Noise oversensing in the atrial lead

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Tracing
N° 5
Manufacturer Biotronik Device Remote monitoring Field Periodic Egm
Patient

This 55-year-old man received an Evia DR-T dual chamber pacemaker for paroxysmal complete atrioventricular block; periodic recording of EGM. 

Graph and trace

Telecardiology tracing

The 3 channels that are displayed for 12 sec are 1) the markers with the time intervals, 2) the atrial sensing channel and 3) the right ventricular sensing channel.

  1. oversensing of noise on the atrial channel; alternating cycles classified As, Ars and Ars (FFP = far field protection);
  2. the pacing mode is DDIR after a mode switch;
  3. end of atrial oversensing; AS-VS cycles with long PR interval;
  4. switch to DDDR mode and AS-VP cycles.
Comments

The atrial lead impedance was normal and the capture threshold was satisfactory. Therefore, the lead was not revised. Oversensing at the level of the atrial lead can, as in this case, cause an inappropriate automatic mode switch because of erroneous diagnosis of atrial arrhythmia. In a defibrillator, it can also interfere with discrimination based on the counts of atrial and ventricular electrograms during tachycardia. This dysfunction, if frequent, must be eliminated in a defibrillator recipient:

  • By decreasing the maximum atrial sensitivity without compromising the detection of sinus rhythm, and of true atrial arrhythmias. This is generally ineffective because the amplitude of noisy signals from fractured leads or other types of interference is often large;
  • By applying a discrimination scheme applicable in single chamber devices;
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