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AAI-SafeR

The SafeR pacing mode has been designed to minimize unnecessary right ventricular pacing in Microport CRM (former Livanova, former Sorin) devices.

  • the device functions in ADI mode as long as the AV conduction is physiologic and switches to DDD mode in case of atrioventricular conduction failure
  • when switched to DDD mode, the device periodically evaluates intrinsic conduction and switches back to AAI accordingly

 

Switch from AAI to DDD

The device functions in AAI mode and switches temporarily in DDD in the following cases:

  1. third degree AV block: the device senses two consecutive blocked sensed or paced atrial events; this parameter is non programmable

 

  1. second degree AV block: the device senses 3 blocked sensed or paced atrial events in the last 12 ventricular cycles; this parameter is non programmable

  1. first degree AV block: PR or AR intervals are longer than the programmed maximum value during 6 consecutive cycles

The AVB I criterion can be programmed to:

  • rest + exercise: the device may switch to DDD during rest and exercise phases
  • exercise only: the device may switch to DDD during exercise phase only

 

Different parameters are programmable:

  • long PR max (atrial sensing): 5 programmable values from 250 to 450 ms
  • long PR min (atrial sensing): 6 programmable values from 200 to 450 ms
  • long AR max (atrial pacing) = long PR max + 100 ms
  • long AR min (atrial pacing) = long PR min + 100 ms

 

  1. pause: a ventricular pause is longer than the programmed value (parameter: Max Pause); this parameter can be programmed to 2, 3 or 4 seconds

 

 

The ventricular pause may last a little bit more than the programmed value in order to synchronize A and V at the time of the switch to DDD:

 

The pause lasts the programmed value + the programmed rest AVD

  • this situation occurs when no atrial contraction has occurred in the last 500 ms of the programmed value of the pause
  • the device first paces the atrium then applies the rest AVD (no pacing/sensing offset added) and switches to DDD
  • the duration of the pause is the programmed duration of the pause + the rest AVD

 

The pause lasts the programmed value + less than programmed rest AVD

  • this situation occurs when a spontaneous atrial contraction has occurred between (programmed pause – AVD and programmed pause)
  • the device starts the rest AVD on the spontaneous atrial contraction and then switches to DDD
  • the duration of the pause is the programmed duration of the pause + less than rest AVD

 

The pause lasts the programmed value

  • this situation occurs when a spontaneous atrial contraction has occurred in the last 500 ms of the programmed value of the pause
  • the device extends the AVD to pace the ventricle at the end of the programmed duration of the pause
  • the duration of the pause is the programmed one

 

Programmable parameters

  • switch on AVB I programmable values: “exercise” and “rest + exercise”
  • long PR min and Long PR max
    • programmable Long PR: 250 – 300 – 350 – 400 – 450 ms
    • programmable Min PR: 200 – 250 – 300 – 350 – 400 – 450 ms
  • pause V max
    • max pause: 2 – 3 – 4 seconds

 

Switch from DDD à AAI

The device switches from DDD to AAI mode:

  • when it senses 12 consecutive spontaneous ventricular events

 

 

  • automatically every 100 paced ventricular cycles

 

After automatic switch in AAI mode and if the native AV conduction is not resumed the device switches again in DDD mode using one of the criteria listed above (third degree AVB, second degree AVB, first degree AVB or the pause).

 

Switch AAI à DDD until 8:00 am next morning

The device switches in DDD mode and remains in DDD mode following 3 criteria:

  • 45 episodes of AV block or more during the last 24 hours
  • 15 episodes of AV block or more per 24 hours during 3 consecutive days
  • 50% DDD pacing or more during one hour

In these cases, it suspends the automatic switch to AAI functioning every 100 ventricular cycles. It remains in DDD mode until next morning at 8:00 am. The only way the device can be back to AAI functioning before 8:00 am is the detection of 12 consecutive spontaneous R waves.

It switches to AAI at 8:00 am trying to promote intrinsic AV conduction. In case of AV conduction failure the device switches back to DDD using one of the criteria listed above (third degree AVB, second degree AVB, first degree AVB or the pause) and it will pace in DDD until the next switch in AAI at 8:00 am next morning except if it senses 12 consecutive R waves; in this case it switches back to AAI.

 

Switch in DDD during exercise

When an AV block occurs during an exercise, after 3 switches the device remains in DDD mode until the end of the exercise.

 

The values of rates at the onset and at the end of exercise depend on the programmed basic rate:

  • when the programmed basic rate is lower or equal to 70 bpm the exercise rate is 100 bpm and the end of exercise rate is 90 bpm
  • when the programmed basic rate is equal or higher to 75 bpm, the exercise rate is the basic rate + 30 bpm and the end of exercise rate is the basic rate + 20 bpm

 

Detection in the safety window

The safety window starts after each paced atrial event and lasts 95 ms. A signal detected in the safety window can correspond to a late PVC, a cross-talk or a conducted ventricular complex following undersensing of an atrial signal. The functioning differs when the device functions in ADI or in DDD.

  • in DDD mode, ventricular sensing during the safety window triggers ventricular pacing at the end of the window
  • in SafeR, ventricular sensing during the safety window is not followed by ventricular pacing at the end of the period; however spontaneous ventricular events sensed in the safety window are considered non valid; a paced atrial event which comes before a ventricular detection in safety window is counted as a blocked atrial event
  • in case of switch from AAI to DDD because of ventricular sensing in the safety window a message will be displayed in AIDA and some of the switches will be displayed in a separate screen

 

 

Programming constraints

When SafeR pacing mode is programmed:

  • mode Switch is ON
  • ventricular Autothreshold is OFF

 

Safe-R follow-up

Information on the number, the history and the distribution of the switches are available:

  • fully documented data
  • EGM at the time of AV block