Subcutaneous chronic implantable defibrillation systems in humans

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

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.

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.

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

Introduction: Subcutaneous ICD (S-ICD) is a promising option for Hypertrophic Cardiomyopathy (HCM) patients at high-risk of Sudden Cardiac Death (SCD). However, its efficacy in terminating ventricular arrhythmias in HCM is yet unresolved. Hypothesis: To determine the efficacy of post-implantation S-ICD defibrillation testing (DT) of Ventricular Fibrillation (VF) in HCM patients and assess possible predictors of failure. Methods: Consecutive HCM patients referred for S-ICD implantation at seven Italian Centers from June 2014 to May 2016 were prospectively enrolled. At S-ICD implantation, patients underwent one or two attempts of VF induction by programmed electrical stimulation. Successful conversion was defined as any 65j shock that terminated VF and did not require rescue shocks. Clinical, ECG and Echocardiographic findings were analyzed to study potential predictors of conversion failure. Results: We evaluated 50 HCM patients (34 males, mean age 40±16) with a mean BMI of 25.2±4.4 kg/m 2 [18.1-36]. Two patients (4%) had a history of cardiac arrest, whereas 48 (96%) were implanted in primary prevention. Mean calculated risk of SCD at 5 years by the ESC score was 6.5±3.9% and all patients had at least one major risk factor. Maximal LV wall thickness (LVMWT) was >25 mm in 19 (38%) patients and ≥ 30 mm in 13 (26 %). In 2/50 patients (4%) no arrhythmias were inducible, while in 7 (14%) only polymorphic sustained ventricular tachycardia (SVT) was induced and correctly cardioverted by the S-ICD. In the remaining 41 (82%) patients, 70 VF episodes were induced (2 VF in 29 and 1 VF in 12 patients), all correctly recognized by the device. Of the 70 VFs, 4 (6%) spontaneously converted into sinus rhythm. In 65/66 (98%) the S-ICD performed successful conversions, but failed in 1 (2%) patient, who needed rescue defibrillation. This patient was severely obese, with a BMI 36 kg/m 2 and LVMWT of 25 mm. VF was induced again and successfully converted by 80j shock with inverted polarity. Conclusions: Acute defibrillation testing at 65j shows the efficacy of S-ICD in terminating VF or polymorphic SVT in HCM patients, despite the presence of extreme LV hypertrophy. Severe obesity was possibly responsible for the single failure observed at 65j in our series.

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.

How the Subcutaneous Implantable Cardioverter Defibrillator Works

How the S-ICD (subcutaneous implantable cardiac defibrillator) senses cardiac signals to minimize cardiac over-sensing and maximize rhythm discrimination

Although conventional implantable cardioverter-defibrillators (ICDs) have proved effective in the prevention of sudden cardiac death (SCD), they still appear to be limited by non-trivial acute and long-term complications. The recent advent of an entirely subcutaneous ICD (S-ICD) represents a further step in the evolution of defibrillation technology towards a less-invasive approach. This review highlights some historical and current issues concerning the S-ICD that may offer a viable therapeutic option in selected patients at high risk of SCD and in whom pacing is not required. After the CE Mark and US Food and Drug Administration (FDA) approvals, the S-ICD is being implanted worldwide with growing clinical data regarding its safety and efficacy (the EFFORTLESS Registry). The recently developed new generation of S-ICD (EMBLEM, Boston Scientific) demonstrates favourable features including a smaller device, longer longevity and remote-monitoring compatibility. Further innovations in the S-ICD system and potential integration with leadless pacing may play an important role in defibrillation therapy and prevention of SCD in the near future.

Subcutaneous implantable cardioverter defibrillators (S-ICDs) are increasingly used to prevent sudden cardiac death. Due to their placement near the left lateral and apical myocardium, S-ICDs can present technical challenges for stereotactic arrhythmia radioablation (STAR) of ventricular tachycardia. This study aimed to evaluate the feasibility of STAR in patients with S-ICDs. Previously acquired cardiac computed tomography data from ten S-ICD patients were retrospectively analyzed. Organs at risk, S-ICD components, and hypothetical planning target volumes (PTV) for segments 8 (septal), 11 (lateral), and 17 (apical) were contoured. For each patient and segment, two treatment plans were calculated with a prescribed PTV dose of 25Gy: one plan sparing the S-ICD from the primary radiotherapy beam ('spared') and one without this constraint ('non-spared'). The S-ICD was successfully spared from the primary beam in 27 out of 30 plans, with D 0.035cm 3<1Gy. In three spared plans (PTV segment 11) with a distance between PTV and S-ICD <4cm, D 0.035cm 3 exceeded 1Gy. Spared plans for PTV segment 11 showed significant higher dose/volume metrics and reduced plan quality compared to non-spared plans (p<0.05), although 9/10 plans remained clinically acceptable. For PTV segment 8 and segment 17, no clinical or statistical differences were observed. The presence of an S-ICD is not a contraindication for STAR, although plan quality may decrease with PTVs in lateral segments. Rare cases with a distance between PTV and S-ICD <4cm may complicate radiation treatment planning.

Background Left ventricular assist devices (LVADs) are an increasingly used strategy for the management of patients with advanced heart failure (HF).Subcutaneous implantable cardioverter defibrillator (S-ICD) might be a viable alternative to conventional ICDs, with a lower risk of short- and long-term of device-related complications and infections. Purpose:The aim of this multicenter study was to evaluate the outcomes and management of S-ICD recipients who underwent LVAD implantation. Methods:The study population included patients with an S-ICD who underwent LVAD implantation for advanced HF despite optimal medical therapy. Results:The study population included 30 patients (25 male;median age 45 [38-52] years).The HeartMate III was the most common LVAD type. Median follow-up in the setting of concomitant use of S-ICDs and LVADs was 7 months (1-20).There were no reports of inability to interrogate S-ICD systems in this population.Electromagnetic interference (EMI) occurred in 21 (70%) patients.The primary sensing vector was the one most significantly involved in determining EMI.Twenty-seven patients (90%) remained eligible for S-ICD implantation with at least one optimal sensing vector.The remaining 3 patients (10%) were ineligible for S-ICD after attempts of reprogramming of sensing vectors. Six patients (20%) experienced inappropriate shocks due to EMI. Six patients (20%) experienced appropriate shocks.No S-ICD extraction because of need for antitachycardia pacing,ineffective therapy or infection was reported. Conclusions: Concomitant use of LVAD and S-ICD is feasible in most patients. However, the potential risk of EMI oversensing, IS,and undersensing in the post-operative period following LVAD implantation should be considered.Careful screening for EMI should be performed in all sensing vectors after LVAD implantation.

BackgroundCardiac contractility modulation (CCM) is an electrical‐device therapy for patients with heart failure with reduced ejection fraction (HFrEF). Patients with left ventricular ejection fraction (LVEF) ≤35% also have indication for an implantable cardioverter‐defibrillator (ICD), and in some cases subcutaneous ICD (S‐ICD) is selected.HypothesisCCM and S‐ICD can be combined to work efficaciously and safely.MethodsWe report on 20 patients with HFrEF and LVEF ≤35% who received CCM and S‐ICD. To exclude device interference, patients received intraoperative crosstalk testing, S‐ICD testing, and bicycle exercise testing while CCM was activated. Clinical and QOL measures before CCM activation and at last follow‐up were analyzed. S‐ICD performance was evaluated while both CCM and S‐ICD were active.ResultsMean follow‐up was 34.3 months. NYHA class improved from 2.9 ± 0.4 to 2.1 ± 0.7 (P < 0.0001), Minnesota Living With Heart Failure Questionnaire score improved from 50.2 ± 23.7 to 29.6 ± 22.8 points (P < 0.0001), and LVEF improved from 24.4% ± 8.1% to 30.9% ± 9.6% (P = 0.002). Mean follow‐up time with both devices active was 22 months. Three patients experienced a total of 6 episodes of sustained ventricular tachycardia, all successfully treated with first ICD shock. One case received an inappropriate shock unrelated to the concomitant CCM. One patient received an LVAD, so CCM and S‐ICD were discontinued.ConclusionsCCM and S‐ICD can be successfully combined in patients with HFrEF. S‐ICD and CCM remain efficacious when used together, with no interference affecting their function.

Early Failure of Subcutaneous ICD in a Patient With a Variant of Rapidly Progressive ARVC

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.

Approximately 5.7% of potential subcutaneous implantable cardioverter-defibrillator (S-ICD) recipients are ineligible by virtue of their vector morphology, with higher rates of ineligibility observed in some at-risk groups. Mathematical vector rotation is a novel technique that can generate a personalized sensing vector, one with maximal R:T ratio, using electrocardiogram (ECG) signal recorded from the present S-ICD location. A cohort of S-ICD ineligible patients were identified through ECG screening of ICD patients with no ventricular pacing requirement and their personalized vectors were generated using ECG signal from a Holter monitor. Subcutaneous ICD eligibility in this cohort was then recalculated. In a separate cohort, episodes of arrhythmia were recorded in patients undergoing arrhythmia induction, and arrhythmia detection in standard S-ICD vectors was compared to rotated vectors using an S-ICD simulator. Ninety-two participants (mean age 64.9 ± 2.7 years) underwent screening and 5.4% were found to be S-ICD ineligible. Personalized vector generation increased the R:T ratio in these vectors from 2.21 to 7.21 (4.54-9.88, P < 0.001) increasing the cohort eligibility from 94.6% to 100%. Rotated S-ICD vectors also showed high ventricular fibrillation (VF) detection sensitivity (97.8%), low time to VF detection (6.1 s), and excellent tachycardia discrimination (sensitivity 96%, specificity 88%), with no significant differences between rotated and standard vectors. In S-ICD ineligible patients, mathematical vector rotation can generate a personalized vector that is associated with a significant increase in R:T ratio, resulting in universal device eligibility in our cohort. Ventricular fibrillation detection efficacy, time to VF detection, and tachycardia discrimination were not affected by vector rotation.