The Subcutaneous ICD: A Review of the UNTOUCHED and PRAETORIAN Trials

Abstract

The ICD is an important part of the treatment and prevention of sudden cardiac death in many high-risk populations. Traditional transvenous ICDs (TV-ICDs) are associated with certain short- and long- term risks. The subcutaneous ICD (S-ICD) was developed in order to avoid these risks and complications. However, this system is associated with its own set of limitations and complications. First, patient selection is important, as S-ICDs do not provide pacing therapy currently. Second, pre-procedural screening is important to minimise T wave and myopotential oversensing. Finally, until recently, the S-ICD was primarily used in younger patients with fewer co-morbidities and less structural heart disease, limiting the general applicability of the device. S-ICDs achieve excellent rates of arrhythmia conversion and have demonstrated noninferiority to TV-ICDs in terms of complication rates in real-world studies. The objective of this review is to discuss the latest literature, including the UNTOUCHED and PRAETORIAN trials, and to address the risk of inappropriate shocks.

Successful repositioning of the subcutaneous implantable cardioverter‐defibrillator lead to avoid inappropriate shock

“…It is the first‐line therapeutic device, especially for young patients, without the need for pacing at the ventricles because there is a lower risk of complications associated with the leads, including vascular injury, lead fracture, or lead infection, than with the TV‐ICD system. S‐ICD has more oversensing than TV‐ICD, but recent reports have shown that S‐ICD has similar or even lower rates of inappropriate shocks compared to TV‐ICD 3 . In our case, changing the sensing vector was not sufficient to avoid inappropriate shock, but it was successfully prevented by repositioning the S‐ICD lead downward.…”

“…S‐ICD has more oversensing than TV‐ICD, but recent reports have shown that S‐ICD has similar or even lower rates of inappropriate shocks compared to TV‐ICD. 3 In our case, changing the sensing vector was not sufficient to avoid inappropriate shock, but it was successfully prevented by repositioning the S‐ICD lead downward.…”

The wearable cardioverter‐defibrillator—Improving comfort and reaching towards noise immunity

“…Misclassifications of SVTs were fewer with the novel WCD which uses electrocardiogram segments rather than the beat‐to‐beat basis for ICD detection (of ICD detected 131 inappropriate detections only one of these resulted in a false positive by the WCD diagnostic algorithm). These results show that cutaneous, as well as subcutaneous sensing systems, are at least noninferior to the gold standard of intracardiac discriminators 3 …”

“…These results show that cutaneous, as well as subcutaneous sensing systems, are at least noninferior to the gold standard of intracardiac discriminators. 3 Significantly, the number of noise detection events with the WCD remained high but the incidence of false alarms was very low. Thus, among 159 non‐VT/VF episodes, 153 were noise‐related, but only three triggered shock alarm markers (i.e., false positives).…”

Patient acceptance: Metrics, meaning, and the “missing piece” in evaluating novel devices

“…2 Relative considerations to be fully discussed in a shared decision-making process relate to patient selection, likely future device needs, and patient device preference remain, but can more fully addressed with the emerging empirical data. 3 Concerns about increased exposure to shocks, due to the lack of ATP, in S-ICD have been quelled somewhat with the encouraging shock rates of UNTOUCHED, which were shown to be comparable to TV-ICD. 4 Few complications occurred in the trial with 1.1% infection rate and 0.5% of patients explanted the S-ICD and implanted an ICD.…”