Chapter 1 · Counters · Case 13

Fast VT and the combined counter

Patient and episode

Patient

  • Male implanted with a dual-chamber defibrillator (Cobalt DR) for ischaemic 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 — Fast VT and the combined counter

EGM

Medtronic ICD electrogram, segment 1 of 1 — Fast VT and the combined counter

From the interrogation

Medtronic ICD electrogram, segment 1 of 1 — Fast VT and the combined counter
  1. What diagnosis is suggested by the interval plot? Three detection zones were programmed: a VT zone from 360 ms, a FVT zone from 310 ms and a VF zone from 280 ms; the episode was classified as FVT by the device (1); the plot shows probable VT with atrioventricular dissociation (2) with cycles oscillating between the limit of the VT-FVT zones; a burst is used to terminate the arrhythmia.
  2. What is your diagnosis? The EGM shows a regular, monomorphic tachycardia, alternately detected in the VT zone and the FVT zone; the combined counter is full, with 35 cycles classified as TS or TF. (7/6 of 30 cycles); analysis of the last 8 cycles before diagnosis shows at least one cycle classified as TF leading to the diagnosis of FVT; the first therapy in the VF zone (a burst) is delivered with termination of the arrhythmia.
  3. What is the diagnosis made by the system? The diagnosis is that of FVT via the combined counter.

Points to remember

  • This plot shows another example of how the combined counter works.
  • The tachycardia oscillates between the VT zone and the FVT zone programmed via VF; therefore the 2 VT and VF counters increment in parallel.
  • The combined counter has been developed to avoid delaying therapy in this scenario.
  • When the combined counter is filled (35 TS or TF cycles in this example), the device analyses the last 8 intervals; here, no cycle is classified as FS, but at least one of the cycles is classified as TF, leading to a diagnosis of FVT.

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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