How do single chamber leadless pacemakers actually work on sinus node dysfunction

I was just reading about the new single chamber Micra AV leadless pacemaker. It says that it provides most of, but not all of, the function of a dual-chamber pacemaker. The one thing that it's lacking is "atrial stimulation, which would be for people who the atrium doesn't beat fast enough, such as in sick sinus syndrome or chronotropic incompetence". In that case, you would still need a leaded pacemaker in order to address these problems.

I have a single chamber Micra Transcatheter Leadless Pacemaker (the model before the new Micra AV). This got me thinking, how is my pacemaker recommened for sinus node dysfunction (as in my case) when the Micra AV isn't? 

Thanks guys



by Tracey_E - 2020-06-24 09:17:20

I believe the micra av is a newer one specifically for av block, so it's different than what you have. 

Warning - personal opinion follows...

by crustyg - 2020-06-24 12:25:56


I understand that leads - placing and maintaining them, is expensive and time consuming, but I really struggle to see a valid rationale for leadless PMs.  And the PM pocket can be a lot of trouble, so a PM inside the heart appears attractive.  But don't get me started on battery life of leadless PMs...

IMHO, in ten years time we'll all look back at RV apical pacing and laugh (or sue our EP docs) due to the common problems of LV-remodelling and reduced %LVEF this can cause.  *IF* it's possible, pacing the bundle of His is much better.

There's evidence that pacing the RA (actually the RA-appendage) is much better for folk with SSS/CI and a tendency to atrial arrhythmias as the PM 'outpaces' the clumps of cells that tend to start AFlut/AFib.  And I don't think the headline conclusions claimed from DANPACE really did show that AAIR is worse than DDDR with RV-apical leads where AV-node function is preserved.

A *LOT* depends on the health of your heart muscle (and by implication the likelihood of developing AV-node failure).  The congenital CHB folk seem to do well with RV-apical pacing, but other people see a lot of LV remodelling and end up with a 3rd lead for cardiac-resynchronisation therapy - an iatrogenic illness treated with more technology (but good that it's available).


great rant crustyg . . .

by Gemita - 2020-06-24 14:18:20

but have you answered Claire's question "How do single chamber leadless pacemakers actually work on sinus node dysfunction"?  You have lost me slightly but I would love to hear your views?

On the question of a better position for the RV lead, I believe they are now placing the RV lead in the septal area (mine is) which of course is not perhaps quite as good as HIS pacing site but it seems to be more beneficial than RV apical pacing position ? 

Could you please copy and paste the DANPACE research document on AAIR as opposed to DDDR pacing mode ?  Many thanks


by AgentX86 - 2020-06-24 14:43:08

If the AV node is healthy, these two modes are equivalent because the V-lead will always inhibit. It's when the AV node is going wonky where the 'D's come into play.

VVI is a whole different kettle of fish.

I think I was trying to avoid actually saying it...

by crustyg - 2020-06-24 18:41:12

I know this facet of leadless PM's isn't something that I've researched, so I was trying to avoid saying in black and white that IMHO leadless PMs don't work [Edited] *well* for SSS/CI.  They can certainly produce a higher ventricular rate, but at the expense of forgoing A=>V synchrony and with the risk of producing LV remodelling.

Francis Bacon (contemporary of William Shakespeare) had a nice quote:

Reading maketh an informed man.  Conference maketh a ready man, and Writing maketh an exact man. 

Once you've written it down, you're stuck with it - even the weasel words that we sometimes hear and see can skewer you later.

I'll revisit the pacing - I recall boasting that I would do this in January this year and here we are 6months later.  Lazy.  Mea culpa maxima.

Medtronic Micra Pacer

by Marybird - 2020-06-24 18:53:41

No expert here, but I just wanted to say that there's a nice downloadable PDF file brochure on the Medtronic website that discusses the features ( including setting, which are Greek to me) of both the Micra leadless and the Micra AV leadless pacers, and compares and contrasts the features of each. 

From what i read there that it seems the first Micra pacer is not indicated for those who require atrial pacing, since it paces in the ventricle only. The brochure ( and other sources) states that people with bradycardia who need only single chamber ( ventricle ) pacing may benefit from the Micra. So it's not indicated for people with SSS who need atrial pacing.

The brochure states that the Micra AV is suitable for people with "some types" of AV node blocks because it senses the atrial activity and coordinates this with ventricular pacing. But the Micra AV does not pace the atrium, so it is not appropriate for those with SSS or other sinus node dysfunctions needing pacing. 

I think I was trying...

by AgentX86 - 2020-06-24 22:15:34

Yeah, I don't quite understand the Micra, either.  As I understand it, the Micra AV (distinct from the Micra) can sense the atrial contraction and pace the ventricle, maintaining AV synchrony. 

I'd be queezy about having a pulser dropped into my heart too.  The idea that when that one's battery is used up that they'll just drop another one in there is really off-putting.  OK, they may be able to go in, at some point, and snake out the plumbing but that doesn't give me much comfort. Not that I have a choice but I think I'd let this one play out for a while.  Conventional PMs just work too well to play with leadless PMs.

Micra pacemaker

by Gemita - 2020-06-25 06:44:04

Crustyg, as usual, I appreciated your thoughtful, honest response and the quotes from Francis Bacon were particularly delightful and meaningful.  Don’t worry about re-visiting the best pacing sites.  It seems to be a changing situation doesn’t it but hopefully with time things will become clearer.

Claire, may I ask what your doctors told you about the Micra pacemaker system prior to implant ?  I presume your doctors felt it was the best choice for you at the time?  I think we are all still learning about this new leadless technology and its potential benefits/disadvantages.  Hopefully as technology advances we can all benefit from leadless devices in the future.  I like the idea of a smaller, less invasive system providing it can match what my present dual chamber pacemaker is providing.  You ask a very good question though and one that might best be answered by your doctors who know your medical history and needs best.  I really hope that your device will be all that you need to stay well in the future and that we can all learn from you about the benefits of this little device.  

AgentX86, thank you for your helpful comment on AAIR/DDDR


by _Claire_ - 2020-06-25 10:37:40

Hi Gemita - Well I had to make a decision in around 5 minutes flat. I was rushed in at night after I collapsed with a pause, the next morning they found the pause on my loop recorder. They said they would implant a pacemaker that day as they couldn't take the risk of waiting. I couldn't take in all the information at that moment in the hospital bed and no family could get to me in time for the op, to advocate for me. They gave me the option of a conventional one or the micra. They focused on telling me about the benefits with reduced recovery time, reduced risk (with wires etc) over the long-term. They didn't tell me anything about the performance of it, other than "it will kick in if your heart stops again". To be honest I knew absolutely nothing about pacemakers, sinus node pauses etc at that moment. Not a thing. I really couldn't have made an informed decision under those circumstances. After the op, I've only ever spoken to a device nurse, and an EP technician not an EP doctor, so I'm going to try and see how I get to speak to an EP doctor as another member here recommended. I did have a medtronic rep come to see me after I requested the automatic threshold testing function to be turned off (as it was bordering on painful every hour that it did its threshold test). I wonder if the rep knows more than the EP doc? Perhaps that's why they sent him. 

In terms of the op and recovery, yes it was amazing! I had a local anaesthetic for the groin incision and some sedation. I was aware of everything and can remember everything from the op. I was terrified but felt no pain, the sedation really helped with the anxiety. (To put it in context, my loop recorder implantations were both far worse than the PM op). They kept me in overnight. I went cycling 2 days after getting out of hospital (on reflection that wasn't wise). From that perspective it's great. But ultimately, I want a PM that will perform to save my life if my heart stops again, not an aesthetically pleasing option. :/

Hi Marybird - thank you, I have looked at that comparison document on the medtronic site now. It was helpful. I have so much to learn. Thanks again :)

Crustyg and AgentX86 - Thank you for your support and knowledge as always. AgentX86 - I agree, I can imagine there must be risks with retrieval that perhaps outweigh the benefits of lower risk on implantation? I know they're keen to leave them in forever. My question is, how many leadless PMs can fit in the RV? If I live to 80 and they have a 10 year battery life (I might need 5). I guess they will get even smaller with longer life batteries. I read a paper (2019 study) if you're interested I can find it. They found equal rates of damage to the tricuspid valve with leadless PMs (I had been looking due to having pulsing in my neck and wondering if a valve could have been damaged), also in the study the mitral valve and biventricular function can be adversely impacted. I'm sure more and more negatives will be found with more research. I do understand your views about conventional PMs being better. I think because my condition isn't complex so far, it might be an okay option for me. I'm not full of confidence though. 



by _Claire_ - 2020-06-25 10:51:29

 Tracey_E - Thank you for your comment too :)

Where best to pace? Micra cf. Micra A-V

by Selwyn - 2020-06-25 11:06:30

This is a complicated problem with different outcomes depending on the studies looked at.

If you want to compare AAIR v. DDDR pacing I woiuld see the recent review:

To answer your question  Clair:

"How is my pacemaker recommened for sinus node dysfunction (as in my case) when the Micra AV isn't? :


The Micra  AV is venticular  placed and is suitable only for sino-atrial nodal  dysfunction. If senses flow of blood related to the atria.


The MIcra AV is venticular placed and is suitable only for atrio-ventricular nodal dysfunction - you have to have a functioning  SA node! ( this PM uses an accelerometer to detect atrial contraction to trigger a ventricular contraction. 

[electrical flow in the heart is from the SA node to the AV node, then via the Bundle of His to the left and right bundles.] Coordination between the pushing of the atrial contraction into the ventricles is important to avoid pushing at the wrong time- this results in muscle thickenng, called 'remodelling and subsequent heart poor performance/failure.

Micra pacemaker

by Gemita - 2020-06-25 12:36:13

Dear Claire,

Thank you for your message.  I can see you did the very best you could at the time.  Elective surgery always gives us time to consider all our options and only move forward when we are confident that our decision is the right one.  You had no such choice and naturally you based your decision on what you were being told at the time.  And was that so wrong ?  Only time will tell.

When I had my investigations/pacemaker implant, it was done by my EP’s team of personal assistants/technicians, not by my EP who was busy doing ablations.  To be honest the senior assistants seemed to have a lot more patience and ability to explain things and spend that extra time with me than did my EP.  Senior doctors/registrars/technicians do all the hard work (in my experience!) and often know the very latest research, so I wouldn’t be too concerned about consulting and trusting in a senior member of your EP's team.  Yes the Medtronic Rep will give your EP’s team all the latest info and can be present when any major changes are required, particularly if you request this.  EPs and their technicians are often guided by the manufacturers’ reps since they naturally have vast knowledge of their own products.

I also had a loop recorder in for 3+ years before being diagnosed with tachy/brady syndrome, AF with rapid ventricular response rate and other arrhythmias.  My implant monitor (a gem of a monitor) also picked up severe pausing leading to intermittent syncope.  I struggled for years to get a diagnosis and felt I was not always believed.  This left me doubting myself at times and wondering if I was bringing all this on myself.

I do feel confident that your Micra will perform when it is required to do so and that you will be safer with it.  I cannot imagine that they would invest the money to put one in if it was of no help.  Additionally with the benefit of your loop recorder data, the indication for a specific treatment would have been confirmed, since these implant monitors give very detailed info.  Nonetheless, I would still look for an EP who you can trust and feel comfortable with, someone who will give you straight, honest answers to so many of your unanswered questions and maybe commit to offering you a better system in the future if it is felt that your present pacemaker fails to meet your needs.

Take good care Claire

How it works

by AgentX86 - 2020-06-25 22:29:47

Include me in the group who was confused about how the Micra works.  The Micra is inserted into the RV (nor RA).  If it were inserted into the RA, there is a possiility that it would migrate to, or even through the tricuspid valve.  Gravity would force it down toward the RV.

From I can find now, the Micra is inserted into the RA and operates in VVI(R) mode (what I thought but couldn't find).  It's good for people with an AV ablation who also have permanent Afib.  This group (meself included) is paced VVIR mode anyway.  AV dyssynchrony is an acccepted fact.  Not sure how they deal with VV synchrony, though.

The Micra AV, OTOH, will sense the atrial response and can be used in AAI(R) mode.


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