Premature atrial contraction and AF prevention algorithm


  • 67-year-old woman
  • Vitalio pacemaker (Boston Scientific) for complete atrioventricular block


Tracing obtained on arrival

  • atrial sensing and ventricular pacing (between 85 and 90 bpm)
  • premature atrial contraction sensed outside any refractory period with compensatory pause


Programming of the APP/ProAct algorithm

  • atrial and ventricular pacing at the rate imposed by this algorithm (AP-PP, VP-PP)
  • premature atrial contraction
  • acceleration of the pacing rate as a result of this atrial contraction
  • gradual slowing of the pacing rate


  • to trigger the onset of an atrial arrhythmia, 3 elements are generally required: a substrate, a context (sympathetic activation/parasympathetic activation ratio) and a trigger (most often a premature atrial contraction)
  • pacemaker cannot interfere with the substrate or with the adrenergic context but may interfere with the occurrence of premature atrial contractions
  • in Boston ScientificTM pacemakers, the ProAct algorithm increases the pacing rate following a premature atrial contraction in order to avoid successive short cycle – long cycle sequences
  • the device measures the ventricular interval preceding the premature atrial contraction and applies a pacing interval to the next cycle corresponding to 75% of this interval
  • the pacing rate is then gradually lowered to the lower rate limit by prolonging the pacing interval by 10 ms if 4 consecutive cycles occur without a premature atrial contraction
  • the indicated APP/ProAct rate is limited by the value of the APP/ProAct maximum pacing rate
  • effectiveness of this type of algorithm for preventing AF episodes has never been clearly demonstrated on large population samples and can lead to a feeling of tachycardia unfavorably felt by the patient


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