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AF with regular ventricular response, PR Logic and Wavelet - Evera XT DR

Patient


Male implanted with a dual-chamber defibrillator (Evera XT DR) for ischaemic cardiomyopathy.


Trace

1- What is the diagnosis made by the defibrillator for this episode?
This episode has been rated SVT-Wavelet by the device.

2- How many detection zones are programmed?
Two detection zones have been programmed with a VT zone of 350 to 270 ms.

3-What diagnosis does the graph suggest?

The graph shows a tachycardia detected in the VT zone with atrial activity faster than ventricular activity and an irregular ventricular response which regularises in a second phase; the graph is in favour of conducted AF.

4- How many discrimination parameters are programmed?
The discrimination parameters (PR Logic and Wavelet) are programmed with a SVT V. Limit of 270 ms.

5- How does the VT counter work?
Some cycles correspond to the VT zone, others do not; cycles classified as VS systematically reset the VT counter to 0.

6- What is the diagnosis made by the defibrillator?
The tachycardia accelerates and becomes regular in the VT zone; after 16 consecutive cycles classified as VT, the VT counter is filled; the PR Logic classifies the episode as VT; Wavelet corrects the diagnosis and leads to a diagnosis of SVT.

7- What are the results of Wavelet?
Wavelet is used because PR Logic has concluded VT; Wavelet leads to the diagnosis of SVT because 7 out of 8 ventricular complexes are classified as similar to the reference template.

Take home message

  • This tracing highlights the different stages of discrimination during an episode of conducted AF; the joint programming of PR Logic and Wavelet considerably reduces the risk of inappropriate therapies in this context.
  • For the device to be fooled into delivering inappropriate therapy during conducted AF, the tachycardia must first stabilise for a sufficient duration in the VT zone without any long cycles that would reset the VT counter; the recommendation to increase the number of cycles required (at least 30 in the VT zone) significantly reduces the risk of inappropriate therapy in this setting (30 consecutive cycles in the VT zone without any long cycles).
  • Secondly, if the VT counter is full, PR Logic intervenes; if the ventricular rhythm is irregular, PR Logic concludes that there is conducted AF; in this example, the various stages of analysis by the PR Logic reveal 1) an atrial rate higher than the ventricular rate, 2) no far-field R wave oversensing, 3) an AF counter > 6, 4) a rhythm judged to be stable over the last 18 cycles with a preponderance of cycles measured at 280 or 290 ms (the 2 most frequent); PR Logic therefore incorrectly concludes that there is bi-tachycardia.
  • For a tachycardia with an atrial rate greater than or equal to the ventricular rate, when PR Logic suspects VT, morphology analysis can correct a diagnostic error; in this example, we can see that 7 of the 8 QRS complexes analysed have a value greater than the programmed threshold of 70%, which is in favour of conducted AF; the final diagnosis is therefore SVT and no therapy is delivered.
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