Differences in underlying cardiac substrate among S-ICD recipients and its impact on long-term device-related outcomes: Real-world insights from the iSUSI registry

BACKGROUND

Outcome comparisons among subcutaneous implantable cardioverter-defibrillator (S-ICD) recipients with nonischemic cardiomyopathies are scarce.

OBJECTIVE

The aim of this study was to evaluate differences in device-related outcomes among S-ICD recipients with different structural substrates.

METHODS

Patients enrolled in the i-SUSI (International SUbcutaneouS Implantable cardioverter defibrillator registry) project were grouped according to the underlying substrate (ischemic vs nonischemic) and subgrouped into dilated cardiomyopathy, hypertrophic cardiomyopathy, Brugada syndrome (BrS), arrhythmogenic right ventricular cardiomyopathy (ARVC). The main outcome of our study was to compare the rates of appropriate and inappropriate shocks and device-related complications.

RESULTS

Among 1698 patients, the most common underlying substrate was ischemic (31.7%), followed by dilated cardiomyopathy (20.5%), BrS (10.8%), hypertrophic cardiomyopathy (8.5%), and ARVC (4.4%). S-ICD for primary prevention was more common in the nonischemic cohort (70.9% vs 65.4%; P = .037). Over a median (interquartile range) follow-up of 26.5 (12.6-42.8) months, no differences were observed in appropriate shocks between ischemic and nonischemic patients (4.8%/y vs 3.9%/y; log-rank, P = .282). ARVC (9.0%/y; hazard ratio [HR] 2.492; P = .001) and BrS (1.8%/y; HR 0.396; P = .008) constituted the groups with the highest and lowest rates of appropriate shocks, respectively. Device-related complications did not differ between groups (ischemic: 6.4%/y vs nonischemic: 6.1%/y; log-rank, P = .666), nor among underlying substrates (log-rank, P = .089). Nonischemic patients experienced higher rates of inappropriate shocks than did ischemic S-ICD recipients (4.4%/y vs 3.0%/y; log-rank, P = .043), with patients with ARVC (9.9%/y; P = .001) having the highest risk, even after controlling for confounders (adjusted HR 2.243; confidence interval 1.338-4.267; P = .002).

CONCLUSION

Most S-ICD recipients were primary prevention nonischemic cardiomyopathy patients. Among those, patients with ARVC tend to receive the most frequent appropriate and inappropriate shocks and patients with BrS the least frequent appropriate shocks.

Left ventricular assist device in the presence of subcutaneous implantable cardioverter defibrillator: Data from a multicenter experience

BACKGROUND

Left ventricular assist devices (LVADs) are an increasingly used strategy for the management of patients with advanced heart failure (HF). Subcutaneous implantable cardioverter defibrillator (S-ICD) might be a viable alternative to conventional ICDs with a lower risk of short- and long-term of device-related complications and infections.The aim of this multicenter study was to evaluate the outcomes and management of S-ICD recipients who underwent LVAD implantation.

METHODS

The study population included patients with a preexisting S-ICD who underwent LVAD implantation for advanced HF despite optimal medical therapy.

RESULTS

The study population included 30 patients (25 male; median age 45 [38-52] years).The HeartMate III was the most common LVAD type. Median follow-up in the setting of concomitant use of S-ICDs and LVADs was 7 months (1-20).There were no reports of inability to interrogate S-ICD systems in this population. Electromagnetic interference (EMI) occurred in 21 (70%) patients. The primary sensing vector was the one most significantly involved in determining EMI. Twenty-seven patients (90%) remained eligible for S-ICD implantation with at least one optimal sensing vector. The remaining 3 patients (10%) were ineligible for S-ICD after attempts of reprogramming of sensing vectors. Six patients (20%) experienced inappropriate shocks (IS) due to EMI. Six patients (20%) experienced appropriate shocks. No S-ICD extraction because of need for antitachycardia pacing, ineffective therapy or infection was reported.

CONCLUSIONS

Concomitant use of LVAD and S-ICD is feasible in most patients. However, the potential risk of EMI oversensing, IS and undersensing in the post-operative period following LVAD implantation should be considered. Careful screening for EMI should be performed in all sensing vectors after LVAD implantation.

Modern physiological approach to inappropriate ICD shocks due to atrial fibrillation with very fast ventricular response. A case report

BACKGROUND

Fast-conducting atrial fibrillation misinterpreted as ventricular tachycardia is the leading cause for inappropriate shocks in patients with implantable cardiac defibrillators (ICD). These inappropriate shocks are associated with significant morbidity and mortality and cause great discomfort and stress.

CASE PRESENTATION

We report the case of a patient with ischemic cardiomyopathy, permanent atrial fibrillation, and a single-chamber DF-1 ICD implanted for the primary prevention of sudden cardiac death, who presented for multiple inappropriate internal shocks due to very fast-conducting atrial fibrillation, which was mislabeled as ventricular fibrillation by the ICD. Since the patient was under maximal atrioventricular nodal blocking medical therapy (beta-blockers and digitalis) and we didn`t find any reversible causes for the heart rate acceleration, we opted for rate control with atrioventricular node ablation. To counteract the risk of pacing-induced cardiomyopathy in this patient who would become totally pacemaker-dependent, we successfully performed left bundle branch area pacing. Because the patient`s ICD had a DF-1 connection and the battery had a long life remaining, we connected the physiological pacing lead to the IS-1 sense-pace port of the ICD. The 6-month follow-up showed an improvement in left ventricular function with no more inappropriate shocks.

CONCLUSIONS

Left bundle branch area pacing and atrioventricular node ablation in patients with an implantable single-chamber DF-1 defibrillator and fast-conducting permanent atrial fibrillation is a cost-efficient and very effective method to prevent and treat inappropriate shocks, avoiding the use of an additional dual-chamber or CRT-D device.

A cluster of inappropriate shocks in a pediatric S-ICD patient - how to troubleshoot?

We present the case of a 16-year-old male pediatric patient diagnosed with hypertrophic cardiomyopathy (HCM, identified as having a high risk of sudden cardiac death (SCD), who underwent a successful subcutaneous implantable cardiac defibrillator (S-ICD) implantation as a primary prevention measure in 2018. His past medical history included ADHD, Autism, and panic attacks. The patient experienced appropriate shocks that successfully terminated VF episodes. However, he also experienced multiple inappropriate shocks from the S-ICD, triggered by anxiety-induced tachycardia during panic episodes. Meticulous assessment of S-ICD tracings and electrocardiograms (ECGs) revealed the erroneous classification of sinus tachycardia as sustained ventricular tachycardia, leading to unwarranted therapeutic interventions. Clinical intervention involved reprogramming of the S-ICD, emphasizing the pivotal role of personalized device configuration in pediatric cases where fine margins matter. While literature on S-ICD use in pediatric populations remains limited, emerging registries underscore the efficacy and safety of S-ICDs in preventing sudden cardiac death while reducing complications associated with intravascular leads. This case underscores the critical nature of customized device programming in pediatric patients, underscoring S-ICDs as a practical defibrillation alternative that addresses distinct concerns within this cohort of patients.

Poorer outcomes associated with more invasive lead management strategies for Abbott Riata® leads: a large, multicenter experience

BACKGROUND

Over 100,000 Abbott Riata® were implanted in the United States before they were recalled in 2010. There are still a significant number of Abbott Riata® leads in use, and it is unclear how these leads should be managed at the time of generator change or lead malfunction. Although data comparing both Sprint Fidelis® and Abbott Riata® leads in this setting is available, there are no multicenter comparative studies of outcomes for various lead management strategies, including lead extraction (LE), lead abandonment/revision (LA), and generator change (GC) only at the time of device at elective replacement interval (ERI) for Abbott Riata® leads.

METHODS

A retrospective, multicenter study was undertaken to compare short-term outcomes (major complications-MC, death, extended or re-hospitalizations within 60 days-RH, lead malfunction-LM) and total outcomes (short-term outcomes & lead malfunction during follow-up) of patients with Riata® leads undergoing LE, LA, or GC.

RESULTS

152 patients (65 ± 13 years, 68% male) were followed for a mean 33 ± 30 months following intervention. Out of 166 procedures, 13 patients underwent LE, 16 patients underwent LA, and 137 patients underwent GC. There was 1 major complication in each group, yielding an event rate of 7.7% for LE, 6.3% for LA, and 0.7% for GC cohorts. There were significantly more short-term and total adverse outcomes in the group of patients getting LE and LA versus GC only (38.5% & 31.3% vs 7.3%, P < 0.001). Total Riata® lead dwell time follow-up was 17,067 months. A total of 3 Riata® lead malfunctions were noted during long-term follow-up. Inappropriate shocks were similar between LE 7.7% (1/13), LA 6.3% (1/16). and GC 11.0% (4/136); P = 0.57.

CONCLUSIONS

There were more short-term and total adverse outcomes in more invasive management strategies (LE and LA) versus GC alone. The failure rate of Riata® leads was substantially lower compared to previous reports. Therefore, we recommend only performing battery exchange when a device with an active Riata® lead is at ERI, unless there is malfunction of the Riata® lead noted on testing. There were significantly more short-term adverse outcomes in the lead extraction (5/13) and lead abandonment/revision (5/16) groups than the generator only (8/137) group (P < 0.001). GIB - Gastrointestinal bleed, CHF - congestive heart failure, NSTEMI - non-ST elevation MI.

Exploiting SMART pass filter deactivation detection to minimize inappropriate subcutaneous implantable cardioverter defibrillator therapies: a real-world single-centre experience and management guide

AIMS

The SMART Pass™ (SP) algorithm is a high-pass filter that aims to reduce inappropriate therapy (IT) in subcutaneous internal cardiac defibrillator (S-ICD), but SP can deactivate due to low amplitude sensed R waves or asystole. The association between IT and SP deactivation and management strategies were evaluated, hypothesizing SP deactivation increases the risk of IT and device re-programming, or lead/generator re-positioning could reduce this risk.

METHODS AND RESULTS

Retrospective single-centre audit of Emblem™ S-ICD devices implanted 2016 to 2020 utilizing health records and remote monitoring data. Cox regression models evaluated associations between SP deactivation and IT. A total of 348 patients (27 ± 16.6 months follow-up) were studied: 73% primary prevention. Thirty-eight patients (11.8%) received 83 shocks with 27 patients (7.8%) receiving a total of 44 IT. Causes of IT were oversensing (98%) and aberrantly conducted atrial fibrillation (2%). SP deactivation occurred in 32 of 348 patients (9%) and was significantly associated with increased risk of IT (hazard ratio 5.36, 95% CI 2.37-12.13). SP deactivation was due to low amplitude R waves (94%), associated with a higher defibrillation threshold at implant and presence of arrhythmogenic right ventricular cardiomyopathy. No further IT occurred 16 ± 15.5 months after corrective interventions, with changing the sensing vector being successful in 59% of cases.

CONCLUSION

To reduce the risk of IT, the cause of the SP deactivation should be investigated, and appropriate reprogramming, device, or lead modifications made. Utilizing the alert for SP deactivation and electrograms could pro-actively prevent IT.

Pre-implant predictors of inappropriate shocks with the third-generation subcutaneous implantable cardioverter defibrillator

AIMS

Despite recent improvements, inappropriate shocks emitted by implanted subcutaneous implantable cardioverter defibrillators (S-ICDs) remain a challenge in 'real-life' practice. We aimed to study the pre-implant factors associated with inappropriate shocks for the latest generation of S-ICDs.

METHODS AND RESULTS

Three-hundred patients implanted with the third-generation S-ICD system for primary or secondary prevention between January 2017 and March 2020 were included in this multicentre retrospective observational study. A follow-up of at least 6 months and pre-implant screening procedure data were mandatory for inclusion. During a mean follow-up of 22.8 (±11.4) months, 37 patients (12.3%) received appropriate S-ICD shock therapy, whereas 26 patients (8.7%) experienced inappropriate shocks (incidence 4.9 per 100 patient years). The total number of inappropriate shock episodes was 48, with nine patients experiencing multiple episodes. The causes of inappropriate shocks included supraventricular arrhythmias (34.6%) and cardiac (30.7%) or extra-cardiac noise (38.4%) oversensing. Using multivariate analysis, we explored the independent factors associated with inappropriate shocks. These were the availability of less than three sensing vectors during pre-implant screening [hazard ratio (HR), 0.33; 95% confidence interval (CI), 0.11-0.93; P = 0.035], low QRS/T wave ratio in Lead I (for a threshold <3; HR, 4.79; 95% CI, 2.00-11.49; P < 0.001), history of supraventricular tachycardia (HR, 8.67; 95% CI, 2.80-26.7; P < 0.001), and being overweight (body mass index > 25; HR, 2.66; 95% CI, 1.10-6.45; P = 0.03).

CONCLUSION

Automatic pre-implant screening data are a useful quantitative predictor of inappropriate shocks. Electrocardiogram features should be taken into consideration along with other clinical factors to identify patients at high risk of inappropriate shocks.

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.

Non-transvenous ICD therapy: current status and beyond

Subcutaneous implantable cardioverter/defibrillators (S-ICDs) have been developed to offer ICD treatment to patients without venous access to the heart and to overcome complications associated with transvenous leads, particularly lead fracture/insulation defects and endocarditis. Several studies and registries have demonstrated the feasibility and safety of S‑ICD in different groups of patients. Further developments in S‑ICD technology involve the combination with devices that can provide anti-bradycardia and anti-tachycardia pacing if needed. The extravascular ICD (EV-ICD) is a new system that similarly offers ICD therapy without a transvenous lead but uses a substernal instead of a subcutaneous lead to facilitate detection of ventricular fibrillation and to provide anti-tachycardia and also temporary anti-bradycardia pacing. The first animal but also clinical data on EV-ICDs have been published. This review discusses the current state, potential advantages and limitations, and future research of both S‑ICD and EV-ICD.

Remote monitoring of implantable defibrillators is associated with fewer inappropriate shocks and reduced time to medical assessment in a remote and rural area

BACKGROUND

Implantable cardioverter defibrillators (ICDs) and cardiac resynchronisation therapy with defibrillators (CRT-D) reduce mortality in certain cardiac patient populations. However, inappropriate shocks pose a problem, having both adverse physical and psychological effects on the patient. The advances in device technology now allow remote monitoring (RM) of devices to replace clinic follow up appointments. This allows real time data to be analysed and actioned and this may improve patient care.

AIM

To determine if RM in patients with an ICD is associated with fewer inappropriate shocks and reduced time to medical assessment.

METHODS

This was a single centre, retrospective observational study, involving 156 patients implanted with an ICD or CRT-D, followed up for 2 years post implant. Both appropriate and inappropriate shocks were recorded along with cause for inappropriate shocks and time to medical assessment.

RESULTS

RM was associated with fewer inappropriate shocks (13.6% clinic vs 3.9% RM; P = 0.030) and a reduced time to medical assessment (15.1 ± 6.8 vs 1.0 ± 0.0 d; P < 0.001).

CONCLUSION

RM in patients with an ICD is associated with improved patient outcomes.

Unexpected inhibition of bradycardia pacing due to oversensing in ICD lead fracture associated with spurious tachyarrhythmia detection and discharges

Ιn a 76-year old man with a dual-chamber ICD implanted five years ago, dizzy spells and significant bradycardia on Holter were not initially recognized as inhibition of bradycardia pacing, due to oversensing. Hospital admission was deemed necessary only after repetitive ICD shocks attributed to right ventricular pace-sense lead fracture. The need to ensure adequate ICD antibradycardia backup pacing in pacing-dependent patients when deleterious sensing errors occur, cannot be overemphasized.

Appropriate and inappropriate shocks in hypertrophic cardiomyopathy patients with subcutaneous implantable cardioverter-defibrillators: An international multicenter study

BACKGROUND

Subcutaneous implantable cardioverter-defibrillators (S-ICDs) are attractive for preventing sudden cardiac death in hypertrophic cardiomyopathy (HCM) as they mitigate risks of transvenous leads in young patients. However, S-ICDs may be associated with increased inappropriate shock (IAS) in HCM patients.

OBJECTIVE

The purpose of this study was to assess the incidence and predictors of appropriate shock and IAS in a contemporary HCM S-ICD cohort.

METHODS

We collected electrocardiographic and clinical data from HCM patients who underwent S-ICD implantation at 4 centers. Etiologies of all S-ICD shocks were adjudicated. We used Firth penalized logistic regression to derive adjusted odds ratios (aORs) for predictors of IAS.

RESULTS

Eighty-eight HCM patients received S-ICDs (81 for primary and 7 for secondary prevention) with a mean follow-up of 2.7 years. Five patients (5.7%) had 9 IAS episodes (3.8 IAS per 100 patient-years) most often because of sinus tachycardia and/or T-wave oversensing. Independent predictors of IAS were higher 12-lead electrocardiographic R-wave amplitude (aOR 2.55 per 1 mV; 95% confidence interval 1.15-6.38) and abnormal T-wave inversions (aOR 0.16; 95% confidence interval 0.02-0.97). There were 2 appropriate shocks in 7 secondary prevention patients and none in 81 primary prevention patients, despite 96% meeting Enhanced American College of Cardiology/American Heart Association criteria and the mean European HCM Risk-SCD score predicting 5.7% 5-year risk. No patients had sudden death or untreated sustained ventricular arrhythmias.

CONCLUSION

In this multicenter HCM S-ICD study, IAS were rare and appropriate shocks confined to secondary prevention patients. The R-wave amplitude increased IAS risk, whereas T-wave inversions were protective. HCM primary prevention implantable cardioverter-defibrillator guidelines overestimated the risk of appropriate shocks in our cohort.

Device updates successfully reduce T‑wave oversensing and inappropriate shocks in subcutaneous ICD patients

Aims

To analyse the impact of device and software updates on the prevention of T‑wave oversensing (TWOS) and inappropriate shocks (IS) in subcutaneous ICD (S-ICD) patients.

Background

TWOS is a feared complication after implantation. It may lead to harmful IS. To date, specific strategies to reduce these events are lacking.

Methods

In this retrospective single-centre trial we analysed 146 S‑ICD patients who were implanted between 2010 and 2016. In all eligible consecutive patients (n = 139), follow-up of at least 6 weeks was studied. The incidence of TWOS/IS was analysed in patients receiving a 2^nd generation S‑ICD (Emblem-S-ICD) between 2014 and 2016 (Emblem). Their outcome was compared with a control group (SQ) treated with the SQ1010 device between 2010 and 2014, who were followed up for a maximum of 2 years. Furthermore, to test if the software update SMR8 reduces inappropriate shocks in the SQ1010-S-ICD population, the incidence of TWOS/IS was evaluated before and after update installation.

Results

Basic characteristics and indications for S‑ICD implantation were similar in both groups. However, the cumulative incidence of TWOS/IS was significantly decreased in Emblem vs. SQ (SQ: 15.4%, n = 14/91 vs. Emblem 4.2%, n = 2/48; p = 0.049). Furthermore, with regards to the SQ population we also observed a trend towards a significant reduction of TWOS/IS after installation of the software update SMR8 in 2014 (before update: 13.4%, n = 11/82 vs. after update: 4.6%, 3/65, p = 0.07).

Conclusion

2^nd generation devices but probably also the SMR8 software update reduce the incidence of TWOS/IS in S‑ICD patients.

An Overview of Clinical Outcomes in Transvenous and Subcutaneous ICD Patients

PURPOSE OF REVIEW

Clear guidelines on when to select a subcutaneous ICD (S-ICD) over a transvenous ICD (TV-ICD) are lacking. This review will provide an overview of the most recent clinical data on S-ICD and TV-ICD therapy by pooling comparison studies in order to aid clinical decision making.

RECENT FINDINGS

Pooling of observational-matched studies demonstrated an incidence rate ratio (IRR) for device-related complication of 0.90 (95% CI 0.58-1.42) and IRR for lead-related complications of 0.15 (95% CI 0.06-0.39) in favor of S-ICD. The IRR for device infections was 2.00 (95% CI 0.95-4.22) in favor of TV-ICD. Both appropriate shocks (IRR 0.67 (95% CI 0.42-1.06)) and inappropriate shocks (IRR 1.17 (95% CI 0.77-1.79)) did not differ significantly between both groups. With randomized data underway, the observational data demonstrate that the S-ICD is associated with reduced lead complications, but this has not yet resulted in a significant reduction in total number of complications compared to TV-ICDs. New technologies are expected to make the S-ICD a more attractive alternative.

The subcutaneous implantable cardioverter defibrillator--review of the recent data

The subcutaneous implantable cardioverter defibrillators (SICD) is an alternative to the transvenous ICD for the prevention of sudden cardiac death (SCD). Multiple studies have shown that the SICD is safe and effective in treating ventricular arrhythmias. While earlier studies mainly enrolled younger patients with channelopathies, more recent reports included patients with “typical” indications for ICD therapy for the prevention of SCD. In this review we summarize the data available to date on the SICD while highlighting its pros and cons.

[Management of inappropriate shocks/T-wave-oversensing in S-ICD®-patients]

Inappropriate shocks are a feared complication after implantable cardioverter-defibrillator (ICD) implantation and have a tremendous impact on quality of life. Inappropriate shocks in patients with subcutaneous ICD (S-ICD®, Boston Scientific, Marlborough, MA, USA) have various underlying causes. This review summarizes the current literature on this topic and lists possible treatment options.

Specific indications and clinical outcome in patients with subcutaneous implantable cardioverter-defibrillator (ICD) - A nationwide multicentre registry

BACKGROUND

Subcutaneous implantable cardioverter-defibrillators (S-ICD) are an innovative and less invasive alternative to transvenous ICD (TV-ICD) in selected patients. We aimed to investigate the underlying diseases and the specific indications for implanting S-ICD in clinical practice, as well as the prevalence of shock delivery and complications.

METHODS AND RESULTS

From December 2012, data of 236 patients (30,5% female; age 48,6±16,8years) were gathered from 12 centres in Austria. Follow-up data over a period of 1,7±1,1years were available for 231 patients (in total 359,2 patient-years). Predominant underlying diseases were ischemic cardiomyopathy (iCMP; 32,0%), idiopathic ventricular fibrillation (22,6%) and dilated cardiomyopathy (dCMP; 17,3%). The most frequent indications for implantation were sudden cardiac death survival (27,4%), primary prevention for iCMP (23,9%) and for dCMP (12,8%), and previous explantation of TV-ICD (12,4%). Appropriate shocks were documented in 16 patients (6,9%), iCMP being the predominant underlying disease. Arrhythmia conversion was successful in all patients, efficacy of the first shock was 96%. Inappropriate shock rate was 5,2%, predominantly caused by oversensing of T wave or artefacts. A device upgrade to an ICD system with pacing function was necessary in <1%. Clinical complications needing surgical revision occurred in 8 patients (3,5%).

CONCLUSIONS

S-ICD were mostly implanted for primary prevention, one fourth of our cases were sudden death survivors. Clinical and functional complication rate was relatively low. In conclusion, S-ICD is a safe and efficient alternative in a larger population of ICD candidates, when no cardiac pacing is needed. EC-number: C-136-17.

Causes and Prevention of Inappropriate Implantable Cardioverter-Defibrillator Shocks

Use of implantable cardioverter-defibrillators as a primary prevention therapy has been shown to reduce mortality in patients after cardiac arrest and also with left ventricular systolic dysfunction. Yet, inappropriate shocks are variably reported and associated with a reduction in quality of life. Inappropriate shocks are the result of environmental causes leading to electromagnetic interference and inappropriate sensing of external noise, device-related causes from inappropriate sensing of physiologic or pathologic signals, and supraventricular arrhythmias. Strategies to reduce inappropriate shocks include aggressive treatment of supraventricular tachycardia, changes in device programming including prolonged detection time, programming antitachycardic pacing and using discriminator algorithms, and cardiac rehabilitation.

Inappropriate shocks in single-chamber and subcutaneous implantable cardioverter-defibrillators: a systematic review and meta-analysis

AIMS

Single-chamber (VR-ICD) and subcutaneous (S-ICD) implantable cardioverter-defibrillators are effective to protect patients against sudden death but expose them to higher risk of inappropriate shock (IS). We sought to quantify the annual rate and influencing factors of ISs in VR- and S-ICDs from the literature.

METHODS AND RESULTS

PubMed, Embase, and Cochrane Library were searched for full text articles with IS rates. Poisson distribution estimated proportion of patients with ISs; rates were annualized based on follow-up duration. Random effects meta-analysis accounted for study-to-study variation. Out of 3264 articles, 16 qualified for the meta-analysis. Across studies, 6.4% [95% confidence interval (CI) 5.1-7.9%] of patients received an IS per year. Meta-regression analyses demonstrated that IS rates were lower in more recent studies [rate ratio (RR) per year: 0.93, 95% CI: 0.87-0.98; P = 0.01] and trended lower in studies with longer follow-up (RR per year: 0.78, 95% CI: 0.60-1.01; P = 0.06). Use of S-ICDs (RR: 1.81, 95% CI: 0.86-3.81; P = 0.12) and ventricular tachycardia zone programmed on (RR: 1.13, 95% CI: 0.65-1.97; P = 0.66) were not associated with a significantly increased change in risk. The IS rate observed in one of the more recent studies was significantly lower than predicted after accounting for covariates (RR: 0.29, 95% CI: 0.14-0.60; P < 0.001).

CONCLUSIONS

A comprehensive review of the literature shows that 6.4% of patients with ICDs experienced their first IS annually. One of the 16 studies was better than predicted with the lowest reported rate (1.9%) and could not be explained by timing of the study or other covariates.

Extended detection time to reduce shocks is safe in secondary prevention patients: The secondary prevention substudy of PainFree SST

BACKGROUND

Prolonged ventricular fibrillation (VF) detection has been shown to reduce implantable cardioverter-defibrillator (ICD) therapies and improve prognosis in primary prevention ICD patients. Data in secondary prevention patients are limited.

OBJECTIVE

The PainFree SST secondary prevention study is the largest trial of secondary prevention patients randomized between standard and prolonged detection to assess the safety of this strategy in these patients.

METHODS

A total of 705 secondary prevention patients implanted with an ICD in the PainFree SST trial were enrolled in this substudy; 353 patients were randomized to VF detection of 18/24 intervals and 352 patients to 30/40. All other VF parameters were standardized by protocol.

RESULTS

The 1-year arrhythmic syncope-free rates in the standard and prolonged groups were 97.7% vs 96.9%, respectively, (P = .0034 for noninferiority). Freedom from all-cause syncope was 96% in both arms (P = .0013 for noninferiority). There was no difference in the time to first appropriate or inappropriate VF therapy. However, the rates of treated VF episodes were lower in the prolonged arm (1.48 per patient per year vs 0.44 per patient per year, P = .0001). A trend toward lower mortality in the prolonged group was not statistically different (5.6% 1 year, 12% 2 years vs 3.8% 1 year, 7.7% 2 years, adjusted hazard ratio = 0.60, P = .061).

CONCLUSION

This large prospective randomized study shows that prolonged detection can safely be programmed in secondary prevention ICD patients with new or existing devices. This programming strategy decreases the rate of treated events and is not associated with an increased risk of syncope or mortality.

Implantable cardioverter-defibrillators in adults with congenital heart disease: a systematic review and meta-analysis

AIMS

Sudden cardiac death is a major cause of mortality in adult congenital heart disease (ACHD) patients. The indications for implantable cardioverter-defibrillator (ICD) implantation in ACHD patients are still not well established. We aim to systematically review the literature on indications and outcome of ICD implantation in ACHD patients.

METHODS AND RESULTS

We performed a comprehensive search in EMBASE, MEDLINE, and Google Scholar to identify all studies on ICD implantation in ACHD patients. We used random effects models to calculate proportions and 95% confidence intervals. Of 1356 articles, 24 studies with 2162 patients were included, with a mean follow-up of 3.6 ± 0.9 years. Half of patients had tetralogy of Fallot. Mean age at implantation was 36.5 ± 5.5 years old and 66% was male. Implantable cardioverter-defibrillators were implanted for primary prevention in 53% (43.5-62.7). Overall, 24% (18.6-31.3) of patients received one or more appropriate ICD interventions (anti-tachycardia pacing or shocks) during 3.7 ± 0.9 years: 22% (16.9-28.8) of patients with primary prevention in 3.3 ± 0.3 years and 35% (26.6-45.2) of patients with secondary prevention in 4.3 ± 1.2 years. Inappropriate shocks occurred in 25% (20.1-31.0) in 3.7 ± 0.8 years and other, particularly lead-related complications in 26% (18.9-33.6) of patients in 3.8 ± 0.8 years. All-cause mortality was 10% during 3.7 ± 0.9 years.

CONCLUSIONS

In ACHD, remarkably high rates of appropriate ICD therapy were reported, both in primary and secondary prevention. Because of the young age and lower death rates, the cumulative beneficial effects are likely greater in ACHD patients than in acquired heart disease patients. However, considering the high rates of inappropriate shocks and complications, case-by-case weighing of costs and benefits, remains essential.

[Multiple inappropriate defibrillator shocks due to insulation failure of a Biotronik Linox defibrillator lead with externalized conductor]

In this article the case of a patient who received a total of 35 inappropriate defibrillator shocks due to insulation failure with externalized conductor of a Biotronik Linox® lead is described. The implanted defibrillator was immediately inactivated and the failed lead was extracted using a laser sheath system.

Clinical and electrocardiographic predictors of T wave oversensing in patients with subcutaneous ICD

BACKGROUND

T wave oversensing (TWOS) is a major drawback of the subcutaneous implantable cardioverter defibrillator (S-ICD). Data on predictors of TWOS in S-ICD recipients are limited. We sought to investigate predictors of TWOS in a cohort of patients receiving an S-ICD at our institution.

METHODS

S-ICD recipients at our center were identified retrospectively and stratified based on the presence or absence of TWOS. Clinical and electrocardiographic parameters were collected and compared between the 2 groups.

RESULTS

Ninety-two patients underwent an S-ICD implantation at our institution between April 2010 and January 2015. Six (6.5%) patients had TWOS. These patients were younger (38.1±13.7 vs. 52.3±16.1 years, p=0.04) and had higher left ventricle ejection fractions (48.5±14.9% vs. 28.4±12.2%, p<0.01) than patients without a history of TWOS. Baseline 12-lead electrocardiogram (ECG) parameters were not different between the 2 groups. Leads I, II, and avF (which mimic the sensing vectors of the S-ICD) were further inspected to identify ECG characteristics that could predict TWOS. The QRS amplitude in ECG lead I was significantly smaller in the TWOS group than in the non-TWOS group (3.7 vs. 7.4 mV, p=0.02).

CONCLUSION

In this study, younger age, higher ejection fraction, and lower QRS amplitude were associated with TWOS. These findings could help identify patients referred for S-ICD at high-risk of TWOS.

Incidence of arrhythmias in a large cohort of patients with current implantable cardioverter-defibrillators in Spain: results from the UMBRELLA Registry

AIMS

The benefit of implantable cardioverter-defibrillators (ICDs) in patients at risk of sudden death has been established in randomized clinical trials (RCTs) using the ICD models available at the time. However, observational large-scale data on the incidence of arrhythmias in up-to-date ICDs implanted according to the current guidelines are scarce. The aim was to assess the incidence of arrhythmias in a large, current ICD population based on a blinded peer review of the detected episodes.

METHODS AND RESULTS

UMBRELLA is a multicentre, observational registry of ICD patients followed by remote monitoring. Stored episodes were classified by a blinded committee of experts. Subgroup analyses were based on clinical profiles established by previous pivotal RCTs of ICDs. Of 1514 enrolled patients, 605 (39.9%) patients had 5951 episodes after 26 ± 17 months follow-up, being 3353 of them (56.3%) sustained ventricular arrhythmias (SVA), and 13.2% of SVA were self-terminated. Appropriate and inappropriate shocks occurred in 11.6 and 5% of patients, respectively. The 3 years cumulative incidence of SVA was 25% (95% CI: 21-28%) in primary prevention patients and 41% (95% CI: 36-47%) in secondary prevention patients (P < 0.001). Male gender, secondary prevention, and atrial fibrillation as basal rhythm were significantly related to a higher incidence of SVA.

CONCLUSION

This real-world analysis suggests that modern ICD patients have a low rate of appropriate and inappropriate shocks. The risk of SVA in secondary prevention patients is less than what has been reported in RCTs.

Admittance to detect alterations in left ventricular stroke volume

BACKGROUND

Implantable cardioverter-defibrillators monitor intracardiac electrograms (EGMs) to discriminate between ventricular and supraventricular tachycardias. The incidence of inappropriate shocks remains high because of misclassification of the tachycardia in an otherwise hemodynamically stable individual. Coupling EGMs with an assessment of left ventricular (LV) stroke volume (SV) could help in gauging hemodynamics during an arrhythmia and reducing inappropriate shocks.

OBJECTIVE

The purpose of this study was to use the admittance method to accurately derive LV SV.

METHODS

Ultrasonic flow probe and LV endocardial crystals were used in canines (n = 12) as the standard for LV SV. Biventricular pacing leads were inserted to obtain admittance measurements. A tetrapolar, complex impedance measurement was made between the Bi-V leads. The real and imaginary components of impedance were used to discard the myocardial component from the blood component to derive instantaneous blood conductance (Gb). Alterations in SV were measured during right ventricular pacing, dopamine infusion, and inferior vena cava occlusion.

RESULTS

Gb tracks steady-state changes in SV more accurately than traditional magnitude (ie, |Y|, without removal of the muscle signal) during right ventricular pacing and dopamine infusion (P = .004). Instantaneous LV volume also was tracked more accurately by Gb than ∣Y∣ in the subset of subjects that underwent inferior vena cava occlusions (n = 5, P = .025). Finite element modeling demonstrates that admittance shifts more sensitivity of the measurement to the LV blood chamber as the mechanism for improvement (see Online Appendix).

CONCLUSION

Monitoring LV SV is possible using the admittance method with biventricular pacing leads. The technique could be piggybacked to complement EGMs to determine if arrhythmias are hemodynamically unstable.

Use of an electrocardiographic screening tool to determine candidacy for a subcutaneous implantable cardioverter-defibrillator

BACKGROUND

An electrocardiographic (ECG) screening test has been developed to identify patients being considered for a totally subcutaneous implantable cardioverter-defibrillator (S-ICD) at risk for T-wave oversensing.

OBJECTIVE

The purpose of this study was to determine the proportion of potential S-ICD recipients who fail the ECG screening test and to identify predictors of failure.

METHODS

Patients who already have an ICD but are not receiving antibradycardia pacing are representative of patients who might be considered for an S-ICD. One hundred such outpatients were enrolled in the study. Surface rhythm strips were recorded along the sensing vectors of the S-ICD system and the screening template applied. Clinical and standard ECG characteristics of patients who failed the test were compared to those who passed.

RESULTS

Patients had the following characteristics: 72% male, age 57 ± 16 years, body mass index 29 ± 6 kg/m(2), left ventricular ejection fraction 43% ± 17%, QRS duration 109 ± 23 ms, QTc interval 447 ± 39 ms, 44% had coronary disease, and 55% had heart failure. Among the 100 patients, 8% failed the screening test. There were no differences in patient clinical characteristics and most standard ECG measurements. However, patients with T-wave inversions in standard ECG leads I, II, and aVF had a 45% chance of failing.

CONCLUSION

Eight percent of potential S-ICD patients were not eligible for the S-ICD after failing the screening test designed to identify patients susceptible to T-wave oversensing. Patients with T-wave inversions in leads I, II, and aVF on a standard ECG were 23 times more likely to fail. More work is needed in S-ICD sensing algorithms to increase patient eligibility for the S-ICD.

Early fatigue fractures in the IS-1 connector leg of a small-diameter ICD lead: value of returned product analysis for improving device safety

BACKGROUND

Conductor fractures may affect the performance of implantable cardioverter-defibrillator leads. During routine surveillance of returned product analyses (RPAs) in the Food and Drug Administration's Manufacturers and User Facility Device Experience database, we found a number of conductor fractures in small diameter implantable cardioverter-defibrillator leads manufactured by St Jude Medical, Inc (SJM, Sylmar, CA).

OBJECTIVES

To determine the location and cause of these fractures and to catalog their clinical signs and consequences.

METHODS

We searched the FDA's Manufacturers and User Facility Device Experience database on April 11, 2013. SJM provided information and data it collected independently.

RESULTS

Our search found 59 leads with fractures in the IS-1 leg. Most fractures were in leads implanted in 2008-2009; no fractures were found in leads implanted after 2010. Outer coil conductor fractures accounted for the majority (51 of 59, 86%). Oversensing and noise were common signs, and 81% of the patients received inappropriate shocks. SJM's RPAs found that the fractures were due to inadequate strain relief and redesigned the IS-1 leg by shortening the crimp bore. Younger age and subpectoral implants appeared to be associated with these fractures. SJM stated the incidence is low (0.040%) and has not seen further fractures of this type in leads with the modified crimp.

CONCLUSIONS

SJM's small diameter leads that were manufactured before 2011 are prone to early outer coil fatigue fractures in the IS-1 leg. The failure mechanism appears to have been mitigated by a design change. RPA is important for improving device safety.

AV nodal reentrant tachycardia causing inappropriate ICD shocks in a patient with arrhythmogenic RV dysplasia

We report a patient with an implantable cardioverter defibrillator (ICD) for arrhythmogenic right ventricular dysplasia (ARVD) who received inappropriate shocks for atrioventricular node reentry tachycardia (AVRNT). Patient had multiple shocks for tachycardia with EGM characteristics of very short VA interval and CL of 300 msec. An electrophysiologic (EP) study reproducibly induced typical AVNRT with similar features. The slow AV nodal pathway ablation resolved the ICD shocks. Despite increasingly sophisticated discrimination algorithms available in modern ICDs, the ability to differentiate SVT from VT can be challenging. Our patient received inappropriate shocks for AVNRT. When device interrogation alone is not conclusive, an EP study may be necessary to determine the appropriate therapeutic course.