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Dual-chamber defibrillator and atrioventricular dissociation - Cobalt DR

Patient

Male implanted with a dual-chamber defibrillator (Cobalt DR) for hypertrophic cardiomyopathy.


Trace

1- What was the diagnosis made by the defibrillator for this episode?
This episode has been classified FVT by the device.

2- How many detection zones are programmed?
Three detection zones have been programmed.

3- What diagnosis does the interval plot suggest?
The graph suggests a diagnosis of VT with atrioventricular dissociation (ventricular rhythm faster than the atrial rhythm); the burst allows reduction.

4- How many discrimination parameters are programmed?
The discrimination parameters (PR Logic and Wavelet) are programmed with a SVT V.limit of 260 ms.

5- What is your diagnosis?
The diagnosis of VT is obvious with atrioventricular dissociation.

6-What are the results of Wavelet?
Wavelet supports the diagnosis of VT, with none of the QRS complexes analysed judged to be similar to the reference template.

 

Take home message

  • A double or triple-chamber defibrillator can be used to compare the atrial and ventricular rates; for both the clinician and defibrillator, the presence of a ventricular rate faster than the atrial rate confirms the ventricular origin of the tachycardia.
  • In a dual or triple chamber defibrillator, the PR Logic algorithm is used to discriminate the origin of the tachycardia and differentiate between ventricular and supra-ventricular tachycardias by studying the relationship between atrial and ventricular activity and comparing the 2 respective rates.
  • Discrimination by PR Logic only applies during the initial detection phase and not during the re-detection phase; PR Logic only works for heart rates below the programmed limit of supra-ventricular tachycardia and can therefore be active in the VF zone depending on programming.
  • PR Logic gives its diagnosis once the initial VT or VF counter has been filled.
  • PR Logic discrimination is based on the continuous and simultaneous assessment of 6 criteria, which can sometimes make it difficult to explain in detail how it works.
  • In this example, the diagnosis of VT is obvious to the doctor because of atrioventricular dissociation, which is most frequently the case; in fact, during an episode of VT, the demonstration of a ventricular rate faster than the atrial rate is much more common than the observation of a 1/1 ratio (retrograde conduction) or a bi-tachycardia.
  • Diagnosis is also straightforward with PR Logic; one of the essential steps in diagnosis using PR Logic is a comparison between ventricular  and atrial rates (measurement of the median value of RR intervals and PP intervals over the last 12 cycles); when the ventricular rate is judged to be faster than the atrial rate, the device concludes that VT has occurred without further analysis.

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