Author + information
- Published online December 18, 2017.
- Daniel W. Carlson, MD and
- Ronald D. Berger, MD, PhD∗ ()
- ↵∗Address for correspondence:
Dr. Ronald D. Berger, Department of Medicine, Johns Hopkins University, Johns Hopkins Hospital, Halsted 570, 600 North Wolfe Street, Baltimore, Maryland 21287.
- device infection
- implantable cardioverter-deﬁbrillator shock
- inappropriate therapy
- subcutaneous implantable cardioverter
- transvenous implantable cardioverter-deﬁbrillator
In the contemporary era, and despite the steady advances in medical care for patients with heart disease, the implantable cardioverter-defibrillator (ICD) remains an indispensable tool to improve survival in those with or at increased risk for sustained ventricular arrhythmia. Over 2 decades, a series of clinical trials demonstrated the ICD is superior to antiarrhythmic drugs for treating sustained ventricular fibrillation and tachycardia and for improving overall survival (1–3). Current ICDs with transvenous leads (TV-ICD) provide pacing for both bradycardia and pace termination of ventricular tachycardia, but lead malfunctions and complications have been the Achilles’ heel of the system. Lead conductor fracture or insulation failure may lead to oversensing and inappropriate shock delivery or undersensing and failure to appropriately deliver needed therapy. Patients with transvenous leads are also at risk for lead infection, which then requires system extraction, a procedure with its own substantial risks (4). Finally, although readily available in TV-ICDs, pacing in those without symptomatic bradycardia actually increases the risk of death or heart failure hospitalization (5).
To avoid the initial complications of TV-ICD implantation, including pneumothorax, as well as the long-term complications of lead failure and infection, the totally subcutaneous ICD (S-ICD) system was developed. The S-ICD consists of a subcutaneous lead with an 8-cm-long shock coil inserted parallel to the sternal midline and connected to an electrically active pulse generator implanted subcutaneously over the apex of the heart (6). Sensing is performed using 1 of 3 potential vectors incorporating the device can as one electrode and 2 smaller electrodes on the subcutaneous lead, 1 proximal and 1 distal to the shock coil. Initial results were encouraging because the device was able to detect and convert ventricular arrhythmias induced during electrophysiologic testing, as well as spontaneous episodes that occurred outside the laboratory (6). Reported complications include pocket infections, need for pocket revision, lead migration, and dislodgements. Inappropriate shocks due to oversensing, especially of T waves, have been reported as well (7). Following the initial feasibility studies, the S-ICD received the CE Mark (Conformité Européene mark) in 2009, and following a pivotal trial in the United States (7), Food and Drug Administration approval in 2012. It is first-line therapy for those patients without transvenous options, but for those patients eligible for either S-ICD or TV-ICD, there is a lack of randomized control data to guide the decision making process.
In this issue of JACC: Clinical Electrophysiology, Basu-Ray et al. (8) present a meta-analysis of the limited number of nonrandomized studies that have compared clinical outcomes between S-ICD and TV-ICD in adult patients, which include lead-related complications and complications unrelated to lead, inappropriate therapies, and appropriate shocks. Six studies were identified, 1 of which was excluded for including pediatric patients. More than 6,000 patients were included, and more than 2,000 of those patients received the S-ICD. One study provided a majority of the patients, 5,760, whereas 3 of the 5 studies contributed fewer than 150 patients each. Only 2 of the studies reported data for appropriate shocks, but there appeared to be no differences between the 2 devices, as both appeared to be equally effective in the detection and treatment of potentially lethal ventricular arrhythmias. Similarly, there were no overall differences in inappropriate therapy among the groups. The transvenous device was more likely to deliver inappropriate therapy for supraventricular tachycardia, whereas the subcutaneous device was more likely to deliver therapy for oversensing (sensing of noise or T-wave oversensing). Neither device failure nor infection risk was different between the S-ICD and the TV-ICD, but lead complications were significantly less in the S-ICD group than in the TV-ICD group, with an odds ratio (OR) of 0.13. In summary, the S-ICD performed as it was designed to, which was to decrease the complications related to transvenous lead placement at the time of and immediately following implantation. The S-ICD still experienced complications not directly attributable to the transvenous lead, including inappropriate therapy, device infection, and device failures. Acknowledged deficiencies of the meta-analysis include the limited number of included studies, the variability of follow-up regimens of the included studies, with the longest being 5 years and the shortest just 217 days, and the fact that candidacy for S-ICD is limited by pre-implantation electrocardiography examination, whereas those undergoing TV-ICD were not pre-screened.
The investigators should be commended for their analysis of the available evidence comparing the 2 available implantable technologies specifically designed to treat sustained ventricular arrhythmias and improve long-term survival in those who are at high risk for sudden cardiac arrest. For those who are candidates, the S-ICD appears to be as effective as the once state-of-the-art TV-ICD, which itself replaced an older technology requiring a thoracotomy and a cardiac surgeon for implantation. As designed, the S-ICD eliminates the hazard of the transvenous lead, the Achilles’ heel of the TV-ICD. In Greek mythology (9), Achilles was the son of the sea nymph Thetis and Peleus, king of the Myrmidons. When Achilles was born, his mother dipped him in the river Styx to make him immortal but left out Achilles’ heel as his only vulnerability. During the Trojan War, Achilles commanded the Myrmidons, as an ally of the Greeks. After the death of his beloved companion Patroclus in battle, Achilles exacted his revenge by killing Hector, the greatest Trojan warrior. Hector’s brother, Paris, retaliated by killing Achilles with an arrow, mystically guided to Achilles’ mortal heel. We must then ask whether the S-ICD has struck a similar blow to the TV-ICD, the hero and incontrovertible winner of a host of randomized clinical trials, including AVID (Antiarrhythmics vs. Implantable Defibrillators), MADIT II (Multicenter Automatic Defibrillator Implantation Trial), and SCD-HeFT (Sudden Cardiac Death in Heart Failure Trial) (1–3). These initial observations will be tested in the much-anticipated PRAETORIAN (Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy) trial (10). This noninferiority trial will randomize 700 patients to receive the S-ICD or the TV-ICD and evaluate the composite of ICD-related complications and inappropriate therapy. If noninferiority is established, statistical analysis will be done for potential superiority. Shock efficacy and patient mortality will also be assessed.
Until the PRAETORIAN trial is published, what then is a clinician to do? Should the TV-ICD be abandoned for the S-ICD, or should the clinician be comforted by the fact that the TV-ICD has been around in one form or another for more than 35 years, that it is manufactured by a number of companies both foreign and domestic, and that the TV-ICD is easily upgradeable to allow for numerous lead and function configurations? We must agree that the S-ICD has certain advantages over the TV-ICD. For those eligible patients not susceptible to T-wave oversensing who do not require bradycardia, biventricular, or antitachycardia pacing, the S-ICD is a good option that avoids the well-described lead-related complications of the TV-ICD. Furthermore, even if the subcutaneous lead requires removal or relocation, this does not entail the risks of transvenous lead extraction. However, the S-ICD does not appear to be either more efficacious or associated with a lower short- to immediate-term risk of complications. The TV-ICD remains proven therapy to improve survival in those with or at increased risk for sustained ventricular arrhythmias.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the authors and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Both authors have reported that they have no relationships relevant to the contents of this paper to disclose.
All authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
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