This patient received a Lumos defibrillator (a relatively old model), which explains the short duration (6 sec before the classification) of remote electrograms recorded. The signals typical of lead fracture are usually identified by the absence of a fixed relationship between the supernumerary signals and the cardiac cycle. The presence of high-amplitude signals saturating the amplifiers is concordant with fracture currents. The tracings are characteristic, with supernumerary signals and interspersed QRS complexes. This indicates the presence of a rupture in the intracardiac segment of the lead, with the various signals generated by the cardiac contraction. While the pacing lead impedance is not systematically affected, an insulation breakdown should be suspected if it is <200 Ohms, versus a lead fracture if it is >2,000 Ohms. Likewise, shock impedance usually varies between 25 and 75 Ohms. A lower value suggests loss of insulation integrity, while a higher value suggests lead fracture.

If an impedance curve has been memorized by the device, it is important to recognize a sudden change in that curve, even if it remains within normal limits. The association of an abnormal impedance and the detection of <140 ms RR cycles is highly suggestive of lead dysfunction. Chest radiographs show a fracture in <50% of cases of lead fractures. This patient was asymptomatic and the interrogation of the device’s memory revealed several episodes of temporary oversensing and charge of the capacitor without therapy delivery. These repetitive charges cause premature depletion of the batteries. Remote monitoring is highly contributory in this kind of subclinical lead dysfunction, by offering an early diagnosis after the first episode of aborted shock, or when the lead impedances changes suddenly, preventing the premature depletion of the pulse generator and the delivery of inappropriate therapies. The patient underwent explantation of the dysfunctional lead and implantation of a new ipsilateral lead.