Introduction

The advent of the subcutaneous (S) implantable cardioverter-defibrillator (ICD) brings with it many benefits as well as specific limitations when compared with standard transvenous (TV) ICDs. The S-ICD solves some of the challenges posed by an increasingly complex population of patients requiring primary or secondary prevention of sudden cardiac death (SCD). Specifically, avoiding the need for TV leads markedly reduces the risk of lead malfunction and systemic infection, which are 2 of the most serious complications with ICD therapy. Given the lack of pacing therapy in the S-ICD system, the early use of this device was often in niche populations enriched with channelopathies and nonischemic cardiomyopathy.¹ Accordingly, there are several unanswered questions that limit the generalizability of the S-ICD to more common ICD patients. One such question is the safety and efficacy of S-ICD implantation in older patients.

The EFFORTLESS (Evaluation oF FactORs ImpacTing CLinical Outcome and Cost EffectiveneSS of the S-ICD) study of primarily European sites and the U.S. IDE (Investigational Device Exemption) trial were early multicenter trials establishing the safety and efficacy of the device to prevent SCD, but at the cost of a high incidence of inappropriate shocks.^2,3 These studies had very few older patients. The more recent studies of the S-ICD, such as the Post Approval Study, PRAETORIAN (Prospective Randomized Comparison of Subcutaneous and Transvenous Implantable Cardioverter Defibrillator Therapy) and UNTOUCHED (Understanding Outcomes With the S-ICD in Primary Prevention Patients With Low Ejection Fraction) trials included more typical cohorts for the S-ICD and showed significant reductions in inappropriate shock rates as programming and discrimination algorithms in the device improved.^4-6 However, there is still an age bias in enrollment, as recent prospective trials included patients with average age <65 years.^4-6

To provide a more comprehensive evaluation of the S-ICD efficacy in older populations, Friedman et al,⁷ in this issue of the Journal of the American College of Cardiology, performed a longitudinal retrospective outcomes study using “big data” by analyzing the National Cardiovascular Data Registry (NCDR) ICD registry to compare S-ICD and TV-ICD patients. To address some of the concerns regarding this database abstraction, thorough quality checks and audits for enrollment sites on an annual basis were performed to demonstrate >90% accuracy for reported data elements. Furthermore, the authors calculated a propensity score for S-ICD use, and overlap weighting was used to account for the differences in S-ICD versus TV-ICD use (991 vs 15,072 patients), as well as a falsification analysis. There were significant differences in characteristics of patients between the 2 groups, such as S-ICD patients being more commonly Black, younger, more frequently dialysis dependent, and less likely to have atrial arrhythmias. There were no differences in primary and secondary endpoints of all-cause mortality, device reoperation, device removal due to infection, device removal without infection, cardiovascular readmission, or all-cause readmission over a median 2.3 years of follow-up. However, there were some important limitations of this study, including the exclusion of secondary prevention patients, the exclusion of many patients due to inability to link to claims data or to loss of Medicare insurance, and the absence of data on inappropriate shocks. It is also important to note that differences in insurance coverage may affect other unreported outcomes due to patients’ likelihood to seek frequent medical care, or by virtue of socioeconomic determinants of health.

Despite these limitations, the present study includes a very large cohort of older patients comparing outcomes of the S-ICD with TV-ICD. A meta-analysis of early case-control studies showed similar outcomes between S-ICD and TV-ICD, but this was a much younger cohort.⁸ The PRAETORIAN study was the first large, randomized trial of S-ICD and TV-ICD. This was a noninferiority study showing that the 2 device types have similar outcomes with regard to the primary endpoint of device-related complications and inappropriate shocks, as well as secondary endpoints of death and appropriate shocks. The median age of this cohort was 63 years, so there were many older patients included. Importantly, age was not a predictor of difference based on prospective subgroup analyses.⁵ Similarly, the PAS (Post Approval Study) and UNTOUCHED studies showed no significant effect of age on outcomes with more contemporary devices.^4,6 Thus, all contemporary S-ICD trials, including the present study, support the concept that age should not be a limiting factor for the use of the S-ICD.

In conclusion, the authors should be commended for performing this large and carefully analyzed assessment of the NCDR database to compare the S-ICD and TV-ICD in older patients. These important results support and extend previous studies suggesting that the age bias in S-ICD use in not warranted with contemporary ICD devices and programming (Figure 1). So, hopefully we can treat older patients with a new trick of avoiding TV leads while still protecting from SCD in the absence of pacing indications.

Source: JACC