Introduction: Runaway pacemaker is a potentially catastrophic complication of any permanent pacing system.
Methods and results: A 70-year-old man was found to have erratic behavior of his implantable cardioverter defibrillator (ICD) during a routine outpatient interrogation. His device was turned off, and he was hospitalized in preparation for a pulse generator replacement. During his hospitalization, his ICD unexpectedly began pacing rapidly. Despite prompt resuscitation attempts, the patient died. Postmortem examination of the device demonstrated a crystal oscillator failure.
Conclusion: A previously unrecognized component malfunction is a potentially lethal complication of ICDs.