P wave oversensing and new discrimination

N° 16
Manufacturer Abbott Device ICD Field Sensing

This 47-year-old man presenting with ischemic cardiomyopathy underwent implantation of an Ellipse, single chamber ICD for secondary prevention of VT.

Graph and trace

This tracing includes a sensing channel (Ampli detection V) and a discrimination channel, corresponding to the signal sensing between the ventricular coil and the pulse generator;

  1. Ventricular activity in the sinus zone;
  2. Oversensing of P wave in the ventricular sensing channel (Ampli detection V);
  3. Comparison of the 3rd unclassified cycle between sensing and discrimination channels (2 of 3 cycles are unclassified); the P wave is oversensed on the sensing though not on the discrimination channel, despite the seemingly greater signal amplitude on the latter. This might be explained by the different autogains of the 2 channels (0.7 mm/mV on the 1st and 1.3 mm/mV on the 2nd), such that a signal of similar amplitude on the tracing is, actually, larger on the sensing channel;
  4. increment of VS² counter;
  5. after 6 VS²: non-sustained lead noise (NSLN) is diagnosed.  

In order to lower the risk of inappropriate therapy delivery, a noise discrimination algorithm, which compares the sensing with the discrimination channel, has been added to the newest ICDs . The sensing parameters of the discrimination channel (0.5 mV sensitivity, 60% adaptation level and 60-ms adaptation delay) are not programmable. This tracing shows that this algorithm also enables the prevention of therapies due to P or R wave oversensing.  

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