Letter from the Editor

Status of the Subcutaneous Defibrillator in the New 2017 AHA/ACC/HRS Ventricular Arrhythmia Guideline

Bradley P. Knight, MD, FACC, FHRS, Editor-in-Chief

Bradley P. Knight, MD, FACC, FHRS, Editor-in-Chief

The subcutaneous implantable defibrillator (S-ICD) has been developed as a revolutionary alternative to a transvenous system. It avoids the implant-related and all too familiar long-term complications related to an intravascular system. It was proven to be sufficiently safe and effective for FDA approval five years ago,1 and has been shown in numerous published studies to be highly effective in detecting and terminating ventricular fibrillation.1-3 The second-generation device that is currently being implanted has been modified to avoid inappropriate shocks, allow for MRI compatibility, permit remote monitoring, have longer battery longevity, and measure at a smaller size. The screening process to identify patients at increased risk for T-wave oversensing by the device was also recently improved to make it easier and more automated. Although the S-ICD is still larger than a transvenous device, and cannot deliver pacing therapy, it has been accepted by many electrophysiologists as a legitimate alternative to a transvenous defibrillator in patients who do not need pacing. It is also considered by many to be the preferred device in patients who are young or have limited vascular access. The implant procedure has also evolved and is now being implanted successfully using a two-incision technique. It is most effective when the device is implanted in a very posterior location, with the lead and device below any fat. 
The “2017 AHA/ACC/HRS Guideline for Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death” was recently published, which supersedes the “ACC/AHA/ESC 2006 Guidelines for Management of Patients with Ventricular Arrhythmias and the Prevention of Sudden Cardiac Death” as well as some sections of the “ACC/AHA/HRS 2008 Guidelines for Device-Based Therapy of Cardiac Rhythm Abnormalities.”4 The 2017 guideline was updated in many aspects, but in particular, it was updated to address the subcutaneous defibrillator. This has long been anticipated given that there was no mention of the S-ICD in either of the former guidelines. 
Surprisingly, in the updated guideline, the recommended indications for the S-ICD are quite limited. In fact, the only Class I recommendation for the S-ICD is restricted to patients who have inadequate vascular access or are at high risk for infection. Although one could make an argument that the S-ICD is preferable in such patients, it is difficult to point to any data to limit the device for those select patients. Implantation of the S-ICD is considered reasonable (Class IIa recommendation) if pacing for bradycardia, VT termination, or as part of CRT is neither needed nor anticipated for patients who have an indication for an ICD. 
There is also a brief discussion of the history and published data related to the S-ICD. Why does the Class I recommendation for the S-ICD not include all patients who meet the indications included in its FDA-approved labeling? The text suggests that the lack of randomized trial data prevents a broader Class I recommendation. The results of the randomized PRAETORIAN trial,5 which has completed enrollment, are widely anticipated. However, such a trial may not fully capture the full benefits of the S-ICD, since most of the complications related to transvenous leads do not manifest for several years. 
According the manufacturer’s indications for use, “The S-ICD System is intended to provide defibrillation therapy for the treatment of life-threatening ventricular tachyarrhythmias in patients who do not have symptomatic bradycardia, incessant ventricular tachycardia, or spontaneous, frequently recurring ventricular tachycardia that is reliably terminated with anti-tachycardia pacing.”6 Many of our young patients have had serious complications from a transvenous ICD, including lead failures and recalls.7 Given the currently available data and collective experience related to the S-ICD, it is difficult to accept that in 2017, advice to a young patient with hypertrophic cardiomyopathy, for example, to undergo implantation of a S-ICD instead of a transvenous system is not considered a Class I recommendation. There are many Class I recommendations that are not supported by large randomized clinical trials but are strongly supported by evidence, experience, and expert opinion. I believe the Class IIa indication for the S-ICD in the guideline should be a Class I recommendation.


  1. Weiss R, Knight BP, Gold MR, et al. Safety and efficacy of a totally subcutaneous implantable-cardioverter defibrillator. Circulation. 2013;128:944-953.
  2. Lambiase PD, Barr C, Theuns DA, et al. Worldwide experience with a totally subcutaneous implantable defibrillator: early results from the EFFORTLESS S-ICD Registry. Eur Heart J. 2014;35:1657-1665.
  3. Burke MC, Gold MR, Knight BP, 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. J Am Coll Cardiol. 2015;65:1605-1615.
  4. Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death: executive summary: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. October 2017. DOI: 10.1016/j.jacc.2017.10.053 
  5. Olde Nordkamp LR, Knops RE, Bardy GH, et al. Rationale and design of the PRAETORIAN trial: A Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy. Am Heart J. 2012;163:753-760.
  6. Indications, Safety and Warnings. The EMBLEM™ MRI S-ICD System. Boston Scientific. Available at http://www.bostonscientific.com/en-US/products/defibrillators/emblem-s-icd-system/safety-information.html. Accessed November 5, 2017.
  7. Thavikulwat AC, Tomson TT, Knight BP, Bonow RO, Choudhury L. Appropriate implantable defibrillator therapy in adults with hypertrophic cardiomyopathy. J Cardiovasc Electrophysiol. 2016;27(8):953-960.
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