High defibrillation threshold with a subcutaneous implantable cardiac defibrillator due to the lead having been positioned in the fat layer.

A 46-year-old female with a body mass index of 38.9 kg/m and no organic heart disease underwent a subcutaneous implantable cardioverter-defibrillator implantation for secondary prevention of sudden cardiac death in the setting of idiopathic ventricular fibrillation. Defibrillation threshold (DFT) testing during implantation detected high shock impedance and high DFT. Fluoroscopy revealed subcoil fat between the lead and the sternum, which we suspected was the reason for the high shock impedance and high DFT. We repositioned the lead to a site just above the sternum and the shock impedance and DFT improved to within the respective normal ranges.