Chapter 1 · Counters · Case 11

Specific features of the fast VT counter

Patient and episode

Patient

  • Man implanted with a single-chamber defibrillator (Visia AF XT VR) for dilated cardiomyopathy.

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 — Specific features of the fast VT counter

EGM

Medtronic ICD electrogram, segment 1 of 1 — Specific features of the fast VT counter

From the interrogation

Medtronic ICD electrogram, segment 1 of 1 — Specific features of the fast VT counter
  1. What diagnosis are you suggesting on this graph? This episode was classified as FVT (1); the plot shows a sudden acceleration with cycles detected mainly in the FVT zone; (2) detection of a FVT episode effectively treated with a burst.
  2. What is your diagnosis? The EGM shows a regular, monomorphic tachycardia, detected in the FVT zone; the TF. marker indicates that the defibrillator is programmed with a FVT via VF zone.
  3. What therapy is delivered? The VF counter was filled with 30 cycles out of 40 classified as TF; analysis of the 8 cycles preceding the diagnosis found only TF cycles with no FS cycle leading to the diagnosis of FVT; the first therapy in the FVT zone, a burst, was delivered; termination of the arrhythmia.
  4. How many zones are programmed? The way in which the zones are programmed can be difficult to understand; you might think that the VF zone starts at 188 bpm and stops at 222 bpm, with the FVT zone starting at 222 bpm; in fact the opposite is true: FVT from 188 to 222 bpm and VF above 222 bpm; the FVT zone is programmed via FV; this reflects the fact that the same VF counter is used for the FVT zone from 188 bpm.

Points to remember

  • When a FVT zone is programmed, it is possible to choose programming via VT or via VF; depending on the choice, the VT counter (consecutive cycles) or the VF counter (probabilistic) is used.
  • As in this example, when a FVT zone is programmed via VF, the same FV counter is used for the FVT zone and the VF zone; therefore the TF and FS classified cycles implement the same probabilistic VF counter.
  • When the VF counter is filled, the device analyses the last 8 intervals; if at least one of the intervals is classified as FS, the diagnosis is VF and the therapies in the VF zone are delivered; if none of the last 8 intervals is classified as FS, the diagnosis is FVT and the therapies in the FVT zone are delivered.

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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