Chapter 3 · Oversensing · Case 12

The benefits of induction at the end of implantation

Patient and episode

Patient

  • Patient implanted with a dual-chamber defibrillator with a Fidelis lead undergoing a box change (Evera XT DR); induction protocol at the end of the procedure.

The recording

Tap a number on the trace, or an entry in the list below

Rate / interval plot

Medtronic ICD electrogram, segment 1 of 1 — The benefits of induction at the end of implantation

EGM

Medtronic ICD electrogram, segment 1 of 1 — The benefits of induction at the end of implantation
  1. What do you think of this interval plot? The plot initially shows an induction protocol with rapid pacing burst; the fact that the low-amplitude electric shock is delivered on the T wave is not indicated on the graph; induction of a probable ventricular arrhythmia detected in the VF zone (appearance compatible with a real ventricular arrhythmia); the first shock delivered (35 Joules) significantly alters the ventricular cycles, with evidence of a cloud of points (very short cycles and longer cycles with great variability); the second shock does not alter the appearance of the ventricular cycles.
  2. What type of procedure is involved? The EGM shows rapid ventricular pacing followed by a low-amplitude shock delivered on the T wave (in the vulnerable period) due to an induction protocol at the end of implantation to check for correct defibrillator function.
  3. What is the effect of the first low output shock? The electric shock induces rapid ventricular tachycardia, which is detected in the VF zone.
  4. What is the effect of the second high output shock? The electric shock terminates the ventricular arrhythmia but is followed by the over-detection of anarchic signals with saturation of the amplifiers, suggesting a diagnosis of lead dysfunction.

Points to remember

  • This plot shows the value of inducing ventricular arrhythmia when changing leads, particularly when the patient is implanted with a lead known to have an increased rate of dysfunction.
  • Lead fracture was unmasked in this patient following detection of an episode of induced VF and the delivery of an electric shock; the electric shock delivered sometimes stretches a lead which had already been stretched and weakened beforehand and causes a definitive fracture; the stimulation impedances were strictly normal prior to this episode and no episode of oversensing had previously been recorded in the device memory; therefore there was no warning sign of lead dysfunction and no other indication for this patient to have an induction protocol performed when the box was changed.
  • This young patient had the faulty lead removed and a new ipsilateral lead implanted.

Practice out loud

Just describe the tracing. What do you think is going on? Describing the numbers can help.

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From Medtronic ICD — clinical cases by P. Bordachar, A. Thiyagarajah, L. Fontagne, M. Strik, S. Ploux. Published by Cardiocases. Every numbered marker on a recording is explained in the list beneath it; tap a marker on the trace or an entry in the list.

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