The tracing suggests a lead fracture (short cycles, intermittent within the cardiac cycle, disorganized, of variable amplitude, sometimes saturating the amplifiers). In this asymptomatic patient, remote monitoring by telemedicine allows an early diagnosis and prevents the delivery of inappropriate shocks. Particular motions of the arm or shoulder might reproduce oversensing. The pacing impedance is not always changed; however, if it is <200 Ohm, it suggests an insulation breakdown, whereas if it is >2,000 Ohms, it suggests a lead fracture. Likewise, the shock impedance generally varies between 25 and 75 Ohm. A lower value suggests insulation breakdown, while a higher value suggests lead fracture. A sudden variation in the impedance curves is important to identify, even if it remains within the normal range.

An association between abnormal impedance and sensing of very short RR cycles (<140 ms) is highly suggestive of a lead dysfunction. Chest radiographs show fracture lines in <50% of instances of lead rupture. In this patient, the lead impedance was low and, and at lead extraction, an insulation breakdown was found with a worn area between the pulse generator and the fractured lead segment.