One short circuit, two novel subcutaneous implantable cardiac defibrillator complications

Background Short circuits from cardiac implantable electronic device (CIED) systems leak current to surrounding tissues, rendering them malfunctional and resulting in unpredictable behaviour. Case summary A 74-year-old gentleman was admitted electively for subcutaneous implantable cardiac defibrillator (SICD) generator change. The generator was exchanged like-for-like without incident. During defibrillation testing (DFT), both shocks were unsuccessful, with the second shock causing a malfunction in the self-adhesive pads attached to the external defibrillator. Following brief cardiopulmonary resuscitation, new pads were attached, resulting in successful external defibrillation. Post-procedure analysis revealed the impedance within the device system was <1Ω, and therefore the defibrillation energy had delivered into a short circuit throughout the patient’s thorax. 120 days later, the patient received a second complication, experiencing a further shock despite tachycardia therapies being programmed off due to a capacitor reformation. Extraction of the device later revealed an insulation breach as the cause of both complications. Discussion In this case, the unpredictable behaviour from CIEDs due to short circuits resulted in two novel SICD complications. High voltage energy dissipated via the short can cause damage to other external devices, uncomfortable ‘inappropriate’ shocks, and patient harm. During DFT, a poor patient outcome was aborted on this occasion due to good team communication. The importance of operator knowledge of capacitor reformation and ability to cause an inadvertent device shock in the presence of a short circuit is emphasized.