Atrial undersensing

N° 3
Manufacturer Medtronic Device PM Field Sensing
  • 69-year-old man
  • Dual chamber pacemaker (Medtronic) for complete atrioventricular block following post-surgical aortic valve replacement
  • Numerous episodes of atrial arrhythmia in the postoperative phase
  • Control 1 month post-implantation
Graph and trace
  • P wave not detected by the device
  • Atrial pacing at the end of the escape period; this pacing occurs in the vulnerable period of the previous undetected P wave; ventricular pacing
  • Intermittent atrial undersensing
  • This tracing reveals an intermittent atrial undersensing
  • Sensing of the P wave presents certain specificities, the slope of the signal and its amplitude being lower than those of a QRS complex
  • The amplitude of the sensed atrial signal may vary according to the position of the patient and as a function of the respiratory cycle
  • Atrial undersensing on exertion in a patient with atrioventricular block may cause a sudden drop in ventricular pacing rate
  • It is therefore necessary to set a sufficient margin to avoid atrial undersensing on exertion
  • Atrial undersensing may have a pro-arrhythmogenic effect if atrial pacing occurs in an atrial vulnerable period with a risk of AF induction
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