Perspective:

The major advantage of an S-ICD is the lack intravascular or intracardiac components that eliminates or greatly diminishes risks such as perforation, pneumothorax, thrombosis/occlusion, and severe infection such as bacteremia/endocarditis. The subcutaneous location also results in a higher defibrillation threshold, i.e., the minimum energy required to convert ventricular fibrillation, as compared to transvenous devices. Data suggest that DFT may be bypassed in most patients receiving a transvenous ICD for primary prevention. However, given higher energy requirements, DFT is recommended at the time of implantation of an S-ICD. This study shows that these recommendations are not adhered to in about one-third of the patients, and this is more likely related to physician preference as compared to patient characteristics. The reasons behind deferral of DFT are unknown, but may be due to physician practice/assumption that DFT does not improve outcomes, the fact that these data were obtained from transvenous patients notwithstanding. Another possibility is the paucity of options (e.g., moving the transvenous electrode, adding or removing coils, etc.) in the setting of ISM.