Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. The subcutaneous implantable cardioverter-defibrillator (ICD) was shown to be noninferior to the transvenous ICD for device-related complications in patients with an indication for ICD therapy but not for pacing therapy.

2. The risk of inappropriate shocks was not significantly different between groups, but trended towards increased risk in the subcutaneous ICD group.

Evidence Rating Level: 1 (Excellent)

Study Rundown:

Implantable cardioverter-defibrillator (ICD) have been shown to be effective in sudden cardiac death prevention. The standard ICD design has been transvenous lead placement; however, there are limitations to the technique such as risk of cardiac perforation and lead dysfunction. Therefore, the subcutaneous ICD was developed to avoid entering the heart and vasculature. This study evaluated whether the subcutaneous ICD was noninferior to the transvenous ICD in regard to device-related complications and inappropriate shocks. The study determined the subcutaneous ICD was noninferior to the transvenous ICD in regard to device-related complications. The difference in risk of inappropriate shock trended towards significance in the subcutaneous ICD but was ultimately not significantly different. This randomized trial was limited by the its trial design. Because it was not double-blinded, the clinical-events committee was aware of the trial-group assignments. Also, the screening data was incomplete, and resulted in potential selection bias. Nonetheless, this study was strengthened by the long-term follow-up and extensive analysis between the two ICD techniques.

In-Depth [randomized controlled trial]:

This randomized control trial enrolled 876 patients in a multicenter study consisting of 39 centers from Europe and the United States. Participants who were 18 years of age or older and had a class I or IIa indication for ICD were included. Participants who had undergone previous ICD implantation and had indications for either bradycardia pacing or biventricular pacing were excluded. The patients were randomized in a 1:1 ratio to receive a subcutaneous ICD or transvenous ICD. The primary end points were device-related complications and inappropriate shocks. Device-related complications consisted of device infection, pocket hematoma, device-related thrombotic event, and lead repositioning. An inappropriate shock was defined as it was delivered for any rhythm other than ventricular fibrillation or ventricular tachycardia. The primary endpoint occurred in 68 patients in the subcutaneous ICD group (estimated cumulative incidence, 15.1%) and 68 patients in the transvenous ICD group (estimated cumulative incidence, 15.7%). The hazard ratio for the primary end point was 0.99 (95% confidence interval [CI], 0.71 to 1.39). Specifically, device-related complications occurred in 31 patients in the subcutaneous ICD group (estimated cumulative incidence, 5.9%) and 44 patients in the transvenous ICD group (estimated cumulative incidence, 9.8%; hazard ratio, 0.69; 95% CI, 0.44 to 1.09). Inappropriate shock occurred in 41 patients in the subcutaneous ICD group (estimated cumulative incidence, 9.7%) and 29 patients in the transvenous ICD group (estimated cumulative incidence, 7.3%; hazard ratio, 1.43; 95% CI, 0.89 to 2.30). The inappropriate shocks most frequently occurred in the subcutaneous group due to cardiac oversensing (58.5% of patients with an inappropriate shock), while the inappropriate shocks in the transvenous ICD group were commonly triggered by supraventricular arrhythmia (93.1% of patients with an inappropriate shock). Taken together, the subcutaneous ICD was shown to be noninferior to the transvenous ICD in regard to device-related complication and inappropriate shocks.

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