Subcutaneous Implantable Cardioverter-defibrillator Research Articles

Abstract 15112: Subcutaneous versus Transvenous Implantable Defibrillator Recipients: A Systematic Review and Meta-Analysis

Introduction: Subcutaneous implantable cardioverter-defibrillator (S-ICD) is an alternative to transvenous implantable cardioverter-defibrillator (T-ICD) in select patients with complex anatomy, high infection risk and venous access issues. T-ICD is known to cause perioperative and long-term complications. Considering expanding indications for S-ICD, ongoing uncertainty in efficacy and unknown utility in low-risk patients, we performed this updated meta-analysis to study device related complications in both the systems. Methods: We performed a meta-analysis using electronic literature search to retrieve studies that compared S-ICD to T-ICD. Outcomes of interest were efficacy and device-related complications. Outcomes were pooled under random-effects and reported as risk ratios (RRs) and 95% CIs. 15 studies (observational, case-control and RCTs), median follow up 31.1 months, with variable heterogeneity for different outcomes (Fig-1), were included to capture real-world data. Results: A total of 21628 patients (S-ICD group n=3594, male 72.6%, mean age 50.1±10y and T-ICD group n=18034, male =72.6%, mean age 53.3±10.6y) were recruited. Lead-related complications were significantly lower in S-ICD, RR {0.21 [0.13, 0.34], P=<0.00001}. There were no significant difference in other device-related endpoints: 30-day complications RR{0.67 [0.38, 1.18], P=0.17}; surgical complications RR{0.70 [0.49, 1.01], P=<0.05}, inappropriate therapy RR{ 0.85 [0.67, 1.07], P=0.16}; appropriate therapy RR{ 0.62 [0.35, 1.09], P=0.10}, infections requiring surgery RR {0.84 [0.44, 1.59], P=0.59} and all-cause mortality RR{0.91 [0.68, 1.2, P=0.52]. Conclusion: Efficacy and safety of S-ICD is non-inferior to T-ICD and superior for lead-related complications.

Abstract 12931: Contemporary Trends of Subcutaneous Implantable Cardioverter Defibrillator Utilization in the United States: Insights From the National Inpatient Sample 2016-2019

Introduction: The subcutaneous implantable cardioverter defibrillator (S-ICD) has emerged as an alternative to the transvenous ICD with comparable efficacy and complication rates in clinical trials. Adoption of this technology and real-world clinical experience are less well described. Methods: This was a retrospective descriptive cohort study using data from National Inpatient Sample (NIS) for calendar years 2016-2019. Outcomes were cardiovascular adverse events, all-cause mortality, 30-day readmission, and resource utilization in patients who had S-ICD implantation. Results: We identified 6655 patients who had S-ICD implantation between 2016-2019. S-ICD implant rates remained between 10-12% of total ICD implants in the US over the study period (Figure 1a), though hospital implant rates were widely distributed (Figure 1b). The mean (SD) age of the population was 56.1 ± 15.9 years, and 2002 patients (30.1%) were female. Median length of stay (IQR) was 6.0 (4.0, 10.0). Hospitalization costs were $ 245937.1 ± 206047.3. Adverse cardiovascular events associated with the hospitalization were: pericardial perforation/cardiac tamponade (0.2%), hemothorax/pneumothorax (1.1%), stroke/TIA (0.5%), cardiogenic shock (8.6%), cardiac arrest (11%), and vascular complications (1.3%). A total of 48 patients (0.7%) died. Non-elective readmission within 30 days post-procedure occurred in 15.7% of cases. Conclusion: S-ICD implant rates were stable over time but varied widely among hospitals. Hospitalization-associated adverse cardiovascular events may be more a reflection of the vulnerable population undergoing S-ICD implant than risk of the procedure.

Abstract 11396: Early-Onset Recurrent Malignant Arrhythmias in a Child With Hypertrophic Cardiomyopathy

Case presentation: A male newborn was diagnosed with severe hypertrophic cardiomyopathy (HCM) because of a heart murmur. A genetic test identified the previously described pathogenic variant Arg719Trp in MHY7, which was not present in the parents. An additional variant in KCNE2, Ile57Thr, considered as a risk factor for acquired long QT, was found in the patient. Corrected QT interval was normal. At age 3, the child suffered cardiac arrest from which he was successfully defibrillated. Maximal wall thickness was 20 mm (z-score +18). With the patient weighing 18 kg, a subcutaneous implantable cardioverter defibrillator (s-ICD) was implanted with the two-incision technique and nadolol 2 mg/kg/day was started. After 3 appropriate ICD therapies in the following 3 months, amiodarone was associated to betablockers, with no QT prolongation. He suffered 8 more ventricular fibrillation-terminating ICD shocks in the following year, prompting the indication of thoracoscopic bilateral cardiac sympathectomy denervation (BCSD) and referring him for heart transplant evaluation. Following BCSD he was symptom free for 6 months, after which he presented with a prolonged cardiac arrest, needing sedation, 4 ICD shocks and external defibrillation to recover consciousness. After experiencing another electrical storm in the following month, he underwent successful cardiac transplantation at age 5. Discussion: This clinical case is noteworthy for different reasons. First of all, even if Arg719Trp mutation in MHY7 has been associated with full penetrance and early expressivity of HCM (mean age at diagnosis 24 years), the child presented with an extremely rare early-onset of recurrent fatal arrhythmias. The pathogenicity of the associated KNCE2 variant, Ile57Thr, has not yet been elucidated but it has been suggested to confer proarrhythmic susceptibility in the presence of other environmental or genetic risk factors. Another worth-mentioning clinical aspect is that s-ICD proved to be a safe and effective therapy in a child weighing much less than 30 kg. In this case in which heart transplant could not be avoided due to life-threatening arrhythmias, the benefit of the preservation of the central venous circulation with the absence of intravascular leads cannot be overstated.

Abstract 13221: A Multidisciplinary Approach to Transvenous Lead Extraction in the Setting of a Large Patent Foramen Ovale

Introduction: Increasing cardiovascular implantable electronic devices (CIED) implantation has been associated with a rising incidence of CIED infection. Treatment includes targeted antimicrobial therapy and device hardware removal although larger lead vegetations have historically undergone surgical removal. As many CIED recipients are at high surgical risk, there is growing need for transvenous approaches for safe debulking of vegetation mass. Case: An 80-year-old man with a history of ischemic cardiomyopathy and an indwelling dual chamber implantable cardioverter defibrillator (ICD) for 17 years with previous appropriate shocks was found to have Enterococcus faecalis bacteremia. Transthoracic echocardiography revealed a 3 cm vegetation on the right ventricular lead involving the tricuspid valve in addition to a large patent foramen ovale (PFO). He was started on intravenous antibiotics. Blood cultures revealed no growth. Decision-making: The large-sized vegetation in presence of a PFO posed a risk for pulmonary or systemic embolization from transvenous lead extraction. A multidisciplinary approach was developed which included temporary PFO occlusion, thrombus aspiration with the Inari FlowTriever thrombus aspiration system, and transvenous laser lead extraction (Figure 1). No residual material remained and the Amplatzer was retrieved. Cultures from the pocket, lead tips, and vegetation were collected. The vegetation culture grew E. faecalis. He underwent subcutaneous ICD implant six weeks later following antibiotic therapy. Conclusions: Vegetation suction with a simple handheld device can be safe and effective for vegetation removal in high-risk cases. Furthermore, temporary PFO occlusion can be performed during vegetation debulking and device extraction. These management strategies may gain wider application with an increasing need for lead extraction in older patients with comorbidities that preclude surgical candidacy.

Abstract 13870: Ventricular Fibrillation Arrest in a 27-Year-Old Woman Due to Takotsubo Cardiomyopathy

Introduction: Sudden cardiac death in young patients may be due to coronary artery disease, primary electrical disease, cardiomyopathy, or congenital anomalies. We explore potential causes for sudden cardiac arrest in a young patient. Case Description: A 27-year-old woman was found unconscious. Initial rhythm showed ventricular fibrillation. Cardiopulmonary resuscitation was done for 5 minutes before return of spontaneous circulation. ECG showed ST elevations in aVL, V4, and V5. She was admitted for therapeutic temperature management. Troponin peaked at 1.86 ng/mL on the evening of arrival. Transthoracic echocardiography (TTE) demonstrated hypokinesis of the mid to distal septum, anterior wall, and apex (Figure 1). Repeat TTE 3 days later showed resolution of the wall motion abnormalities. She reported marijuana use and a domestic dispute with her significant other the night prior. Coronary CT angiography showed calcium score of 0 with normal coronary anatomy, no significant coronary artery stenosis, and incidental finding of bilateral pulmonary artery filling defects. Lower limb venous duplex was unremarkable. Therapeutic dose of enoxaparin was started. Cardiac MRI showed no myocardial infarction, scar, or infiltrative disease. An electrophysiology study revealed adequate QT shortening during epinephrine infusion and no inducible ventricular arrhythmias. Genetic testing was unremarkable. She was discharged with a wearable defibrillator before ultimately receiving a subcutaneous implantable cardioverter-defibrillator. Discussion: The presentation of transient regional wall motion abnormalities, with ST-segment elevations and negative ischemic workup, is highly suggestive of Takotsubo cardiomyopathy, mid-ventricular variant. Marijuana use is a risk factor, and the domestic dispute is a potential emotional trigger. This case highlights Takotsubo cardiomyopathy as a possible cause of sudden cardiac arrest in young patients.

Early experience with subcutaneous implantable cardioverter-defibrillators: results from an emerging implantation centre

Early experience with subcutaneous implantable cardioverter-defibrillators: results from an emerging implantation centre

Subcutaneous versus transvenous implantable cardioverter defibrillators in children and young adults: A meta-analysis.

The implantable cardioverter defibrillator (ICD) has been demonstrated to successfully prevent sudden cardiac death (SCD) in children and young adults. A wide range of device-related complications/malfunctions have been described, which depend on the intrinsic design of the defibrillation system (transvenous-implantable cardioverter defibrillator [TV-ICD] vs. subcutaneous-implantable cardioverter defibrillator [S-ICD]). To compare the device-related complications and inappropriate shocks with TV-ICD versus S-ICD. Electronic databases were queried for studies focusing on the prevention of SCD in children and young adults with TV-ICD or S-ICD. The effect size was estimated using a random-effect model as odds ratio (OR) and relative 95% confidence interval (CI). The primary endpoint was a composite of any device-related complications and inappropriate shocks. We identified a total of five studies including 236 patients (Group S-ICD: 76 patients; Group TV-ICD: 160 patients) with a mean follow-up time of 54.2±24.9months. S-ICD implantation contributed to a significant reduction in the risk of the primary endpoint of any device-related complications and inappropriate shocks (OR: 0.18; 95% CI: 0.05-0.73; p=.02). S-ICD was also associated with a significantly lower incidence of inappropriate shocks (OR: 0.28; 95% CI: 0.11-0.74; p=.01) and lead-related complications (OR: 0.18; 95% CI: 0.05-0.66; p=.01). A trend toward a higher risk of pocket complications (OR: 5.91; 95% CI: 0.98-35.63; p=.05) was recorded in patients with S-ICD. Children and young adults undergoing S-ICD implantation may have a lower risk of a composite of device-related complications and inappropriate shocks, compared to TV-ICD patients.

Clinical outcomes of subcutaneous vs. transvenous implantable defibrillator therapy in a polymorbid patient cohort.

The subcutaneous implantable cardioverter-defibrillator (S-ICD) has been designed to overcome lead-related complications and device endocarditis. Lacking the ability for pacing or resynchronization therapy its usage is limited to selected patients at risk for sudden cardiac death (SCD). The aim of this single-center study was to assess clinical outcomes of S-ICD and single-chamber transvenous (TV)-ICD in an all-comers population. The study cohort comprised a total of 119 ICD patients who underwent either S-ICD (n = 35) or TV-ICD (n = 84) implantation at the University Hospital Frankfurt from 2009 to 2017. By applying an inverse probability-weighting (IPW) analysis based on the propensity score including the Charlson Comorbidity Index (CCI) to adjust for potential extracardiac comorbidities, we aimed for head-to-head comparison on the study composite endpoint: overall survival, hospitalization, and device-associated events (including appropriate and inappropriate shocks or system-related complications). The median age of the study population was 66.0 years, 22.7% of the patients were female. The underlying heart disease was ischemic cardiomyopathy (61.4%) with a median LVEF of 30%. Only 52.9% had received an ICD for primary prevention, most of the patients (67.3%) had advanced heart failure (NYHA class II-III) and 16.8% were in atrial fibrillation. CCI was 5 points in TV-ICD patients vs. 4 points for patients with S-ICD (p = 0.209) indicating increased morbidity. The composite endpoint occurred in 38 patients (31.9 %), revealing no significant difference between patients implanted with an S-ICD or TV-ICD (unweighted HR 1.50, 95 % confidence interval (CI) 0.78-2.90; p = 0.229, weighted HR 0.94, 95% CI, 0.61-1.50, p = 0.777). Furthermore, we observed no difference in any single clinical endpoint or device-associated outcome, neither in the unweighted cohort nor following inverse probability-weighting. Clinical outcomes of the S-ICD and TV-ICD revealed no differences in the composite endpoint including survival, freedom of hospitalization and device-associated events, even after careful adjustment for potential confounders. Moreover, the CCI was evaluated in a S-ICD cohort demonstrating higher survival rates than predicted by the CCI in young, polymorbid (S-)ICD patients.

Bradycardia in Patients with Subcutaneous Implantable Defibrillators-An Overestimated Problem? Experience from a Large Tertiary Centre and a Review of the Literature.

The subcutaneous ICD (S-ICD) has developed as a valuable alternative to transvenous implantable cardioverter defibrillator (ICD) systems. However there are certain peculiarities which are immanent to the S-ICD and may limit its use. Besides oversensing the main issue is the missing option for antibradycardia pacing. To evaluate the actual need for pacing during follow-up and changes to transvenous ICD we analyzed our large tertiary centre registry and compared it with data from other large cohorts and trials. We found out that in the 398 patients from our centre, there was a need for changing to a transvenous ICD in only 2 patients (0.5%) during a follow-up duration of almost 3 years. This rate was comparable to data obtained from other large data sets so that in the pooled analysis of almost 4000 patients the rate of bradycardia-associated complications was only 0.3%. The use of the S-ICD is safe in a variety of heart diseases and the need for antibradycardia stimulation is a very rare complication throughout many different large studies. Clinicians may take these results into account when opting for a certain ICD system and the S-ICD may be chosen more often also in elderly patients, in whom the risk for bradycardia is deemed higher.

Effects and Complications of Subcutaneous Implantable Cardioverter-Defibrillator in the Prevention of Sudden Cardiac Death: A Narrative Review.

An implantable cardioverter-defibrillator (ICD) is one of those devices that is a big boom for the prevention of sudden deaths due to heart failure. This particular device has been in use for just a couple of years, but its impact in the domain has brought about a considerable change in the way a specific issue of the cardiovascular system is tackled. Although subcutaneous or hypodermic implantable cardioverter-defibrillator (S-ICD) is considered to be a better alternative as far as transvenous implantable cardioverter-defibrillator (TV-ICD) is concerned, the former, being a newer introduction in the market, needs to be assessed in depth to clearly understand its effects andcomplications. Various types of research have been conducted on the efficacy of this device, and in most of the studies, the supremacy of this device is clearly evident when compared with other devices that are used for the same purpose. Better innovations insubcutaneous or hypodermic implantable cardioverter-defibrillators would enable them to be manufactured in a more efficient and cost-effective way so that a huge lot of people are benefited from this device. This review article is a whole peepinto the various studies done in this domain, thereby providing adequate scientific insights aboutsubcutaneous or hypodermic implantable cardioverter-defibrillators in a very simple and comprehensive manner.

The eligibility of patients with an inherited cardiac disease for therapy with a subcutaneous implantable cardioverter-defibrillator

Abstract Introduction The subcutaneous implantable cardioverter-defibrillator (S-ICD) is considered especially beneficial in young patients with an inherited cardiac disease, but data on these patient groups is limited. Purpose To evaluate the eligibility of patients with an inherited cardiac disease for therapy with a subcutaneous implantable cardioverter-defibrillator Methods We retrospectively analysed all patients with an inherited cardiac disease who received an S-ICD in our tertiary center between February 2009 and June 2021. ECG parameters and data on appropriate and inappropriate shocks were collected. Different diagnoses were compared using a chi-square test. Results We analysed 109 patients who were diagnosed with IVF (DPP6-based, N=41, 37.6%), HCM (N=36, 33.0%), Brugada syndrome (BrS, N=13, 11.9%), ARVC (N=9, 8.3%), PLN (N=3, 2.8%), LQTS (N=2, 1.8%) and other cardiomyopathies (N=5, 4.6%). Mean follow-up was 5.5±3.4 years. ECG parameters did not significantly change during follow-up. HCM patients were most likely to receive an appropriate shock (10/36, P=0.01), followed by ARVC (2/9, P=0.57) and Brugada patients (1/13, P=0.40). Patients with LQTS had most frequently inappropriate shocks (1/2, P=0.06), followed by BrS (4/13, P=0.008) and HCM patients (4/36, P=0.8). Conclusion Patients with an inherited cardiac disease are eligible for S-ICD therapy, but comes with a risk of inappropriate shocks, especially in patients with LQTS and BrS. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Dutch Heart Foundation (CVON 2018-10 PREDICT2)

Intermuscular technique for implantation of the subcutaneous implantable defibrillator: a propensity-matched case-control study

Abstract Background A previous randomized study (PRAETORIAN) demonstrated that the subcutaneous implantable cardioverter–defibrillator (S-ICD) was noninferior to transvenous ICD with respect to device-related complications and inappropriate shocks. However, that was performed prior to the widespread adoption of pulse generator implantation in the intermuscular (IM) space instead of the traditional subcutaneous (SC) pocket. Purpose To compare survival from device-related complications and inappropriate shocks between patients who underwent S-ICD implantation with the generator positioned in an IM position in comparison with a SC pocket. Methods We analyzed 1577 consecutive patients who had undergone S-ICD implantation from 2013 to 2021 and were followed up until December 2021. SC patients were propensity-matched with patients of the IM group, and their outcomes were compared. Results SC implantations were performed in 367 (23%) patients. These patients were propensity-matched with 367 IM patients. Intra-procedural complications were reported in 9 (2.5%) patients in the SC Group and 7 (1.9%) in the IM Group. During a median follow-up of 29 months, device-related complications were reported in 55 (7.5%) patients and inappropriate shocks were reported in 54 (7.4%) patients. The risk of the composite primary endpoint was lower in the matched IM Group than in the SC Group (unadjusted hazard ratio 0.67, 95% CI 0.45–0.99, p=0.042), while the risk of appropriate shocks was similar between groups (unadjusted hazard ratio 0.99, 95% CI 0.60–1.64, p=0.976). There was no significant interaction between generator positioning and variables such as gender, age, body mass index, ejection fraction and generation of the device. Conclusions In this experience, IM S-ICD generator positioning was superior to SC positioning in reducing device-related complications and inappropriate shocks. Funding Acknowledgement Type of funding sources: None.

Subcutaneous Implantable Defibrillator programming: an analysis of Italian clinical practice and its evolution

Abstract Background The UNTOUCHED study (designed in 2017 and published in 2021) demonstrated high success rate for termination of ventricular arrhythmias, and very low inappropriate shock rate in subcutaneous implantable cardioverter-defibrillator (S-ICD) recipients. The prescribed device programming included a conditional zone between 200 and 250 beats per minute (bpm) with discrimination algorithms employed to avoid delivering inappropriate shocks in this range, and a shock zone based on the rate alone for arrhythmias >250 bpm. Whether these results influenced clinical practice is unknown. Methods We assessed the programming at implantation and changes in programmed parameters at follow-up (≥1 year) in a cohort of S-ICD recipients enrolled in the Rhythm Detect registry at 56 centers. Results From 2013 to 2021, 1521 consecutive patients (aged 49±15 years; 79% male, 52% dilated cardiomyopathy, 31% arrhythmic syndromes, 16% hypertrophic cardiomyopathy) were analyzed. At implantation, the programmed sensing vector was the Primary in 59% of patients, the Secondary in 35%, the Alternate in 6%. At follow-up, the sensed vector was changed in 13% of patients. The programmed conditional zone cutoff was set to 200 [200–220] bpm (median [25–75 percentile]), and the shock zone cutoff to 230 [210–250] bpm. At follow-up, the conditional zone cutoff was reprogrammed in 13% of patients, but the median value in the overall population did not change (200 [200–220] bpm; p>0.05). The shock zone cutoff was reprogrammed in 43% of cases, and the overall median value was 250 [230–250] bpm (p<0.001 versus implantation). Sorting patients by implantation date, we observed that in the first 764 patients (implanted ≤2017) the shock zone cutoff was set to 210 [210–230] bpm at implantation and to 240 [230–250] bpm at follow-up (reprogrammed in 66% of cases). While in patients implanted >2017, it was already set to 250 [230–250] bpm at implantation and to 250 [240–250] bpm at follow-up (reprogrammed in 20% of cases, p<0.001 versus ≤2017). Conclusions S-ICD programming parameters are rarely changed during follow-up (approximately 13% of patients). The only exception in clinical practice was the shock zone cutoff. Centers have begun to program high cutoffs in recent years. This happened at the time of implantation for new S-ICD recipients and at follow-up for pre-existing implants. This behavior is consistent with a substantial adoption of published trial findings and could contribute to reduce the incidence of inappropriate shocks in clinical practice. Funding Acknowledgement Type of funding sources: None.

Feasibility and image quality of myocardial perfusion imaging by CMR in patients with conditional and non-conditional cardiac devices

Abstract Purpose First, to determine image quality using different cardiovascular magnetic resonance (CMR) perfusion protocols in patients with all available active device types in a real-world setting, including non-conditional devices. Second, to demonstrate feasibility of high-quality perfusion imaging using spoiled gradient echo (sGE) protocols for non-invasive stress-testing. Methods From August 2020 to March 2022, N=222 patients with active cardiac implantable electronic devices (CIED) were scanned on a 1.5-T MR scanner (Philips Ingenia and Ambition). Our CMR scanning protocol was tailored to the clinical indication, and whenever myocardial perfusion imaging was possible, both a conventional steady-state-free-precession (SSFP)-based and a modified sGE-perfusion protocol were applied. Such a tailored perfusion protocol was performed in N=119 patients (70% men) with exclusively left-sided devices (pacemaker (PM), n=45; implantable cardioverter-defibrillator (ICD), n=46; subcutaneous ICD (S-ICD), n=15 and cardiac resynchronization therapy-pacemaker (CRT-P, n=5) or -defibrillator (CRT-D, n=8) with a percentage of 10% non-conditional devices. For assessment of image quality, a semi-quantitative 4-point grading scale was used based on a standard 16-segment model. Results A total of N=33 stress-tests with either regadenosone, adenosine or dobutamine and N=86 rest perfusion protocols were performed. Asynchronous pacing was required in 34% of the patients due to a heart rate of <40bpm. Device interrogation before and after CMR scanning showed no significant changes. Image quality was substantially better in sGE-based perfusion protocols compared to conventional SSFP-based perfusion in ICD, CRT-D and S-ICD patients (p<0.001). In patients with PM/ CRT-P image quality was neither significantly impaired in SSFP- nor in sGE-based protocols. Most device artefacts were located primarily in the anterior myocardial segments (1, 7, 13) in transvenous implanted devices and lateral in SICD-patients. A significant relationship between the extent of device artefacts and the parameters LVEDV (p=0.03), LVESV (p=0.005) and non-conditional devices (p=0.029) in SSFP-perfusion protocols were found in patients with PM/CRT-P. In contrast, there was no correlation between clinical and CMR-parameters in patients with ICD/ CRT-D. In S-ICD-patients, there was an inverse relationship between the extent of device artefact and age (p=0.006), BMI (p=0.001) in sGE-perfusion. Conclusion Myocardial perfusion imaging by CMR is safe and feasible with high image-quality in patients with all kinds of CIEDs – including MR-conditional as well as non-conditional devices. When performing CMR-based myocardial perfusion imaging in patients with left-sided ICD/CRT-D/S-ICD, a sGE-based perfusion-protocol should be preferred compared to conventional SSFP-based perfusion protocols in order to achieve artefact-free and well interpretable images. Funding Acknowledgement Type of funding sources: None.

A new window on subcutaneous ICD system performance: Z-lead impedance change over time in devices with and without extracellular matrix envelope use

Abstract Background Device impedance for subcutaneous ICDs (S-ICDs) may rise over time reflecting changes in tissue electrical conduction due to fibrosis from the natural foreign body response, increasing the risk of defibrillation failure. A biologic envelope optimized for S-ICDs may mitigate fibrosis and encourages angiogenesis around the device possibly decreasing impedance rise over time. The S-ICD system performs routine low-voltage Z-lead (LVZ) impedance testing (impedance between shocking coil and can) that may provide insight into the impedance changes on device functionality and efficacy over time. Purpose Explore early and late impedance changes over time in S-ICDs implanted with and without envelopes using periodic LVZ measurements. Methods 30 patients received S-ICDs (15 with envelope) between 1/2017 and 3/2021, after excluding those with device complications, uncontrolled comorbidities, or recent cardiac surgery. Impedance data was recorded at initial implantation. LVZ impedance data was extracted from the wireless remote monitoring system, trended over 0–4 years post implant, and analyzed blinded to patient information. Results 24 patients (12 envelope) had evaluable implant and chronic data sets. Baseline clinical characteristics were similar between groups. Impedance in general was higher in the envelope group at initial implantation (LVZ mean 89 Ω vs 74 Ω) and throughout the first year. Comparing envelope to no envelope, the initial average shock impedance was 87.3±30.50 vs 66.7±10.40, followed by an average low-V impedance drop of 29 Ω vs 17 Ω during the first month, with a recovery to 109 Ω vs 91 Ω at 30 months post implant. After 30 months, impedance trends demonstrated a modest linear increase up to 48 months in the no envelope group in comparison with a modest decrease in the envelope group (sample sizes too small to determine significance) (Figure 1). Conclusion The results demonstrate periodic LVZ testing in the S-ICD monitoring system can reliably trend changes in system impedance over time. Impedance measurements within the first 6–7 months (and most markedly within the first 3 months) appear to be transiently lower than the values seen after this timepoint suggesting that early impedance measurements may not predict steady-state impedance. Further studies are needed to explore the impact of envelope use and the S-ICD impedance changes beyond 30 months. Funding Acknowledgement Type of funding sources: None.

Air entrapment as a cause of S-ICD inappropriate shocks.

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is noninferior to the transvenous ICD concerning device-related complications or inappropriate shocks (IASs) in patients with an indication for defibrillator therapy and not in need of pacing. 1 Knops R.E. Olde Nordkamp L.R.A. Delnoy P.P.H.M. et al. Subcutaneous or transvenous defibrillator therapy. N Engl J Med. 2020; 383: 526-536 Crossref PubMed Scopus (149) Google Scholar The main causes of IAS in S-ICD recipients are T-wave oversensing, oversensing of ventricular tachycardia/ventricular fibrillation below the therapy zone, myopotentials, and low-amplitude signals. 2 Burke M.C. Aasbo J.D. El-Chami M.F. et al. 1-Year prospective evaluation of clinical outcomes and shocks. JACC Clin Electrophysiol. 2020; 6: 1537-1550 Crossref PubMed Scopus (15) Google Scholar ,3 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. Circulation. 2021; 143: 7-17 Crossref PubMed Scopus (45) Google Scholar Subcutaneous air entrapment has recently been considered an underdiagnosed cause of early postimplant IAS, accounting for a part of oversensing of low-amplitude signals. 4 Chinitz J.S. Nadraus P. Darge A. Cacciabaudo J. Altman E.J. Inappropriate shocks within 24 hours after implantation of a subcutaneous defibrillator with a two-incision technique. J Innovations Card Rhythm Manag. 2016; 7: 2295-2298 Crossref Google Scholar ,5 Nishinarita R. Kishihara J. Matsuura G. et al. Early inappropriate shock in a subcutaneous cardiac defibrillator due to subcutaneous air. J Arrhythm. 2019; 35: 682-684 Crossref PubMed Scopus (2) Google Scholar Few data are available about the incidence, prevention, and management of postprocedural IAS due to subcutaneous air entrapment. We searched for case reports on IAS due to subcutaneous air entrapment published in PubMed, Google Scholar, Scopus, and EMBASE from 2012 to December 2021. For each of them, we analyzed the patients’ clinical characteristics, the S-ICD implantation technique, the timing and mode of IAS diagnosis, and the management of complications. A total 15 patients with S-ICD (66% male) with a median age of 55 years (interquartile range 17–75 years) were included. The indication for S-ICD implantation was primary prevention in 6 patients (40%) and secondary prevention in 9 patients (60%). A 3-incision technique was used in 7 patients (46.6%) and a 2-incision technique in 6 patients (40%). IAS was experienced on the same day of the procedure in 66.6% of cases and after discharging in 33.3%, always within 4 days of S-ICD implantation. Intraprocedural chest radiography was performed for checking the correct S-ICD system positioning in 40% of cases; in none of them, the presence of air entrapment has been reported. Subcutaneous air entrapment was diagnosed by postoperative chest radiography in 11 cases (73.3%), whereas the diagnosis was based on device interrogation and reproduction of the electrogram alterations by manipulation in 2 cases (13.3%). The most common localization of air entrapment was around the proximal electrode (46.6%, n = 7), followed by the distal electrode (26.6%, n = 4) and ICD generator (20.0%, n = 3); in 1 case, the precise localization was not investigated. Reprogramming the sensing vector and waiting the time necessary for oversensing resolution and air reabsorption were the most common strategies used to manage this complication (80.0%, n = 12). After 2 weeks, in 73.3% of patients, no further shocks occurred and chest radiography did not show residual air. Table 1 summarizes patients’ clinical characteristics, timing and management of IAS from 14 case reports/case series. On the basis of these data, the air entrapment should be considered an early complication (<24 hours) and an uncommon cause of IAS in S-ICD recipients, even if its epidemiology may be biased by misdiagnosing and underreporting. The relationship between air entrapment and S-ICD implantation technique is still controversial; however, a slightly increased incidence with the 3-incision technique was shown. The diagnosis should be made by performing a systematic approach including device interrogation, provocative maneuvers, and chest radiography. Reprogramming a different sensing vector or temporally switching off the S-ICD system, until air reabsorption, are part of the management of acute complications. Reassessing patients at 2 weeks with further device interrogation during provocative maneuvers may be useful. Value are presented as mean ± SD or n (%). DCM = dilatative cardiomyopathy; HCM = hypertrophic cardiomyopathy; IAS = inappropriate shock; ICD = implantable cardioverter-defibrillator; IHD = ischemic heart disease; PMs = physical maneuvers.

Clinical impact of ECG changes on oversensing of subcutaneous implantable cardioverter-defibrillators.

Inappropriate shocks delivered by subcutaneous implantable cardioverter-defibrillators (S-ICDs) are most frequently caused by cardiac oversensing. However, the predictors for oversensing of S-ICD remain unclear. We aimed to investigate the predictors for oversensing of S-ICD, especially clinical impact of an electrocardiographic (ECG) change. We retrospectively enrolled 99 consecutive patients who underwent S-ICD implantation between 2013 and 2021. Oversensing events were defined as inappropriate charge of the capacitors induced by cardiac or noncardiac signals other than tachycardia. During a median follow-up period of 34 months (interquartile range 20-50 months), 11 of 99 patients (11%) experienced 34 oversensing events and 4 patients (4%) received inappropriate shocks during their events. Six patients exhibited ECG changes (bundle branch block, 3; ventricular pacing, 1; inverted T wave, 1; poor R-wave progression, 1) during the follow-up period. Oversensing events were observed in 4 of 6 patients with ECG change (67%), and 3 patients underwent S-ICD removal because of inevitable shock. Contrastingly, of the remaining patients without ECG change, all 7 patients who experienced oversensing events could continue using S-ICD with the reprogramming sensing vector and/or restriction of excessive exercise. Logistic regression analysis showed that lower voltage of Sokolow-Lyon ECG (V1S + V5R) was the predictor of oversensing in patients without ECG change. When the cutoff value was 2.1 mV, the sensitivity, specificity, positive predictive value, and negative predictive value were 85.7%, 62.7%, 15.7%, and 98.1%, respectively. Unavoidable oversensing resulting in S-ICD removal is caused by ECG change. Oversensing in patients without ECG change can be managed.

The subcutaneous implantable cardioverter-defibrillator should be reserved for niche indications.

Since the introduction of the first implantable cardioverter-defibrillator (ICD) in 1980, ICDs have undergone significant improvements to become the pillar of sudden death prevention today. The first device consisted of a 250-g abdominal generator with a surgically applied pericardial patch.1 Over time, the generator decreased to one-fifth of its original size, and the pericardial patch was replaced by transvenous leads with integrated defibrillation coils. However, for patients with impaired venous access or children with congenital heart disease, epicardial systems remained their only option until the development of the subcutaneous implantable cardioverter-defibrillator (S-ICD).

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

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.1–5 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.

Subcutaneous Implantable Cardioverter Defibrillators for the Prevention of Sudden Cardiac Death: Pediatric Single-Center Experience.

Background: The subcutaneous implantable cardioverter defibrillator (S-ICD) was developed as an alternative to the transvenous ICD, to prevent lead-related complications associated with the latter. The absence of intravascular or intracardiac components offers potential advantages to pediatric patients. Aims: The aim of the study is to present an overview of our experience with S-ICDs in the pediatric center that, currently, has performed the largest number of implantations in children in Poland. Methods: Retrospective analysis of data from medical history, qualification, implantation procedure, and S-ICD post-implantation observations in 11 pediatric patients were performed. Results: S-ICDs were implanted in 11 patients, 8 boys and 3 girls, aged 12–17 years. The S-ICD was implanted for primary prevention in seven patients: four with hypertrophic cardiomyopathy (HCM), two with dilated cardiomyopathy (DCM), and one with arrhythmogenic right ventricular cardiomyopathy (ARVC). It was implanted for secondary prevention in four patients: two with sudden cardiac arrest (SCA) in the course of idiopathic ventricular fibrillation (IVF), one with long QT syndrome (LQTS) after probable SCA, and one with Brugada syndrome after SCA. In all patients, the device was implanted intramuscularly. One patient did not have a defibrillation test performed due to the presence of an intracardiac thrombus. In one patient, during screening, it was decided to implant an electrode on the right side of the sternum. There were no early or late complications with any of the procedures. So far, no inadequate discharges have been observed. Conclusions: Our results prove the efficacy of the S-ICD treatment option along with technically simple surgery, which supports its further and more widespread application in children.