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PR Logic and conducted AF - Cobalt Quad CRTD

Patient


Male implanted with a triple-chamber defibrillator (Cobalt Quad CRTD) for ischaemic cardiomyopathy.


Trace

1-What was the diagnosis made by the defibrillator for this episode?
This episode has been classified SVT-AF by the system.

2-Which programmed zone appears on the graph?
A monitor zone is programmed from 450 ms.

3-What diagnosis does the interval plot suggest?
The graph shows a tachycardia detected in the monitor zone with atrial activity faster than ventricular activity and an irregular ventricular response; 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 260 ms.

5- What is your diagnosis?
The pattern is suggestive of conducted AF.

6- What are the results of Wavelet?
Wavelet supports the diagnosis of SVT, as the 8 QRS complexes analysed were considered similar to the reference template.

Comments

  • This patient presented with episodes of atrial fibrillation detected in the monitor zone and correctly classified by the defibrillator; this trace details the various stages leading to the diagnosis of AF by PR Logic.
  • The device compares the atrial and ventricular rates; for a diagnosis of conducted AF, the median atrial interval must be less than or equal to 94% of the median ventricular interval; in this example, the atrial rate is clearly faster than the ventricular rate; this tracing corresponds to an episode with V<A.
  • The device checks that there is no far-field R wave oversensing (oversensing of the R wave on the atrial channel); PR Logic detects a far-field R wave if it detects both a succession of «short-long» sequences of A-A intervals (difference > 30 ms) and a short A-V interval (< 60 ms) or a short V-A interval (< 160 ms); to diagnose far-field R wave oversensing, the device must sense a far-field R wave in at least 4 of the 12 most recent ventricular intervals; in this example, this type of sequence is not found, as the sensed atrial signals all correspond to atrial activity.
  • The device analyses the atrial rhythm and assesses for the presence of atrial fibrillation; to do this, it counts the number of sensed atrial cycles between 2 sensed R waves (2 or more atrial signals between 2 ventricular signals => Counter +1, no atrial signals between 2 ventricular signals => Counter -1, 1 atrial signal between 2 ventricular signals => Counter +0 if different from the previous cycle); diagnosis compatible with AF if AF counter is greater than 6; in this example, the AF counter is well above 6 (in the majority of cycles, there are at least 2 atrial signals between 2 ventricular signals); at this stage, the 3 diagnoses to be differentiated are: bi-tachycardia (VT + AF), conducted AF, conducted atrial flutter.
  • The device analyses the regularity of the ventricular rhythm using a different criterion to that used for a single-chamber defibrillator; the device counts the number of times the 2 most frequent ventricular intervals have occurred out of the last 18 ventricular intervals; if the sum of the 2 most frequent intervals represents more than 75% of the total cycles, the rhythm is considered to be regular; this is not the case in this example; the rhythm is irregular (the 2 most frequent cycles represent less than 50% of the total cycles); the device eliminates the diagnoses of bi-tachycardia and conducted flutter (regular ventricular rhythm) and retains the diagnosis of conducted AF.
  • If PR Logic concludes conducted AF, Wavelet is not included in the discrimination and therefore cannot modify the diagnosis; on the other hand, if the PR Logic concludes double tachycardia (AF + VT), Wavelet is included in discrimination and can possibly correct the diagnosis.

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