The Totally Subcutaneous Implantable Defibrillator

Shock Without Wires: A Look at Subcutaneous Implantable Cardioverter-Defibrillator Compared to Transvenous Implantable Cardioverter-Defibrillator for Ventricular Arrhythmias

Sudden cardiac death is a major cause of cardiovascular mortality in the United States with 250,000-450,000 deaths annually. Transvenous Implantable Cardioverter-Defibrillator (ICD) has been conventionally used for both primary and secondary prevention of ventricular tachycardia or fibrillation (VT/VF). It is also associated with a high risk of complications like hemothorax, pneumothorax, cardiac tamponade, lead failure, and increased risk for infections. Subcutaneous ICD (S-ICD) poses as a viable alternative with reduced chances of complications. This manuscript aims to review S-ICD as an alternative to conventional transvenous ICD and its efficacy. We conducted a Medline search of "Subcutaneous," "ICD," "transvenous," and "ventricular tachycardia or fibrillation (VT/VF)" to identify pivotal trials published before June 2021, for inclusion in this review. Major practice guidelines, trial bibliographies, and pertinent reviews were examined to ensure the inclusion of relevant trials. The following section reviews data from pivotal trials to review the efficacy of S-ICD for the termination of VT/VF. The S- ICD system consists of a pulse generator positioned over the sixth rib between the midaxillary and anterior axillary line and a tripolar parasternal electrode with the proximal and distal sensing electrodes positioned adjacent to the xiphoid process and manubriosternal junction, respectively. The conversion of the efficacy of the S-ICD after the first shock ranges from 88%-90.1% and 98.2%-100% after 5 shocks based on the current evidence. The device also has a 99% complication-free rate at 180 days with no increased complications even in ESRD patients. The PRAETORIAN trial showed non-inferiority of the S-ICD to transvenous ICD concerning device-related complications or inappropriate shocks in patients. S-ICD has several advantages including no need for fluoroscopy for implantation, decreased risk of infections, complications, and evidence of safety even in high-risk populations like ESRD. The limitations include the inherent lack of pacing abnormalities, the increase in inappropriate shocks compared to transvenous ICD, and non-reliability if there are baseline T wave abnormalities, especially in the inferior leads. Thus, S-ICD can be considered as an alternative to transvenous ICD in patients with an indication for defibrillator therapy but with no indication for pacing.

Subcutaneous ICD screening with the Boston Scientific ZOOM programmer versus a 12-lead ECG machine

BACKGROUND

The subcutaneous implantable cardioverter-defibrillator (S-ICD) requires preimplant screening to ensure appropriate sensing and reduce risk of inappropriate shocks. Screening can be performed using either an ICD programmer or a 12-lead electrocardiogram (ECG) machine. It is unclear whether differences in signal filtering and digital sampling change the screening success rate.

METHODS

Subjects were recruited if they had a transvenous single-lead ICD without pacing requirements or were candidates for a new ICD. Screening was performed using both a Boston Scientific ZOOM programmer (Marlborough, MA, USA) and General Electric MAC 5000 ECG machine (Fairfield, CT, USA). A pass was defined as having at least one lead that fit within the screening template in both supine and sitting positions.

RESULTS

A total of 69 subjects were included and 27 sets of ECG leads had differing screening results between the two machines (7%). Of these sets, 22 (81%) passed using the ECG machine but failed using the programmer and five (19%) passed using the ECG machine but failed using the programmer (P < 0.001). Four subjects (6%) passed screening using the ECG machine but failed using the programmer. No subject passed screening with the programmer but failed with the ECG machine.

CONCLUSION

There can be occasional disagreement in S-ICD patient screening between an ICD programmer and ECG machine, all of whom passed with the ECG machine but failed using the programmer. On a per lead basis, the ECG machine passes more subjects. It is unknown what the inappropriate shock rate would be if an S-ICD was implanted. Clinical judgment should be used in borderline cases.

Implantation of subcutaneous implantable cardioverter defibrillators in Europe: results of the European Heart Rhythm Association survey

AIMS

The purpose of this European Heart Rhythm Association (EHRA) survey is to provide an overview of the current use of subcutaneous cardioverter defibrillators (S-ICDs) across a broad range of European centres.

METHODS AND RESULTS

A questionnaire was sent via the internet to centres participating in the EHRA electrophysiology research network. Questions included standards of care and policies used for patient management, indications, and techniques of implantation of the S-ICDs. In total, 52 centres replied to the questionnaire. More than one-fourth of the responding centres does not implant the S-ICD (n = 14, 27%). The majority reported to have implanted <10 (50%) or 10-29 (23%) S-ICDs during the last 12 months. Lack of reimbursement (25%), non-availability (19%), and cost of the device (25%) seem to limit the use of the S-ICD. The most commonly reported indications for S-ICD implantation are a difficult vascular access (82%), a history of previous complicated transvenous ICD (8O%), young age (69%), or an anticipated higher risk of infection (63%). Inappropriate therapies were the most frequently reported major problems (38%), but the majority of respondents (51%) never encountered any issue after an S-ICD implantation. Most of the respondents (83%) anticipate significant increase of S-ICD use within the next 2 years.

CONCLUSION

This survey provides a contemporary insight into S-ICD implantation and management in the European electrophysiology centres, showing different approaches, depending on local policies. Cost issues or lack of reimbursement strongly influence the dissemination of the device. However, most respondents retain that S-ICD use will significantly increase in a very short time.

New directions in cardiac arrhythmia management: present challenges and future solutions

Cardiac arrhythmias are a major contributor to population morbidity and mortality. Enormous advances in arrhythmia management have occurred over the 60 years since the founding of the Montreal Heart Institute, but important challenges remain. The purpose of this article is to identify the areas of cardiac arrhythmia therapy that need improvement and to discuss the evolving approaches that promise solutions. Challenges in diagnosis, detection, and risk-stratification include difficulties in separating benign from high-risk syncope and pinpointing the underlying causes, the detection of silent atrial fibrillation in patients at risk of stroke, and inadequate identification of sudden-death risk. Implantable devices are limited by the need for battery and device replacements, device complications like infection and dysfunction, and lead complications like fracture, infection, or displacement. Antiarrhythmic drug therapy, although widely used, is plagued by a very limited range of available agents, supply issues, insufficient efficacy, and significant adverse effect risk. Health economic concerns include the high cost of new technologies, challenges in establishing cost effectiveness, and restrictive practices of government or third-party payers. Major improvements in arrhythmia management can be expected from new discoveries and technological developments in genetics, innovative diagnostic tools for arrhythmia monitoring, imaging and analysis, new approaches to antiarrhythmic drug development, biological therapies, and continuing improvement in implantable device technology like further miniaturization, leadless technology, and use of novel energy sources. As exciting as the developments in arrhythmia management have been in the past, we can look forward to exponential improvement in our ability to manage arrhythmia patients in the near future.