Biotronik CLS algorithm causing problem

Hello, another newbie here!

Biotronik 8 DR-T implanted four weeks ago to treat total heart block. Just had first, four week, check up.

Prior to this, I had been exercising by walking down and up our village hill. Heart rate monitor recorded bpm. Noticed that on the second half of the uphill climb, my heart rate would suddenly jump to 120 bpm and stay there for the rest of the walk. It would not increase, even though I pushed myself harder. Seemed clunky, rather than smoothly progressive. I assumed that I had hit an in-built upper-rate limit.

At the checkup I asked to have this changed, but things turned out to be much more complicated than I had imagined. Brilliant staff at the hospital eventually had me walking up and down stairs whilst they recorded the effects of different settings. The data showed that, up to about 110bpm, the pacemaker was taking its cue from my own native sinus node signal and pacing the right ventricle accordingly. Beyond that, the Biotronik "response" algorithm took over believing it knew better than my own body when to beat my heart. This happened with both the CLS and, when tried separately, the other one - whatever it's called. The result was that these algorithms limited my heart rate to less than 120 bpm, leaving me slightly short of breath - just like I'd experienced on my village walks.

When these functions were disabled, and the pacemaker was responding only to my own sinus rhythm, everything went better and my heart rate increased smoothly up to about 130-140 bpm. I felt better too, breathing more easily at the end of the exercise.

Anyone else experienced this issue with the pacemaker suddenly deciding it knew best? Avid for more input around this issue!


CLS (closed loop stimulation) algorithm well known to be difficult to optimise for each patient

by Gemita - 2023-08-06 04:50:53

Repero, firstly welcome.  I see you have a Biotronik.  I have a Medtronic pacemaker.  There are quite a few members who experienced the same problems as you with their CLS system or Accelerometer motion sensor and I hope they will see your message and respond.  It really is a matter of patiently working with a technician or manufacturer rep to get your settings optimised for you.  Easier said than done, I know.

I think many of us have problems getting our heart rates up for exercise and keeping them that way and Rate Response features in my Medtronic, or the Closed Loop Stimulation algorithm/Accelerometer motion sensor in the Biotronik can be extremely difficult to get right for each one of us.   I attach a link below that should be copied into your main browser to open.  It might be worth reading.  Although it is about a specific model of Biotronik, it gives good  information about the Closed Loop stimulation sensor/Accelerometer motion sensor:- 

There are sensitivity settings with the CLS system that can be adjusted and if these are not adjusted properly, they will lead to sudden rate drops when exercising and then the rate may be difficult to get back up.  Working with a qualified technician or the manufacturer rep is essential to get the CLS + the Accelerometer motion systems working well for you.  You could also ask about the possibility of getting your upper limit raised slightly to see if this might help?

I don’t think this is about the pacemaker deciding it knows best but about what the technician/doctor has set up.  The pacemaker can only do what it is programmed to do and Biotronik CLS/Accelerometer can be extremely difficult to optimise for each patient without a Biotronik representative who knows the product well, being present.  Hope this helps and I wish you lots of luck.

CLS optimisation

by Repero - 2023-08-06 05:10:03

Many thanks Gemita for your welcome and for your clear and focused response. I look forward to further input from other members of this supportive group.

I understand what you say about optimisation of the CLS parameters and, since it can really only be done by trial and error, I imagine that this can be a lengthy process involving multiple visits to the technicians/medics. I am lucky to have excellent support from my local hospital cardiology department.

In fact, the solution (hopefully - we'll see) in my case was to switch off both rate-response functions. I have complete heart block, but my sinus node is operating as normal. The PM therefore only needs to by-pass the block and ensure that my ventricles receive the message! I do not, at present, need the PM to deduce the intensity of my physical activity, my body is still doing that. Do you, or anyone, see any disadvantages in this strategy?

I have yet to try out this new setup and will be repeating my hill walk later today. I will also go to the link you kindly provided and continue my reading on the subject.

Thanks again.

Further to my last

by Repero - 2023-08-06 05:43:57

I just realised that I failed to pick up on the point about having my upper limit raised slightly.

This was discussed at the hospital, but they were reluctant to do it until I had tried living with it as it is, 130 bpm I believe. They made the seemingly valid point that my fitness will have taken a knock recently and we couldn't judge the practical consequences of the current limit until I was a bit more like my normal self. They were open to raising it though.

The main problem with the Biotronik rate-response algorithms kicking in unexpectedly was that they come with an in-built 120 bpm upper limit.

Upper Limit

by Gemita - 2023-08-06 06:00:17

Repero, I see you are in the UK.  Yes it will probably mean lots of visits to the clinic and some treadmill testing to optimise your settings, but it will be well worth it in the end, wouldn’t you say?  Yes you are lucky to have lots of support from your local hospital.  I am with a main London hospital (St. Thomas') and have great support too.

Yes I hope other Biotronik members will see your post and respond.  Member Mad Hatter has recently done a lot of research on his Biotronik pacemaker, so you might care to private message him for advice if he doesn’t see your post and respond.  

Yes I believe you are correct.   Like me, you do not appear to have a problem getting your heart rate up.  Some technicians are now telling me I do not have “chronotropic incompetence”, so do not need rate response switched on, but I do struggle with exercise sometimes when I reach my upper limit.  They won’t reduce my upper limit setting because of my Atrial Fibrillation and tachy arrhythmias.  It would just be too dangerous.  My own heart rate cannot be stopped from going higher, but my pacemaker will never assist this with my upper limit of 130 bpm.  

Your problem seems more to be in the area of hitting a roof (like upper limit) and then struggling too.  Your Biotronik settings won’t be helping and once adjusted you should notice some improvements.

Update:  Upper Limit.  If you don't have a problem with arrhythmias and have no other heart problems, then raising this limit could well be the answer, but I agree with your team about rushing in too quickly following implant to change things.  There is the usual healing period - up to 3 months - and sometimes our hearts settle and settings won't need changing at all.  However my upper limit is also kept at factory setting of 130 bpm and is often too low for me.

If you can be patient and disciplined not to push too hard, too quickly, I see no harm in asking for the upper rate to be raised now to see whether your symptoms improve.  If they say no, ask when it would be possible to "safely" raise this.

Doing it's own thing

by piglet22 - 2023-08-06 07:16:43

There certainly are things that have less than desirable outcomes presumably when some part of the program decides to do something else.

I would add ectopic beats which can have the opposite effect and send the pacemaker on a go slow.

I have a base rate set to 70-BPM, recently raised from 60-BPM.

I have developed in the last 7-months rather more ectopcs which the PM doesn't seem able to cope with.

Typically, I wake up every day with a heart rate of 40 or less BPM. I have to kickstart the normal rhythm by moving around. It can also affect me if I get up after sitting down.

The effects are really unpleasant ranging from dizziness to full blown blackout.

It worries me a lot that the device that was implanted to treat the symptoms of heart block now isn’t doing the job. If I’m waking up to slow heart rates and everything that goes with it – low BP and low SpO2, then what’s it doing while I’m asleep?

Others may disagree, but I'm certain it's to do with the programming and the ectopics (PVCs) are interfering with the PM timing.

If it's the case, then it surprising that out of sequence pulses cannot be dealt with.

In coding, missing pulse detection is commonly used, so the inverse of extra beats shouldn't be difficult to filter out.

To date, no-one has given me a satisfactory answer to why a PM with a base rate of 70 is allowing palpable rates of 40 or less.

All non-surgical methods of correcting this, mainly increasing beta-blockers (Bisoprolol) from 1.25 to 10-mg daily have failed so far.

Allowing our hearts to do the work

by Gemita - 2023-08-06 07:36:05

Repero, I didn’t answer your question:  “I do not, at present, need the PM to deduce the intensity of my physical activity, my body is still doing that. Do you, or anyone, see any disadvantages in this strategy?“

I agree, if we don’t need it, why use it and there is evidence suggesting that many of us benefit from allowing our own hearts to do the work (if they can) otherwise we and our hearts become lazy and of course we use up more battery power as well.  So if we do not suffer from Chronotropic Incompetence, we do not need Rate Response assistance and can manage perfectly well on our own.  

The same could apply to the Lower Rate Limit.  My lower rate limit is set at 70 bpm and many would argue that this fairly high setting will not allow my own heart to do the work sometimes.  However, 70 bpm as opposed to 60 or lower bpm works best for me to help (overdrive pace) some of my arrhythmias.  We always say here that it is “how we feel” that counts.  The percentages and numbers we see on our records however normal and good they may look, are meaningless if the patient doesn’t “feel well”.  Whenever I go for my checkups, my Electrophysiologist is only interested in hearing about my symptoms and is less interested in studying my pacemaker data, unless anything, like a high heart rate “event”, is flagged.

Good advice

by Repero - 2023-08-06 07:45:20

Thank you Gemita for your further advice, and you too piglet22 for your input.

Joining this group I am already realising that I appear to be fortunate in having just the one heart problem at the moment. I am content to try to live with 130 upper tracking rate and see how it goes. I will not rush things, but the acid test will come at the beginning of September when I restart Morris dancing practice! I imagine I will hit the stops in some of the more energetic dances, but we'll see! If I do, I will get straight back to them to discuss raising the upper limit.

Piglet22, it does indeed seem strange that with your lower limit set at 70 you can wake up with a heart rate of 40! I know that I am just a beginner here, but whilst massively impressed by the sophisticated technology of modern PMs, I am also beginning to wonder if at times they are just a little too clever for their (and our) own good? I know that heart management is an immensely complex issue, and the software has to be immense too to cope with all eventualities and combinations of problems, but is it sometimes working against itself? I wouldn't like to be in charge of software development at Biotronik!

My own experience fuels this, perhaps irrational, suspicion. Why did CLS kick in at higher heart rates when my own sinus rhythm was capable of doing a more appropriate job?

Yes, it's how we feel that counts

by Repero - 2023-08-06 07:50:48

Gemita, just picked up on your last. It is indeed easy to get obsessed with the technology and the numbers if we're that way inclined (I am), but if it seems to be working then that should be good enough. But conversely, as you say, if the numbers look good but we still don't feel well, then that's the only thing that counts.

Me too

by Lavender - 2023-08-06 09:34:29

I have a normal working sinus node and a dead AV node. Rate response isn't on because I don't need it. I'm set 60-130. I take no meds and have no other heart issues. 

re: Me too

by Repero - 2023-08-06 09:41:39

Yes, Lavender, the same situation exactly. Reassuring that you have not encountered any drawbacks.

Just completed my 20 minute exercise walk with CLS turned off: downhill for 1km and then back up again. Heart rate got up to about 110, then to 116 when I jogged for a few yards. Rate subsided gently as would normally be expected. Much more rational heart response than before when CLS would kick in and beat my heart at 120 when there was no apparent need for it. I begin to think that I am going to get good value out of my 130 upper limit. Maybe there will be no need to increase it: we'll see.

Got it all figured out.

by PacedNRunning - 2023-08-07 03:14:08

Seems you have it figured out. I too do not need rate response. They had it on in the beginning since I have significant sinus bradycardia. I got a PM for AV block. Complete block now. So I mainly need the bottom pacing. Rate response to me was awful. Felt old and out of breath with walking etc. I have a lower limit of 50 and max of 185bpm. That max comes into play if you need the PM to get there. Some have a normal AV node with exercise and their own heart takes over at a certain point. Which is nice! Mine does not so I need the max to be high so I don't reach it but still receive the pacing support I need. See how it goes. Your max may not matter because your own heart will exceed it. PM won't stop your own heart from going higher. Only lower. 


by Repero - 2023-08-07 05:01:59

Thanks PacedNRunning. I know what you mean about feeling old - I am! My age related max rate is just 145, so the standard Upper Tracking Rate of 130 takes me to 90% of that. Remains to be seen whether I will need higher, but as I am not a runner and only indulge in occasional energetic dancing, I am hopeful it will suffice. If not, the cardio team are willing to increase it. I suppose there is no reason why it shouldn't actually be 145?

It would be great to think that my heart block might occasionally stand aside to let my own heart ask for a higher rate. If I ever observe a rate exceeding 130, I will now know why. Thanks again.

You’re welcome

by PacedNRunning - 2023-08-08 03:40:16

Not sure about the 145bpm. My doctor just explained to me how they don't like the pace the heart fast in the ventricle and most patients can't tolerate it. He was more worried about me tolerating it. So we started at 160. I usually try and stay under 160  I just wanted room to not be held back. See how it goes. 

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