1-Year Evaluation of Outcomes and Shocks in Subcutaneous ICD Post Approval Study

Quick Takes

  • This observational cohort study demonstrates the efficacy of the S-ICD in terminating ventricular arrhythmias.
  • Further research is needed (and is forthcoming) to continue and lower the inappropriate shock rate and assess long-term outcomes.

Study Questions:

What are 1-year clinical outcomes and rate of spontaneous arrhythmias in patients with the subcutaneous implantable-cardioverter defibrillator (S-ICD)?


The S-ICD PAS (Subcutaneous Implantable Cardioverter-Defibrillator Post Approval Study) is a prospective registry of 1,637 patients from 86 centers in the United States undergoing S-ICD implant between August 2013 and May 2016. Data collected up to 1-year post-implantation were analyzed. An independent Clinical Events Committee adjudicated appropriate and inappropriate shocks and procedure-related complications. Treated and untreated events were recorded. Unclassifiable events were excluded. Descriptive statistics and multivariate logistic regression analysis were performed.


Patients were predominantly (68.5%) men, 42.9% had ischemic cardiomyopathy, 76.6% had primary prevention of sudden cardiac death as the indication, 73.9% had heart failure, and 13.4% were on dialysis. The complication-free rate was 92.5%; 5.4% (89/1,637) were deceased by 1 year, with 40/89 (44.9%) due to noncardiac, 39/89 (43.8%) cardiac, and 10/89 (11.2%) unknown causes. Of the 39 cardiac deaths, 11 were arrhythmic. No deaths were attributed to S-ICD malfunction, although one was related to the implantation procedure. The appropriate shock (AS) rate was 5.3%; the inappropriate shock (IAS) rate was 6.5% and mainly due to oversensing. A total of 395 ventricular tachycardia (VT) or fibrillation (VF) episodes were appropriately sensed; first and final shock efficacy (up to 5 shocks) for the 127 discrete AS episodes were 91.3% and 100.0%, respectively; 131 (33.2%) were self-terminating. For the 19 storm events in 18 subjects, 84.2% were successfully converted. Most patients (76.9%) had the conditional zone cutoff (for therapy) of ≥200 bpm.


After 1-year follow-up, a predominantly primary prevention population implanted with the S-ICD had a high complication-free rate and high spontaneous event shock efficacy for monomorphic and polymorphic VT and VF arrhythmias.


This observational cohort study adds evidence to a previous report from the S-ICD PAS and the EFFORTLESS (Evaluation of Factors Impacting Clinical Outcome and Cost Effectiveness of the S-ICD) and PRAETORIAN (Prospective Randomized Comparative Trial of Subcutaneous Implantable Cardioverter-Defibrillator Implantation) studies.

Limitations include the observational nonrandomized design, only 1-year follow-up, variability of clinical practice at the sites, and utilization of the older (first) generation S-ICD that lacks the enhanced filtering in the newest generation. Five-year follow-up will provide important data on longitudinal safety, efficacy, and clinical outcomes.

The 6.5% IAS rate was lower than prior studies but higher than the AS rate in the current study and also higher than the IAS rate in the UNTOUCHED study, which utilized the newest generation S-ICD (not used in S-ICD PAS); enhanced programming and further research on oversensing should continue to reduce the IAS rate.

Clinical Topics: Arrhythmias and Clinical EP, Heart Failure and Cardiomyopathies, Prevention, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Acute Heart Failure

Keywords: Arrhythmias, Cardiac, Cardiomyopathies, Death, Sudden, Cardiac, Defibrillators, Implantable, Heart Failure, Primary Prevention, Renal Dialysis, Shock, Tachycardia, Ventricular, Ventricular Fibrillation

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