SMART Pass automatic deactivation of subcutaneous implantable cardioverter-defibrillators

BACKGROUND

The SMART Pass algorithm for subcutaneous implantable cardioverter-defibrillator prevents inappropriate shocks due to oversensing. The mechanisms and significance of SMART Pass deactivation remain unclear.

OBJECTIVE

The objective of this study was to assess whether SMART Pass deactivation is associated with inappropriate shocks and to elucidate the underlying mechanism.

METHODS

We retrospectively investigated 115 patients who underwent subcutaneous implantable cardioverter-defibrillator implantation between 2016 and 2021. SMART Pass deactivation and inappropriate shocks during follow-up were assessed. The QRS amplitudes of the subcutaneous (S-ECG) and 12-lead electrocardiogram (ECG) at the time of implantation (pre) and SMART Pass deactivation (post) were measured. The patients were divided into the SP-ON group with SMART Pass consistently on and the SP-OFF group with the experience of SMART Pass deactivation.

RESULTS

Three of 12 patients in the SP-OFF group experienced inappropriate shocks during a median follow-up of 1094 (interquartile range, 887-1502) days compared with 4 of 87 patients in the SP-ON group. Pre- and post-S-ECG QRS amplitudes were significantly lower in the SP-OFF group than in the SP-ON group (both P < .05), despite similar 12-lead ECG QRS amplitude in both groups. A significant temporary drop in the QRS amplitude of the S-ECG led to SMART Pass deactivation (pre-QRS amplitude vs amplitude at deactivation, P = .015; 95% CI, 0.3-1.9).

CONCLUSION

The rate of inappropriate shocks was numerically higher after SMART Pass deactivation. A low QRS amplitude in S-ECG was a potential risk factor for SMART Pass deactivation. Careful follow-up and suitable management are required for managing patients with risks of SMART Pass deactivation.

Efficacy and safety of the subcutaneous implantable cardioverter-defibrillator in patients with and without obesity: A meta-analysis

BACKGROUND

The subcutaneous implantable cardioverter-defibrillator (S-ICD) has emerged as an alternative to transvenous systems for prevention of sudden cardiac death. However, concerns have been raised regarding its efficacy and safety in obese individuals.

OBJECTIVE

The purpose of this study was to perform a meta-analysis to evaluate the efficacy and safety of the S-ICD in patients with obesity by assessing the relationship between body mass index (BMI) and clinical outcomes.

METHODS

A comprehensive search of multiple databases was conducted for English-language peer-reviewed studies reporting clinical outcomes in S-ICD recipients with (BMI ≥30 kg/m2) and without obesity (BMI <30 kg/m2). Data on preimplantation screening failure, defibrillation testing, complications, appropriate and inappropriate shocks, and survival were analyzed using standard, random-effects, meta-analytical techniques.

RESULTS

Twenty-nine studies involving 20,486 patients were included. There was no statistically significant difference in mean BMI values of patients with failed or successful preimplantation screening (mean difference -0.60 kg/m2; 95% confidence interval [CI] -2.06 to 0.86). Obesity was associated with higher rates of failed defibrillation testing at ≤65 J (odds ratio [OR] 2.16; 95% CI 1.39-3.35), and malpositioning/suboptimal positioning occurred more frequently in obese compared to nonobese patients (OR 3.37; 95% CI 1.76-6.44). Increased BMI as a continuous variable (per increase in 1 kg/m2 BMI) was associated with elevated defibrillation thresholds (OR 1.05; 95% CI 1.03-1.08); higher risk of complications (hazard ratio [HR] 1.04; 95% CI 1.02-1.05); a trend toward an increased number of appropriate shocks (HR 1.02; 95% CI 1.00-1.04); and no significant increase in the risk of inappropriate shocks (HR 1.01; 95% CI 0.99-1.03).

CONCLUSION

This meta-analysis underscores the importance of considering obesity in S-ICD implantation decisions. Although S-ICD remains effective in obese patients, attention to potential technical challenges and higher complication rates is warranted.

Lights and shadows of subcutaneous implantable cardioverter-defibrillator in Brugada syndrome

Currently the cornerstone of therapy for ventricular arrhythmic complications and sudden cardiac death prevention in Brugada syndrome (BrS) is an implantable cardioverter-defibrillator (ICD). BrS patient population differs from the majority of patients with an ICD implanted for structural heart disease, and as widely known, transvenous ICD (TV-ICD) systems have been associated with high complication rates in patients with BrS. Technological evolution of these devices has certainly reduced complications due to the device itself, but a careful preimplant screening of these patients is still essential. To date, criteria for an adequate screening process to select suitable candidates for a subcutaneous implantable cardioverter-defibrillator (S-ICD) from patients with BrS are sometimes nonstandardized and often lack important precautions that are instead fundamental to select the most suitable type of ICD for these patients. To better select suitable candidates for an S-ICD from patients with BrS, a full screening process should include screening during or immediately after an exercise test and after a drug provocation challenge test. We report an analysis of the "lights and shadows" of S-ICD for a correct use of this device in patients with BrS.

Brugada Syndrome

Brugada syndrome (BrS) is an "inherited" condition characterized by predisposition to syncope and cardiac arrest, predominantly during sleep. The prevalence is ∼1:2,000, and is more commonly diagnosed in young to middle-aged males, although patient sex does not appear to impact prognosis. Despite the perception of BrS being an inherited arrhythmia syndrome, most cases are not associated with a single causative gene variant. Electrocardiogram (ECG) findings support variable extent of depolarization and repolarization changes, with coved ST-segment elevation ≥2 mm and a negative T-wave in the right precordial leads. These ECG changes are often intermittent, and may be provoked by fever or sodium channel blocker challenge. Growing evidence from cardiac imaging, epicardial ablation, and pathology studies suggests the presence of an epicardial arrhythmic substrate within the right ventricular outflow tract. Risk stratification aims to identify those who are at increased risk of sudden cardiac death, with well-established factors being the presence of spontaneous ECG changes and a history of cardiac arrest or cardiogenic syncope. Current management involves conservative measures in asymptomatic patients, including fever management and drug avoidance. Symptomatic patients typically undergo implantable cardioverter defibrillator insertion, with quinidine and epicardial ablation used for patients with recurrent arrhythmia. This review summarizes our current understanding of BrS and provides clinicians with a practical approach to diagnosis and management.

Evaluation of subcutaneous implantable cardioverter-defibrillator performance in patients with ion channelopathies from the EFFORTLESS cohort and comparison with a meta-analysis of transvenous ICD outcomes

Background

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an alternative to conventional transvenous ICD (TV-ICD) therapy to reduce lead complications.

Objective

To evaluate outcomes in channelopathy vs patients with structural heart disease in the EFFORTLESS-SICD Registry and with a previously reported TV-ICD meta-analysis in channnelopathies.

Methods

The EFFORTLESS registry includes 199 patients with channelopathies (Brugada syndrome 83, long QT syndrome 24, idiopathic ventricular fibrillation 78, others 14) and 786 patients with structural heart disease.

Results

Channelopathy patients were younger (39 ± 14 years vs 51 ± 17 years; P < .001) with left ventricular ejection fraction 59% ± 9% vs 41% ± 18% (P < .001). The complication rate (follow-up: 3.2 ± 1.5 years vs 3.0 ± 1.5 years) was similar: 13.6% vs 11.2% (P = .42). Appropriate shocks rates were 9.5% vs 10.8% (P = .70), with shocks for monomorphic ventricular tachycardia being 2.0% vs 6.9% (P < .02) and for polymorphic ventricular tachycardia/ventricular fibrillation (VT/VF) 8.0% vs 5.7% (P = .30). Conversion effectiveness of VT/VF episodes was similar: 36 of 37 (97.3%) vs 151 of 155 (97.4%, P = .59). VT/VF storm event (2% vs 0.9%, P = .33) and lower inappropriate shock (IAS) (8.5% vs 12.5%, P = .12) rates were statistically similar between channelopathy and non-channelopathy patients, with 45.5% channelopathy vs 31.4% non-channelopathy patients managed with a conditional zone > 200 beats per minute (P = .0002). Annualized appropriate shock, IAS, and complication rates appear to be lower for the S-ICD vs meta-analysis TV-ICD patients, particularly lead complications.

Conclusion

EFFORTLESS demonstrates similar S-ICD efficacy and a nonsignificant, lower rate of IAS in channelopathy patients as compared to structural heart disease. Comparable IAS rates were achieved with the device programmed to higher rates for channelopathy patients.

Brugada syndrome: Eligibility for subcutaneous implantable cardioverter-defibrillator after exercise stress test

INTRODUCTION

Brugada syndrome (BrS) is a channelopathy associated with ventricular arrhythmias and sudden cardiac death. In patients at high risk of sudden death, an implantable cardioverter-defibrillator is indicated. Subcutaneous implantable cardioverter-defibrillators (S-ICDs) are an alternative to transvenous systems, with reduced risk of infection and complications associated with system extraction or explantation.

OBJECTIVE

To test electrocardiographic eligibility for S-ICD placement after exercise stress testing (EST) in patients with BrS.

METHODS

The sample included 35 consecutive patients with BrS. Electrocardiographic eligibility was assessed using the Boston Scientific model 2889 EMBLEM™ S-ICD automated screening tool, in four phases: decubitus and orthostatism, and before and after EST. Those who had at least one acceptable vector in the four measurements were considered eligible.

RESULTS

In this study, 71.4% of patients were male and mean age was 53.86±12 years. In screening prior to EST, 14.3% of patients (n=5) were not eligible for an S-ICD. There was a statistically significant association between ineligibility and presence of complete right bundle branch block and history of syncope. After EST, 16.7% of initially eligible patients no longer had eligible vectors (n=5).

CONCLUSION

In this study, 16.7% of patients previously eligible for an S-ICD were no longer eligible after EST. This result demonstrates the importance of screening after EST in all patients with BrS and with indication for an S-ICD, and may influence decisions concerning which ICD to implant or whether to institute pharmacological measures that avoid inappropriate therapies.

Myopotential Oversensing Is a Major Cause of Inappropriate Shock in Subcutaneous Implantable Defibrillator in Japan

Previous study has identified marked differences in patient characteristics and causes of inappropriate shock (IAS) between Japan and the Western societies in terms of subcutaneous implantable cardioverter-defibrillator (S-ICD). However, evidence of IAS in Asian populations including Japan has been limited to one observational study.Thus, we conducted a single-center registry study that tracks the postoperative course of 61 consecutive patients who received S-ICD from February 2016 to January 2020. Our findings showed that IAS occurred in 9.8% of the study population (6/61), which is comparable to the previously reported incidence. Remarkably, T-wave oversensing did not result in an IAS (0/6). Instead, myopotential oversensing was determined to have caused the most IAS events (4/6), while atrial fibrillation ranked second (2/6). A provocation maneuver (e.g., abdominal clench, push-ups, lifting a heavy item) reproduced myopotential noise disguised as R-waves, which should potentially trigger an IAS if uninterrupted. R-wave amplitude of the IAS group appeared relatively low compared to that of the non-IAS group although this finding was not tested significant. Furthermore, no temporal changes were noted in R-wave amplitude between the time of implantation and IAS events, suggesting that it is neither constantly low nor acutely dropped R-wave amplitude but a relatively high noise level that drives IAS. All the myopotential-IAS patients were found to be male. Right-sided lead implantation was associated with a higher incidence of IAS.This study highlights the fact that IAS continues to occur due to myopotential noise oversensing instead of T-wave oversensing. To minimize the risk of IAS, it is desirable to search and secure high R-wave voltage.

Spotlight on S-ICD™ therapy: 10 years of clinical experience and innovation

Subcutaneous ICD (S-ICD™) therapy has been established in initial clinical trials and current international guideline recommendations for patients without demand for pacing, cardiac resynchronization, or antitachycardia pacing. The promising experience in ‘ideal’ S-ICD™ candidates increasingly encourages physicians to provide the benefits of S-ICD™ therapy to patients in clinical constellations beyond ‘classical’ indications of S-ICD™ therapy, which has led to a broadening of S-ICD™ indications in many centres. However, the decision for S-ICD™ implantation is still not covered by controlled randomized trials but rather relies on patient series or observational studies. Thus, this review intends to give a contemporary update on available empirical evidence data and technical advancements of S-ICD™ technology and sheds a spotlight on S-ICD™ therapy in recently discovered fields of indication beyond ideal preconditions. We discuss the eligibility for S-ICD™ therapy in Brugada syndrome as an example for an adverse and dynamic electrocardiographic pattern that challenges the S-ICD™ sensing and detection algorithms. Besides, the S-ICD™ performance and defibrillation efficacy in conditions of adverse structural remodelling as exemplified for hypertrophic cardiomyopathy is discussed. In addition, we review recent data on potential device interactions between S-ICD™ systems and other implantable cardio-active systems (e.g. pacemakers) including specific recommendations, how these could be prevented. Finally, we evaluate limitations of S-ICD™ therapy in adverse patient constitutions, like distinct obesity, and present contemporary strategies to assure proper S-ICD™ performance in these patients. Overall, the S-ICD™ performance is promising even for many patients, who may not be ‘classical’ candidates for this technology.

Candidacy for a Subcutaneous Implantable Cardioverter Defibrillator in Patients with Cardiac Resynchronization Therapy

In patients requiring an implantable cardioverter defibrillator (ICD), the combined use of a prior pacemaker and a subcutaneous ICD (S-ICD) could be an alternative treatment option to implantation of new leads or upgrading of pacemakers to an ICD if vascular access is limited. Here, we assessed the prevalence of S-ICD's eligibility according to surface electrogram screening in those receiving cardiac resynchronization therapy (CRT). S-ICD's eligibility was assessed in patients with a CRT pacemaker or a CRT defibrillator using the S-ICD template screening tool. Eligibility was defined as fulfillment of the template in both supine and upright positions in one or more leads during biventricular pacing. Among 44 patients (34 men, age: 67 ± 12), 36 (82%) were found to be eligible. The T/QRS amplitude ratio in lead II was significantly lower in those who were eligible (0.31 ± 0.16 versus 0.44 ± 0.18 in the ineligible group, P = 0.04). The lead position, underlying disease, and other electrocardiographic findings were not different between those who were eligible and those who were not. The majority of patients with biventricular pacing were eligible for S-ICD based on current screening tests and may benefit from this treatment. Further study is required.