Ten years of subcutaneous defibrillator therapy: Consolidated clinical evidence and future perspectives

The subcutaneous implantable cardioverter defibrillator (S-ICD) was developed as an alternative to the traditional transvenous implantable cardioverter defibrillator (TV-ICD), aiming to provide easier implantation, simplified detection algorithm of malignant ventricular arrhythmias and prevention from placing components in the cardiovascular system. The S-ICD is implanted subcutaneously or intramuscularly with the generator placed in the left midaxillary line and the lead tunneled subcutaneously in the left para-sternal region. Preimplant electrocardiogram screening is recommended to prevent implantation in patients at high risk of T wave over-sensing. Currently, the S-ICD is unsuitable for patients requiring pacing or cardiac resynchronization. Since the beginning, the S-ICD underwent extensive preclinical investigation until the first prospective multicentre trial demonstrating high efficacy and safety led to market release. While earlier studies focused on younger patients with higher ejection fraction, more recent studies showed favorable outcomes even in patients with comorbidities similar to those typically observed in patients receiving TV-ICD. The development of second and third generation devices has contributed to reduce inappropriate shocks and overcome previous limitations. The aim of this paper is to review the evidence in the literature over the past decade supporting S-ICD as a valid alternative to TV-ICD in terms of safety and efficacy, highlighting the improvements in technology, as well as outcomes.

Intra-Abdominal Hemorrhage Triggering Inappropriate Therapy From a Subcutaneous Defibrillator

The SMART Pass filter (Boston Scientific) aims to reduce inappropriate shocks (IASs) from subcutaneous implantable cardioverter-defibrillators by filtering out low-frequency signals such as T waves. However, this filter is deactivated in the presence of diminished R-wave sensing. We describe a case of IAS in the setting of extensive intra-abdominal hemorrhage.

Inappropriate Subcutaneous Implantable Cardioverter-defibrillator Shocks-A Rare Case of Triple Counting

Sudden cardiac death (SCD) caused by ventricular tachyarrhythmias is a significant contributor to cardiovascular deaths worldwide. Implantable cardioverter-defibrillators (ICDs) have shown efficacy in preventing and reducing mortality from SCD, but traditional transvenous ICDs have inherent challenges and drawbacks, such as lead fractures, lead-associated endocarditis, and lead failure. To address these issues, subcutaneous ICDs (S-ICDs) have been developed. S-ICDs lack pacing capacity but are a valid alternative for patients at high risk for infection or with difficult venous access. Pre-implantation screening can help prevent inappropriate device shocks. We present a case in which a patient received inappropriate S-ICD therapy, which was attributed to the triple counting of P-, R-, and T-waves in a patient with sinus rhythm. This is an unusual occurrence, and, to the best of our knowledge, there are only a limited number of case reports documenting inappropriate shocks due to the oversensing of P-waves and T-waves.

Voltage gradients in transvenous and subcutaneous defibrillation and their risk of myocardial damage

INTRODUCTION

Transvenous implantable cardioverter-defibrillator (ICD) shocks have been associated with cardiac biomarker elevations and are thought in some cases to contribute to adverse clinical outcomes and mortality, possibly from myocardium exposed to excessive shock voltage gradients. Currently, there are only limited data for comparison with subcutaneous ICDs. We sought to compare ventricular myocardium voltage gradients resulting from transvenous (TV) and subcutaneous defibrillator (S-ICD) shocks to assess their risk of myocardial damage.

METHODS

A finite element model was derived from thoracic magnetic resonance imaging (MRI). Voltage gradients were modeled for an S-ICD with a left-sided parasternal coil and a left-sided TV-ICD with a mid-cavity, a septal right ventricle (RV) coil, or a dual coil lead (TV mid, TV septal, TV septal +  superior vena cava [SVC]). High gradients were defined as > 100 V/cm.

RESULTS

The volumes of ventricular myocardium with high gradients > 100 V/cm were 0.02, 2.4, 7.7, and 0 cc for TV mid, TV septal, TV septal + SVC, and S-ICD, respectively.

CONCLUSION

Our models suggest that S-ICD shocks produce more uniform gradients in the myocardium, with less exposure to potentially damaging electrical fields, compared to TV-ICDs. Dual coil TV leads yield higher gradients, as does closer proximity of the shock coil to the myocardium.

Subcutaneous versus transvenous implantable cardioverter defibrillators in children and young adults: A meta-analysis

INTRODUCTION

The implantable cardioverter defibrillator (ICD) has been demonstrated to successfully prevent sudden cardiac death (SCD) in children and young adults. A wide range of device-related complications/malfunctions have been described, which depend on the intrinsic design of the defibrillation system (transvenous-implantable cardioverter defibrillator [TV-ICD] vs. subcutaneous-implantable cardioverter defibrillator [S-ICD]).

OBJECTIVE

To compare the device-related complications and inappropriate shocks with TV-ICD versus S-ICD.

METHODS AND RESULTS

Electronic databases were queried for studies focusing on the prevention of SCD in children and young adults with TV-ICD or S-ICD. The effect size was estimated using a random-effect model as odds ratio (OR) and relative 95% confidence interval (CI). The primary endpoint was a composite of any device-related complications and inappropriate shocks. We identified a total of five studies including 236 patients (Group S-ICD: 76 patients; Group TV-ICD: 160 patients) with a mean follow-up time of 54.2 ± 24.9 months. S-ICD implantation contributed to a significant reduction in the risk of the primary endpoint of any device-related complications and inappropriate shocks (OR: 0.18; 95% CI: 0.05-0.73; p = .02). S-ICD was also associated with a significantly lower incidence of inappropriate shocks (OR: 0.28; 95% CI: 0.11-0.74; p = .01) and lead-related complications (OR: 0.18; 95% CI: 0.05-0.66; p = .01). A trend toward a higher risk of pocket complications (OR: 5.91; 95% CI: 0.98-35.63; p = .05) was recorded in patients with S-ICD.

CONCLUSION

Children and young adults undergoing S-ICD implantation may have a lower risk of a composite of device-related complications and inappropriate shocks, compared to TV-ICD patients.

Subcutaneous Implantable Cardioverter Defibrillators for the Prevention of Sudden Cardiac Death: Pediatric Single-Center Experience

BACKGROUND

The subcutaneous implantable cardioverter defibrillator (S-ICD) was developed as an alternative to the transvenous ICD, to prevent lead-related complications associated with the latter. The absence of intravascular or intracardiac components offers potential advantages to pediatric patients.

AIMS

The aim of the study is to present an overview of our experience with S-ICDs in the pediatric center that, currently, has performed the largest number of implantations in children in Poland.

METHODS

Retrospective analysis of data from medical history, qualification, implantation procedure, and S-ICD post-implantation observations in 11 pediatric patients were performed.

RESULTS

S-ICDs were implanted in 11 patients, 8 boys and 3 girls, aged 12-17 years. The S-ICD was implanted for primary prevention in seven patients: four with hypertrophic cardiomyopathy (HCM), two with dilated cardiomyopathy (DCM), and one with arrhythmogenic right ventricular cardiomyopathy (ARVC). It was implanted for secondary prevention in four patients: two with sudden cardiac arrest (SCA) in the course of idiopathic ventricular fibrillation (IVF), one with long QT syndrome (LQTS) after probable SCA, and one with Brugada syndrome after SCA. In all patients, the device was implanted intramuscularly. One patient did not have a defibrillation test performed due to the presence of an intracardiac thrombus. In one patient, during screening, it was decided to implant an electrode on the right side of the sternum. There were no early or late complications with any of the procedures. So far, no inadequate discharges have been observed.

CONCLUSIONS

Our results prove the efficacy of the S-ICD treatment option along with technically simple surgery, which supports its further and more widespread application in children.

Significantly less inappropriate shocks in ischemic patients compared to non-ischemic patients: The S-ICD experience of a high volume single-center

BACKGROUND

The subcutaneous cardioverter-defibrillator (S-ICD) continues to be preferentially used in relatively young patients, with less advanced heart disease.

OBJECTIVE

We, therefore, studied the short and long-term efficacy and safety of the S-ICD in subgroups of patients, which are underreported at present.

METHODS

A total of 218 patients between November 2010 and February 2019 undergoing S-ICD with a follow up of at least 6 months implantation were included in a prospective registry. Mean follow up was 38 months.

RESULTS

The most common indication for S-ICD implantation was ischemic cardiomyopathy (n = 106, 49%). Complication rate needing invasive intervention was 9% (n = 21). Appropriate shock rate in patients with an S-ICD was 3.5%/year. A total of 30 inappropriate shocks (IAS) occurred in 19 patients (8.7%; 2.7%/year). The proportion of appropriate and inappropriate shock rates in patients with different cardiomyopathies shows remarkable variances. There were significant more IAS (3.6%/year vs. 1.7%/year, p = .048) in patients with non-ischemic cardiomyopathy versus patients with ischemic cardiomyopathy. Multivariate analysis identified, besides type of cardiomyopathy, atrial fibrillation (AF) as predictor for IAS.

CONCLUSION

In this real-world prospective registry we analyzed S-ICD performance in the more traditional ICD patient. Patients with ischemic cardiomyopathy had significantly less inappropriate therapy compared to patients with non-ischemic cardiomyopathy and appear to be appropriate patients for this type of device.

Novel Use of a Rotating Mechanical Dilator Sheath for S-ICD Lead Extraction

A 53-year-old man with a subcutaneous implantable cardioverter-defibrillator (S-ICD) presented with inappropriate shocks. He underwent device extraction, and the lead was freed using a rotating mechanical dilator sheath. As patients with S-ICDs get older, extractions will become more complicated and more common. We have described a novel method of S-ICD lead extraction. (Level of Difficulty: Advanced.).

Rate and impact on patient outcome and healthcare utilization of complications requiring surgical revision: Subcutaneous versus transvenous implantable defibrillator therapy

INTRODUCTION

Comparison data on management of device-related complications and their impact on patient outcome and healthcare utilization between subcutaneous implantable cardioverter-defibrillator (S-ICD) and transvenous ICD (TV-ICD) are lacking. We designed this prospective, multicentre, observational registry to compare the rate, nature, and impact of long-term device-related complications requiring surgical revision on patient outcome and healthcare utilization between patients undergoing S-ICD or TV-ICD implantation.

METHODS AND RESULTS

A total of 1099 consecutive patients who underwent S-ICD or TV-ICD implantation were enrolled. Propensity matching for baseline characteristics yielded 169 matched pairs. Rate, nature, management, and impact on patient outcome of device-related complications were analyzed and compared between two groups. During a mean follow-up of 30 months, device-related complications requiring surgical revision were observed in 20 patients: 3 in S-ICD group (1.8%) and 17 in TV-ICD group (10.1%; p = .002). Compared with TV-ICD patients, S-ICD patients showed a significantly lower risk of lead-related complications (0% vs. 5.9%; p = .002) and a similar risk of pocket-related complications (0.6 vs. 2.4; p = .215) and device infection (0.6% vs. 1.2%; p = 1.000). Complications observed in S-ICD patients resulted in a significantly lower number of complications-related rehospitalizations (median 0 vs. 1; p = .013) and additional hospital treatment days (1.0 ± 1.0 vs. 6.5 ± 4.4 days; p = .048) compared with TV-ICD patients.

CONCLUSIONS

Compared with TV-ICD, S-ICD is associated with a lower risk of complications, mainly due to a lower risk of lead-related complications. The management of S-ICD complications requires fewer and shorter rehospitalizations.

Subcutaneous implantable cardioverter-defibrillator electrode fracture: Follow-up, troubleshooting, and evaluation

The subcutaneous-implantable cardioverter-defibrillator (S-ICD) and its electrode were developed to avoid long-term complications of transvenous leads in the vasculature. We report a case of unexpected, inappropriate S-ICD shocks due to oversensing of high-amplitude, nonphysiologic, electrical noise artifacts that were not preceded by high-impedance alerts or sensing electrogram noise detections. Following explant, high-magnification X-ray imaging of the S-ICD electrode demonstrated partial fracture of the distal sensing conductor located near a short radius bend in the electrode at the electrode-header interface. Clinicians should be aware of a potential for fatigue failure fracture of the S-ICD electrode. Recommendations for systematic S-ICD follow-up and troubleshooting are discussed.

Outcomes of two versus three incision techniques: Results from the subcutaneous ICD post-approval study

BACKGROUND

Traditionally, implantation of the subcutaneous implantable cardioverter defibrillator (S-ICD) requires incisions near the lateral chest wall, the xyphoid, and the superior sternal region (three-incision technique [3IT]). A two-incision technique (2IT) avoids the superior incision and has been shown to be a viable alternative in small studies with limited follow-up.

OBJECTIVES

To report on the long-term safety and efficacy of the 2IT compared to the 3IT procedure in a large patient cohort.

METHODS

Patients enrolled in the S-ICD post approval study (PAS) were stratified by procedural technique (2IT vs. 3IT). Baseline demographics, comorbidities and procedural outcomes were collected. Complications and S-ICD effectiveness in treating ventricular arrhythmias through an average 3-year follow-up period were compared.

RESULTS

Of 1637 patients enrolled in the S-ICD PAS, 854 pts (52.2%) were implanted using the 2IT and 782 were implanted using the 3IT (47.8%). The 2IT became more prevalent over time, increasing from 40% to 69% of implants (Q1-Q4). Mean procedure time was shorter with 2IT (69.0 vs. 86.3 min, p < .0001). No other differences in outcomes were observed between the two groups, including rates of infection, electrode migration, inappropriate shocks and first shock efficacy for treating ventricular arrhythmias.

CONCLUSION

In this large cohort of patients implanted with an S-ICD and followed for 3 years the 2IT was as safe and effective as the 3IT while significantly reducing procedure time.

A novel screening tool to unmask potential interference between S-ICD and left ventricular assist device

INTRODUCTION

In patients with a left ventricular assist device (LVAD), the subcutaneous implantable cardioverter-defibrillator (S-ICD) can be an alternative to transvenous ICD systems due to reduced risk of systemic infection, which could lead to extraction of the ICD as well as the LVAD. S-ICD eligibility is lower in patients with LVAD than in patients with end-stage heart failure without LVAD. Several reports have shown inappropriate S-ICD therapy in the coexistence of LVAD and S-ICD. The aim of the present study was to evaluate S-ICD eligibility in patients with LVAD using the established electrocardiogram (ECG)-based screening test as well as a novel device-based screening test to identify potentially inappropriate S-ICD sensing in this specific patient cohort.

METHODS AND RESULTS

The present study included 115 patients implanted with an LVAD. The standard ECG-based screening test and a novel device-based screening test were performed in all patients. Eighty patients (70%) were eligible for S-ICD therapy with the standard ECG-based screening test. Performance of the novel device-based screening test identified device-device interference in 14 of these 80 patients (12%).

CONCLUSION

Using a novel extended device-based S-ICD screening method, a small number of patients with LVAD deemed eligible for S-ICD with the standard ECG-based screening test exhibit device-device interference. Careful S-ICD screening should be performed in patients with LVAD, who are candidates for S-ICD therapy, to prevent inappropriate sensing or ICD therapy.

1-Year Prospective Evaluation of Clinical Outcomes and Shocks: The Subcutaneous ICD Post Approval Study

OBJECTIVES

This study evaluated spontaneous arrhythmias and clinical outcomes in the S-ICD System PAS (Subcutaneous Implantable Cardioverter-Defibrillator Post Approval Study) cohort.

BACKGROUND

The U.S. S-ICD PAS trial patient population more closely resembles transvenous ICD cohorts than earlier studies, which included many patients with little structural heart disease and few comorbidities. Early outcomes and low peri-operative complication rates were demonstrated in the S-ICD PAS cohort, but there are no data detailing spontaneous arrhythmias and clinical outcomes.

METHODS

The S-ICD PAS prospective registry included 1,637 de novo patients from 86 U.S. centers. Descriptive statistics, Kaplan-Meier time to event, and multivariate logistic regression were performed using data out to 365 days.

RESULTS

Patients (68.5% men; mean ejection fraction of 32.0%; 42.9% ischemic; 13.4% on dialysis) underwent implantation for primary (76.6%) or secondary prevention indication. The complication-free rate was 92.5%. The appropriate shock (AS) rate was 5.3%. A total of 395 ventricular tachycardia (VT) or fibrillation (VF) episodes were appropriately sensed, with 131 (33.2%) self-terminating. First and final shock efficacy (up to 5 shocks) for the 127 discrete AS episodes were 91.3% and 100.0%, respectively. Discrete AS episodes included 67 monomorphic VT (MVT) and 60 polymorphic VT (PVT)/VF, with first shock efficacy of 95.2% and 86.7%, respectively. There were 19 storm events in 18 subjects, with 84.2% conversion success. Storm episodes were more likely PVT/VF (98 of 137).

CONCLUSIONS

In the first year after implantation, a predominantly primary prevention population with low ejection fraction demonstrated a high complication-free rate and spontaneous event shock efficacy for MVT and PVT/VF arrhythmias at rapid ventricular rates. (Subcutaneous Implantable Cardioverter-Defibrillator System Post Approval Study [S-ICD PAS; NCT01736618).

S-ICD is effective in preventing sudden death in arrhythmogenic cardiomyopathy athletes during exercise

Here, we describe the cases of two elite athletes, with a diagnosis of arrhythmogenic cardiomyopathy (ACM), in which a subcutaneous implantable cardioverter defibrillator (S-ICD) has been implanted. Both patients experienced a ventricular tachycardia during exercise and received effective S-ICD shocks that interrupted arrhythmias. This report reveals for the first time that the S-ICD is effective in reverting arrhythmias in ACM patients, even during exercise. Moreover, these cases may confirm that competition/physical activity is associated with ICD shocks.

Simultaneous leadless pacemaker and subcutaneous implantable cardioverter-defibrillator implantation-When vascular options have run out

An end-stage renal failure patient who was planned for a left brachioaxillary arteriovenous graft required an implantable cardioverter-defibrillator for secondary prevention of ventricular tachycardia and a pacemaker for complete heart block but was found to have a right subclavian venous occlusion. Due to the lack of vascular access, we performed a successful subcutaneous implantable cardioverter-defibrillator (S-ICD) and leadless pacemaker implantation. There was no interaction between the devices at the time of implantation, during defibrillation testing and following an appropriate defibrillation therapy.

An indissoluble knot: An unexpected troubleshooting during Micra implantation

Micra is a transcatheter leadless pacing system delivered percutaneously through femoral vein access into the right ventricle. We are going to describe an initially standard procedure, with an unexpected troubleshooting at the end: the impossibility to release the device and retract the delivery due to a knot in the tether.

Streamlined Surgical Draping Reduces Subcutaneous Implantable Cardioverter-defibrillator Implant Procedure Preparation Time

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is a proven alternative to transvenous implantable cardioverter-defibrillator systems. One critique of S-ICD use, however, has been the time required for implantation. Here, we discuss the use of an alternative surgical draping technique to reduce preparation time for device implantation.

Change of sensing vector in the subcutaneous ICD during follow-up and after device replacement

BACKGROUND

The subcutaneous implantable cardioverter defibrillator (S-ICD) has been established as a valuable alternative to transvenous ICD for prevention of sudden cardiac death. The system automatically chooses the optimal sensing vector. However, during follow-up and especially after device replacement we observed a change of the suggested sensing vector in automatic setup. Therefore, we analyzed frequency and reasons of vector change and its impact on inappropriate shocks (IAS).

MATERIAL AND METHODS

Between June 2010 and December 2017, a total of 216 patients with S-ICD^® were included in this analysis. In all patients sensing vectors at the time of implantation, during follow-up, and after device replacement were investigated. Median follow-up time was 27.3 ± 25.3 months.

RESULTS

A change of the initial vector was seen in 77 patients (35.7%). The most frequent reason for vector change was the postoperative setup in supine and erect position in 54 patients (70.1%). In 12 patients (15.5%), the vector was manually changed due to inappropriate sensing and/or therapies. Routine setup during follow-up led to automatic vector change in 10 cases (13.0%). In only 1 patient the vector was manually changed due to oversensing in an exercise treadmill test. In 27 patients, the device was replaced due to battery depletion and in 6 of these patients the sensing vector was changed by the automatic setup. Vector change did not have an impact for inappropriate therapies in the follow-up; only 1 patient received an IAS due to an inadvertent vector change after device replacement.

CONCLUSION

In the present study, a significant number of S-ICD^® patients had a manual or automatic vector change during follow-up and after device replacement. The study underlines the importance of a thoroughly performed screening and at least two valuable sensing vectors preimplant. Further studies are needed to evaluate the necessity of a routine automatic setup during follow-up.

Clinical parameters to optimize patient selection for subcutaneous and transvenous implantable defibrillator therapy

BACKGROUND

The subcutaneous implantable cardioverter-defibrillator (S-ICD) lacks the antitachycardia pacing (ATP) capability of tranvenous ICDs (TV-ICD). S-ICD patient selection can be challenging as some patients may benefit from ATP. We aim to identify clinical predictors of ATP benefit, in order to improve patient selection for S-ICD or TV-ICD therapy.

METHODS

De novo single- and dual-chamber TV-ICD patients implanted between March 2011 and December 2015 were included. Ventricular arrhythmias terminated by ATP and not followed by a shock were considered successful ATP therapy. Cox proportional hazard analysis was performed to assess the adjusted effect of multiple predictors for appropriate ATP and shock therapy.

RESULTS

Note that 431 patients were included with a median follow-up of 26 months. Ninety-nine patients (23%) received appropriate ATP therapy, which terminated the arrhythmia in 67%. A history of nonsustained ventricular tachycardia (NSVT) or monomorphic VT (MVT) was the only predictor of appropriate ATP therapy in the multivariable model (hazard ratio [HR] 2.73, P < 0.001). Sixty-five of 221 patients with a history of NS (VT) received appropriate ATP (29%) versus 24 patients (11%) without a history NS (VT) (P < 0.001). A secondary prevention indication was the only predictor in the multivariate model for appropriate shock therapy (HR 1.82, P  =  0.05).

CONCLUSION

A history of NSVT or MVT is a significant predictor for appropriate and successful ATP therapy. One in three patients with NSVT or MVT received appropriate ATP versus one in 10 patients without a history of NSVT or MVT over a 2-year period of follow-up.

Cardiac implantable electronic device and vascular access: Strategies to overcome problems

For arrhythmia treatment or sudden cardiac death prevention in hemodialysis patients, there is a frequent need for placement of a cardiac implantable electronic device (pacemaker, implantable cardioverter defibrillator, or cardiac resynchronization device). Leads from a cardiac implantable electronic device can cause central vein stenosis and carry the risk of tricuspid regurgitation or contribute to infective endocarditis. In patients with end-stage kidney disease requiring vascular access and cardiac implantable electronic device, the best strategy is to create an arteriovenous fistula on the contralateral upper limb for a cardiac implantable electronic device and avoidance of central vein catheter. Fortunately, cardiac electrotherapy is moving toward miniaturization and less transvenous wires. Whenever feasible, one should avoid transvenous leads and choose alternative options such as subcutaneous implantable cardioverter defibrillator, epicardial leads, and leadless pacemaker. Based on recent reports on the leadless pacemaker/implantable cardioverter defibrillator effectiveness, in patients with rapid progression of chronic kidney disease (high risk of renal failure) or glomerular filtration rate <20 mL/min/1.73 m², this option should be considered by the implanting cardiologist for future access protection.

Safety, Efficacy and Evidence Base for Use of the Subcutaneous Implantable Cardioverter Defibrillator

The trans-venous implantable cardioverter defibrillator (TV-ICD) is effective in treating life-threatening ventricular arrhythmia and reduces mortality in high-risk patients. However, there are significant short- and long-term complications that are associated with intravascular leads. These shortcomings are mostly relevant in young patients with long life expectancy and low risk of death from non-arrhythmic causes. Drawbacks of trans-venous leads recently led to the development of the entirely subcutaneous implantable cardioverter defibrillator (S-ICD). The S-ICD does not require vascular access or permanent intravascular defibrillation leads. Therefore, it is expected to overcome many complications associated with conventional ICDs. This review highlights data on safety and efficacy of the S-ICD and is envisioned to help in identifying the role of this device in clinical practice.

Inappropriate shock in a subcutaneous cardiac defibrillator due to residual air

Inappropriate shock due to residual air in subcutaneous implantable cardiac defibrillators is not a well‐known complication. Obtaining overpenetrated X‐rays, recognizing electrocardiogram findings, limiting blunt finger dissection, and switching to sense at another vector are techniques which might lead to avoidance of unnecessary wound exploration or device removal.

Advances in implantable cardioverter defibrillator therapy

Since the first implant in 1980, implantable cardioverter defibrillator (ICD) technology has progressed rapidly. Modern ICD's have hundreds of programmable options with the general goal of preventing inappropriate shocks and providing shocks for truly life threatening symptomatic ventricular arrhythmias. New studies on ICD programming have shown the benefits of prolonged detection intervals in reaching this goal. Anti-tachycardia pacing (ATP) therapy has become an important adjunct to defibrillator shocks. Remote monitoring technologies have surfaced which have been shown to identify arrhythmias and problems with the device in an expedient fashion. The subcutaneous ICD offers the advantage of avoiding intravascular leads and their inherent risks. Lastly, the current understanding of the effects of MRI in ICD patients has advanced creating new opportunities to provide MRI safely to such patients.

The Entirely Subcutaneous Defibrillator - A New Generation and Future Expectations

Although conventional implantable cardioverter-defibrillators (ICDs) have proved effective in the prevention of sudden cardiac death (SCD), they still appear to be limited by non-trivial acute and long-term complications. The recent advent of an entirely subcutaneous ICD (S-ICD) represents a further step in the evolution of defibrillation technology towards a less-invasive approach. This review highlights some historical and current issues concerning the S-ICD that may offer a viable therapeutic option in selected patients at high risk of SCD and in whom pacing is not required. After the CE Mark and US Food and Drug Administration (FDA) approvals, the S-ICD is being implanted worldwide with growing clinical data regarding its safety and efficacy (the EFFORTLESS Registry). The recently developed new generation of S-ICD (EMBLEM, Boston Scientific) demonstrates favourable features including a smaller device, longer longevity and remote-monitoring compatibility. Further innovations in the S-ICD system and potential integration with leadless pacing may play an important role in defibrillation therapy and prevention of SCD in the near future.

Use of a subcutaneous ICD in a patient with short QT syndrome

Short QT syndrome carries the risk for inappropriate therapies using transvenous ICD because of overdetection of the ample T wave. SQT syndrome may also benefit from subcutaneous ICD, although additional cases are needed to affirm the safety of such device in this setting.