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PR Logic and atrial flutter - InSync Sentry

Patient

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


Trace


1- What was the diagnosis made by the defibrillator for this episode?
This episode has been classified AFib/AFlutter by the system.

2- How many detection zones are programmed?
Three detection zones have been programmed with a VT zone of 370 to 300 ms.

3- What diagnosis does the interval plot suggest?
The graph shows a regular tachycardia in the atrium and a regular tachycardia in the ventricle.

4- How many discrimination parameters are programmed?
The discrimination parameters (PR Logic and Stability) are programmed with a SVT V. Limit of 300 ms.

5- What is the most likely diagnosis?
The most likely diagnosis is atrial flutter with 2/1 conduction.

6- What is the diagnosis made by the defibrillator?
The device diagnoses AF/AFlutter and inhibits therapies.

Take home message

  • This patient presented with episodes of atrial flutter with 2/1 conduction; this tracing details the various stages leading to the diagnosis of atrial flutter by PR Logic.
    Is the ventricular rate faster than the atrial rate? If so, PR Logic diagnoses VT without further analysis; if, as in this example, the atrial rate is faster than the ventricular rate, the analysis will continue.
  • Is there far-field R wave oversensing that could cause an error in the analysis of the atrial rate? PR Logic concludes that the far-field R wave has been oversensed by the atrial channel if it detects a succession of short- long atrial cycles and either a short PR interval (<60 ms) or a short RP interval (< 160 ms); in this example, we do not find this type of sequence, as the PP intervals are perfectly regular (180 ms).
  • Is the atrial rate compatible with an atrial arrhythmia? An AF counter analyses the number of atrial signals detected between 2 ventricular complexes; when the device detects at least 2 atrial events between 2 R waves, the counter is incremented (+1); when the device does not detect an atrial event between 2 R waves, the counter is decremented (-1); when the device detects an atrial event between 2 R waves, the counter is decremented (-1) if the previous cycle was identical (one atrial event between 2 R waves); the counter is not modified if the previous cycle was different; the diagnosis of AF is possible if this counter (once any far-field R wave oversensing has been corrected) is at least +6; in this example, the AF counter increases with each cycle and is therefore well above +6; the 3 possible diagnoses at this stage are: conducted AF, conducted flutter and double tachycardia (AF/flutter + VT).
  • Is the ventricular rhythm irregular and therefore in favour of conducted AF? The analysis of ventricular stability differs from the way stability is assessed with a single-chamber defibrillator; the device analyses the RR intervals over 18 consecutive cycles (only cycles longer than 240 ms are analysed) and determines the percentage of cycles observed for a given interval (…360ms, 350 ms, 340 ms, 330 ms, 320 ms, 310 ms, 300 ms …).); the device sums the percentages of the 2 most frequently encountered intervals; if the sum of the 2 percentages is greater than 75%, the rhythm is considered to be regular; if, on the other hand, the sum is less than 50% (high cycle variability), the rhythm is considered to be irregular and in favour of conducted AF; in this example, the rhythm is perfectly stable (360 ms) which means that the diagnosis of conducted AF can be ruled out; the 2 possible diagnoses at this stage are therefore : conducted atrial flutter and double tachycardia (AF/flutter + VT).
  • Is there atrio-ventricular association (conducted flutter) or atrio-ventricular dissociation (double tachycardia)? Atrio-ventricular dissociation is diagnosed if for at least 4 of the last 8 RR intervals there is either no atrial event or there is a difference of more than 40 ms between the PR interval analysed and the average of the previous 8 PR intervals; in this example, the PR intervals are perfectly fixed, which explains why the device arrives at the final diagnosis of conducted atrial flutter and therapies are not delivered.
  • If PR Logic concludes atrial flutter, Wavelet is not included in discrimination and therefore cannot modify the diagnosis; on the other hand, if the PR Logic concludes double tachycardia, Wavelet is included in discrimination.

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