Quiz

Fallback algorithm (Boston Scientific) Copy Copy

Patient

  • 76-year-old woman
  • Vitalio pacemaker (Boston Scientific) for sinus dysfunction
  • fallback episodes (ATR) in the device memory

Tracing

  • atrial pacing and ventricular sensing
  • acceleration of atrial activity with one out of 2 intervals sensed in the noise window; these intervals are not integrated in the calculation of the atrial rate
  • one out of 2 atrial activities sensed in the PVARP; all intervals (AS and (AS)) are integrated in the calculation of the atrial rate; the atrial rate exceeds the trigger rate; each fast atrial interval increments the entry counter by 1
  • after 8 atrial intervals faster than the fallback rate (entry count programmed to 8 cycles), the entry counter is filled; the Duration begins (ATR-Dur)
  • certain fast atrial intervals fall in the noise window, are not counted with diagnosis of long atrial intervals (438, 438, 465, 453); these intervals increment the exit counter
  • after 8 ventricular events during which the atrial arrhythmia persists (Duration programmed on 8 cycles), switching to an asynchronous mode (ATR-FB)
  • termination of the arrhythmia; atrial and ventricular pacing of gradually decreasing rate
  • slow atrial intervals increment the exit counter (atrial intervals slower than the programmed fallback rate)
  • the exit counter is filled (programmed at 8); the device switches back to a synchronous mode

Comments

  • fallback algorithm of Boston ScientificTM devices operates in various steps
  • the atrial tachycardia rate is exceeded; atrial events classified as AS or refractory (AS) are included in the computation of the atrial rate unlike the intervals in the blanking periods or in the noise windows which are not counted
  • the entry counter is filled; this counter corresponds to a number of atrial intervals faster than the fallback rate; this counter is incremented by 1 (+1) for each interval faster than the fallback rate and decremented by 1 (-1) for each slower sensed or paced interval; when the counter is fulfilled, the Duration begins
  • the duration criterion is satisfied; the duration corresponds to the number of ventricular cycles during which the arrhythmia must persist before the mode switch
  • mode switching to asynchronous mode; this switch starts at the end of duration and persists as long as the exit counter is not filled
  • gradual reduction in ventricular pacing rate; the pacing rate gradually decreases to reach either the programmed minimum fallback rate or rate response
  • the exit counter is filled; this counter counts the atrial intervals slower than the programmed fallback rate and starts at the beginning of the duration; this counter is incremented by 1 (+1) for each interval faster or equal to the fallback rate and decremented by 1 (-1) for each slower sensed or paced interval; if this counter reaches 0 during the duration, there is no mode switch; if this counter reaches 0 after a mode switch, the device switches to a synchronous mode
  • different parameters can be programmed
  • ATR trigger rate corresponds to the rate threshold that defines a fast atrial interval
  • the entry counter is the number of sensed fast atrial events necessary to satisfy the initial sensing and to activate the duration and the exit counter
  • ATR Duration is the number of ventricular cycles during which atrial events continue to be assessed after initial sensing
  • fallback time controls the rate at which the paced rate decreases during the fallback at the minimum fallback rate or sensor rate
  • exit counter is the number of sensed slow atrial events required to return to an atrial tracking mode