Lead dysfunction revealed by an electrical shock

N° 26
Manufacturer Medtronic Device ICD Field Oversensing

Patient implanted with a dual-chamber ICD having undergoing a change of generator (Evera XT DR); induction procedure at the end of the procedure; this tracing shows how an electrical shock can reveal a lead dysfunction.

Graph and trace

The graph initially shows a fast pacing burst, given that the low amplitude electrical shock cannot to be visualized; induction of a probable ventricular arrhythmia detected in the VF zone; delivery of the first shock (35 Joules) significantly modifies the ventricular intervals with highlighting of a scatter plot pattern (very short intervals and longer intervals with high variability); the second shock does not alter the pattern of the ventricular intervals.

  1. the EGM reveals the rapid ventricular pacing followed by the low amplitude shock;
  2. induction of a ventricular arrhythmia detected in the VF zone;
  3. a first electrical shock is delivered;
  4. the electrical shock terminates the arrhythmia but is followed by the sensing of disorganized signals with saturation of the amplifiers suggestive of lead dysfunction;
  5. the second electrical shock had no effect on this pattern.

This tracing suggests the need to induce an episode of ventricular arrhythmia during a change of generator, especially when the patient is implanted with a lead known to have an increased rate of dysfunction. The lead fracture is revealed in this patient after the sensing of an induced VF episode and the delivery of an electrical shock. The delivered electrical shock occasionally stretches an already previously taut and fragile lead thereby favoring its fracture. The pacing impedances were strictly normal prior to this episode and no oversensing episode had been recorded in the memory of the previous device. There was therefore no warning sign of lead dysfunction, leading to a discussion as to the particular relevance of performing an induction at the time of the change of generator. This type of observation has prompted some teams to perform a systematic induction when replacing the generator.

This young patient underwent the extraction of the defective lead and the implantation of a new ipsilateral lead.