The extravascular implantable cardioverter-defibrillator: The pivotal study plan

Systematic review of leadless pacemaker

Conventional pacing systems consist of a pacemaker and one or more leads threaded from the device pocket through veins into the heart conducting the pacing therapy to the desired pacing site. Although these devices are effective, approximately one in eight patients treated with these traditional pacing systems experiences a complication attributed to the pacemaker pocket or leads. With the technological advances in electronics, leadless pacemakers that small enough to implant within the heart were introduced. Leadless pacemakers have been developed to overcome many of the challenges of transvenous pacing including complications related to leads or pacemaker pockets. This review aims to provide an overview of advantages of leadless pacemaker, complications and limitations of leadless pacemaker, leadless pacemaker candidate, and future directions of this promising technology.

Patient-reported quality of life and acceptance of the extravascular implantable cardioverter-defibrillator: Results from pivotal study

INTRODUCTION

The pivotal study of the extravascular implantable cardioverter-defibrillator (EV ICD) recently demonstrated primary efficacy and safety endpoints comparable to previous ICD systems. Patient experience with this novel device has not been reported. The current study examined the standardized patient-reported outcome (PRO) metrics of quality of life (QOL) and patient acceptance of the device.

METHODS

The EV ICD Pivotal Study was a prospective, single-arm, nonrandomized, global, premarket approval trial. Patients completed the 12-Item Short Form Survey (SF-12) QOL surveys at baseline and at 6 months following implant. Additionally, patients completed the Florida Patient Acceptance Survey (FPAS) QOL survey at 6 months.

RESULTS

From baseline to 6 months, patients within the EV ICD Pivotal Study (n = 247) reported statistically significant SF-12 improvements in physical QOL (45.4 ± 9.4 vs. 46.8 ± 9.1 respectively, p = .020) and no changes in mental QOL (49.3 ± 10.4 vs. 50.5 ± 9.7, p = .061). No differences were noted by sex, atrial fibrillation, or the experience of ICD shock. EV ICD patients reported better total FPAS patient acceptance of their ICD than TV-ICD or S-ICD patients using historical norms comparisons (80.4 ± 15.7 vs. 70.2 ± 17.8, p < .0001 for S-ICD and 73.0 ± 17.4, p = .004 for TV-ICD).

CONCLUSION

The initial PROs for EV ICD patients indicated that patients had improvements in physical QOL from baseline to 6-month follow-up and markedly better overall acceptance of their ICD compared to a previous study with S-ICD and TV-ICD data. These initial results suggest that the EV ICD is evaluated positively by patients.

Transvenous versus subcutaneous implantable cardioverter defibrillators in young cardiac arrest survivors

Secondary prevention implantable cardioverter defibrillators (ICDs) are indicated in young patients presenting with aborted sudden cardiac death (SCD) because of ventricular arrhythmias. Transvenous-ICDs (TV-ICDs) are effective, established therapies supported by evidence. The significant morbidity associated with transvenous leads led to the development of the newer subcutaneous-ICD (S-ICD). This review discusses the clinical considerations when selecting an ICD for the young patient presenting with out-of-hospital cardiac arrest. The major benefits of TV-ICDs are their ability to pace (antitachycardia pacing [ATP], bradycardia support and cardiac resynchronisation therapy [CRT]) and the robust evidence base supporting their use. Other benefits include a longer battery life. Significant complications associated with transvenous leads include pneumothorax and tamponade during insertion and infection and lead failure in the long term. Comparatively, S-ICDs, by virtue of having no intravascular leads, prevent these complications. S-ICDs have been associated with a higher incidence of inappropriate shocks. Patients with an indication for bradycardia pacing, CRT or ATP (documented ventricular tachycardia) are seen as unsuitable for a S-ICD. If venous access is unsuitable or undesirable, S-ICDs should be considered given the patient is appropriately screened. There is a need for further randomised controlled trials to directly compare the two devices. TV-ICDs are an effective therapy for preventing SCD limited by significant lead-related complications. S-ICDs are an important development hindered largely by an inability to pace. Young patients stand to gain the most from a S-ICD as the cumulative risk of lead-related complications is high. A clinical framework to aid decision-making is presented.

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.

Prevention of Cardiac Implantable Electronic Device Infections: A Review

The importance of cardiac implantable electronic devices (CIEDs) in the treatment of cardiac rhythm disturbances, heart failure, and the prevention of sudden cardiac death is indisputable. However, CIED therapy is associated with complications, among which infections are particularly unfavourable in terms of prognosis. The diagnosis and management of CIED infections remain complex, with a significant impact on mortality and healthcare costs. For these reasons, the risk factors for CIED infections and methods of their prevention have been assessed in recent years. This review summarises the current state of knowledge on the subject. We also outlined the role of alternative methods, such as subcutaneous defibrillators, leadless pacemakers, and wearable cardioverter defibrillators.

Leadless Cardiac Pacing: New Horizons

Since the introduction of transvenous cardiac pacing leads, pacemaker system design has remained similar for several decades. Progressive miniaturisation of electronic circuitry and batteries has enabled a smaller, single pacing unit comprising the intracardiac electrodes, generator and computer. This review explores the development of leadless pacing, the clinical trials comparing leadless to transvenous pacing in addition to the future developments of multi-chamber leadless pacing.

Quantifying Cardiothoracic Variation with Posture and Respiration to Inform Cardiac Device Design

PURPOSE

With extravascular implantable cardioverter defibrillator leads placed beneath the sternum, it is important to quantify heart motion relative to the rib cage with postural changes and respiration.

METHODS

MRI scans from five males and five females were collected in upright and supine postures at end inspiration [n = 10 each]. Left and right decubitus [n = 8 each] and prone [n = 5] MRIs at end inspiration and supine MRIs at end expiration [n = 5] were collected on a subset. Four cardiothoracic measurements, six cardiac measurements, and six cardiac landmarks were collected to measure changes across different postures and stages of respiration.

RESULTS

The relative location of the LV apex to the nearest intercostal space was significantly different between the supine and decubitus postures (average ± SD difference: - 15.7 ± 11.4 mm; p < 0.05). The heart centroid to xipho-sternal junction distance was 9.7 ± 7.9 mm greater in the supine posture when compared to the upright posture (p < 0.05). Cardiac landmark motion in the lateral direction was largest due to postural movement (range 23-50 mm) from the left decubitus to the right decubitus posture, and less influenced by respiration (5-17 mm). Caudal-cranial displacement was generally larger due to upright posture (13-23 mm caudal) and inspiration (7-20 mm cranial).

CONCLUSIONS

This study demonstrates that the location of the heart with respect to the rib cage varies with posture and respiration. The gravitational effects of postural shifts on the heart position are roughly 2-3 times larger than the effects of normal respiration.

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.).

Emerging Concepts on Infection of Novel Cardiac Implantable Devices

Novel cardiac devices, including the MitraClip system, occluder devices, leadless pacemakers, and subcutaneous implantable cardioverter defibrillators (S-ICD), are mostly used in the management of patients who are at high risk for surgery and/or developing infections. Several mechanisms render most of these devices resistant to infection, including avoiding long transvenous access and novel manufacturing material. Since subjects who use these devices already endure several comorbid conditions, uncommon cases of device-associated infection could result in serious complications and increased mortality. In this review, we aim to summarize the current state of evidence on the incidence, clinical presentation, management, and prognosis of new cardiac devices' associated infection.

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.

S-ICDs: advantages and opportunities for improvement

INTRODUCTION

The subcutaneous implantable cardioverter defibrillator (S-ICD) is currently in its third generation and has been adopted in guidelines and in mainstream clinical practice. Considerable improvements have been made since the introduction of this device over a decade ago.

AREAS COVERED

A literature search was undertaken in Pubmed on articles relating to the S-ICD.

EXPERT OPINION

The therapy has been proven to be safe and effective and is a valuable option in selected patients. Nevertheless, there remain many shortcomings of the S-ICD which are discussed in this review, and which hopefully will be addressed by future generations of the device.