Chapter 4 · Discrimination · Case 14

Double-chamber discrimination and exertion in a young patient

Patient and episode

Patient

  • 31-year-old male implanted with a triple-chamber defibrillator (Amplia Quad CRTD) 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 — Double-chamber discrimination and exertion in a young patient

EGM

Medtronic ICD electrogram, segment 1 of 1 — Double-chamber discrimination and exertion in a young patient

From the interrogation

Medtronic ICD electrogram, segment 1 of 1 — Double-chamber discrimination and exertion in a young patient
  1. What was the diagnosis made by the defibrillator for this episode? This episode has been classified SVT- Sinus Tach by the device.
  2. How many detection zones are programmed? Three detection zones have been programmed with a VT zone of 340 to 330 ms.
  3. What diagnosis does the interval plot suggest? The graph shows a 1/1 tachycardia with progressive acceleration then deceleration suggestive of sinus tachycardia.
  4. How many discrimination parameters are programmed? The discrimination parameters (PR Logic and Wavelet) are programmed with a SVT V. Limit of 260 ms; the other SVT 1:1 criterion is set to ‘Off’.
  5. What is your diagnosis? The diagnosis of sinus tachycardia seems likely, with a succession of AS-VS then AS-TS cycles.
  6. What is the diagnosis made by the system? As indicated on the trace, the device diagnoses sinus tachycardia (ST).
  7. What are the results of Wavelet? Wavelet supports the diagnosis of SVT, with all the QRS complexes analysed judged to be similar; Wavelet was not used because it was superseded by other criteria (PR Logic).

Points to remember

  • This young patient had experienced episodes of symptomatic VT requiring programming of a VT zone starting at 340 ms, increasing the risk of overlap with sinus rates during exercise.
  • This episode had the characteristics of a sinus tachycardia (1:1 ratio between the atria and ventricles, progressive acceleration and deceleration), well diagnosed by PR Logic.
  • When the Sinus tach option is set to ‘On’, there are various stages involved in diagnosing sinus tachycardia.
  • The first step is to demonstrate that there is a 1:1 ratio between the atria and ventricles (check that there is no far-field R wave oversensing).
  • The second step is to determine whether the RR intervals are compatible with a sinus tachycardia; for each ventricular interval, the device determines an adaptive range of expected RR intervals (based on an average value of the previous RR intervals); each RR interval is therefore defined as expected (within the range expected for a sinus tachycardia) or unexpected (outside the range expected for a sinus tachycardia).
  • The third step is to determine whether PR intervals are compatible with a sinus tachycardia; for each interval, the device determines an adaptive range of expected PR intervals (based on an average value of the previous PR intervals); each PR interval is therefore defined as expected (within the range expected for a sinus tachycardia) or unexpected (outside the range expected for a sinus tachycardia).
  • In the fourth step, the device establishes a sinus tachycardia counter based on the analysis of successive RR intervals and PR intervals.
  • During a 1/1 tachycardia, if PR Logic concludes sinus tachycardia, Wavelet is not included in discrimination and therefore cannot modify the diagnosis; on the other hand, if PR Logic concludes VT with retrograde conduction, Wavelet is included in the discrimination; if the morphology of the ventricular complexes in tachycardia is considered different from the reference, the device confirms the VT diagnosis; on the other hand, if the morphology is considered similar, the device corrects the diagnosis and concludes supra-ventricular tachycardia.
Figure
Figure

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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