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Using single-chamber discriminators in a dual-chamber defibrillator - EnTrust

Patient

Male implanted with a dual-chamber defibrillator (EnTrust) for ischaemic cardiomyopathy.

Trace

1- What was the diagnosis made by the defibrillator for this episode?
This episode was classified as SVT-Onset by the system.

2- How many detection zones are programmed?
Two detection zones have been programmed with a VT zone of 430 to 320 ms.

3-What diagnosis does the interval plot suggest?
The graph shows atrioventricular dissociation (ventricular rhythm faster than atrial rhythm); the ventricular rhythm oscillates around the lower limit of the VT zone.

4- How many discrimination parameters are programmed?
All the discrimination parameters (stability, hard start, PR Logic) available on this legacy platform are set to ‘On’.

5- What is your diagnosis?
The diagnosis of VT is obvious, as the ventricular rhythm is faster than the atrial rhythm; the Reset. Onset marker reflects the fact that the sudden onset criterion has not been fulfilled; the cycles are therefore classified as VS even when they correspond to the VT zone.

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Take home message

  • On a dual-chamber or triple-chamber defibrillator, it is possible to program the 2 single-chamber discrimination parameters (other discriminations: sudden onset and stability) separately or in association with PR Logic; these parameters take precedence over analysis by PR Logic; in other words, if sudden onset is programmed in conjunction with PR Logic, the first discrimination step consists of validating the single-chamber criterion; if, as in this example, the device does not find a sudden onset, it concludes that there is an SVT without further analysis and without consulting PR Logic.
  • In this patient, the diagnosis of VT seemed obvious to the cardiologist who analysed the tracing, the atrioventricular dissociation being pathognomonic; an analysis using PR Logic would also have led to the diagnosis of VT, the ventricular rate being faster than the atrial rate.
  • This patient presents with a tachycardia oscillating around the lower limit of the VT zone, which explains why the analysis is misleading and why the defibrillator considers that there was no sudden onset; the most likely scenario is that the ventricular rate went from a normal rate (60 beats/minute) to a rapid rate just below the VT zone at the start of the tachycardia (138 to 139 beats/minute) with a slight acceleration of the rate thereafter into the VT zone (140-141 beats/minute).
  • This tachycardia therefore had a sudden onset but was not diagnosed by the device; in fact, the criterion is calculated by comparing the first intervals corresponding to the VT zone with the 4 previous cycles; the device is therefore fooled in this example (no jump in rate between the 4 cycles at 139 beats/minute and the 4 cycles at 140 beats/minute).
  • The easiest solution in this patient is to turn off this discrimination criterion in favour of PR Logic.
  • The third single-chamber discrimination parameter (Wavelet) can be programmed in conjunction with PR Logic; its position in the diagnostic tree differs from that of the other 2 parameters and will be described in more detail when subsequent tracings are analysed.

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