Therapy From a Novel Substernal Lead

Characterization of the substernal space with computed tomography imaging in patients with and without median sternotomy: Assessing a novel implant location for extravascular defibrillation lead placement

BACKGROUND

Implantable cardioverter-defibrillators (ICDs) provide clinically significant therapy for the prevention of sudden cardiac death. This study aimed to characterize the substernal space using computed tomography (CT) in patients with and without prior midline sternotomy to investigate the feasibility of substernal ICD lead implantation in post-sternotomy patients.

METHODS

High-quality electrocardiogram-gated CT images from 100 patients (71% male, average body mass index 23.5 ± 2.9) were retrospectively collected, including 50 patients with prior midline sternotomy (S-group) and 50 patients with no prior sternotomy (NS-group). Distances were measured from the retrosternal surface to the epicardial surface of the heart and segmented into four regions from the xiphoid tip and superiorly along the sternum.

RESULTS

Results generally showed a measurable but narrower average sternum-to-heart distance in the prior sternotomy group compared to the non-sternotomy group in all four regions (p < .05). In the S-group, the sternum-to-heart distances across all regions ranged from 0 to 32.0 mm, while in the NS-group, the distances ranged from 0 to 39.9 mm.

CONCLUSION

Small but measurable separations between the heart and sternum were observed in patients with prior sternotomy, particularly near the xiphoid region, indicating the potential viability of extravascular substernal ICD lead implantation in post-sternotomy patients.

Initial Experience With Intercostal Insertion of an Extravascular ICD Lead Compatible With Existing Pulse Generators

BACKGROUND

This study assessed safety and feasibility of a novel extravascular implantable cardioverter defibrillator (ICD) lead when inserted anteriorly through a rib space and connected to various commercially available ICD pulse generators (PGs) placed in either a left mid-axillary or left pectoral pocket. Currently available or investigational, extravascular-ICDs include a subcutaneous or subxiphoid lead connected to customized extravascular-ICD PGs.

METHODS

This novel extravascular-ICD (AtaCor Medical Inc, San Clemente, CA) employs a unique intercostal implant technique and is designed to function with commercial DF-4 ICD PGs. In this nonrandomized, single-center, acute study, 36 de novo or replacement ICD (transvenous ICD) patients enrolled to receive a concomitant extravascular-ICD lead inserted through an intercostal space along the left parasternal margin. extravascular-ICD leads were connected to DF-4 compatible ICD PGs positioned in either a left mid-axillary or pectoral pocket for acute sensing and defibrillation testing. Defibrillation testing started at 30 Joules (J) and stepped up or down in 5 to 10 joule increments depending on the success and limitations of the generator used.

RESULTS

Successful acute defibrillation using ≤35 J was noted in 100% of left mid-axillary PG subjects (n=27, mean 16.3±8.6 J) and 83% of left pectoral PG subjects (n=6, mean 21.0±8.4 J). Furthermore, 24 of 27 (89%) of patients tested with a left, mid-axillary intermuscular PG had successful VF conversion with defibrillation energies at least 10 J below the maximum delivered output of the device. All evaluable episodes (n=93) were automatically sensed, detected, and shocked. No serious device-related intraoperative adverse events were observed.

CONCLUSIONS

This first-in-human study documented the safe and reliable placement of a novel extravascular ICD lead with effective sensing and defibrillation of induced ventricular fibrillation using commercial DF-4 ICD PGs.

Substernal Extravascular Implantable Cardioverter-Defibrillator System Infections in Large Animals

The extravascular implantable cardioverter-defibrillator (EV ICD) with lead implantation in the substernal space may provide clinical advantages over transvenous and subcutaneous systems. This is the first reported examination of substernal infection in large animals implanted with the EV ICD system.The system was implanted in 13 large animals (canine, porcine, and ovine). The porcine were co-implanted with a transvenous cardiac resynchronization therapy with defibrillator (CRT-D) system. Infection was promoted through a cadence of immunosuppressive monitors and study interventions. The animals were monitored for clinical presentation of infection over 12-18 weeks, and cultures were collected to confirm infection. Treatment was bifurcated: 1) some infections were treated only with antibiotics ( "antibiotics only" ), whereas 2) some infections were treated with system removal and antibiotics ( "antibiotics + explant" ). Histopathology was conducted at the study closure.Five infections were confirmed over the course of the study, four of which involved infection of the EV ICD system and one infection of only the concomitantly implanted transvenous CRT-D system without EV ICD-related infection. Among the four EV ICD infections, two of two infections treated with antibiotics only did not resolve whereas two of two infections treated with antibiotics + explant resolved, as shown by histology. The transvenous CRT-D system infection progressed to septicemia and endocarditis, requiring early study discontinuation. No EV ICD-related infection progressed to blood stream infection, and the sternal bone did not become infected when infection was present in the substernal tissues.The study findings suggest that EV ICD-related infections are treatable with system removal and antibiotic therapy.

Subcutaneous Implantable Cardioverter Defibrillator: A Contemporary Overview

The difference between subcutaneous implantable cardioverter defibrillators (S-ICDs) and transvenous ICDs (TV-ICDs) concerns a whole extra thoracic implantation, including a defibrillator coil and pulse generator, without endovascular components. The improved safety profile has allowed the S-ICD to be rapidly taken up, especially among younger patients. Reports of its role in different cardiac diseases at high risk of SCD such as hypertrophic and arrhythmic cardiomyopathies, as well as channelopathies, is increasing. S-ICDs show comparable efficacy, reliability, and safety outcomes compared to TV-ICD. However, some technical issues (i.e., the inability to perform anti-bradycardia pacing) strongly limit the employment of S-ICDs. Therefore, it still remains only an alternative to the traditional ICD thus far. This review aims to provide a contemporary overview of the role of S-ICDs compared to TV-ICDs in clinical practice, including technical aspects regarding device manufacture and implantation techniques. Newer outlooks and future perspectives of S-ICDs are also brought up to date.

Evolution of extravascular implantable cardioverter-defibrillator therapy for ventricular arrhythmias

Implantable cardioverter-defibrillators have become an established therapy for the prevention of sudden cardiac death due to life-threatening ventricular arrhythmias in the last decades. In all those years, the use of transvenous leads has proven to be the most vulnerable part of the system. The development of the completely subcutaneous implantable cardioverter-defibrillator opened a new era of device therapy outside of the vascular system. The next step, enabling extravascular devices with the option of antitachycardia pacing, is just around the corner. This may become an important option for all patients without a bradycardia pacing indication that are in need for antitachycardia pacing because of monomorphic ventricular tachycardia.

Efficacy and Safety of an Extravascular Implantable Cardioverter-Defibrillator

BACKGROUND

The extravascular implantable cardioverter-defibrillator (ICD) has a single lead implanted substernally to enable pause-prevention pacing, antitachycardia pacing, and defibrillation energy similar to that of transvenous ICDs. The safety and efficacy of extravascular ICDs are not yet known.

METHODS

We conducted a prospective, single-group, nonrandomized, premarket global clinical study involving patients with a class I or IIa indication for an ICD, all of whom received an extravascular ICD system. The primary efficacy end point was successful defibrillation at implantation. The efficacy objective would be met if the lower boundary of the one-sided 97.5% confidence interval for the percentage of patients with successful defibrillation was greater than 88%. The primary safety end point was freedom from major system- or procedure-related complications at 6 months. The safety objective would be met if the lower boundary of the one-sided 97.5% confidence interval for the percentage of patients free from such complications was greater than 79%.

RESULTS

A total of 356 patients were enrolled, 316 of whom had an implantation attempt. Among the 302 patients in whom ventricular arrhythmia could be induced and who completed the defibrillation testing protocol, the percentage of patients with successful defibrillation was 98.7% (lower boundary of the one-sided 97.5% confidence interval [CI], 96.6%; P<0.001 for the comparison with the performance goal of 88%); 299 of 316 patients (94.6%) were discharged with a working ICD system. The Kaplan-Meier estimate of the percentage of patients free from major system- or procedure-related complications at 6 months was 92.6% (lower boundary of the one-sided 97.5% CI, 89.0%; P<0.001 for the comparison with the performance goal of 79%). No major intraprocedural complications were reported. At 6 months, 25 major complications were observed, in 23 of 316 patients (7.3%). The success rate of antitachycardia pacing, as assessed with generalized estimating equations, was 50.8% (95% CI, 23.3 to 77.8). A total of 29 patients received 118 inappropriate shocks for 81 arrhythmic episodes. Eight systems were explanted without extravascular ICD replacement over the 10.6-month mean follow-up period.

CONCLUSIONS

In this prospective global study, we found that extravascular ICDs were implanted safely and were able to detect and terminate induced ventricular arrhythmias at the time of implantation. (Funded by Medtronic; ClinicalTrials.gov number, NCT04060680.).

The Development of the Extravascular Defibrillator with Substernal Lead Placement: A New Frontier for Device-Based Treatment of Sudden Cardiac Arrest

Introduction

The extravascular implantable cardioverter‐defibrillator (EV ICD) system with substernal lead placement is a novel nontransvenous alternative to current commercially available ICD systems. The EV ICD provides defibrillation and pacing therapies without the potential long‐term complications of endovascular lead placement but requires a new procedure for implantation with a safety profile under evaluation.

Methods

This paper summarizes the development of the EV ICD, including the preclinical and clinical evaluations that have contributed to the system and procedural refinements to date.

Results

Extensive preclinical research evaluations and four human clinical studies with >140 combined acute and chronic implants have enabled the development and refinement of the EV ICD system, currently in worldwide pivotal study.

Conclusion

The EV ICD may represent a clinically valuable solution in protecting patients from sudden cardiac death while avoiding the long‐term consequences of transvenous hardware. The EV ICD offers advantages over transvenous and subcutaneous systems by avoiding placement in the heart and vasculature; relative to subcutaneous systems, EV ICD requires less energy for defibrillation, enabling a smaller device, and provides pacing features such as antitachycardia and asystole pacing in a single system.

Three-Year Extraction Experience of a Novel Substernal Extravascular Defibrillation Lead in Sheep

Background

The extravascular implantable cardioverter‐defibrillator (EV ICD) with lead implantation in the substernal space may provide an alternative to transvenous and subcutaneous systems. This is the first‐reported chronic extraction experience for EV ICD leads. The aim of the study is to evaluate the chronic encapsulation and extractability of EV ICD leads.

Methods

Two EV ICD leads and one transvenous lead were implanted in each of 24 mature sheep. A subset of animals was evaluated yearly for histology and lead extractability. Extractions were performed using simple traction or extraction tools. Histology evaluated the encapsulating tissue.

Results

At 1 year, extraction was performed successfully for two of five EV ICD leads with traction alone using ≤3.1 kg‐force (kgf) and the remainder extracted successfully with extraction tools; no transvenous leads were removed with traction alone. At 2 years, no EV ICD or transvenous leads were extracted with traction alone, while at 3 years, one of eight EV ICD leads and two of four transvenous leads were extracted with traction (0.8 and ≤2.3 kgf, respectively). There was one observation of hemopericardium resulting in tamponade with EV ICD extraction but without injury to cardiovascular structures and related to the unique implant tract. Among transvenous leads, inversion of the ventricle with loss of cardiac output resulted in abandonment of traction for two animals.

Conclusions

Chronic extraction of EV ICD leads from the substernal space was successfully performed using traction and simple tools through 3 years in sheep with one observation of hemopericardium that did not originate from cardiovascular injury.

Non-transvenous ICD therapy: current status and beyond

Subcutaneous implantable cardioverter/defibrillators (S-ICDs) have been developed to offer ICD treatment to patients without venous access to the heart and to overcome complications associated with transvenous leads, particularly lead fracture/insulation defects and endocarditis. Several studies and registries have demonstrated the feasibility and safety of S‑ICD in different groups of patients. Further developments in S‑ICD technology involve the combination with devices that can provide anti-bradycardia and anti-tachycardia pacing if needed. The extravascular ICD (EV-ICD) is a new system that similarly offers ICD therapy without a transvenous lead but uses a substernal instead of a subcutaneous lead to facilitate detection of ventricular fibrillation and to provide anti-tachycardia and also temporary anti-bradycardia pacing. The first animal but also clinical data on EV-ICDs have been published. This review discusses the current state, potential advantages and limitations, and future research of both S‑ICD and EV-ICD.

The extravascular implantable cardioverter-defibrillator: characterization of anatomical parameters impacting substernal implantation and defibrillation efficacy

Aims

The aim of this study is to provide a thorough, quantified assessment of the substernal space as the site of extravascular implantable cardioverter-defibrillator (ICD) lead placement using computed tomography (CT) scans and summarizing adverse events and defibrillation efficacy across anatomical findings. Subcutaneous ICDs are an alternative to transvenous defibrillators but have limitations related to ICD lead distance from the heart. An alternative extravascular system with substernal lead placement has the potential to provide defibrillation at lower energy and pacing therapies from a single device.

Methods and results

A multi-centre, non-randomized, retrospective analysis of 45 patient CT scans quantitatively and qualitatively assessing bony, cardiac, vascular, and other organ structures from two human clinical studies with substernal lead placement. Univariate logistic regression was used to evaluate 15 anatomical parameters for impact on defibrillation outcome and adjusted for multiple comparisons. Adverse events were summarized. Substernal implantation was attempted or completed in 45 patients. Defibrillation testing was successful in 37 of 41 subjects (90%) using ≥10 J safety margin. There were two intra-procedural adverse events in one patient, including reaction to anaesthesia and an episode of transient atrial fibrillation during ventricular fibrillation induction. Anatomical factors associated with defibrillation failure included large rib cage width, myocardium extending very posteriorly, and a low heart position in the chest (P-values <0.05), though not significant adjusting for multiple comparisons.

Conclusion

Retrospective analysis demonstrates the ability to implant within the substernal space with low intra-procedural adverse events and high defibrillation efficacy despite a wide range of anatomical variability.

Non-traditional implantable cardioverter-defibrillator configurations and insertion techniques: a review of contemporary options

Implantable cardioverter-defibrillators (ICDs) have revolutionized the treatment of acquired or inherited cardiac diseases associated with a high risk of sudden cardiac death due to ventricular tachyarrhythmias. Contemporary ICD devices offer reliable arrhythmia detection and discrimination algorithms and deliver highly efficient tachytherapies. Percutaneously inserted transvenous defibrillator coils with pectoral generator placement are the first-line approach in the majority of adults due to their extensively documented clinical benefit and efficiency with comparably low periprocedural implantation risks as well as the option of providing pain-free tachycardia treatment via anti-tachycardia pacing (ATP), concomitant bradycardiaprotection, and incorporation in a cardiac resynchronization therapy if indicated. Yet, expanding ICD indications particularly among younger and more complex patient groups as well as the increasingly evident long-term consequences and complications associated with intravascular lead placements promoted the development of alternative ICD configurations. Most established in daily clinical practice is the subcutaneous ICD but other innovative extravascular approaches like epicardial, pericardial, extra-pleural, and most recently substernal defibrillator coil placements have been introduced as well to overcome shortcomings associated with traditional devices and allow for individualized treatment strategies tailored to the patients characteristics and needs. The review aims to provide practical solutions for common complications encountered with transvenous ICD systems including restricted venous access, high defibrillation/fibrillation thresholds (DFTs), and recurrent device infections. We summarize the contemporary options for non-traditional extravascular ICD configurations outlining indications, advantages, and disadvantages.

The extravascular implantable cardioverter-defibrillator: The pivotal study plan

Background

Transvenous implantable cardioverter defibrillators (TV ICD) provide life‐saving therapy for millions of patients worldwide. However, they are susceptible to several potential short‐ and long‐ term complications including cardiac perforation and pneumothorax, lead dislodgement, venous obstruction, and infection. The extravascular ICD system's novel design and substernal implant approach avoids the risks associated with TV ICDs while still providing pacing features and similar generator size to TV ICDs.

Study Design

The EV ICD pivotal study is a prospective, multicenter, single‐arm, nonrandomized, premarket clinical study designed to examine the safety and acute efficacy of the system. This study will enroll up to 400 patients with a Class I or IIa indication for implantation of an ICD. Implanted subjects will be followed up to approximately 3.5 years, depending on when the patient is enrolled.

Objective

The clinical trial is designed to demonstrate safety and effectiveness of the EV ICD system in human use. The safety endpoint is freedom from major complications, while the efficacy endpoint is defibrillation success. Both endpoints will be assessed against prespecified criteria. Additionally, this study will evaluate antitachycardia pacing performance, electrical performance, extracardiac pacing sensation, asystole pacing, appropriate and inappropriate shocks, as well as a summary of adverse events.

Conclusion

The EV ICD pivotal study is designed to provide clear evidence addressing the safety and efficacy performance of the EV ICD System.

A Historical Perspective of Cardiac Implantable Electronic Device Infection: How a Menace Can Drive Technological and Clinical Improvement

In recent decades there has been a relevant increase in the implantation rate of cardiac implantable electronic devices (CIEDs), albeit with relevant geographical inhomogeneities. Despite the positive impact on clinical outcomes, the possibility of major complications is not negligible, particularly with respect to CIED infections. CIED infections significantly affect morbidity and mortality, especially in instances of delayed diagnosis and appropriate treatment. In the present review, we will start to depict the factors underlying the development of CIED infection as well as the difficulties related to its diagnosis and treatment. We will explain the reasons underlying the need to focus on prophylaxis rather than treatment, in view of the poor outcomes despite improvements in lead extraction procedures. This will lead to the consideration of management of this complication in a hub-spoke manner, and to our analysis of the several technological and procedural improvements developed to minimize this complication. These include prolongation of CIED longevity, the development of leadless devices, and integrated prophylactic approaches. We will conclude with a discussion regarding new devices and strategies under development. This complete excursus will provide the reader with a new perspective on how a major complication can drive technological improvements.

Innovations in Cardiac Implantable Electronic Devices

Cardiac implantable electronic devices (CIEDs) are essential for the management of a variety of cardiac conditions, including tachyarrhythmias, bradyarrhythmias, and medically refractory heart failure (HF). Recent advancements in CIED technology have led to innovative solutions that overcome shortcomings associated with traditional devices or address unmet needs. Leadless pacemakers, subcutaneous implantable cardioverter defibrillators (ICDs), and extravascular ICDs eliminate lead-related complications common with conventional pacemakers or ICDs. Conduction system pacing (His bundle pacing and left bundle branch pacing) is a more physiologic method of pacing and avoids the deleterious consequences associated with long-term right ventricular pacing. For HF-related devices, cardiac contractility modulation is an emerging therapy that bridges a gap for many patients ineligible for cardiac resynchronization therapy and has been shown to improve HF symptoms and decrease hospitalizations and mortality in select patients. Implantable pulmonary artery pressure monitors help guide HF management and reduce hospitalizations. Lastly, new phrenic nerve stimulating devices are being utilized to treat central sleep apnea, a common comorbidity associated with HF. While further long-term studies are still underway for many of these new technologies, it is anticipated that these devices will become indispensable therapeutics in the expanding cardiovascular armamentarium.

Cardiac Electronic Devices: Future Directions and Challenges

Cardiovascular implantable electronic devices (CIEDs) are essential management options for patients with brady- and tachyarrhythmias or heart failure with concomitant optimal pharmacotherapy. Despite increasing technological advances, there are still gaps in the management of CIED patients, eg, the growing number of lead- and pocket-related long-term complications, including cardiac device–related infective endocarditis, requires the greatest care. Likewise, patients with CIEDs should be monitored remotely as a part of a comprehensive, holistic management approach. In addition, novel technologies used in smartwatches may be a convenient tool for long-term atrial fibrillation (AF) screening, especially in high-risk populations. Early detection of AF may reduce the risk of stroke and other AF-related complications. The objective of this review article was to provide an overview of novel technologies in cardiac rhythm–management devices and future challenges related to CIEDs.

State-of-the-art consensus on non-transvenous implantable cardioverter-defibrillator therapy

Within the last decade, implantable cardioverter-defibrillator (ICD) systems with non-transvenous leads were developed in order to minimize complications related to the cardiovascular position of transvenous ICD leads. This national expert consensus gives an overview of potential indications for the implantation of non-transvenous ICD systems, and provides specific recommendations for implantation, follow-up, and complication management in patients with subcutaneous ICD. Regarding particular issues like the necessity for shock efficacy testing, or the clinical outcome as compared to transvenous ICD, randomized data are expected in the near future.

Evolution of extravascular implantable defibrillator technologies

The implantable cardioverter-defibrillator (ICD) has been successfully treating patients with lethal ventricular arrhythmias for decades. The main acute and chronic complications of this therapy modality are related to the use of a transvenous lead. An entirely extravascular ICD concept was developed over the last 20 years, with emergence of the subcutaneous ICD (S-ICD). This device was approved for clinical use seven years ago, and accumulating real-life experience confirms its safety and efficacy. The main limitations related to this system include the lack of pacing capabilities for bradycardia, tachycardia or resynchronization therapy, a large size, and relatively high energy requirements for effective defibrillation. This review article summarizes current knowledge and potential future developments of the extravascular ICD technologies.