The Entirely Subcutaneous Defibrillator – A New Generation and Future Expectations

Introduction: In pediatric patients prevention of Sudden Cardiac Death (SCD) using Implantable Cardioverter Defibrillators (ICD) is associated with a higher risk of complications than in the adult population. Surgical re-interventions due to infection, lead dislocation or migration and inappropriate shocks on intra and extracardiac oversensing are the most prevalent complications. The Subcutaneous ICD (S-ICD) has been introduces as a less invasive and extravascular alternative to overcome some of these complications. The scientific data that has led to the approval of the S-ICD did not include pediatric patients. Contradicting reports in small cohorts have been published on the effectiveness of S-ICD therapy in the pediatric population. We here report the largest pediatric cohort with the longest follow up to date where the S-ICD has been used for SCD prevention. Hypothesis: The S-ICD is safe and effective for the prevention of SCD in a diverse pediatric population. Methods: We retrospectively studied all consecutive pediatric patients (age<18 yrs)that were implanted with a S-ICD in our center. Results: Fifteen S-ICDs were implanted in 14 patients (mean age 14, range 8-17), 71% were male, mean BMI was 18.8 (range 17.2-28.8), 57% had a secondary prevention indication, 77% had a genetic arrhythmia diagnosis and the median follow up was 21 months (range 1- 57). The first shock efficacy of induced and spontaneous episodes was 100% (n=13 and n =2 respectively). Inappropriate shocks due to intracardiac oversensing occurred in 3 (21%) patients. No lead failures or dislocations were observed. Two patients (14%) experienced a complication requiring re-intervention: one infection and one pocket erosion. After the pocket erosion the S-ICD has been successfully re-implanted. In one patient the S-ICD was removed after cardiac transplantation. None of the patients died during follow up. Conclusions: The S-ICD is safe and effective in a diverse pediatric populations. There was a very high efficacy of defibrillation therapy (100%) and a relative low and mild occurrence of complications. The S-ICD should be considered as a viable alternative for transvenous ICD's in pediatric patients.

Implantable cardioverter-defibrillators (ICD) are routinely used for the primary and secondary prevention of sudden cardiac death due to ventricular tachycardias. A subcutaneous ICD (S-ICD) system has been recently developed with a lead just implanted under the skin instead of 1 or 2 transvenous leads traditionally implanted in a body. This may greatly reduce the complexity of the implantation procedure without or with less fluoroscopy, and avoid the complications due to transvenous leads. Although the safety and efficacy of the S-ICD has been evaluated in the clinical study, to date, a theoretical research has never been performed to study the conduction of the defibrillation currents in human bodies due to the defibrillation shocks of S-ICD systems. The conduction pattern of defibrillation currents may help improve the defibrillation effect through finding a better implantation site of the S-ICD generator or lead, and a better defibrillation protocol. As the defibrillation current or voltage in the body is impossible to be accurately measured due to the electrode polarization during the defibrillation shock, we performed the computer simulation to study the defibrillation effects of S-ICD systems in 4 suggested configurations. The defibrillation threshold (DFT) and myocardial damage for each configuration were estimated from the simulation results. The configuration with a left lateral pulse generator and an 8-cm coil electrode positioned at the left parasternal margin demonstrated the lowest DFT and minimum myocardial damage in the simulation. The simulation result of DFT is consistent with previous clinical studies, and the simulation method may serve as a tool to find an improved implantation configuration for an S-ICD system.

BackgroundOptimal management of asymptomatic Brugada syndrome (BrS) with spontaneous type I electrocardiographic pattern is uncertain.Methods and ResultsWe developed an individual‐level simulation comprising 2 000 000 average‐risk individuals with asymptomatic BrS and spontaneous type I electrocardiographic pattern. We compared (1) observation, (2) electrophysiologic study (EPS)‐guided implantable cardioverter‐defibrillator (ICD), and (3) upfront ICD, each using either subcutaneous or transvenous ICD, resulting in 6 strategies tested. The primary outcome was quality‐adjusted life years (QALYs), with cardiac deaths (arrest or procedural‐related) as a secondary outcome. We varied BrS diagnosis age and underlying arrest rate. We assessed cost‐effectiveness at $100 000/QALY. Compared with observation, EPS‐guided subcutaneous ICD resulted in 0.35 QALY gain/individual and 4130 cardiac deaths avoided/100 000 individuals, and EPS‐guided transvenous ICD resulted in 0.26 QALY gain and 3390 cardiac deaths avoided. Compared with observation, upfront ICD reduced cardiac deaths by a greater margin (subcutaneous ICD, 8950; transvenous ICD, 6050), but only subcutaneous ICD improved QALYs (subcutaneous ICD, 0.25 QALY gain; transvenous ICD, 0.01 QALY loss), and complications were higher. ICD‐based strategies were more effective at younger ages and higher arrest rates (eg, using subcutaneous devices, upfront ICD was the most effective strategy at ages 20–39.4 years and arrest rates >1.37%/year; EPS‐guided ICD was the most effective strategy at ages 39.5–51.3 years and arrest rates 0.47%–1.37%/year, and observation was the most effective strategy at ages >51.3 years and arrest rates <0.47%/year). EPS‐guided subcutaneous ICD was cost‐effective ($80 508/QALY).ConclusionsDevice‐based approaches (with or without EPS risk stratification) can be more effective than observation among selected patients with asymptomatic BrS. BrS management should be tailored to patient characteristics.

Implantation of a transvenous implantable cardioverter-defibrillator (ICD) is a recognized method of secondary prevention of sudden cardiac death [1]. In some patients with indications for such a device, circumstances may occur that render ICD implantation difficult or impossible. Implantation of a subcutaneous ICD (S-ICD), not requiring introduction of any elements into the cardiovascular system, might be a solution in such cases. Another feature that distinguishes the S-ICD from the ICD is the inability to terminate arrhythmias with antitachycardia pacing, but only with an electrical 80 J shock. Moreover, bradycardia pacing is limited only to the immediate post-shock period (50 bpm for 30 s). The S-ICD system consists of a 145 g can, placed subcutaneously over the 5th and 6th left intercostal space in the midaxillary line, and the lead, also placed in the subcutaneous tissue, along the left margin of the sternum. The battery life is approximately 5 years [2]. If correctly implanted, the device provides detection of ventricular arrhythmias with a sensitivity of nearly 100% and specificity of differentiation from supraventricular arrhythmias of 98%, which is more than in traditional transvenous systems [3]. Possible problems include sensing disturbances due to the oversensing of T-waves or myopotentials, which may lead to inadequate interventions. That problem may affect 5% to 16% of patients [4–6]. Due to that fact, S-ICD implantation is indicated only in patients with a positive screening test result, aimed to assess the amplitude and relation of R and T waves. Until recently, defibrillators of such kind had not been implanted in Poland. The reported case is one of the two first implantations in Poland.

The Brugada syndrome (BrS) is an inherited disorder associated with the risk of ventricular fibrillation and sudden cardiac death (SCD). The current main therapy is an implantable cardioverter-defibrillator (ICD). However, the risk stratification and management of patients remain challenging. Here, we present a case of BrS representative of the pitfalls that clinicians may encounter in the management of Brugada patients in routine clinical practice. A 39-year-old man with BrS and recurring syncope was implanted with a subcutaneous ICD (S-ICD) (EMBLEM MRI S-ICD, Boston Scientific). Syncope recurred some months later. Subcutaneous ICD interrogation showed no arrhythmic events, but SMART Pass (high-pass filter) deactivation was noted. A query was sent to Boston Scientific clinical service, unveiling an extremely long asystolic pause as syncope determinant. Subcutaneous ICD was explanted and replaced by conventional single chamber ICD in the pre-pectoral region. Brugada syndrome patients with high-risk features are candidates for ICD implantation to prevent SCD. Recent evidence highlighted that symptomatic patients carry a substantially higher risk compared with asymptomatic ones. Syncope may represent a pivotal symptom in BrS patients, but young patients with Type 1 Brugada pattern may experience syncope other than from tachyarrhythmias. Subcutaneous ICD is an advisable option in young ICD recipients to avoid lifetime complication related to standard transvenous systems. However, S-ICD lacks pacing capabilities and, therefore, is not indicated when an anti-bradycardia system is needed. The diagnostic workup of syncope in Brugada patients may be ineffective in elucidating the underlying aetiology whose understanding is essential to offer a personalized therapeutic approach.

Sudden Cardiac Arrest (SCA) is the leading cause of sudden death (SCD). In athletes under 35 years, SCA is believed to be mostly arrhythmogenic and often due to an underlying structural or electrical pathological heart condition, whereas coronary atherosclerosis is the most frequent aetiology of SCA among athletes above 35 years. Implantable Cardioverter Defibrillators (ICDs) with a transvenous lead are the therapy of choice for individuals at risk of SCD in both primary and secondary prevention. It bears the risk of lead-associated complications (fracture, dislocations, infection), which occur significantly more often in physically active patients like athletes. Considering these limitations,a completely subcutaneous ICD (S-ICD) system was designed to provide the life-saving benefit of the conventional TV-ICD, while avoiding the shortcomings of TV-lead ICD systems. Randomized comparison of S-ICD versus traditional TV-ICD sconfirmed S-ICD systems as a valid alternative in patients in whom bradycardia pacing or cardiac resynchronization therapy is not required. Because lead complications are associated with physical activity level (i.e. chest/shoulder/upper arm), S-ICD is the better ICD-therapy not only in young patients with an anticipated long-term need for defibrillation function but also in athletes.

Rationale and design of the PRAETORIAN trial: A Prospective, RAndomizEd comparison of subcuTaneOus and tRansvenous ImplANtable cardioverter-defibrillator therapy

Incidence of myopotential induction in subcutaneous implantable cardioverter-defibrillator patients: Is the oversensing issue really solved?

Subcutaneous implantable cardioverter-defibrillator (S-ICD) therapy has become a viable alternative to conventional transvenous ICD implantation. Patients with congenitally corrected transposition of the great arteries (ccTGA) have a high risk of sudden cardiac death due to malignant arrhythmia. The interaction between the S-ICD system and the transvenous pacemaker system is not fully understood. We report a case of S-ICD implantation in a patient with ccTGA and a DDD pacemaker. The patient was a 30-year-old man with a previously placed pacemaker with diagnoses of congenital heart disease, ccTGA (SLL), left atrioventricular valve insufficiency, and third-degree atrioventricular block. He presented with an out-of-hospital cardiac arrest, and an S-ICD was implanted to prevent sudden cardiac death. Defibrillation checks were performed successfully. We tested the compatibility of the DDD pacemaker with the S-ICD and found that there was no interference between them. In conclusion, an S-ICD system is a reasonable and safe option in patients with ccTGA.

Cardiac device therapy has significantly evolved since the introduction of the first implantable pacemaker and the subsequent development of the implantable cardioverter-defibrillator (ICD). ICDs are highly effective; however, their main weakness lies in lead-related complications. To avoid the need for venous access and the complications associated with transvenous leads, a fully subcutaneous ICD (S-ICD) system was developed. Despite these advancements, the S-ICD system is limited by its inability to provide bradycardia pacing and antitachycardia pacing. This limitation prompted the development of a modular cardiac rhythm management system, integrating a new leadless pacemaker with an S-ICD that uses unidirectional communication to command the pacemaker to deliver antitachycardia pacing.Conduction system pacing, including His bundle pacing and left bundle branch area pacing (LBBAP), has emerged as a physiological alternative to biventricular resynchronisation therapy and conventional pacing, pending results of large clinical trials. LBBAP offers superior electrical parameters and long-term performance compared with His bundle pacing. The capability to provide defibrillation via the same lead used for LBBAP represents an unresolved challenge that is currently under ongoing research.This state-of-the-art review presents the latest developments and innovations in cardiac device therapy, offering a comprehensive overview of current technologies that increasingly enable therapy to be tailored to individual patient needs.

In 2012, the first totally Subcutaneous Implantable Cardioverter-Defibrillator (S-ICD) was approved by the Food and Drug Administration (FDA) in the United States. A possible benefit of this device is that it does not involve placing leads 'in' or 'on' the heart, potentially reducing complications. Ninety-one S-ICD and 182 single chamber TV-ICD implants were performed between 10/22/2012 and 9/22/2015. During this period of time, 91 patients with S-ICD were matched to TV-ICD patients using single centre NCDR ICD Registry Data based on dialysis status, gender, and age. Intra- and post-operative complications and deaths were examined within the first 180 days following implantation. Patients with S-ICDs had higher creatinine (2.3 ± 2.5 vs. 1.1 ± 0.7, P < 0.001) and were more likely to be on chronic dialysis (20.9% vs. 5.5%, P < 0.001) than TV-ICD patients. Patients in the S-ICD group were more likely to have had prior device infections (14.3% vs. 3.3%, P = 0.021) as well as prior TIA/CVA (14.3% vs. 4.4%, P = 0.049) compared to patients in the TV-ICD group. Seven patients experienced 7 complications or death in TV-ICD group and 5 patients experienced 7 complications or death in SQ-ICD group, P = 0.774. In this retrospective matched single centre cohort study, there was no significant difference in implantation complications or death in patients receiving single chamber TV-ICDs compared to S-ICDs within 6 months following implantation. This occurred despite more severe preexisting illness in the S-ICD group. Further investigation is needed to determine outcomes after longer-term follow-up.

Funding Acknowledgements Type of funding sources: Private company. Main funding source(s): Boston Scientific OnBehalf EFFORTLESS Registry Introduction Patients (pts) implanted with transvenous (TV) implantable cardioverter-defibrillator (ICD) experience complications (Cx) associated with TV leads and inappropriate shocks (IAS) for atrial fibrillation (AF) or other supraventricular tachycardias (SVT). The EFFORTLESS S-ICD Registry is a 5-year (yr) follow-up (f/u) study of pts implanted with the subcutaneous ICD (S-ICD). Purpose To report on the 5-yr outcomes of pts with a wide range of S-ICD indications implanted with early generation devices. Methods Pts were enrolled at 43 centers February 2011-December 2014. Kaplan-Meier Cx, appropriate shock (AS), and IAS rates are reported. Results 994 pts (495 retrospective) were enrolled in the EFFORTLESS study and 984 pts (28% female, 48 ± 17 yrs, BMI 27 ± 6 kg/m2, ejection fraction 43 ± 18%) underwent S-ICD implantation. Mean study f/u was 4.4 ± 1.6 yrs. The pt cohort had diverse etiologies: 31% ischemic heart disease, 19% non-ischemic cardiomyopathy, 11% hypertrophic cardiomyopathy, 17% channelopathies, and 20% of pts miscellaneous. Total system- and procedure-related Cx (table) were 9.4% at 5 yrs. AS and IAS rates at 5 yrs were 15.9% and 16.9%, respectively and the IAS rates for AF/SVT and t wave oversensing were 3.1% and 5.8%, respectively. More pts experienced Cx and IAS in the first yr than in yrs 2-5 altogether (8.7 vs 8.2%), the most common as a result of discomfort/erosion (38%), IAS (26%), system infection (9%), and premature battery depletion (9%). Of these late Cx, 74% were experienced by retrospective pts. Spontaneous conversion efficacy for the first shock and final shocks was 89.7% and 97.7%. Of the 91 (9.2%) deaths reported, none were associated with the S-ICD system or procedure. Cause of death was cardiac for 40 pts, non-cardiac for 40 pts, other for 4 pts, and unknown for 7 pts. Only 20 (2.0%) pts had their S-ICD replaced for a TV device for pacing: 4 bradycardia, 7 anti-tachycardia, and 9 for biventricular pacing. Conclusions The EFFORTLESS registry provides 5-year follow-up for a diverse, large, multinational S-ICD registry. Complications primarily occurred in the first year but remained low through 5 years. Inappropriate shock rates were typically observed in older generation devices prior to introduction of the SMART Pass filter. Replacement for TV-ICD due to the need for pacing was rare. Outcome 30 day 1 yr 2 yr 3 yr 4 yr 5yr Annual Complications (Kaplan-Meier) 2.0 5.3 6.8 7.6 8.6 9.4 1.9 IAS, overall (Kaplan-Meier) 1.7 8.7 11.6 13.1 14.6 16.9 3.4 IAS, t wave oversensing 3.4 5.8 1.2

BackgroundArrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D) is an inherited cardiomyopathy characterized histologically by the replacement of ventricular myocardium with fibrous and fatty tissue, and clinically by ventricular tachycardia arrhythmias primarily of right ventricular (RV) origin. Implantable cardioverter defibrillator (ICD) is the only proven therapy to reduce mortality in ARVC/D patients. However, it has the risk of inappropriate anti-tachycardia pacing (ATP) or shocks. This study aimed to assess the occurrence of appropriate and inappropriate ICD therapies in ARVC/D patients who underwent ICD implantation in a single Cardiac Centre.MethodsRetrospective analysis of the data of patients with the diagnosis of ARVC/D based on the 2010 revised Task Force Criteria, who underwent ICD implantation in the Heart Centre, at King Faisal Specialist Hospital and Research Center (KFSH&RC), Riyadh between January 1997 and May 2016. The clinical data and information about appropriate and inappropriate ICD therapies were obtained from medical records with the review of the available intra-cardiac electrograms (EGMs).ResultsTwenty-two ARVC/D patients with ICD implantation (20 males (91%), mean age at ICD implantation: 32 ± 14 years). ICD was implanted for secondary prevention of sudden cardiac death (SCD) in 15 patients (68.2%), and for primary prevention in 7 patients (31.8%). At mean follow-up of 9.4 ± 4.8 years, 11 patients (50%) had appropriate ICD therapies, and five patients (22.7%) had inappropriate ICD therapies. Out of 950 ICD therapies, 865 (91%) were appropriate (586 episodes of VT/VF treated with ATP (61.3%), and 279 episodes treated with shocks (29.37%)) and 85 (9.4%) were inappropriate (45 episodes treated with ATP (4.73%), and 40 treated with shocks (4.21%)).ConclusionARVC/D patients are at risk of VT/VF arrhythmias. ICD therapy is the only proven life-saving therapy in those patients. Most of ICD therapies in our patient’s population are appropriate, and ATP therapy is effective in terminating most of VT episodes. Although we do not have any patient with subcutaneous ICD, the high success rate of ATP suggests that transvenous ICD would be more appropriate in ARVC/D patients.

A new algorithm to reduce T-wave over-sensing based on phase space reconstruction in S-ICD system

The recent introduction of subcutaneous implantable cardioverter defibrillator (S-ICD) has raised attention about the potential of this technology for clinical use in daily clinical practice. We review the methods and results of the four studies conducted in humans for approval of this innovative technology for daily practice. Two studies using a temporary S-ICD system (acute human studies) were conducted to search for an appropriate lead configuration and energy requirements. For this purpose, 4 S-ICD configurations were tested in 78 patients at the time of transvenous (TV)-ICD implantation. The optimal configuration was tested in 49 more patients to comparatively assess the subcutaneous defibrillation threshold (S-DFT) versus the standard TV-ICD. Long-term implants were evaluated in 55 patients using an implanted system (chronic human study). The acute humans studies led to an optimal S-ICD configuration comprising a parasternal electrode and left anterolateral thoracic pulse generator. Both configurations successfully terminated 98% of induced ventricular fibrillation (VF), but significantly higher energy levels were required with S-ICD than with TV-ICD systems (36.6 ± 19.8 J vs. 11.1 ± 8.5 J). In the chronic study, all 137 VF episodes induced at time of implant were detected with a 98% conversion rate. Two pocket infections and four lead revisions were required during 10 ± 1 months of follow-up. During this period, survival was 98%, and 12 spontaneous ventricular tachyarrhythmias were detected and treated by the device. These data show that the S-ICD systems here consistently detected and converted VF induced at time of implant as well as sustained ventricular tachyarrhythmias occurring during follow-up (248).