Chapter 1 · Counters · Case 4

Change of detection zone

Patient and episode

Patient

  • Male with ischemic cardiomyopathy; implanted with Momentum triple-chamber defibrillator

Summary

  • Episode initially classified in the VT zone then in the VF zone
  • A burst of ATP delivered followed by a 41 Joule shock

The recording

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

Boston Scientific ICD electrogram, segment 1 of 6 — Change of detection zone
Boston Scientific ICD electrogram, segment 2 of 6 — Change of detection zone
Boston Scientific ICD electrogram, segment 3 of 6 — Change of detection zone
Boston Scientific ICD electrogram, segment 4 of 6 — Change of detection zone
Boston Scientific ICD electrogram, segment 5 of 6 — Change of detection zone
Boston Scientific ICD electrogram, segment 6 of 6 — Change of detection zone
  1. Spontaneous rhythm in the atrium and biventricular pacing
  2. Onset of ventricular tachycardia (regular, monomorphic, with atrioventricular dissociation)
  3. Cycles initially classified in the VT zone
  4. Cycles classified as VF
  5. V-epsd marker for VT zone (5 cycles in VT zone + 3 cycles in VF zone); start of initial duration for VT zone (2.5 seconds)
  6. After 8 cycles in the VF zone, criterion 8/10 verified for the VF zone; start of initial duration of VF zone
  7. End of duration for the VT zone (V-Dur) but criterion 6/10 is still valid for the VF zone; VT zone therapies are therefore not delivered.
  8. After 5 consecutive cycles classified as VT, the 6/10 criterion is no longer met for the VF zone; the first VT zone therapy can be delivered
  9. Burst
  10. Ineffective burst and ongoing arrhythmia
  11. On this cycle, the 8/10 criterion for redetection is fulfilled for the VT zone (1 VT cycle and 7 VF cycles); start of post-redetection duration for the VT zone (1 second).
  12. On this cycle, the 8/10 redetection criterion is validated for the VF zone (8 VF cycles); start of post-redetection duration for the VF zone (1 second).
  13. End of post-redetection duration for VT zone (V-Dur) but VF zone duration is still active
  14. End of VF zone duration (switches to VF zone detection with therapies corresponding to this zone)
  15. Start of capacitor charging
  16. End of charge and start of diversion window
  17. Shock delivered on the second rapid cycle
  18. Effective shock

From the interrogation

Interval plot — Change of detection zone
Interval plot

Points to remember

  • In a Boston Scientific defibrillator, 1, 2 or 3 detection zones can be programmed; the rate thresholds of adjacent zones must differ by at least 20 beats/minute ; in a double- or triple-chamber defibrillator, the rate threshold of the VT zones must be at least 5 beats/minute higher than the maximal tracking rate (MT) and the sensor indicated rate (FMC); in a single-chamber defibrillator, the rate threshold of the VT zones must be at least 15 beats/minute higher than the lower rate limit (Fmin).
  • If several detection zones are programmed, each zone has its own detection window; a cycle in a faster zone (VF for VT, for example) increments its zone counter (VF) as well as that of the slower zone (VT and VT-1); when the 8 fast cycles/10 criterion is met for one of the zones, the initial detection criterion is met
  • Different durations can be programmed for each detection zone; the duration of each zone ends independently of the others; the duration of the faster zones must be shorter than (or equal to) those of the slower zones; if criterion 8/10 is met for the VT zone first and then for the VF zone, the 2 durations continue in parallel; if the VT zone duration ends while the VF zone duration is in progress (criterion 6/10 met in the VF zone), no therapy is delivered before the end of the VF zone duration; if criterion 6/10 is no longer met for the VF zone, as in this example, the VT zone therapies are delivered.
  • If the device diagnoses a VT episode and delivers an ATP sequence, and if criterion 8/10 is then verified for the VF zone (acceleration of arrhythmia), the redetection time (1 second in VF zone) of the VF zone and not the initial time (often programmed at a longer interval) is applied so as to not delay the onset of therapies
This figure shows that the 8/10 criterion for the VT zone is initially met, then this criterion is also met for the VF zone; at the end of the VT zone duration, the VF zone duration is still active and VT zone therapies are not delivered; the 6/10 criterion for the VF zone is then no longer fulfilled and the burst (first programmed VT zone
This figure shows that the 8/10 criterion for the VT zone is initially met, then this criterion is also met for the VF zone; at the end of the VT zone duration, the VF zone duration is still active and VT zone therapies are not delivered; the 6/10 criterion for the VF zone is then no longer fulfilled and the burst (first programmed VT zone

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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