Inappropriate high-rate ventricular pacing in a patient with a defibrillator

We describe a patient who presented with high rate ventricular pacing secondary to dysfunction of his implantable cardioverter defibrillator (ICD). The device was also unable to communicate with the programmer and unable to treat ventricular fibrillation. Immediate disconnection of the ICD from the leads was the only effective recourse. Subsequent detailed technical analysis of the device revealed a different electrical circuit problem from that found in typical cases of runaway pacing. To our knowledge this is the first description of a malfunction of precisely this nature.