Case: A 62-year-old man attended electively for implantation of a subcutaneous implantable cardioverter defibrillator (S-ICD) for primary prevention due to dilated cardiomyopathy with severe left ventricular systolic dysfunction (LVSD). His past medical history included type II diabetes. Screening prior to implant demonstrated that the primary and alternative vectors were acceptable. The S-ICD was implanted under general anaesthetic using a two-incision technique. The generator was placed in an intermuscular position. Both pockets were flushed with normal saline. The sensing was programmed to the primary vector. Routine defibrillation threshold testing was performed successfully with a shock impedance of 68 Ohms. On return to the ward, the patient received two inappropriate shocks due to noise (Figure 1). Interrogation revealed a drop in R wave amplitude and intermittent noise seen in both the primary and alternate vectors. These both utilize the proximal electrode. A chest X-ray demonstrated a small amount of air overlying the proximal electrode (Figure 1). device was briefly deactivated to allow for resorption. Unfortunately, the patient re-presented 10 weeks later with a further inappropriate shock, which again was due to noise and a transient drop in R wave amplitude. Repeat chest X-rays showed resorption of the air previously seen and that the pin remained through the header. The sensing was still programmed to the primary vector. On interrogation of the device, noise was reproducible with patient movement on the secondary vector, but not on either the primary or alternate vectors. The device was deactivated. After seeking advice from Boston, the patient attended for explant and re-implant of a new S-ICD system. Visual inspection at the time of explant confirmed that the pin was through the header and screwed in. The device was returned to Boston for further analysis. Analysis of both the generator and lead failed to identify any issue that could have caused or contributed to the inappropriate shocks. To date, the patient has not had any issues with the new device. ❑
