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Use of a specific algorithm - Cobalt VR

Patient


Male implanted with a single-chamber defibrillator (Cobalt VR) for primary prevention of ischaemic cardiomyopathy.


Trace

1-How was this episode classified?
This episode was classified as T wave oversensing.

2- What is your diagnosis?
This is an episode of T wave oversensing.

3- Has therapy been provided?
When the combined counter is full (35 cycles classified as VT or VF), the defibrillator concludes that the T wave has been oversensed and inhibits therapies; the analysis then continues cycle by cycle with inhibition (T wave marker).

4- How do you analyse the Wavelet analysis?
Wavelet would have concluded the diagnosis of SVT (50% of cycles considered similar); as previously indicated, Wavelet was not used as the ventricular cycles were too short (faster than the programmed SVT limit of 260 ms).

Take home message

  • In this episode of T wave oversensing delivery of therapies is inhibited following intervention by an algorithm specifically designed for this purpose.
  • Visually, making the diagnosis of T wave oversensing is not very difficult for a clinician, given the alternation between 2 signals with different appearances and fixed coupling; this algorithm present on MedtronicTM defibrillators is based on this principal.
  • R waves and T waves are differentiated by means of a differential filter which amplifies the difference between the 2 signals; the algorithm recognises T wave oversensing by identifying the repetition of sequences alternating between 2 signals of differing frequency (a high frequency signal, a softer signal) with fixed intervals (fixed RT intervals, fixed TR intervals); various parameters are therefore analysed and if the diagnostic criteria are met over 6 consecutive intervals, the T wave oversensing counter is incremented by +1 ; if a criterion is not met, all 6 consecutive intervals are classified as normal; the next group of 6 intervals is then assessed using a sliding window; as long as 4 of the last 20 sequences meet the T wave discrimination criterion, the device retains the diagnosis of T wave oversensing and the therapies are not delivered.
  • This algorithm is nominally programmed on.
  • This algorithm works even if the detected frequency exceeds the programmed SVT limit (unlike Wavelet or PR Logic).
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