subcutaneously from the PG to the left parasternal border. The standard implantation technique of the S-ICD system was originally described using a 3-incision technique for lead placement and subcutaneous placement of the PG along the submammary crease or midaxillary region.
      • Bardy G.H.
      • Smith W.M.
      • Hood M.A.
      • et al.
      An entirely subcutaneous implantable cardioverter-defibrillator.
      Since then, alternative techniques, including a 2-incision technique for lead placement, and subfascial and submuscular implantation of the PG have also been described.
      • Brouwer T.F.
      • Miller M.A.
      • Quast A.B.
      • et al.
      Implantation of the subcutaneous implantable cardioverter-defibrillator: an evaluation of 4 implantation techniques.
      • Brouwer T.F.
      • Driessen A.H.G.
      • Olde Nordkamp L.R.A.
      • et al.
      Surgical management of implantation-related complications of the subcutaneous implantable cardioverter-defibrillator.
      • Smietana J.
      • Frankel D.S.
      • Serletti J.M.
      • et al.
      Subserratus implantation of the subcutaneous implantable cardioverter-defibrillator.
      • Knops R.E.
      • Olde Nordkamp L.R.
      • de Groot J.R.
      • Wilde A.A.
      Two-incision technique for implantation of the subcutaneous implantable cardioverter-defibrillator.
      For patients, these alternative implantation strategies may have cosmetic or comfort advantages. The 2-incision technique uses 2 incisions rather than 3, including 1 small incision at the xiphoid for lead placement in addition to the incision required for PG insertion.
      • Knops R.E.
      • Olde Nordkamp L.R.
      • de Groot J.R.
      • Wilde A.A.
      Two-incision technique for implantation of the subcutaneous implantable cardioverter-defibrillator.
      Alternative techniques using 2 incisions reduce procedural time, and submuscular implantation may lower shock impedance and improve defibrillation efficacy.
      • Smietana J.
      • Frankel D.S.
      • Serletti J.M.
      • et al.
      Subserratus implantation of the subcutaneous implantable cardioverter-defibrillator.
      The submuscular technique is considered a preferred mode of PG implantation, especially in obese patients, because it reduces the distance between the coil and the PG, thus reducing shock impedance and defibrillation energy requirements.
      • Heist E.K.
      • Belalcazar A.
      • Stahl W.
      • Brouwer T.F.
      • Knops R.E.
      Determinants of subcutaneous implantable cardioverter-defibrillator efficacy: a computer modeling study.
      The improvement in implantation techniques, device programming (prespecified with a conditional zone between 200 and 250 bpm), arrhythmia discrimination algorithm, and SMART Pass filter have also resulted in lower IAS rates and better outcomes.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      ,
      • Brisben A.J.
      • Burke M.C.
      • Knight B.P.
      • et al.
      A new algorithm to reduce inappropriate therapy in the S-ICD system.
      • Theuns D.
      • Brouwer T.F.
      • Jones P.W.
      • et al.
      Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
      • Boersma L.V.
      • El-Chami M.F.
      • Bongiorni M.G.
      • et al.
      Understanding Outcomes with the EMBLEM S-ICD in Primary Prevention Patients with Low EF Study (UNTOUCHED): clinical characteristics and perioperative results.
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      In addition, >95% of S-ICD implants can be safely performed using anatomic landmarks and require zero or minimal fluoroscopic guidance.
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      This offers some additional advantage to the operator, the staff, and the patient in helping to reduce the cumulative lifetime level of radiation exposure.

      Early studies of the S-ICD

      Several major S-ICD studies have shown that the S-ICD consistently demonstrates favorable safety and efficacy outcomes when used for the primary and secondary prevention of SCD (Table 2).
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      • Boersma L.
      • Barr C.
      • Knops R.
      • et al.
      Implant and midterm outcomes of the subcutaneous implantable cardioverter-defibrillator registry: the EFFORTLESS study.
      • Gold M.R.
      • Aasbo J.D.
      • El-Chami M.F.
      • et al.
      Subcutaneous implantable cardioverter-defibrillator post-approval study: clinical characteristics and perioperative results.
      The IDE (S-ICD System Investigational Device Exemption Clinical Investigation) study and the EFFORTLESS S-ICD (Evaluation of Factors Impacting Clinical Outcome and Cost Effectiveness of the S-ICD) registry, 2 earlier studies conducted in the United States and Europe, respectively, demonstrated the safety and feasibility of the S-ICD system for the primary and secondary prevention of SCD.
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      ,
      • Dabiri Abkenari L.
      • Theuns D.A.
      • Valk S.D.
      • et al.
      Clinical experience with a novel subcutaneous implantable defibrillator system in a single center.
      ,
      • Lambiase P.D.
      • Barr C.
      • Theuns D.A.
      • et al.
      Worldwide experience with a totally subcutaneous implantable defibrillator: early results from the EFFORTLESS S-ICD Registry.
      The IDE study and the EFFORTLESS registry demonstrated high first-shock conversion efficacy of 88% and 92.1%, respectively, for any spontaneous ventricular arrhythmias. In a pooled analysis of 882 patients (results from the IDE study and the EFFORTLESS registry with mean follow-up of 22-months), the S-ICD continued to demonstrate favorable safety and efficacy.
      • Burke M.C.
      • Gold M.R.
      • Knight B.P.
      • et al.
      Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry.
      This study also noted an estimated 3-year all-cause mortality rate of 4.7% and a very low rate of lead issues (<1%) over the course of 3-year follow-up.
      • Burke M.C.
      • Gold M.R.
      • Knight B.P.
      • et al.
      Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry.
      It is also important to note the S-ICD had a very low rate of infection (<2%). In particular, there were no S-ICD related cases of endocarditis or bacteremia in the cohort with infection over the course of 3-year follow-up.
      • Burke M.C.
      • Gold M.R.
      • Knight B.P.
      • et al.
      Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry.
      Table 2Published major studies on S-ICD
      Study, year (Reference no.)DesignStudy descriptionNo. of patientsAge (y)Primary prevention (%)LVEF (%)DFT success (%)IAS (%)Complications (%)Data available
      CE study, 2011
      • Dabiri Abkenari L.
      • Theuns D.A.
      • Valk S.D.
      • et al.
      Clinical experience with a novel subcutaneous implantable defibrillator system in a single center.
      Prospective, nonrandomizedInitial clinical experience of the S-ICD3153 ± 166738.8 ± 1510016.19.7286 d (median)
      S-ICD IDE study, 2013
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      Prospective, nonrandomized, multicenter, observationalPremarket safety and efficacy32151.9 ± 15.579.436.1 ± 15.910013.1 (mean 11–mo follow-up)7.9 (180-d complication rate)180 d
      Global EFFORTLESS S-ICD Registry, 2017
      • Boersma L.
      • Barr C.
      • Knops R.
      • et al.
      Implant and midterm outcomes of the subcutaneous implantable cardioverter-defibrillator registry: the EFFORTLESS study.
      Nonrandomized, multicenter, registryPostapproval safety and efficacy
      S-ICD generation 1.
      98548 ± 1764.943 ± 1899.52.3 (mean 3.1-y follow-up)11.1 (mean 3.1-y follow-up)5 y
      S-ICD system PAS study, 2017
      • Gold M.R.
      • Aasbo J.D.
      • El-Chami M.F.
      • et al.
      Subcutaneous implantable cardioverter-defibrillator post-approval study: clinical characteristics and perioperative results.
      Nonrandomized, multicenter, registryPostapproval safety and efficacy
      S-ICD generation 2.
      163753.2 ± 1576.732 ± 14.698.70.2 (at 30 d)3.8 (at 30 d)30 d
      PRAETORIAN trial, 2020
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      International, randomized, noninferiorityHead-to-head comparison for safety and efficacy
      S-ICD (patient received either generation 1 or generation 2).
      426
      S-ICD (patient received either generation 1 or generation 2).
      vs 423
      TV-ICD group.
      63 (54–69)
      S-ICD (patient received either generation 1 or generation 2).
      vs 64 (56–70)
      TV-ICD group.
      81.2
      S-ICD (patient received either generation 1 or generation 2).
      vs 80.1
      TV-ICD group.
      30 (25–35)
      S-ICD (patient received either generation 1 or generation 2).
      TV-ICD group.
      99.3
      S-ICD (patient received either generation 1 or generation 2).
      9.7
      S-ICD (patient received either generation 1 or generation 2).
      vs 7.3
      TV-ICD group.
      (4-y cumulative incidence)
      5.9
      S-ICD (patient received either generation 1 or generation 2).
      vs 9.8
      TV-ICD group.
      (4-y cumulative incidence)
      49.1 mo (median)
      UNTOUCHED trial, 2021
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      Multinational, prospective, nonrandomizedPrimary prevention using standardized programing and improved sensing algorithms
      S-ICD generation 2 and generation 3.
      111655.8 ± 12.410026.4 ± 5.899.24.1 (at 18 mo)7.3 (at 18 mo)18 mo
      ATLAS trial, 2022
      • Gold M.R.
      • Theuns D.A.
      • Knight B.P.
      • et al.
      Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study.
      Randomized, multicenter, open-label, parallel groupHead-to-head comparison for safety and efficacy with the focus on younger patients251
      S-ICD generation 3 or subsequent newer generation.
      vs 252
      TV-ICD group.
      48 ± 12
      S-ICD generation 3 or subsequent newer generation.
      vs 50 ± 11
      TV-ICD group.
      63.7
      S-ICD generation 3 or subsequent newer generation.
      vs 69.4
      TV-ICD group.
      NANA6.4
      S-ICD generation 3 or subsequent newer generation.
      vs 2.8
      TV-ICD group.
      (at 6-mo follow-up)
      4.4
      S-ICD generation 3 or subsequent newer generation.
      vs 5.6
      TV-ICD group.
      (at 6-mo follow-up)
      6 mo
      Values are given as number of patients, percentage (%), median (interquartile range), or mean ± SD.
      ATLAS = Avoid Transvenous Leads in Appropriate Subjects; DFT = defibrillation threshold; EFFORTLESS S-ICD = Evaluation of Factors Impacting Clinical Outcome and Cost Effectiveness of the S-ICD; IAS = inappropriate shock; IDE = S-ICD System Investigational Device Exemption Clinical Investigation; LVEF = left ventricular ejection fraction; NA = not available; PAS = S-ICD System Post-Approval; PRAETORIAN = Prospective Randomized Comparison of Subcutaneous and Transvenous Implantable Cardioverter Defibrillator Therapy; S-ICD = subcutaneous implantable cardioverter-defibrillator; TV-ICD = transvenous implantable cardioverter-defibrillator; UNTOUCHED = Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction.
      S-ICD generation 1.
      S-ICD generation 2.
      S-ICD (patient received either generation 1 or generation 2).
      TV-ICD group.
      § S-ICD generation 2 and generation 3.
      ∗∗ S-ICD generation 3 or subsequent newer generation.
      After publication of these studies that included observational and large registry data,
      • Burke M.C.
      • Gold M.R.
      • Knight B.P.
      • et al.
      Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry.
      recommendations were published in the 2015 European Society of Cardiology (ESC) guidelines and the 2017 American Heart Association/American College of Cardiology/Heart Rhythm Society (AHA/ACC/HRS) guidelines, giving the S-ICD a class IIa recommendation for patients who meet criteria for ICD implantation and do not require pacing therapy for bradycardia, ventricular tachyarrhythmia, or cardiac resynchronization.
      • Priori S.G.
      • Blomstrom-Lundqvist C.
      • Mazzanti A.
      • et al.
      2015 ESC Guidelines for the management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: the Task Force for the Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death of the European Society of Cardiology (ESC). Endorsed by: Association for European Paediatric and Congenital Cardiology (AEPC).
      ,
      • Al-Khatib S.M.
      • Stevenson W.G.
      • Ackerman M.J.
      • et al.
      2017 AHA/ACC/HRS Guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.
      In addition, these guidelines gave the S-ICD a class I indication for the prevention of SCD in patients with limited vascular access or at high risk for infection who do not require pacing therapy for bradycardia, ventricular tachyarrhythmia, or cardiac resynchronization therapy.
      • Al-Khatib S.M.
      • Stevenson W.G.
      • Ackerman M.J.
      • et al.
      2017 AHA/ACC/HRS Guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society.

      Heart failure and other comorbidities

      After initial approval by the FDA in 2012, the S-ICD was initially utilized in a minority of patients meeting indications for ICD therapy (2.0 % in 2016 NCDR publication
      • Kremers M.S.
      • Hammill S.C.
      • Berul C.I.
      • et al.
      The National ICD Registry Report: version 2.1 including leads and pediatrics for years 2010 and 2011.
      and 3.4% in 2019 Q1 NCDR registry quarterly report, according to data supplied by the NCDR registry to participating centers), often used as a “niche” device. Recent FDA recalls of the S-ICD system (due to risk of a short circuit, accelerated battery depletion, and electrode body fracture) also might have affected increased adoption of this technology in the United States.
      U.S. Food & Drug Administration
      Boston Scientific Recalls EMBLEM S-ICD Subcutaneous Electrode (Model 3501) Due to Risk of Fractures 2020.
      ,
      U.S. Food & Drug Administration
      Boston Scientific Corporation recalls EMBLEM S-ICD (Subcutaneous Implantable Cardioverter Defibrillator) System Due to Risk of Short-Circuit.
      In the United States, the majority of patients (∼3/4) who undergo ICD implantation have a primary prevention indication, particularly for ischemic or nonischemic cardiomyopathy with reduced left ventricular (LV) function, a cohort who often have multiple comorbidities.
      • Kremers M.S.
      • Hammill S.C.
      • Berul C.I.
      • et al.
      The National ICD Registry Report: version 2.1 including leads and pediatrics for years 2010 and 2011.
      However, it should be noted that previous S-ICD studies also included patients with heart failure, low ejection fraction (EF), and multiple comorbidities. Low EF patients were well represented in the IDE trial (mean 36% ± 16%, and 70% of patients with EF ≤35%).
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      In the EFFORTLESS registry, patients with a broad range of underlying heart disease were represented, including 29% with ischemic cardiomyopathy and 17% with nonischemic cardiomyopathy.
      • Boersma L.
      • Barr C.
      • Knops R.
      • et al.
      Implant and midterm outcomes of the subcutaneous implantable cardioverter-defibrillator registry: the EFFORTLESS study.
      In the combined EFFORTLESS registry + IDE study, 42% had congestive heart failure and 35% had previous myocardial infarction.
      • Burke M.C.
      • Gold M.R.
      • Knight B.P.
      • et al.
      Safety and efficacy of the totally subcutaneous implantable defibrillator: 2-year results from a pooled analysis of the IDE study and EFFORTLESS registry.
      In the NCDR ICD registry, 74% had heart failure, 40% had previous myocardial infarction and 20% were on dialysis.
      • Friedman D.J.
      • Parzynski C.S.
      • Varosy P.D.
      • et al.
      Trends and in-hospital outcomes associated with adoption of the subcutaneous implantable cardioverter defibrillator in the United States.
      The UNTOUCHED (Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction) study included only patients with primary prevention ICDs who had LVEF ≤35% (1111 patients implanted with an S-ICD).
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      Compared with patients included in MADIT-RIT (Multicenter Automatic Defibrillator Implantation Trial-Reduce Inappropriate Therapy), which included only TV-ICDs, LVEF in UNTOUCHED was similar (27% ± 7% vs 26% ± 6%, respectively).
      • Boersma L.V.
      • El-Chami M.F.
      • Bongiorni M.G.
      • et al.
      Understanding Outcomes with the EMBLEM S-ICD in Primary Prevention Patients with Low EF Study (UNTOUCHED): clinical characteristics and perioperative results.
      ,
      • Moss A.J.
      • Schuger C.
      • Beck C.A.
      • et al.
      Reduction in inappropriate therapy and mortality through ICD programming.
      In the PRAETORIAN (Prospective Randomized Comparison of Subcutaneous and Transvenous Implantable Cardioverter Defibrillator Therapy) trial, 426 patients had undergone S-ICD implantation, including 68% with ischemic cardiomyopathy, 23% with nonischemic cardiomyopathy, 66% with New York Heart Association functional class II–IV heart failure, and median EF 30%.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      Because there is a large amount of experience with the S-ICD in low EF populations with heart failure and multiple comorbidities, the S-ICD should not be considered a “niche” device.

      The evidence and why choose the S-ICD over a TV-ICD?

      The S-ICD may be preferred over the TV-ICD because of to the low rates of lead failure and clinically significant infections, specifically bacteremia, due to the absence of a transvenous lead. Specifically, this device may be preferred in patients with limited venous access, those with previous transvenous infection, those with conditions associated with a high risk of infection, such as dialysis or immunodeficiency states, and in patients with hypertrophic cardiomyopathy (who may have a high defibrillation threshold with TV-ICDs). Younger patients with an active lifestyle may be at higher risk for long-term lead failure and women may be at higher risk for procedural complications from transvenous leads, also potentially favoring the S-ICD (Figure 1).
      Figure thumbnail gr1
      Figure 1Factors influencing selection of subcutaneous implantable cardioverter-defibrillator (S-ICD). CRT = cardiac resynchronization therapy; ECG = electrocardiogram; ICD = implantable cardioverter-defibrillator; MMVT = monomorphic ventricular tachycardia; PMVT = polymorphic ventricular tachycardia; TV = transvenous; TV-ICD = transvenous implantable cardioverter-defibrillator; VT = ventricular tachycardia.
      Additional evidence supporting the S-ICD includes real-world data from registries. The NCDR ICD registry examined trends and in-hospital outcomes of S-ICD implantation in the United States (2012–2015), reporting outcomes of 3717 patients who underwent S-ICD implantation.
      • Friedman D.J.
      • Parzynski C.S.
      • Varosy P.D.
      • et al.
      Trends and in-hospital outcomes associated with adoption of the subcutaneous implantable cardioverter defibrillator in the United States.
      In contrast to the IDE study and the EFFORTLESS registry, patients on chronic dialysis represented 20% of patients who underwent S-ICD implantation in this registry. Patients with the S-ICD had a high success rate of defibrillation testing (99.7%) at ≤80 J and low overall in-hospital complication rates (<1.0%) as well as low in-hospital mortality rates (0.1%), similar to outcomes of patients with single- or dual-chamber TV-ICDs.
      • Friedman D.J.
      • Parzynski C.S.
      • Varosy P.D.
      • et al.
      Trends and in-hospital outcomes associated with adoption of the subcutaneous implantable cardioverter defibrillator in the United States.
      PRAETORIAN was the first head-to-head trial comparing the S-ICD (426 patients) with the TV-ICD (423 patients) in general populations with an indication for ICD therapy who did not have cardiac pacing indications.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      At median follow-up of 49.1 months, the S-ICD was deemed noninferior to the TV-ICD in the primary composite endpoint (hazard ratio 0.99; P = .01) with respect to device-related complications and IAS.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      In the UNTOUCHED trial (1116 patients), the S-ICD was proven to be safe and effective for use, even in older patients with multiple comorbidities and poorer cardiovascular function.
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      This study also demonstrated a high defibrillation success rate (>92%), high complication-free rate (92.7%), and high IAS-free rate (95.9%) at 18 months without compromising patient safety.
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      Evidence from these trials supports the use of the S-ICD in older patients and in patients with multiple comorbidities and lower EF.
      IAS delivery is one adverse event of ICD therapy that has gained attention with both S-ICDs and TV-ICDs. Studies have shown that IAS greatly reduce quality of life and are associated with increased risk of all-cause mortality.
      • Poole J.E.
      • Johnson G.W.
      • Hellkamp A.S.
      • et al.
      Prognostic importance of defibrillator shocks in patients with heart failure.
      • van Rees J.B.
      • Borleffs C.J.
      • de Bie M.K.
      • et al.
      Inappropriate implantable cardioverter-defibrillator shocks: incidence, predictors, and impact on mortality.
      • Li A.
      • Kaura A.
      • Sunderland N.
      • Dhillon P.S.
      • Scott P.A.
      The significance of shocks in implantable cardioverter defibrillator recipients.
      Previous investigation has demonstrated overall similar rates of IAS among TV-ICD and S-ICD recipients, but the reasons for IAS delivery were more often related to supraventricular arrhythmias with the TV-ICD and T-wave oversensing with the S-ICD in a meta-analysis of case-controlled studies.
      • Basu-Ray I.
      • Liu J.
      • Jia X.
      • et al.
      Subcutaneous versus transvenous implantable defibrillator therapy: a meta-analysis of case-control studies.
      Use of the SMART Pass filter technology (available in third-generation S-ICDs) and programming the S-ICD with a conditional zone between 200 and 250 bpm have greatly reduced T-wave oversensing and IAS delivery among S-ICD recipients without affecting safety outcomes.
      • Theuns D.
      • Brouwer T.F.
      • Jones P.W.
      • et al.
      Prospective blinded evaluation of a novel sensing methodology designed to reduce inappropriate shocks by the subcutaneous implantable cardioverter-defibrillator.
      ,
      • Gold M.R.
      • Lambiase P.D.
      • El-Chami M.F.
      • et al.
      Primary results from the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) trial.
      ,
      • Weiss R.
      • Knight B.P.
      • Gold M.R.
      • et al.
      Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator.
      ,
      • Gold M.R.
      • Theuns D.A.
      • Knight B.P.
      • et al.
      Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study.
      ,
      • Mesquita J.
      • Cavaco D.
      • Ferreira A.
      • et al.
      Effectiveness of subcutaneous implantable cardioverter-defibrillators and determinants of inappropriate shock delivery.
      In the START (Subcutaneous versus Transvenous Arrhythmia Recognition Testing) study, the S-ICD even surpassed performance of TV-ICD algorithms in head-to-head comparisons of sensitivity and specificity using induced arrhythmias in vitro.
      • Gold M.R.
      • Theuns D.A.
      • Knight B.P.
      • et al.
      Head-to-head comparison of arrhythmia discrimination performance of subcutaneous and transvenous ICD arrhythmia detection algorithms: the START study.
      Figure 2 demonstrates a comparison of annual IAS rates across different major S-ICD and TV-ICD studies.
      Figure thumbnail gr2
      Figure 2Annual inappropriate shocks rates across different ICD studies. ∗Overall incidence was over the 11-month average follow-up. †Overall incidence was over the 46-month average follow-up. ADVANCE III = Avoid DeliVering TherApies for Non-sustained Arrhythmias in ICD PatiEnts III; ATLAS = Avoid Transvenous Leads in Appropriate Subjects; EFFORTLESS= Evaluation of Factors Impacting Clinical Outcome and Cost Effectiveness of the S-ICD; ICD = implantable cardioverter-defibrillator; IDE = S-ICD System Investigational Device Exemption Clinical Investigation; MADIT-RIT = Multicenter Automatic Defibrillator Implantation Trial-Reduce Inappropriate Therapy; PAS = S-ICD System Post-Approval; PRAETORIAN = Prospective Randomized Comparison of Subcutaneous and Transvenous Implantable Cardioverter Defibrillator Therapy; S-ICD = subcutaneous implantable cardioverter-defibrillator; SCD-HeFT = Sudden Cardiac Death in Heart Failure Trial; TV-ICD = transvenous implantable cardioverter-defibrillator; UNTOUCHED = Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction.
      In addition, recent data from the ATLAS (Avoid Transvenous Leads in Appropriate Subjects) trial have once again proven that the S-ICD has lower major lead-related complications compared with the TV-ICD (0.4% vs 4.8%; P <.0003) at 6-month follow-up.
      • Healey J.
      Subcutaneous versus transvenous defibrillators: the ATLAS trial.
      In this study, there was no significant difference in ICD performance between the 2 devices with respect to the rate of IAS and failed first shock/arrhythmic death during 6-month follow-up.
      • Healey J.
      Subcutaneous versus transvenous defibrillators: the ATLAS trial.
      It is important to note that younger patients aged 18 to 60 years were enrolled in the ATLAS trial. Previous studies have shown that younger patients are at higher risk for TV lead failure/fracture, and there is an increased need for early reoperation in this age group.
      • Ranasinghe I.
      • Parzynski C.S.
      • Freeman J.V.
      • et al.
      Long-term risk for device-related complications and reoperations after implantable cardioverter-defibrillator implantation: an observational cohort study.
      ,
      • Olgun H.
      • Karagoz T.
      • Celiker A.
      • Ceviz N.
      Patient- and lead-related factors affecting lead fracture in children with transvenous permanent pacemaker.
      ,
      • Lee J.C.
      • Shannon K.
      • Boyle N.G.
      • Klitzner T.S.
      • Bersohn M.M.
      Evaluation of safety and efficacy of pacemaker and defibrillator implantation by axillary incision in pediatric patients.
      Therefore, we would highly recommend the S-ICD for primary prevention of SCD in younger patients with no indication for pacing.
      Last, but not least, a recent systematic review and meta-analysis, which was a pooled analysis of 5 high-quality studies (1195 patients received S-ICD; 1192 patients received TV-ICD), reported that patients implanted with the S-ICD had a lower risk of lead-related complications (risk ratio [RR] 0.14; P <.0001) at 30 to 60 months of follow-up.
      • Fong K.Y.
      • Ng C.J.R.
      • Wang Y.
      • Yeo C.
      • Tan V.H.
      Subcutaneous versus transvenous implantable defibrillator therapy: a systematic review and meta-analysis of randomized trials and propensity score-matched studies.
      Both the S-ICD and TV-ICD seemed to have similar rates of device-related complications (RR 0.59; P = .07), similar rates of infection (RR 0.94; P = .897), similar rates of appropriate shock therapy (RR 0.87; P = .732), and no significant differences in IAS therapy (RR 1.06; P = .695) and all-cause mortality (RR 1.02; P = .943).
      • Fong K.Y.
      • Ng C.J.R.
      • Wang Y.
      • Yeo C.
      • Tan V.H.
      Subcutaneous versus transvenous implantable defibrillator therapy: a systematic review and meta-analysis of randomized trials and propensity score-matched studies.
      In summary, there certainly are many important points and tradeoffs to consider when selecting either the S-ICD or the TV-ICD. The implanting physician should be open-minded and consider the evidence because both types of devices are indicated for many patients undergoing ICD implantation. This can be a tough decision for patients. Hence, it is utterly important for us, their trusted health care providers, to adopt a shared decision-making model and provide the most up-to-date clinical evidence when selecting between the S-ICD and the TV-ICD for sudden death prevention. Figure 1 outlines considerations for device selection and situations for which the S-ICD may be preferred, or not preferred, over TV-ICDs.

      Current limitations of the S-ICD

      There are some current known limitations of the S-ICD system as mentioned previously (Table 1), including shorter battery lifespan, larger PG size, lack of pacing support, and lack of direct atrial arrhythmia recording. However, major improvements and advancements have been made in S-ICD technology over the past few years. These include enhanced battery longevity, smaller PG size, and algorithms to help with detection of atrial arrhythmias despite absence of an atrial lead. In appropriately selected patients, there is a very low risk of needing a TV-ICD system for pacing indications.
      • Knops R.E.
      • Olde Nordkamp L.R.A.
      • Delnoy P.H.M.
      • et al.
      Subcutaneous or transvenous defibrillator therapy.
      Investigation is underway evaluating the combination of a leadless pacemaker or a cardiac contractility modulation device with the S-ICD system, which seems to be feasible and effective in small animal and human case studies.
      • Tjong F.V.
      • Brouwer T.F.
      • Smeding L.
      • et al.
      Combined leadless pacemaker and subcutaneous implantable defibrillator therapy: feasibility, safety, and performance.
      • Roger S.
      • Borggrefe M.
      • Kuschyk J.
      Heart failure with reduced ejection fraction and a narrow QRS complex: combination of a subcutaneous defibrillator with cardiac contractility modulation.
      • Kuschyk J.
      • Stach K.
      • Tulumen E.
      • et al.
      Subcutaneous implantable cardioverter-defibrillator: First single-center experience with other cardiac implantable electronic devices.
      • Sidhu B.S.
      • Gould J.
      • Porter B.
      • et al.
      Completely leadless cardiac resynchronization defibrillator system.
      • Elliott M.K.
      • Sidhu B.S.
      • Mehta V.S.
      • Gould J.
      • Martic D.
      • Rinaldi C.A.
      The importance of leadless pacemaker positioning in relation to subcutaneous implantable cardioverter-defibrillator sensing in completely leadless cardiac resynchronization and defibrillation systems.
      The concept of combined leadless pacing with the S-ICD currently is being evaluated in a larger study—MODULAR ATP (Effectiveness of the EMPOWER™ Modular Pacing System and EMBLEM™ Subcutaneous ICD to Communicate Antitachycardia Pacing).
      Boston Scientific Corporation
      Effectiveness of the EMPOWER™ Modular Pacing System and EMBLEM™ Subcutaneous ICD to Communicate Antitachycardia Pacing (MODULAR ATP) 2023.
      Until then, the S-ICD is indicated in a wide variety of patients without cardiac pacing indications for all the reasons noted here and should be strongly considered as upfront therapy at the time of initial ICD implantation in the shared decision-making process.

      Conclusion

      Available evidence strongly supports use of the S-ICD in patients without cardiac pacing indications for the primary and secondary prevention of SCD. Although previous guidelines gave the ICD a class IIa indication, they were written before the availability of data from more recent trials, and it is anticipated that this level of recommendation will be elevated with the next guideline update. In addition, the S-ICD may be preferable to TV-ICD systems in certain special populations, including younger patients, women, those with vascular access issues, patients at high-risk for CIED infection (previous CIED infection, recent endocarditis, prosthetic heart valve replacement, dialysis, or immunodeficiency states), and those with complex congenital heart disease. It may also be a good device for patients with hypertrophic cardiomyopathy (who may have high defibrillation thresholds with TV-ICDs) and inherited arrhythmogenic syndromes (often young patients with a low risk for development of monomorphic ventricular tachycardia). In any case, a patient-centered approach and a shared decision-making model that provides the most up-to-date clinical evidence should be utilized when selecting between the S-ICD and the TV-ICD for sudden death prevention.

      Funding Sources

      The authors have no funding sources to disclose.

      Disclosures

      Dr Russo reports research and funding to Cooper Health System from Boston Scientific , Kestra, MediLynx, and Medtronic; consulting fees from Abbott, AtriCure, Bayer, Biosense Webster , Boston Scientific, Medtronic, and PaceMate; honoraria/speaking fees from Biotronik, BMS/Pfizer, Medtronic, and Sanofi; and royalties from Up-to-Date. Dr Tan has no conflicts to disclose.

      Authorship

      All authors attest they meet the current ICMJE criteria for authorship.

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