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Auto Mode Switch (AMS)

The Auto Mode Switch® algorithm switches the mode from DDD(R) to a non-tracking mode when the atrial rate exceeds the Atrial Tachycardia Detection Rate setting.The Auto Mode Switch® (AMS) uses a filtered atrial rate, and not the current one, based on a comparison between the current atrial rate and a filtered rate that is updated continuously, in order to distinguish a sustained tachycardia from fast intermittent beats.

 

Filtered atrial rate interval and Auto Mode Switch®

The device measures the current PP interval for each beat and calculates a filtered atrial rate interval (FARI) using the following rule:

  • if current PP ≤ FARI: FARI decremented by 39 ms; FARInew = FARIold – 39ms (when PP intervals are shorter than FARI)
  • if current PP > FARI: FARI incremented by 23 ms
  • P waves falling in the PVARP (AR marker) followed by atrial sensing (AS) are taken into account when calculating the FARI
  • in the most recent platforms, P waves falling in the PVARP are not taken into account in the FARI calculation when they are followed by atrial pacing, to avoid inappropriate AMS due to far-field R wave oversensing (repetition sequences AP-VP-AR)
  • P waves falling in the post-ventricular pacing atrial blanking are ignored
  • the ATDR (atrial tachycardia detection rate) is the programmable rate at which the device will switch modes in the presence of atrial tachyarrhythmias
  • when FARI < ATDR interval: AMS entry
  • ATDR programmable between 110 and 300 bpm
  • ATDR must be at least 20 ppm higher than maximal tracking rate or maximum sensor rate

 

 

AMS mode and rate

  • different auto modes switch can be programmed: DDI, DDIR, DDTR, VVI, VVIR, Off
  • during AMS the device paces at AMS base rate rather than the programmed base rate; the AMS base rate can be programmed to base rate + 0 to base rate + 35 bpm (steps of 5 bpm)

 

Auto Mode Switch Termination

  • if current PP > FARI: FARI incremented by 23 ms; FARInew = FARIold + 23ms (when PP intervals are longer than FARI)
  • when FARI is longer (slower in rate) than the Maximum Tracking Rate (MTR) or Maximum Sensor Rate (MSR), whichever is higher, the device switches back to the programmed tracking mode