Failure to deliver therapy by a Riata Lead with internal wire externalization and normal electrical parameters during routine interrogation.

We present a case of failure to deliver a shock by a St. Jude Medical defibrillator involving a Riata lead that was discovered incidentally while the device was attempting to deliver inappropriate therapy. Routine interrogation, including high voltage (HV) impedance, failed to reveal any abnormality. Failure to deliver therapy was confirmed during DFT testing, which revealed extremely low HV impedance only while attempting to deliver therapy. Fluoroscopy indicated moderate externalization of internal wires. This case highlights an under-recognized issue with St. Jude Medical systems, namely the possibility that therapy may not be delivered despite the presence of normal electrical parameters during routine surveillance.