Ventricular Fibrillation Conversion Testing After Implantation of a Subcutaneous Implantable Cardioverter Defibrillator: Report From the National Cardiovascular Data Registry

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 preventing sudden cardiac death. However, concerns have been raised regarding its efficacy and safety in obese individuals.

OBJECTIVE

This meta-analysis aims 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 pre-implantation screening failure, defibrillation testing, complications, appropriate and inappropriate shocks, and survival were analysed using standard random-effect meta-analytical techniques.

RESULTS

Twenty-nine studies involving 20,486 patients were included. There was no statistically significant difference in the mean BMI values of patients with failed or successful preimplantation screening (mean difference -0.60 kg/m2, 95% CI -2.06 to 0.86). Obesity was associated with higher rates of failed defibrillation testing at ≤65J (OR 2.16, 95% CI 1.39-3.35), and mal-/suboptimal positioning occurred more frequently in obese compared to non-obese 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), a higher risk of complications (HR 1.04, 95% CI 1.02-1.05), a trend towards increased number of appropriate shocks (HR 1.02, 95% CI 1.00-1.04), and no significant increase in the risk for 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. While S-ICD remains effective in obese patients, attention to potential technical challenges and higher complication rates is warranted.

Postapproval Study of a Subcutaneous Implantable Cardioverter-Defibrillator System

BACKGROUND

The subcutaneous implantable cardioverter-defibrillator (S-ICD) was developed to avoid complications related to transvenous implantable cardioverter-defibrillator (TV-ICD) leads. Device safety and efficacy were demonstrated previously with atypical clinical patients or limited follow-up.

OBJECTIVES

The S-ICD PAS (Subcutaneous Implantable Cardioverter-Defibrillator System Post Approval Study) is a real-world, multicenter, registry of U.S. centers that was designed to assess long-term S-ICD safety and efficacy in a diverse group of patients and implantation centers.

METHODS

Patients were enrolled in 86 U.S. centers with standard S-ICD indications and were observed for up to 5 years. Efficacy endpoints were first and final shock efficacy. Safety endpoints were complications directly related to the S-ICD system or implantation procedure. Endpoints were assessed using prespecified performance goals.

RESULTS

A total of 1,643 patients were prospectively enrolled, with a median follow-up of 4.2 years. All prespecified safety and efficacy endpoint goals were met. Shock efficacy rates for discrete episodes of ventricular tachycardia or ventricular fibrillation were 98.4%, and they did not differ significantly across follow-up years (P = 0.68). S-ICD-related and electrode-related complication-free rates were 93.4% and 99.3%, respectively. Only 1.6% of patients had their devices replaced by a TV-ICD for a pacing need. Cumulative all-cause mortality was 21.7%.

CONCLUSIONS

In the largest prospective study of the S-ICD to date, all study endpoints were met, despite a cohort with more comorbidities than in most previous trials. Complication rates were low and shock efficacy was high. These results demonstrate the 5-year S-ICD safety and efficacy for a large, diverse cohort of S-ICD recipients. (Subcutaneous Implantable Cardioverter-Defibrillator [S-ICD] System Post Approval Study [PAS]; NCT01736618).

Subcutaneous and Transvenous ICDs: an Update on Contemporary Questions and Controversies

PURPOSE OF REVIEW

While the subcutaneous (S-) implantable cardioverter-defibrillator (ICDs) is an alternative to the transvenous (TV-) ICD in many patients, optimal use remains unclear. In this review, we summarize recent clinically relevant data on sensing algorithms, inappropriate shocks, defibrillation testing, and battery and electrode failures.

RECENT FINDINGS

Changes in sensing algorithms and S-ICD programming have significantly decreased inappropriate shock rates. Avoiding fat below the S-ICD coil and can is key for reducing the defibrillation threshold. While S-ICD battery and electrode failures have resulted in recalls, system components remain commercially available since failure rates are low and no other similar devices are available. The S-ICD is a good alternative to the TV-ICD for many patients, and particularly in light of recently developed device algorithms and improvements in implant technique. Future research will need to better understand: the impact of S-ICD electrode and battery failures and the potential for integrating leadless pacing into a modular S-ICD platform.

OUP accepted manuscript

Aims

To report 5-year outcomes of EFFORTLESS registry patients with early generation subcutaneous implantable cardioverter-defibrillator (S-ICD) devices.

Methods and results

Kaplan–Meier, trend and multivariable analyses were performed for mortality and late (years 2–5) complications, appropriate shock (AS) and inappropriate shock (IAS) rates. Nine hundred and eighty-four of 994 enrolled patients with diverse diagnoses (28% female, 48 ± 17 years, body mass index 27 ± 6 kg/m², ejection fraction 43 ± 18%) underwent S-ICD implantation. Median follow-up was 5.1 years (interquartile range 4.7–5.5 years). All-cause mortality was 9.3% (95% confidence interval 7.2–11.3%) at 5 years; 703 patients remained in follow-up on study completion, 171 withdrew including 87 (8.8%) with device explanted, and 65 (6.6%) lost to follow-up. Of the explants, only 20 (2.0%) patients needed a transvenous device for pacing indications. First and final shock efficacy for discrete ventricular arrhythmias was consistent at 90% and 98%, respectively, with storm episode final shock efficacy at 95.2%. Time to therapy remained unaltered. Overall 1- and 5-year complication rates were 8.9% and 15.2%, respectively. Early complications did not predict later complications. There were no structural lead failures. Inappropriate shock rates at 1 and 5 years were 8.7% and 16.9%, respectively. Self-terminating inappropriately sensed episodes predicted late IAS. Predictors of late AS included self-terminating appropriately sensed episodes and earlier AS.

Conclusion

In this diverse S-ICD registry population, spontaneous shock efficacy was consistently high over 5 years. Very few patients underwent S-ICD replacement with a transvenous device for pacing indications. Treated and self-terminating arrhythmic episodes predict future shock events, which should encourage more personalized device optimization.

Implantable cardioverter-defibrillators for hypertrophic cardiomyopathy: The Times They Are a-Changin'

The implantable cardioverter-defibrillator (ICD) is a life-saving therapy in patients with hypertrophic cardiomyopathy (HCM) at high risk of sudden cardiac death. The heterogeneity of clinical scenarios in HCM and the availability of ICDs with distinct characteristics emphasizes the need for selecting the right device for the right patient. There is growing awareness that unnecessarily complex devices can lead to short- and long-term complications without adding significant clinical benefits. Young patients have the greatest potential years of life gained from the ICD but are also most exposed to device-related complications. This increases the complexity of decision-making of ICD prescription in these often otherwise well patients in whom device selection should be tailored to preserve survival benefit without introducing morbidity. In the light of the multiple clinical phenotypes characterizing HCM, the present article offers evidence-based perspectives helpful in predicting the individual impact of the ICD and choosing the most appropriate device.

The Role of Subcutaneous ICDs in the Prevention of Sudden Cardiac Death

The ICD is an important therapy in the prevention of sudden cardiac death. The transvenous-ICD (TV-ICD) has been the primary device used for this purpose. However, mechanical and infectious complications occur with traditional TV-ICDs increasing morbidity and mortality. The subcutaneous-ICD (S-ICD) system was developed to circumvent some of these complications, but S-ICDs have their inherent set of limitations as well. These include inappropriate shock delivery, lack of bradycardia, antitachycardia or CRT pacing therapy and shorter device longevity. The S-ICD is now included in guidelines as an acceptable alternative to TV-ICDs among patients without pacing indications. This review discusses the rationale for S-ICDs by reviewing studies including the PRAETORIAN, PAS and UNTOUCHED trials.

Acute shock efficacy of the subcutaneous implantable cardioverter-defibrillator according to the implantation technique

BACKGROUND

The traditional technique for subcutaneous implantable cardioverter defibrillator (S-ICD) implantation involves three incisions and a subcutaneous (SC) pocket. An intermuscular (IM) 2-incision technique has been recently adopted.

AIMS

We assessed acute defibrillation efficacy (DE) of S-ICD (DE ≤65 J) according to the implantation technique.

METHODS

We analyzed consecutive patients who underwent S-ICD implantation and DE testing at 53 Italian centers. Regression analysis was used to determine the association between DFT and implantation technique.

RESULTS

A total of 805 patients were enrolled. Four groups were assessed: IM + 2 incisions (n = 546), SC + 2 incisions (n = 133), SC + 3 incisions (n = 111), and IM + 3 incisions (n = 15). DE was ≤65 J in 782 (97.1%) patients. Patients with DE ≤65 J showed a trend towards lower body mass index (25.1 vs. 26.5; p = .12), were less frequently on antiarrhythmic drugs (13% vs. 26%; p = .06) and more commonly underwent implantation with the 2-incision technique (85% vs. 70%; p = .04). The IM + 2-incision technique showed the lowest defibrillation failure rate (2.2%) and shock impedance (66 Ohm, interquartile range: 57-77). On multivariate analysis, the 2-incision technique was associated with a lower incidence of shock failure (hazard ratio: 0.305; 95% confidence interval: 0.102-0.907; p = .033). Shock impedance was lower with the IM than with the SC approach (66 vs. 70 Ohm p = .002) and with the 2-incision than the 3-incision technique (67 vs. 72 Ohm; p = .006).

CONCLUSIONS

In a large population of S-ICD patients, we observed a high defibrillation success rate. The IM + 2-incision technique provides lower shock impedance and a higher likelihood of successful defibrillation.

Defibrillation Safety Margin Testing in Patients With Congenital Heart Disease: Results From the NCDR

OBJECTIVES

This study analyzed the predictors of defibrillation safety margin (DSM) testing at the time of implantable cardioverter-defibrillator (ICD) insertion and factors associated with inadequate DSM in patients with congenital heart disease (CHD).

BACKGROUND

There are few data about the prevalence and safety of DSM testing in those with CHD.

METHODS

A retrospective analysis was performed of all patients with atrial or ventricular septal defect, tetralogy of Fallot, transposition of the great vessels, Ebstein anomaly, or common ventricle undergoing a transvenous ICD procedure in the National Cardiovascular Data Registry (NCDR) ICD Registry from April 2010 to March 2016, and DSM testing was assessed. Inadequate DSM was defined as a lowest successful energy tested <10 J than the maximum output of the ICD generator.

RESULTS

Of all ICD recipients (N = 7,024), DSM testing was performed in 52.0% (n = 3,654). The mean lowest successful energy tested was 20.7 ± 7.3 J. Of those with DSM adequacy data available (n = 3,623), an inadequate DSM occurred in 13.8% (n = 501). After multivariable adjustment, DSM testing was not associated with in-hospital complications or death (odds ratio [OR]: 1.00; 95% confidence interval [CI]: 0.79 to 1.28) but was associated with lower odds of prolonged hospital stay (>3 days) (OR: 0.71; 95% CI: 0.60 to 0.84; p < 0.0001). An inadequate DSM was not associated with in-hospital death or complications (OR: 1.27; 95% CI: 0.79 to 2.04) or prolonged hospital stay (OR: 1.34; 95% CI: 0.995 to 1.81).

CONCLUSIONS

DSM testing is being performed less frequently over time and seems safe in those with CHD. An inadequate DSM was not associated with worse in-hospital outcomes.

The impact of transvenous cardioverter-defibrillator implantation on quality of life, depression and optimism in dialysis patients: report on the secondary outcome of QOL in the randomized controlled ICD2 trial

RATIONALE

The impact of prophylactic implantable cardioverter-defibrillator (ICD) implantation on the psychological well-being of patients on dialysis is unknown.

OBJECTIVE

We aimed to identify the effect of primary ICD implantation on quality of life (QoL), mood and dispositional optimism in patients undergoing dialysis.

METHODS AND RESULTS

We performed a prespecified subanalysis of the randomized controlled ICD2 trial. In total, 177 patients on chronic dialysis, with an age of 55-81 years, and a left ventricular ejection fraction of ≥ 35%, were included in the per-protocol analysis. Eighty patients received an ICD for primary prevention, and 91 patients received standard care. The Short Form-36 (SF-36), Geriatric Depression Scale-15 (GDS-15), Revised Life Orientation Test (LOT-R) questionnaires were administered prior to ICD implantation (T0), and at 1-year follow-up (T1) to assess QoL, depression and optimism, respectively. The patients were predominantly male (76.0%), with a median age of 67 years. Hemodialysis was the predominant mode of dialysis (70.2%). The GDS-15 score difference (T1 - T0) was 0.5 (2.1) in the ICD group compared with 0.3 (2.2) in the control group (mean difference - 0.3; 95% CI - 1.1 to 0.6; P = 0.58). The LOT-R score difference was - 0.2 (4.1) in the ICD group compared with - 1.5 (4.0) in the control group (mean difference - 1.1 (0.8); 95% CI - 2.6 to 0.4; P = 0.17). The mean difference scores of all subscales of the SF-36 were not significantly different between randomization groups.

CONCLUSIONS

In our population of patients on dialysis, ICD implantation did not affect QoL, mood or dispositional optimism significantly during 1-year follow-up.

CLINICAL TRIAL REGISTRATION

Unique identifier: ISRCTN20479861. http://www.controlled-trials.com .

Is 40 Joules Enough to Successfully Defibrillate With Subcutaneous Implantable Cardioverter-Defibrillators?

OBJECTIVES

This study evaluated the efficacy of conversion test performed at 40 J (defibrillation margin ≥40 J), and factors potentially associated with test failure were identified.

BACKGROUND

Current subcutaneous implantable cardioverter-defibrillator (S-ICD) devices deliver a maximum of 80 J. Functional defibrillation testing is recommended at S-ICD implantation, and it is usually conducted by delivering a shock energy of 65 J to ensure a safety defibrillation margin ≥15 J. Although high rates of successful conversion were reported at 65 J, limited data exist on the defibrillation margin extent.

METHODS

Ventricular fibrillation was induced and conversion test was performed by delivering a 40-J shock in 308 patients. Success was defined as termination of ventricular fibrillation by the first shock delivered in standard polarity. The S-ICD system positioning was evaluated with the PRAETORIAN score using bidirectional chest X-rays.

RESULTS

The generator was positioned in an intermuscular pocket in 301 patients (98%) and the lead was implanted by means of a 2-incision technique. The PRAETORIAN score was <90 (low risk of conversion failure) in 293 (95%) patients. Overall, ventricular fibrillation termination occurred in 259 (84%) patients with 40 J. Male gender (odds ratio [OR]: 3.79; 95% confidence interval [CI]: 1.09 to 13.14; p = 0.036), body mass index (OR: 1.09; 95% CI: 1.01 to 1.19; p = 0.036), dilated cardiomyopathy with reduced ejection fraction (OR: 0.42; 95% CI: 0.20 to 0.87; p = 0.019), and PRAETORIAN score >50 (OR: 2.93; 95% CI: 1.26 to 6.83; p = 0.013) were independently associated with conversion failure.

CONCLUSIONS

The authors showed a high rate of defibrillation success with 40-J shocks in S-ICD systems implanted by means of modern surgical techniques. The variables associated with shock failure were male gender, higher body mass index, and suboptimal device position according to the PRAETORIAN score.

Trends in Use and In-Hospital Outcomes of Subcutaneous Implantable Cardioverter Defibrillators in Patients Undergoing Long-Term Dialysis

BACKGROUND AND OBJECTIVES

Patients on dialysis are at high risk of complications related to implantable cardioverter defibrillator (ICD) implantation; use of subcutaneous ICDs may be preferred over transvenous devices due to lower risk of bloodstream infection and interference with vascular access sites. We evaluated trends in use and in-hospital outcomes of subcutaneous compared with transvenous ICDs among patients on dialysis in the United States.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Retrospective analysis of ICD implants from 2012 to 2018 among patients on dialysis reported to the National Cardiovascular Data Registry ICD Registry, a nationally representative US ICD Registry. We examined overall trends in subcutaneous ICD adoption as a proportion of all eligible ICD implants among patients on dialysis and then compared in-hospital outcomes between eligible subcutaneous ICD and transvenous ICD recipients using inverse probability of treatment weighting.

RESULTS

Of the 23,136 total ICD implants in patients on dialysis during the study period, 3195 (14%) were subcutaneous ICDs. Among eligible first-time ICD recipients on dialysis, the proportion of subcutaneous ICDs used increased yearly from 10% in 2012 to 69% in 2018. In propensity score-weighted analysis of 3327 patients, compared with transvenous ICDs, patients on dialysis receiving subcutaneous ICDs had a higher rate of in-hospital cardiac arrest (2% versus 0.4%, P=0.002), but there was no significant difference in total in-hospital complications (2% versus 1%, P=0.08), all-cause death, or length of hospital stay.

CONCLUSIONS

The utilization of subcutaneous ICDs among US patients on dialysis has been steadily increasing. The overall risk of short-term complications is low and comparable with transvenous ICDs, but higher risks of in-hospital cardiac arrest merits closer monitoring and further investigation.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2020_09_23_CJN07920520.mp3.

Approaches to Minimizing Periprocedural Complications During Subcutaneous Implantable Cardioverter-defibrillator Placement

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is the latest option among devices clinically available for the prevention of sudden cardiac death, with experience from previous trials and postmarketing studies supporting the feasibility and safety of this kind of system. The extracardiac positioning of the S-ICD obviates the need for transvenous leads, which translates into lower incidence rates of lead-related complications and systemic infections. This review will highlight the results of pertinent studies related to the perioperative management of S-ICDs and review potential approaches to minimizing the risk of complications such as hematoma at the pulse generator location, unsuccessful defibrillation due to suboptimal S-ICD lead and generator positioning, and postoperative pain. An extensive literature search using PubMed was conducted to identify relevant articles.

Application of Neural Networks to 12-Lead Electrocardiography - Current Status and Future Directions

The 12-lead electrocardiogram (ECG) is a fast, non-invasive, powerful tool to diagnose or to evaluate the risk of various cardiac diseases. The vast majority of arrhythmias are diagnosed solely on 12-lead ECG. Initial detection of myocardial ischemia such as myocardial infarction (MI), acute coronary syndrome (ACS) and effort angina is also dependent upon 12-lead ECG. ECG reflects the electrophysiological state of the heart through body mass, and thus contains important information on the electricity-dependent function of the human heart. Indeed, 12-lead ECG data are complex. Therefore, the clinical interpretation of 12-lead ECG requires intense training, but still is prone to interobserver variability. Even with rich clinically relevant data, non-trained physicians cannot efficiently use this powerful tool. Furthermore, recent studies have shown that 12-lead ECG may contain information that is not recognized even by well-trained experts but which can be extracted by computer. Artificial intelligence (AI) based on neural networks (NN) has emerged as a strong tool to extract valuable information from ECG for clinical decision making. This article reviews the current status of the application of NN-based AI to the interpretation of 12-lead ECG and also discusses the current problems and future directions.

Complications involving the subcutaneous implantable cardioverter-defibrillator: Lessons learned from MAUDE

BACKGROUND

Reports on the subcutaneous implantable cardioverter-defibrillator (S-ICD) cumulatively demonstrate a low rate of complications, but clinical experience with this technology is limited compared with transvenous devices.

OBJECTIVE

The purpose of this study was to describe and analyze S-ICD complications reported to the Food and Drug Administration's Manufacturer and User Facility Device Experience database.

METHODS

We reviewed all S-ICD events reported to the Manufacturer and User Facility Device Experience submitted over 24 months (from February 2016 through February 2018) through a prospective and standardized approach at a time when an estimated 15,000 S-ICDs were in service.

RESULTS

After removing duplicate entries and nonclinical events (n = 493), 1604 events remained. A total of 542 instances of infection were reported with system removal in 414/542 (77.5%). Inappropriate shocks occurred in 550 patients, and 382 (69%) were attributed to oversensing; in response, 254 (56%), 147 (33%), and 80 (18%) patients underwent system reprogramming, removal, or revision, respectively. There were 15 deaths, and causes included defibrillation failure during follow-up (n = 2), ventricular fibrillation induced by the device (n = 4), device-device interaction resulting in undersensing (n = 1), procedure-related complications (n = 4), and uncertain etiology (n = 4). There were 137 reports of system migration, and in 57 (42%) of these, there were associated inappropriate shocks. System migration events were managed with a combination of system revision (69 [51%]), reprogramming (25 [18%]), and system removal (44 [32%]).

CONCLUSION

Several S-ICD complications have been reported that appear to be related to the ICD's design and function over time. A better understanding of these complications may help inform patient selection, implant technique, and postimplantation management.

Subcutaneous implantable cardioverter-defibrillator in primary and secondary prevention of sudden cardiac death: A meta-analysis

BACKGROUND

Subcutaneous implantable cardioverter-defibrillator (S-ICD) is gaining in popularity for primary and secondary prevention of sudden cardiac death. The objective was to evaluate the safety and clinical effectiveness of the S-ICD for prevention of sudden cardiac death compared to transvenous cardioverter-defibrillator (TV-ICD).

METHODS

A systematic review with meta-analyses was performed. The electronic databases MEDLINE, EMBASE, SCI, and Cochrane Central Register of Controlled Trials were consulted in March 2018 with no restrictions on publication date. Predefined criteria were used to determine inclusion of studies and to assess their methodologic quality.

RESULTS

Ten longitudinal-observational studies with comparison group presenting moderate methodologic flaws were included (N = 7820). The combination of results indicates that health-related quality of life is not significantly different between S-ICD and TV-ICD groups (Physical health: MD = 2.90; 95% CI = -3.88, 9.68/Mental health: MD = 0.13; 95% CI = -2.11, 2.37). Mortality occurred in 4.4% of S-ICD patients and 5.9% of TV-ICD patients died (OR = 0.79; 95% CI = 0.50, 1.24). The incidence of infections (OR = 1.79; 95% CI = 0.93, 3.43) and inappropriate shocks (OR = 1.28, 95% CI = 0.91, 1.78) is not significantly different between both groups. The S-ICD reduces complications related to electrodes/leads (OR = 0.13, 95% CI = 0.05, 0.29) and has lower electrodes/leads movement compared with TV-ICD (OR = 0.26; 95% CI 0.10, 0.67). In contrast, pneumothorax is more likely in TV-ICD than S-ICD (OR = 0.17; 95% CI = 0.03, 0.97).

CONCLUSIONS

S-ICD reduces electrodes/leads movement, electrodes/leads related complications, and pneumothorax. Our study did not demonstrate a statistically significant difference in mortality, health-related quality of life, and infection rate between S-ICD and TV-ICD.

Successful defibrillation verification in subcutaneous implantable cardioverter-defibrillator recipients by low-energy shocks

BACKGROUND

The subcutaneous implantable cardioverter-defibrillator (S-ICD) is an effective alternative to the transvenous one. Defibrillation efficacy depends on maximum device output and on the optimal device location at device implantation.

HYPOTHESIS

We sought to investigate the defibrillation safety margin in real life clinical practice.

METHODS

We sought to understand what is the efficacy of induced ventricular fibrillation (VF) termination at S-ICD implantation using lower energies than the recommended 65 J.

RESULTS

Sixty-four consecutive S-ICD recipients underwent VF termination attempts at implantation with energies ranging from 20 to 50 J. Overall, VF termination occurred in 84% of patients with ≤40 J, in 88% with 45 J, and in 100% with 60 J. Intermuscular S-ICD placement was associated with 94% VF termination at ≤40 J. An ejection fraction <35% was associated to higher energy requirement for defibrillation; however, an intermuscular S-ICD placement conferred 90% defibrillation efficacy at 31 ± 5 J in this patients subset.

CONCLUSIONS

This is a hypothesis-generating observation that prompts a methodologically correct investigation to prove that a 60 J output S-ICD can provide an adequate safety margin to terminate VF in clinical practice. This would enable superior device longevity and/or device downsizing for pediatric/small size patients.

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.

Defibrillation Threshold Testing: Current Status

When the transvenous ICD initially came into use for primary and secondary prevention of sudden cardiac death, defibrillation threshold (DFT) testing was universally performed. However, DFT testing is no longer routinely recommended for transvenous ICD implantation except in certain situations. Risk scores can help guide the decision to perform DFT testing. The subcutaneous ICD represents an area of uncertainty, with limited data available regarding the role of DFT testing in these devices. Current guidelines give a class I recommendation for performing DFT testing at the time of implant. Further studies are needed before this recommendation can be safely dismissed.