An entirely subcutaneous implantable cardioverter defibrillator (ICD) differs from a transvenous ICD in that a single lead is placed subcutaneously. This single lead comprises 2 sensing ring electrodes and a shocking coil. The subcutaneous ICD senses cardiac signals, but the lead is not directly attached to the heart. Also, unlike a conventional transvenous ICD, the subcutaneous device is not designed to provide long-term pacing.
The implantation procedure is carried out with the patient under general anaesthesia, or with local anaesthesia and sedation. Implantation is guided by anatomical landmarks with or without the use of fluoroscopy or other medical imaging. A subcutaneous pocket for the generator is created on the left side of the chest. The lead is tunnelled subcutaneously from the pocket to a small incision at the lower end of the sternum. Then, it is tunnelled to the upper end of the sternum so that the sensing ring electrodes and shocking coil lie alongside the sternum. The lead can be secured using either a 2- or 3‑incision technique, and is then connected to the generator in the pocket. Finally, the incisions are closed and the sensing and recording functions of the subcutaneous ICD are adjusted using an external programmer. Ventricular fibrillation is induced to test that the subcutaneous ICD can appropriately detect and correct it.