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Triple-chamber defibrillator and V limit. SVT - Claria Quad CRTD

Patient

Male implanted with a triple-chamber defibrillator (Claria Quad CRTD) for dilated cardiomyopathy.


Trace

1- What is 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?
Two detection zones have been programmed.

3-What diagnosis does the interval plot suggest?
The graph shows atrioventricular dissociation (ventricular rhythm faster than the atrial rhythm) with very rapid and irregular ventricular cycles; a maximum output shock terminates the arrhythmia.

4- How many discrimination parameters are programmed?
The discrimination parameters (sudden onset, PR Logic, Wavelet) are programmed with a SVT V. Limit of 260 ms.

5-What is your diagnosis?
The diagnosis of VF is obvious with atrioventricular dissociation and wide, irregular, polymorphic QRS complexes.

6- Why isn’t Wavelet used in this episode?
Wavelet and PR Logic were not used, as the ventricular intervals were too fast and exceeded the programmed SVT V. Limit.

Take home message

  • This episode corresponds to ventricular fibrillation with intervals measured at 200 ms (300 bpm).
  • For this heart rate range, it is necessary for the defibrillator to differentiate between physiological arrhythmia and oversensing of noise (lead dysfunction) or oversensing of the T wave; in fact, when oversensing occurs, the cycles detected can be very fast; this explains why the RV lead noise and T wave algorithms remain active for very high rates.
  • Conversely, the probability of a supraventricular arrhythmia reaching these very high rates is very low; as with a single-chamber defibrillator, a SVT V. Limit can be programmed independently of the detection zone programming.
  • The SVT V. Limit applies to both PR Logic and Wavelet.
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