experience with Micra AV and exercise?

53 yo male. I developed bradycardia suddenly a little over a month ago. I was initially in a state of complete heart block, but after going off a medication (imipramine), I am now in first degree AV block, with a long PR interval (432 ms). My cardiologists don't know the cause but they believe it was not from a heart attack. I am awaiting a heart MRI to check for sarcoidosis in the heart, which is unlikely, but since the cause of the heart block is a mystery they want to check. (They have also eliminated medications, Lyme disease, and thyroid issues as possible causes.)

Given that a pacemaker seems inevitable, one cardiologist suggested the Medtronic Micra AV as the pacemaker he would recommend by default. A second cardiologist said that the Micra AV switches to an accelerometer mode above 115 bpm (programmable upper tracking rate 115 bpm) so it's not always ideal for those who regularly bring their bpm over that. I'm not a major athlete but I do play squash a couple times a week, and go on hikes and moderately strenuous walks.

My understanding is that most/all pacemakers use an accelerometer. I don't understand much about the interplay between the accelerometer and other inputs/mechanisms pacemakers use, but from what the second cardiologist said, it sounds like the Micra AV switches to a "pure" accelerometer mode above a certain bpm in a way that other pacemakers don't?

In any case, I'm trying to understand what it actually feels like with the Micra AV when you raise your heart beat up to the level of moderate or above-moderate exertion.

Does anybody have a Micra AV? Do you do sports with it? Does the 115 bpm limit or "switch-over" (as I'm imagining it) affect you? What does it feel like when your bpm goes to 140 or 150 or whatever as you're exercising? Were you able to adjust/tune the pacemaker settings to make it work for you?

Thanks for any information.



PM in a young person

by ar_vin - 2020-11-11 17:20:22

First, welcome to the club no one wants to belong to - you're not yet a full member ;)!

Disclaimer: I know nothing about Micra PMs BUT please read the following post regardless.

A few important things to do:

- seek out a competent board certified electrophysiologist  (EP) (and do NOT work with a general cardiologist)

- research and learn as much as you can about your condition: from your EP, from asking questions here and elsewhere

- research the different brands of pacemakers (lots of info here but you'll need to search the site) and ask questions

- do NOT jump at the latest and greatest whiz bang PM technologies; make sure whatever PM you choose (in consultation with your EP) fits your lifestyle choices: hiking, running, squash, swimming, scuba diving etc etc. The Micra line is still relatively new.

You are very young and will likely need several PMs over the course of your life given that a PM lasts around 10 years before needing to be replaced. It's unclear to me if the Micra can be extracted once it's implanted. Discuss these considerations carefully with your EP!

The major PM brands: Boston Scientiifc, Biotronik, Medtronic and others allow for significant adjustment of settings to suit your lifestyle. I don't know what level of settings adjustments are possible on the Micra line.

Good luck on your adventures!






Thanks ar_vin

by michaelk - 2020-11-11 18:00:08

Yeah, I felt a bit strange posting before being a card-carrying member :), but on the other hand all the advice here including yours is to get as much information as you can before the implant. Even though it is not 100% sure I will need a pacemaker at this point, it is close to 100%, and my guess is that once it's determined I do need one the process will go quickly so I want to be prepared.

To clarify, both of the cargiologists I mention in my post are board certified cardiac electrophysiologists.

My understanding is that the Micra AV is just deactivated and not removed when it needs to be replaced. I read that the heart can acommodate at least three of them.

Yes, I believe the Micra AV has many settings, as with all pacemakers. However, the comment from the second cardiologist (from my original post) led me to believe that it has a fundamental 115 bpm physiological tracking limit and then switches over to a pure accelerometer function. (I'm not sure if I'm using the right words here.) So that seemed important to understand. I will discuss it more with the EP, but pacemakerclub.com is currently my best hope for trying to gain an understanding of what it's like to live an athletic lifestyle with the Micra AV.


Not all pacemakers

by AgentX86 - 2020-11-11 21:02:55

Not all pacemakers use (only) accelerometers for rate response.  Whether accelrometer based rate response is right for you depends on your activities.  Accelerometers aren't great for cyclists or swimmers because the torso doesn't move much.  Some have "minute ventilaton" sensors so will "better" track exercise by monitoring your breathing.

The Micra A/V is a brand new device.  I'd certainly be very hesitant to go that way.  The Micra sits in the right ventricle so can only pace the RV.  It cannot pace the right atrium and can only sense the RA indirectly.

The "A/V" version senses (somehow) the natural pacing signal from the RA and (after a delay) paces the RV.  Again, it can't pace the RA.  I don't completely understand it but your point about switching to accelerometer based pacing fills in some blanks.  This is certainly something to check out completely before you jump.  If the A/V can't sense atrial activity above 115bpm, then relies on the accelerometer then you're going to be in A/V dyssynchrony.  If this conclusion is correct, you really don't want to go here.  A classical pacemaker will function much more naturally. 

What does it feel like when you go into dyssynchrony?  A brick wall perhaps.  Your atria give about a 20% "kick"  to your heart's performance.  When you go into A/V dyssynchrony (the two chambers are no longer beating together) you lose this 20%.  In reality it's more because in addition to not supplying this performance "kick", they're working against each other.

I'm not 100% sure of the above but I'd certainly get your EP to explain why this doesn't happen.  If it doesn't, what exactly does the accelerometer do and why is it needed?

BTW, I live in A/V dyssynchrony but it's not horrible for me because I'm out of sync by design.  It's the lesser of evils and I don't switch in and out, so don't feel it.

Thanks AgentX86

by michaelk - 2020-11-11 22:24:58

Thanks for the explanation of AV dyssynchrony. I will talk with the EP to understand if indeed after 115 BPM you get AV dyssynchrony with the Micra AV. I have also messaged some members here with a Micra AV implanted to try to see what their experience has been.


Micra AV

by AgentX86 - 2020-11-11 23:03:12

Note that there is a difference between a "Micra" and "Micra AV".  Micra AV is much newer.

Good luck

by Gemita - 2020-11-12 03:16:03


Firsrly you mention you were on Imipramine.  I wonder if that was the source/cause of your block and now that you are off it, whether your electrical problems will resolve over time?  I would take your time before you proceed with a pacemaker of any description.

I am so glad you are finding your way around this site and have already private messaged Micra members.  They will really provide you with the best advice since most of us here have conventional devices with leads, including me.

My advice would be to ask your current doctors, if eventually you find you need a pacemaker, whether the Micra is really the best choice for you or whether you would be better getting a device with leads?   Limited at present to only providing single chamber pacing and concerns about what to do with the device on battery expiration seem to be the main problems with this new exciting technology.  I expect you have read all the pros and cons of the Micra as compared with a conventional pacemaker but it is important that you get it right before you go down the leadless pacemaker route.  It sounds a promising technology but it is still in its infancy and safety data is still therefore limited.  I attach a link which might be helpful to read.  Go to Table 3 for a quick list of advantages/disadvantages although I expect you will already be aware of these.  I hope for the very best


Thanks Gemita

by michaelk - 2020-11-12 05:48:03

The situation with the imipramine is confusing/disappointing. They had me go off of it right away, and after going off of it I moved from complete heart block to first degree heart block (with a very long PR interval) within a few days. In fact my GP sent me a message after my second ECG: "Great news! You are out of complete heart block. This is consistent with the imipramine being the cause of the heart block." So that sounded promising, but neither of the two cargiologists are saying anything about waiting to see if the effect of going off the imipramine will improve further over time. My understanding is that, while being on the imipramine exacerbated the situation, being on it was not the underlying cause, and going off of it is not the cure. (So I actually think that statement by the GP was irresponsible.) Furthermore, for what it's worth, it does not feel subjectively like the situation is changing/improving with time. It's been a over month since going off the imipramine and each day feels about the same.

Thanks for the link to the science direct article. This article is like others I've read, in that it says that a single chamber leadless device is indicated for bradycardia like I have. But none of them say anything about the (quite low) upper limit on physiological tracking (again, not sure if I'm using the correct words), which is the issue raised by the second cardiologist, and which seems like the true potential deal-breaker for me with the Micra AV.



by Gemita - 2020-11-12 06:25:41

Michael, hi yes, maybe you would have gone on to develop these problems eventually even without the Imipramine although this medication would certainly not have helped you at all.

Have you tried contacting the manufacturers or searching their websites for the upper limit info?  We are asking challenging questions aren't we and I can see that you are doing your homework.  

I am new to this game with only 2+ years dual lead pacemaker experience but I can recommend it.  They are able to fine tune the settings to suit each one of us and we can choose from a range of pacemakers/models at the outset to suit our lifestyle.  I do not believe the Micra can offer so much choice or are able to be so fine tuned, so that should also be considered.

Additionally with dual pacing systems we can keep the heart potentially healthier and avoid heavy right ventricular pacing potentially leading to dyssynchrony.  Fortunately it doesn't happen to everyone, but some patients can develop heart failure symptoms from right ventricular pacing, so that is an important factor to consider and a factor that has been discussed at length here.  Additionally over time our pacing requirements may change, requiring an upgrade of our pacing system.  This I believe would be easier to achieve with a conventional system than with a leadless system.  I note however that the new Micra AV provides a level of AV synchrony so hopefully this particular problem will be addressed?

Hope you will hear from Micra AV members to help with your decision making.

Thanks Gemita

by michaelk - 2020-11-12 07:51:45

Yeah, from what I can tell, imipramine can make heart conditions worse, in people who already have a heart problem, but it doesn't tend to cause those problems in people with otherwise healthy hearts. In any event, both my GP and two cardiologists think the source of my bradycardia is a mystery, and they do not blame it on the imipramine.

I agree with the various reasons you give that a traditional pacemaker will be better for me. I will keep researching and will hopefully talk to some Micra AV users here. I guess even if I were to get a traditional pacemaker now, by the time it needs to be replaced the leadless technology might have improved significantly, or at least the safety issues better understood.


MIcra A/V

by PacedNRunning - 2020-11-12 15:05:41

I believe the micra A/V will sense the Atrium but will only pace in the ventricle.  You may only pace when your resting or sleeping.  When you exercise the PM may not be needed. Most people with bradycardia don't pace with exercise if they can increase their own heart rate on their own. Have you had an exercise stress test? This may help shed some light on if you will need pacing with exercise or not. If you will, then the MIcra AV may not be a good choice.  Most PM's on the market are essentially the same. Some have more bells and whistles than others but overall they are essentially the same. Best of luck! HOpefully you won't need one!

Thanks PacedNRunning

by michaelk - 2020-11-12 15:45:31

Every since September 27, 2020 my heartbeat never goes over 60, no matter how much I'm exerting. I think it maybe got to 70 once. It spends a lot of time around 50, and goes down to 38 when I'm sleeping. I have to walk up hills and stairs very slowly because I get out of breath.


Just to be clear?

by AgentX86 - 2020-11-12 17:27:44

PacedNRunning, I assume that when you said that most pacemakers are the same that you meant that they're similart to each other and not so similar to the Micra.

The Micra can only pace and sense ventrical (VVI, VVO, VOO, and such).  The Micra AV can also pace VDO but I have no idea how they sense the atrium without an atrial lead.

Edit: Edit:  I got to thinking about what I wrote.  VDO isn't in there, it's VOO (need new glasses).  VOO makes sense butnot great.  Hoever it does support OVO and ODO which seem to be nonsensical.   VDI makes sense but I don't know how it senses atrial activity.  A primer on these devices would really be interesting.


by PacedNRunning - 2020-11-13 05:12:40

When I say all pacemakers are essentially the same. It's minus the leadless because they are leadless. There are 2 Leadless on the market. Micra and Micra AV. Micra AV can sense the atrium but only pace the ventricle. The Micra (original) can only pace and sense the ventricle. The key with Micra AV is you can't have sinus node dysfunction. 


Over 115pm

by PacedNRunning - 2020-11-13 05:17:31

Michael- I believe it will pace over 115bpm. I don't remember the max track for the micra AV but I know recently had this discussion because I thought the same but found it's higher than 115bpm. I think the 115bpm was a typo. :). Sounds like you need at traditional PM based on what your heart does with exertion. 


by AgentX86 - 2020-11-14 00:02:36

My question was not whether the Micra AV could sense atrial activity.  It clearly can because it will do VDI and VDD modes. My question was how since it sits in the LV and has no connection to the RV?

BTW, St. Jude has a leadless PM, the "NanoStim", now as well. See:


(The attribution in Table 1 is to my EP)

FWIW: 5 seconds of explanation

by michaelk - 2020-11-14 13:42:21

The very end of this video says that the Micra AV "utilizes an internal sensor within the device to sense movement in the right atrium. Sensing this movement allows the device to make calculated adjustments and pace the ventrical in coordination with the atrium, providing AV synchronous pacing therapy."



Micra AV

by SNORTINGDONKEY - 2020-11-22 17:16:00

Hi there...

I am an endurance athlete...my main activities are running and cycling and as some folks have noted before, cycling is a problem when you have a PM (generally speaking - I know that some folks like Frank have gotten past that.)

Having said that, my EP had told me that I was the PERFECT candidate for the Micro AV...to the extent that he'd spoken to the now-retired(?) CEO of Medtronic about me. I was desparately waiting for it, and once I it was released, I read up on it and asked lots of questions to my EP. Because it was so new, he did not have answers to all the questions, and so reached out to someone who had access to data from the clinical trials. Unfortunately, he came back with the same answer that you have - which is that it has a tracking limit of 110 bpm (I know that yours told you that it is 115 bpm...not sure who is right but doesn't really matter I guess.)

After a lot of back and forth and asking probing questions, I came to a realization that it is something that Medtronic has put in place to reduce risk. There is no other reason from what I can tell. This problem can be solved by AI/ML, and in fact, I am trying my hardest to convince my employer and Microsoft to work on developing a solution for this problem. This is after all the holy grail of personalized medicine and value-based care. I am happy to be the guinea pig. 

Lastly, I am certainly no doc, but seems like a traditional PM might work for you. 

Also, AgentX86 asked how does Micra AV detect atrial activity - my EP told me that it uses custom software that was developed to detect atrial contractions. (So in fact they are using SOME AI/ML already.) 



by michaelk - 2020-11-22 18:17:50

Some comments and questions:

(1) Do you think your EP was just unaware of the details/lminitations of the Micra AV when he originally recommended it?

(2) Do you have a sense of what it *feels* like that the Micra AV has a tracking limit of 110 (or 115)? I only have a vague sense that it probably feels like it's not keeping up or not in sync. Can you describe what you imigine it feels like if you have a Micra AV and your HR (coming out of the sinus node) goes up to 150 or whatever?

(3) Comment: From what I understand (just from one video animation I saw), the Micra AV detects what's happening in the atrium by sensing the blood flowing into the ventrical from the atrium. My guess had been that there's some limit to the accuracy with which such blood flow can be measured (i.e., at a certain rate the sensors just can't keep track of what's happening). But as you say, perhaps it could be that improved AI could detect subtle changes and raise the limit. I have no idea.

(4) How did you end up settling on the Azure XT device you have? I have heard that the "minute ventilation" in Boston Scientific models is good for things like cycling where there is breathing but not much upper body motion?



by SNORTINGDONKEY - 2020-11-22 20:03:22

Hi there!

(1) Yes, he was unaware - but that's because it was so new. I do like my EP and he is supposedly one of the best. Also, according to them, I/we are outliers. Most of the people that have PMs are sedentary individuals and almost no one has asked them all these questions before. The great thing is that he listens to me because I bring solid data. My suggestion is that if you do end up getting a PM, log everything from day 1 using an Apple Watch/Fitbit/diary/etc.! It will come in handy in convincing people.

(2) I absolutely know what it will feel like - as someone commented earlier, it's like hitting a brick wall. You are trying to go faster but but you feel as if your heart is weighed down. I have had that happen to me many times recently while trying to adjust my PM for my activities. For example, before the PM was put in, my HR while running was in the 150s. But one of the settings I was trying had my max HR to 140...and it felt like what I described above. It happens to me every week while I am cycling (and trying to go faster or climbing), because my PM won't switch from my "activities of daily living" mode into "exercise mode". So basically, I am stuck at the pace I can bike at 125 bpm.

(3) Well, I do know that sensor technologies are really taking huge leaps in miniaturization and the art of the possible. I thought I read somewhere that the Micra AV has a 3 axis-accelerometer which is new...perhaps not new new but new for the form factor. I work for one of the world's largest manufacturing companies and we make medical devices for well-known brands...I am privy to all the research and it's amazing to see the innovations that are coming down the road. 

(4) It all happened all of a sudden...I started to have syncope episodes two years ago and all of a sudden found myself in ER. I knew zero about PMs and my docs didn't really ask me about my lifestyle and put in this device. It was only after I started to get back into my activities that I started to notice all these problems. I did come across Boston Sci and in fact I ride with the rep from Boston Sci and spoke to him at length about my probs. Unfortunately, I am a very complicated case and it won't work for me. The science behind it makes sense, but if you do some research, you'll come across many instances when it just doesn't work as advertised (I don't know why).



by michaelk - 2020-11-22 22:53:17


(1) Yeah, I think my EP is aware that I plan to have my heart rate up regularly, but I will log as you say.

(2) My impression/understanding is that the Micra AV would go above 115, but just in a different mode. So it wouldn't be like hitting a wall. More like moving into a weird mode where things didn't feel right. But maybe it's hitting a wall as you say.

(3) Yes, my impression is that by the time I need a new device in 10 years or whatever there will be quite different technology.

(4) It seems like when you look close into any of these devices you find that things are more complicated than they sounded. :( But I know there are people here who are quite happy.


No issues above 115 to report

by Mek - 2020-12-13 08:44:22

Hi, I recived the micra AV earlier in the year (age 37) mainly for AV block but also had bradycardia (resting normally below 40bpm).  As an (older) international athele my heart rate needs to be regularly +170bmp or I am not training propoerly!

It has a number of setting and algorithms that can be turned on and off as needed.  I started out with the accelerometor being used but found it wasnt working well for me so had it re-programmed.  In summary I have had no issues at high bpm and I am occasionally coming close to my max (186bpm) at high intensity sessions.

All has not been plane sailing but I am able to play my sports as I did before the operation without any noticable affects.  It is at lower bpm where I have found the difficulties and changes harder.

I hope this helps, even just a little, 

Best regards,



Thanks Mek

by michaelk - 2020-12-20 17:32:00

Well, what you say certainly changes the impression I had of the limitations of the Micra AV. I would discuss with my doctor but it turns out that in the meantime I will be getting an ICD, so the Micra question has become moot. But I thank you for your detailed answer.


Micra or Micra AV - MEK

by Ram - 2021-06-25 14:47:37

Just a 2 months ago by coincidence I was told I have AV Block stage 3 with 4 sec. pauses and will need a PM asap although I am asymptomatic.  I've seen two cardiac electrophysicist specialists.  One says traditional PM in case some day my sinus node stops working and the other says Micra and if for any reason my sinus node does stop working they can turn it off and put in a traditional PM.  I was glad to hear of MEK's report using the Micra AV as far as exercise but wondering what was meant by the difficulties when a low bpm and how low?

Anymore experiences with the Micra from anyone too?

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