Feasibility of entirely subcutaneous ICD™ systems in patients with coronary artery disease

Opportunities and drawbacks of the subcutaneous defibrillator across different clinical settings

INTRODUCTION

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an established therapy for the prevention of sudden cardiac death (SCD) and an alternative to a transvenous implantable cardioverter-defibrillator system in selected patients. Beyond randomized clinical trials, many observational studies have described the clinical performance of S-ICD across different subgroups of patients.

AREAS COVERED

Our review aimed to describe the opportunities and drawbacks of the S-ICD, focusing on their use in special populations and across different clinical settings.

EXPERT OPINION

The choice to implant S-ICD should be based on the patient's tailored approach, which takes into account the adequate S-ICD screening at rest or during stress, the infective risk, the ventricular arrhythmia susceptibility, the progressive nature of the underlying disease, the work or sports activity, and the risk of lead-related complications.

Subcutaneous Versus Transvenous Implantable Defibrillator Therapy: A Systematic Review and Meta-Analysis of Randomized Trials and Propensity Score-Matched Studies

Background

Subcutaneous implantable cardioverter‐defibrillators (S‐ICDs) have been of great interest as an alternative to transvenous implantable cardioverter‐defibrillators (TV‐ICDs). No meta‐analyses synthesizing data from high‐quality studies have yet been published.

Methods and Results

An electronic literature search was conducted to retrieve randomized controlled trials or propensity score–matched studies comparing S‐ICD against TV‐ICD in patients with an implantable cardioverter‐defibrillator indication. The primary outcomes were device‐related complications and lead‐related complications. Secondary outcomes were inappropriate shocks, appropriate shock, all‐cause mortality, and infection. All outcomes were pooled under random‐effects meta‐analyses and reported as risk ratios (RRs) and 95% CIs. Kaplan–Meier curves of device‐related complications were digitized to retrieve individual patient data and pooled under a 1‐stage meta‐analysis using Cox models to determine hazard ratios (HRs) of patients undergoing S‐ICD versus TV‐ICD. A total of 5 studies (2387 patients) were retrieved. S‐ICD had a similar rate of device‐related complications compared with TV‐ICD (RR, 0.59 [95% CI, 0.33–1.04]; P=0.070), but a significantly lower lead‐related complication rate (RR, 0.14 [95% CI, 0.07–0.29]; P<0.0001). The individual patient data–based 1‐stage stratified Cox model for device‐related complications across 4 studies yielded no significant difference (shared‐frailty HR, 0.82 [95% CI, 0.61–1.09]; P=0.167), but visual inspection of pooled Kaplan–Meier curves suggested a divergence favoring S‐ICD. Secondary outcomes did not differ significantly between both modalities.

Conclusions

S‐ICD is clinically superior to TV‐ICD in terms of lead‐related complications while demonstrating comparable efficacy and safety. For device‐related complications, S‐ICD may be beneficial over TV‐ICD in the long term. These indicate that S‐ICD is likely a suitable substitute for TV‐ICD in patients requiring implantable cardioverter‐defibrillator implantation without a pacing indication.

Pitfalls of the S-ICD therapy: experiences from a large tertiary centre

Aim

The subcutaneous ICD (S-ICD) has evolved to a potential first option for many patients who have to be protected from sudden cardiac death. Many trials have underlined a similar performance regarding its effectiveness in relation to transvenous ICDs and have shown the expected benefits concerning infective endocarditis and lead failure. However, there have also been problems due to the peculiarities of the device, such as oversensing and myopotentials. In this study, we present patients from a large tertiary centre suffering from complications with an S-ICD and propose possible solutions.

Methods and results

All S-ICD patients who experienced complications related to the device (n = 40) of our large-scale single-centre S-ICD registry (n = 351 patients) were included in this study. Baseline characteristics, complications occurring and solutions to these problems were documented over a mean follow-up of 50 months. In most cases (n = 23), patients suffered from oversensing (18 cases with T wave or P wave oversensing, 5 due to myopotentials). Re-programming successfully prevented further oversensing episode in 13/23 patients. In 9 patients, generator or lead-related complications, mostly due to infectious reasons (5/9), occurred. Further problems consisted of ineffective shocks in one patient and need for antibradycardia stimulation in 2 patients and indication for CRT in 2 other patients. In total, the S-ICD had to be extracted in 10 patients. 7 of them received a tv-ICD subsequently, 3 patients refused re-implantation of any ICD. One other patient kept the ICD but had antitachycardic therapy deactivated due to inappropriate shocks for myopotential oversensing.

Conclusion

The S-ICD is a valuable option for many patients for the prevention of sudden cardiac death. Nonetheless, certain problems are immanent to the S-ICD (limited re-programming options, size of the generator) and should be addressed in future generations of the S-ICD.

Graphic abstract

Clinical experience regarding safety and diagnostic value of cardiovascular magnetic resonance in patients with a subcutaneous implanted cardioverter/defibrillator (S-ICD) at 1.5 T

BACKGROUND

Cardiovascular magnetic resonance (CMR) studies in patients with implanted cardioverter/defibrillators (ICD) are increasingly required in daily clinical practice. However, the clinical experience regarding the feasibility as well as clinical value of CMR studies in patients with subcutaneous ICD (S-ICD) is still limited. Besides safety issues, image quality and analysis can be impaired primarily due the presence of image artefacts associated with the generator.

METHODS

Twenty-three patients with an implanted S-ICD (EMBLEM, Boston Scientific, Marlborough, Massachusetts, USA; MR-conditional) with suspected cardiomyopathy and/or myocarditis underwent multi-parametric CMR imaging. Studies were performed on a 1.5 T CMR scanner after device interrogation and comprised standard a) balanced steady state free precession cine, b) T2 weighted-edema, c) velocity-encoded cine flow, d) myocardial perfusion, e) late-gadolinium-enhancement (LGE)-imaging and f) 3D-CMR angiography of the aorta. In case of substantial artefacts, alternative CMR techniques such as spoiled gradient-echo cine-sequences and wide-band inversion-recovery LGE (wb-LGE) sequences were applied.

RESULTS

Successful CMR studies could be performed in all patients without any case of unexpected early termination or relevant technical complication other than permanent loss of the S-ICD system beeper volume in 52% of our patients. Assessment of cine-CMR images was predominantly impaired in the left ventricular (LV) anterior, lateral and inferior wall segments and a switch to spoiled gradient echo-based cine-CMR allowed an accurate assessment of cine-images in N = 17 (74%) patients with only limited artefacts. Hyperintensity artefacts in conventional LGE-images were predominantly observed in the LV anterior, lateral and inferior wall segments and image optimisation by use of the wb-LGE was helpful in 15 (65%) cases. Aortic flow measurements and 3D-CMR angiography were assessable in all patients Perfusion imaging artefacts precluded a meaningful assessment in at least one half of the patients. A benefit in clinical-decision making was documented in 17 (74%) patients in the present study.

CONCLUSION

Safe 1.5 T CMR imaging was possible in all patients with an S-ICD, though the majority had permanent loss of the S-ICD beeper volume. Achieving good image quality may be challenging in some patients - particularly for perfusion imaging. Using spoiled gradient echo-based cine-sequences and wb-LGE sequences may help to reduce the extent of artefacts, thereby allowing accurate cardiac assessment. Thus, 1.5 T CMR studies should not be withhold in patients with S-ICD for safety concerns and/or fear of extensive imaging artefacts precluding successful image analysis.

Outcome differences and device performance of the subcutaneous ICD in patients with and without structural heart disease

BACKGROUND

The performance of the subcutaneous ICD (S-ICD™) has been described in different kinds of heart disease and has been proven to be an important advance in prevention of sudden cardiac death (SCD). While positive experiences with the S-ICD™ initially came from collectives of patients without structural heart diseases, positive results have also been collected from cohorts with structural heart disease.

MATERIALS AND METHODS

All S-ICD™ patients with either ischemic cardiomyopathy (ICM), dilated cardiomyopathy (DCM) or hypertrophic cardiomyopathy (HCM) as the main indication for ICD implantation (n = 144 patients) or electrical heart disease/idiopathic ventricular fibrillation (n = 83 patients) in our large-scaled single-center S-ICD™ registry were included in this study. Baseline characteristics, appropriate and inappropriate shocks, and complications were documented in a mean follow-up of 18 ± 15 months.

RESULTS

Baseline characteristics were significantly different between the two groups in most categories. In contrast, there was no difference concerning neither appropriate nor inappropriate shock delivery between the two groups. Also other outcome parameters such as need for surgical revisions and all-cause mortality did not differ. There was a significant difference between the first- and second-generation S-ICDs™ in inadequate shocks mainly driven by patients with HCM.

CONCLUSION

In our study, S-ICD™ performance was similar in patients with and without structural heart disease. Decision pro- or contra-S-ICD™ should be made rather on the basis of expected shock rate and probability of the need for future anti-tachycardia or anti-bradycardia pacing than in dependence of the underlying heart disease.