Chapter 4 · Discrimination · Case 4

Single-chamber defibrillator and new recommendations

Patient and episode

Patient

  • Male implanted with a single-chamber defibrillator (Visia AF XT VR) for primary prevention of 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 — Single-chamber defibrillator and new recommendations

From the interrogation

Medtronic ICD electrogram, segment 1 of 2 — Single-chamber defibrillator and new recommendations
Medtronic ICD electrogram, segment 2 of 2 — Single-chamber defibrillator and new recommendations

EGM

Medtronic ICD electrogram, segment 1 of 1 — Single-chamber defibrillator and new recommendations
  1. What was the diagnosis made by the defibrillator for this episode? This episode has been classified as VF by the system.
  2. How many detection zones are programmed? A single detection zone (VF 320 ms) has been programmed.
  3. What diagnosis does the interval plot suggest? The graph shows an initially stable rhythm of around 125 bpm with sudden acceleration and cycles recorded in the VF zone; a burst is delivered with a return to the initial heart rate.
  4. How many discrimination parameters are programmed? Wavelet is the only discrimination criterion programmed (70% match); the stability and sudden onset criteria are set to ‘Off’’.
  5. How do you analyse the EGM in tachycardia? This is a regular, monomorphic tachycardia with a wide QRS (shock channel) that has a different morphology to the QRS complexes recorded in the absence of tachycardia.
  6. What therapy is delivered? The VF counter is completed after 30 cycles classified as FS; a burst before charging is delivered; this helps to terminate tachycardia.
  7. What do you think of the Wavelet results? The Wavelet appearance of the analysed complexes is clearly different from the reference complex, with similarity percentages ranging from 34% to 52%; the 8 complexes were therefore considered to be different, leading to a diagnosis of ventricular arrhythmia.

Points to remember

  • In this example, the single-chamber defibrillator is programmed according to the latest HRS/EHRA/APHRS/LAHRS recommendations of 2019 for a primary prevention indication: programming of a single VF zone at a rate of 188 bpm, VF counter programmed to 30/40 for initial detection, programming of a monitor zone, Wavelet only discrimination programmed for cycle lengths up to 260 ms, programming of the T wave oversensing and RV lead noise algorithms.
  • These international recommendations include 2 important messages in terms of single-chamber discrimination: 1) it is recommended that discrimination should be based solely on the Wavelet; therefore the criteria of sudden onset and stability should be programmed ‘Off’ in the first instance; in fact, when all 3 parameters are programmed ‘On’, all 3 must be fulfilled for the arrhythmia to be diagnosed and treated (sudden onset, stable rhythm, different morphology QRS to the reference); simultaneous programming of these 3 parameters may therefore reduce the sensitivity of the device; when Wavelet is functioning correctly in a given patient, discrimination based solely on this parameter enables virtually all tachycardias to be discriminated effectively (with the exception of SVT with aberrant conduction); 2) Wavelet must be programmed to function up to high heart rates, with a SVT V. Limit of 230 beats/minute, to reduce the risk of inappropriate therapies occurring for episodes of rapid AF (class I indication).

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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