Minimising Ventricular Pacing 4 – Genuine Example AAI<=>DDD Sorin SafeR

Sorin SafeR

Sorins SafeR – Minimising Ventricular Pacing!!!!
Lets get our Geek on…

A little bit different from our usual post in that it is a little bit techie! but this will be my last post on Minimising Ventricular Pacing for a bit and I wanted to let you have a little insight into the real world of a pacemaker technician. This is a simplified version of what technicians might receive telling us how an algorithm (fancy bit of pacemaker software) works.
Sorin SafeR the brand name of the Sorins version of the AAI<=>DDD Algorithm
Available on:- Not all software is on all pacemakers, so we have to make sure we give a patient one of these pacemakers if they require the SafeR software! This would be a little bit like a car salesman making sure that the car is exactly what the client wants… “you need speed sir? look at this Lamborghini… oh you want good economy? The Smart Car is nice…”

Some snazzy pacemaker names:-
How it does its THING… We next get some pictures and jargon telling us how it works and how the software makes decisions!
Temporary switches from AAI into DDD mode:- The device operates in AAI mode (Pacing just the top atria if necessary) and switches temporarily to DDD (paces the Atria and Ventricles when required) in the following cases:
Third degree AV block
The device detects two consecutive blocked atrial events (paced or sensed).


So whether the Atria contracts on its own (sensed) OR is stimulated to contract by the pacemaker (paced) the Ventricles should follow sequence and contract. If the signal that travels from the Atria to the Ventricles is BLOCKED the pacemaker can see this. If it happens once, then the Sorin SafeR will turn a blind eye. If it happens twice in consecutive beats (like in image 1) then the pacemaker believes a significant heart block is occurring and switches to DDD Mode where it will Pace the Ventricle if the Ventricle is not contracting as it should.
Sorin SafeR Pacemaker Minimise Ventricular Pacing
The Atrial Events are shown by spikes on the top Egram (grey line 
with spikes on it). The Ventricular events are shown on the bottom
Egram. The Atrial events are regular but you can see that two of the
Atrial spikes (contractions) are not followed by Venticular spikes 
(contractions). This has happened twice in succession so the device
changes its mode from AAI to DDD (see top).

Second degree AV block
The device detects 3 blocked atrial events in the last 12 ventricular cycles.

In the example above one non conducted Atrial event (where the atria contracts but the ventricles don’t follow suit) is acceptable but 2 back to back isn’t! This part of the algorithm says “well even if there aren’t to blocked events back to back, if it happens 3 times out of 12 heart beats, then I am going to intervene anyway and switch modes to DDD.”
Sorin SafeR Pacemaker Minimise Ventricular Pacing
There are no back to back blocked Atrial events but 3 occur within 12
beats so the pacemaker switched modes to DDD anyway and intervenes.
First degree AV block
The  device  detects  6 consecutive  PR  or  AR  intervals  longer  than  the  programmed
maximum value.
We dont’t always need an Atrial event to be totally blocked from reaching the ventricle. Sometimes we can say the signal is just taking to long to travel between the two (the PR interval)! Remember really long gaps between the top of the heart and the bottom of the heart contracting is not great news physiologically. So on the SafeR software we can say, we don’t want a PR interval over 300ms. If there are 6 consecutive delays over this length of time the device will switch to DDD and pace the Ventricle much closer to when the Atria contracts. It makes more sense if we remind ourselves that the PR interval can change from beat to beat or throughout the day!
Sorin SafeR Pacemaker Minimise Ventricular Pacing
There are 6 consecutive long PR intervals so the device switched to DDD
and you can see that the VS (Ventricular Sensed events) switch to VP
Ventricular Paced events with a shorter delay! 🙂

A pause between Ventricular Events of a Programmed Length
The technician can program a period of time for the pause mode switch, If they program 2s then if there is ever a pause of 2s in AAI then the pacemaker will switch to DDD. Imagine if whilst waiting for 2 blocked Atrial events (like in image 1) there was a pause of 2s… the pacemaker forgets about all othe criteria and switches to DDD.
Sorin SafeR Pacemaker Minimise Ventricular Pacing
If there is a Ventricular Pause of 2s (in this example) the pacemaker drops
what it is doing and swaps from AAI to DDD.

What I have never mentioned before is how the Pacemaker goes back to the desired AAI mode once it has switched to DDD mode.

The device switches back from DDD to AAI when
• it has detected 12 consecutive natural ventricular events
• automatically every 100 paced ventricular cycles.
The device switches to DDD mode and remains in DDD mode when it has:
• 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 the automatic switch to AAI following every 100 ventricular paced cycles
is suspended. It remains in DDD mode until 8:00 am the next morning where it has a quick look to see if it can switch back to DDD.
Further explanation around these topics and more is available in the book Pacemakers Made Easy by Carl Robinson.

Sorry if this is a bit techie but I hope it was a nice way to round off the Minimising Ventricular Pacing series and I hope its an indication of how improved your understanding of pacemakers has come!
Time to put the oven on for a lazy pizza!
Thanks for reading 
Cardiac Technician
All images courtesy of Sorin Group

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