Atrial flutter response algorithm Copy Copy


  • 71-year-old woman
  • Ingenio pacemaker (Boston Scientific) for sinus dysfunction
  • hospitalization for palpitations, dyspnea and edema of the lower limbs


Tracing obtained on arrival

  • fast and regular atrial activity corresponding to atrial tachycardia or atrial flutter; some intervals are classified AS while others are in the PVARP
  • fast ventricular pacing with Wenckebach sequences; gradual prolongation of the AV delay so as not to exceed the programmed upper rate limit (VP-MT); the (AS) intervals are not followed by an AV delay causing a temporary slowing of the pacing rate


Modification of the maximum tracking rate (from 150 to 120 bpm)

  • atrial flutter pattern with 2:1 ventricular tracking (one out of every two atrial activities is marked (AS) and does not generate an AV delay)
  • no fallback, the atrial rate remaining below the programmed fallback rate


Programming of the atrial flutter response (AFR) algorithm with an intervention rate of 160 bpm (375 ms)

  • absence of ventricular pacing, the intervals marked AS-Fl do not trigger an AV delay and open a new sensing window
  • reappearance of intrinsic rhythm



  • the proper functioning of a fallback algorithm requires the appropriate adjustment of the minimum detection rate of atrial arrhythmias
  • in this patient, the mode switching algorithm was not triggered because the programmed rate (175 bpm) was faster than the tachycardia rate
  • Boston Scientific pacemakers have a specific atrial flutter search algorithm that provides immediate “fallback” when the atrial rate is higher than the programmable rate and avoids pacing in a vulnerable atrial period
  • when this algorithm is programmed, the sensing of an atrial signal in the PVARP triggers an AFR sensing window of programmable duration (if the flutter sensing rate is programmed at 230 bpm, the duration of the corresponding AFR window is 260 ms)
  • if an atrial signal is sensed in this window, it does not trigger ventricular pacing (which prevents runaway) and triggers a new AFR window
  • in the presence of atrial flutter, all atrial activities succeed one another in this window, causing an immediate “fallback” on the first fast atrial signal (no flutter wave triggers ventricular pacing)
  • ventricular pacing occurs at the lower rate limit or sensor rate