PR Logic and Wavelet

N° 37
Manufacturer Medtronic Device ICD Field Discrimination

Same patient as in the previous tracing.

Graph and trace

The graph is relatively similar to the previous graph however the device concludes to SVT based on the morphology criterion.

  1. the EGM is also relatively similar to the previous tracing;
  2. when the rhythm stabilizes in the VT zone, the ventricular intervals appear to be more regular than on the previous tracing;
  3. no therapy is delivered, the device concluding to SVT based on Wavelet (PR Logic in favor of VT).

This tracing allows emphasizing the different stages of discrimination during a conducted AF episode. The joint programming of PR Logic and Wavelet significantly reduces the risk of inappropriate therapies in this setting. Indeed, in order for the device to be fooled, the tachycardia must necessarily stabilize sustainably in the VT zone without any long interval which would reset the VT counter. The recommendation to increase the number of required intervals (at least 30 in the VT zone) significantly limits the risk of inappropriate therapies in this setting (30 consecutive intervals in the VT zone without any long interval). In a second step, if the VT counter is filled, PR Logic intervenes. We have seen on the previous tracing that if the ventricular rhythm is irregular, PR Logic concludes to a conducted AF. In this example, the different analysis steps of the PR Logic algorithm reveal:

  1. an atrial rate higher than the ventricular rate,
  2. an absence of far-field R-wave oversensing,
  3. an AF counter > 6, 4) a rhythm judged stable over the last 18 intervals with a preponderance of intervals measured at 280 or 290 ms (the 2 most frequent); PR logic thus wrongly concludes to double tachycardia.

For a tachycardia with an atrial rate greater than or equal to the ventricular rate, when PR Logic suspects a VT, the morphology analysis can correct a diagnostic error. In this example, it can be seen that 7 of the 8 analyzed QRS complexes display a value greater than the programmed threshold of 70%, which is indicative of a conducted AF; the final diagnosis is therefore SVT and no therapy is delivered.

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