The Design of the Understanding Outcomes with the S-ICD in Primary Prevention Patients with Low EF Study (UNTOUCHED)

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.

Rationale and design of the HINODE study: Heart failure indication and sudden cardiac death prevention trial Japan

BACKGROUND

Randomized trials in Western countries have provided evidence that prophylactic implantable cardioverter-defibrillator (ICD) therapy reduces mortality in heart failure (HF) patients with reduced left ventricular ejection fraction. However, the risk of life-threatening ventricular arrhythmias in Japanese HF patients sharing similar risk factors is still unknown.

METHODS

The Heart Failure Indication and Sudden Cardiac Death Prevention Trial Japan trial (NCT03185832) is a prospective, multicenter registry designed to collect data on ventricular arrhythmia, HF events, and mortality in Japanese HF patients. Japanese patients with HF and 2-5 predefined risk factors who were indicated for cardiac device implantation based on European Society of Cardiology guidelines were enrolled in four treatment arms: implantable cardioverter-defibrillator (ICD), cardiac resynchronization therapy defibrillator (CRT-D), HF pacing (PA; Pacemaker and cardiac resynchronization pacemaker), and nondevice (ND) cohorts and followed for a minimum of 12 months. Since it is anticipated that some baseline patient characteristics and risk factors will differ significantly from those reported in predominantly Western populations, event rates will be compared to a propensity-matched population from the MADIT RIT trial. Primary endpoints are composite rates of first appropriately treated ventricular arrhythmias (VA) or/and life-threatening VA symptoms for the ICD and CRT-D cohorts. For nondevice and PA cohorts, the primary outcome is all-cause mortality.

CONCLUSIONS

The Heart Failure Indication and Sudden Cardiac Death Prevention Trial Japan is a large prospective multicenter registry with defined device treatment cohorts and will provide data for risk stratification for cardiovascular events in Japanese HF patients.

Primary Results From the Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction (UNTOUCHED) Trial

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Background:

The subcutaneous (S) implantable cardioverter-defibrillator (ICD) is safe and effective for sudden cardiac death prevention. However, patients in previous S-ICD studies had fewer comorbidities, had less left ventricular dysfunction, and received more inappropriate shocks (IAS) than in typical transvenous ICD trials. The UNTOUCHED trial (Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction) was designed to evaluate the IAS rate in a more typical, contemporary ICD patient population implanted with the S-ICD using standardized programming and enhanced discrimination algorithms.

Methods:

Primary prevention patients with left ventricular ejection fraction ≤35% and no pacing indications were included. Generation 2 or 3 S-ICD devices were implanted and programmed with rate-based therapy delivery for rates ≥250 beats per minute and morphology discrimination for rates ≥200 and <250 beats per minute. Patients were followed for 18 months. The primary end point was the IAS-free rate compared with a 91.6% performance goal, derived from the results for the ICD-only patients in the MADIT-RIT study (Multicenter Automatic Defibrillator Implantation Trial–Reduce Inappropriate Therapy). Kaplan-Meier analyses were performed to evaluate event-free rates for IAS, all-cause shock, and complications. Multivariable proportional hazard analysis was performed to determine predictors of end points.

Results:

S-ICD implant was attempted in 1116 patients, and 1111 patients were included in postimplant follow-up analysis. The cohort had a mean age of 55.8±12.4 years, 25.6% were women, 23.4% were Black, 53.5% had ischemic heart disease, 87.7% had symptomatic heart failure, and the mean left ventricular ejection fraction was 26.4±5.8%. Eighteen-month freedom from IAS was 95.9% (lower confidence limit, 94.8%). Predictors of reduced incidence of IAS were implanting the most recent generation of device, using the 3-incision technique, no history of atrial fibrillation, and ischemic cause. The 18-month all-cause shock-free rate was 90.6% (lower confidence limit, 89.0%), meeting the prespecified performance goal of 85.8%. Conversion success rate for appropriate, discrete episodes was 98.4%. Complication-free rate at 18 months was 92.7%.

Conclusions:

This study demonstrates high efficacy and safety with contemporary S-ICD devices and programming despite the relatively high incidence of comorbidities in comparison with earlier S-ICD trials. The inappropriate shock rate (3.1% at 1 year) is the lowest reported for the S-ICD and lower than many transvenous ICD studies using contemporary programming to reduce IAS.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT02433379.

The subcutaneous ICD for prevention of sudden cardiac death: Current evidence and future directions

Despite major advances in medical therapy, sudden cardiac death remains an important cause of cardiovascular mortality. In order to improve the risk-benefit balance of transvenous implantable cardioverter-defibrillator (ICD) systems, a totally subcutaneous ICD (S-ICD) system was developed and approved for use in Europe in 2009. The currently available S-ICD system has undergone several important hardware- and software-related modifications and improvements over the last 10 years aimed at further improving its efficacy and safety. The results of the PRAETORIAN trial, that is, the first randomized comparison of S-ICD versus transvenous ICDs, of the prospective UNTOUCHED study, and the overall consistent observational data underline that current generation S-ICD systems may be a valid alternative in patients with an ICD indication in whom bradycardia pacing or cardiac resynchronization therapy is not required due to a lower risk of system-related problems. This review summarizes the key differences between the two systems, improvements in hardware components and algorithms over time, as well as most recent clinical evidence regarding the efficacy and safety of the S-ICD.

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).

The subcutaneous implantable cardioverter-defibrillator: Current trends in clinical practice between guidelines and technology progress

The subcutaneous implantable cardioverter defibrillator (S-ICD) is a valuable alternative to the conventional trans-venous ICD (TV-ICD) for the prevention of sudden cardiac death (SCD). Prospective registries showed that the S-ICD is safe and effective in treating ventricular tachyarrhythmias in high-risk patients without pacing indications. While in earlier studies patients implanted with S-ICDs were young and mostly affected by channelopathies, contemporary S-ICD cohorts include patients with severely impaired left ventricular function and significant comorbidities. This review focuses on S-ICD evidence-based use and highlights current gaps between guidelines recommendations and real-world clinical practice.

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.

The Subcutaneous Implantable Cardioverter-Defibrillator: New Insights and Expanding Populations

Implantable cardioverter defibrillators (ICDs) have become a mainstay of treatment in patients at risk for sudden cardiac death. The majority of contemporary ICDs are implanted transvenously; however, this approach carries acute procedural and long-term risks. The subcutaneous ICD (S-ICD) was developed, in part, to circumvent some of these adverse events or as an alternative option in patients unable to undergo transvenous implantation. Early promising trials evaluating the S-ICD were small and focused on niche populations. More recently, larger trials included broader populations with worse heart failure and co-morbidities that may be more representative of typical ICD recipients. These studies have consistently demonstrated positive results. This review describes the S-ICD system, implantation, and the safety and efficacy of the device.

Recent advances in the management of ventricular tachyarrhythmias

Ventricular arrhythmias are an important cause of cardiovascular morbidity and mortality, particularly in those with structural heart disease, inherited cardiomyopathies, and channelopathies. The goals of ventricular arrhythmia management include symptom relief, improving quality of life, reducing implantable cardioverter defibrillator shocks, preventing deterioration of left ventricular function, reducing risk of arrhythmic death, and potentially improving overall survival. Guideline-directed medical therapy and implantable cardioverter defibrillator implantation remain the mainstay of therapy to prevent sudden cardiac death in patients with ventricular arrhythmias in the setting of structural heart disease. Recent advances in imaging modalities and commercial availability of genetic testing panels have enhanced our mechanistic understanding of the disease processes and, along with significant progress in catheter-based ablative therapies, have enabled a tailored and more effective management of drug-refractory ventricular arrhythmias. Several gaps in our knowledge remain and require further research. In this article, we review the recent advances in the diagnosis and management of ventricular arrhythmias.