Atrial undersensing during exercise Copy Copy


  • 53-year-old man
  • Evia DR-T dual-chamber pacemaker (Biotronik) for complete atrioventricular block
  • lipothymia on exertion
  • sudden drop in heart rate during exercise test


  • atrial undersensing (P wave not sensed); low amplitude signal
  • in the absence of atrial sensing, no ventricular pacing and pause (ventricular rate divided by 2) explaining the discomfort felt by the patient
  • important beat to beat variation in the amplitude of the atrial signals (breathing cycles)


  • this patient was very symptomatic on exertion with marked limitation of his exercise capacity
  • the tracing showed intermittent atrial undersensing
  • atrial EGM analysis revealed a wide variability in the amplitude of atrial signals as a function of the respiratory cycles
  • in a patient with complete atrioventricular block, atrial undersensing results in a sudden drop in rate, which is often highly symptomatic
  • atrial undersensing is probably much more frequent than a 2:1 block or ventricular oversensing or loss of capture of the 2 leads, which constitute the other causes of a sudden drop in rate on exertion
  • the amplitude of the sensed atrial signal may vary according to the position of the patient and as a function of the respiratory cycle
  • appropriate atrial sensing may be systematically tested with deep respiration to unmask significant fluctuations of the signal with breath