Chapter 1 · Counters · Case 5

Spontaneous termination and shock diversion

Patient and episode

Patient 1

  • Male with ischemic cardiomyopathy implanted with a Resonate single-chamber defibrillator

Summary

  • Episode classified in the VF zone
  • ATP in the VF zone
  • Diverted shock

Patient 2

  • Male with ischemic cardiomyopathy; implanted with Autogen dual-chamber defibrillator

Summary

  • Episode classified in the VF zone
  • ATP in the VF zone
  • Diverted charge

The recording

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

Trace 1

Boston Scientific ICD electrogram, segment 1 of 4 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 2 of 4 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 3 of 4 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 4 of 4 — Spontaneous termination and shock diversion
  1. Spontaneous polymorphic ventricular arrhythmia
  2. V-Epsd marker (criterion 8/10 fulfilled) for VT-1 zone (1 VT-1 cycle, 5 VT cycles, 2 VF cycles)
  3. 8/10 criterion for the VT zone; the initial detection time for the VT zone begins on this beat
  4. 8/10 criterion for the VF zone; initial detection time for the VF zone begins on this beat
  5. End of duration for the VF zone; burst in the VF zone (ATP Quick-Convert)
  6. Ineffective burst and start of capacitor charging
  7. Spontaneous termination
  8. Criterion 6/10 no longer fulfilled; charge diverted

Trace 2

Boston Scientific ICD electrogram, segment 1 of 5 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 2 of 5 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 3 of 5 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 4 of 5 — Spontaneous termination and shock diversion
Boston Scientific ICD electrogram, segment 5 of 5 — Spontaneous termination and shock diversion
  1. Sinus rhythm and ventricular pacing
  2. Ventricular extrasystole occurring in the ventricular noise window after atrial pacing (VS marker in square brackets); no pacing inhibition and ventricular pacing (VP) at the end of the programmed AV delay.
  3. Spontaneous polymorphic ventricular arrhythmia
  4. V-Epsd marker (criterion 8/10 fulfilled); criterion fulfilled for VT-1 zone (1 cycle in VT-1 zone + 1 cycle in VT zone + 6 cycles in VF zone); initial detection time for VT-1 zone begins on this beat
  5. 8/10 criterion for VT zone; initial detection time for the VT zone begins on this beat
  6. 8/10 criterion for VF zone; initial detection time for the VF zone begins on this beat
  7. End of duration for VF zone
  8. Burst in VF zone (ATP Quick-Convert)
  9. Ineffective burst and start of capacitor charging
  10. Spontaneous termination
  11. End of charge and start of 500 ms diversion window
  12. The first ventricular cycle following the 135 ms end-of-charge blanking is not counted (--)
  13. 2 slow cycles out of 3; diverted charge

From the interrogation

Interval plot — Spontaneous termination and shock diversion
Interval plot

Points to remember

  • The main aim of programming is to reduce, as far as possible, the number of inappropriate or avoidable therapies; programming an initial duration of 5 seconds in the VF zone and a first shock of maximum output as first-line treatment (i.e. with a charge duration of more than 8 seconds) extends the delay between the onset of arrhythmia and shock delivery, allowing spontaneous termination; these 2 tracings show 2 episodes of ventricular arrhythmia with spontaneous termination and interruption of charging or charge diversion after the diversion window
  • Shock therapy can be programmed to be reconfirmed or not reconfirmed; the aim of reconfirmation is to prevent delivery of an unnecessary shock when the arrhythmia has spontaneously terminated; the device looks for spontaneous termination during and immediately after capacitor charging
  • If the Shock not reconfirmed function is set to On, the shock is systematically delivered synchronized to the first sensed R wave following a 500 ms delay at the end of capacitor charging (whether the arrhythmia is sustained or not); therefore, if capacitor charging begins, the shock is automatically delivered
  • If the Shock not reconfirmed function is set to Off, charging can be interrupted if the device diagnoses spontaneous termination; if 5 slow beats (sensed or paced) are counted within a detection window of 10 beats (6/10 fast criterion not fulfilled), the device interrupts charging (first trace); if the charge has been completed, post-charge reconfirmation is performed at the end of the charge; after the post-charge refractory period and the first uncounted sensed event, if 2 of the 3 post-charge intervals have a rate below the lowest rate threshold, the shock is not delivered.
This figure shows the charge interruption following spontaneous reduction and the detection of 5 consecutive slow cycles.
This figure shows the charge interruption following spontaneous reduction and the detection of 5 consecutive slow cycles.

Practice out loud

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

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From Boston Scientific ICD — clinical cases by P. Bordachar, M. Strik, A. Thiyagarajah, 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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