HR completely screwed up while running or cycling


In December 2018, I had to have a pacemaker implanted. It is a Medtronic Azure XT SR MRI SureScan with a SINGLE lead into the lower chamber of my heart. (They could not put the second lead into the atrium due to small veins. My AV node is not working at all and so the important lead was to the lower chamber.) 

I am a male, 52 years old and a recreational athlete...used to run 6 - 8 miles at a 11:30 min/mile pace 2 - 3 times a week. I also biked 50 miles at approx 16 mph once a week. Have also done a few Olympic and Sprint triathlons. I am 5' 8" tall and my weight was 156 lb before it is 164 lbs.

Anyway, it's been six months now and I have been trying to run and bike but am seeing a few issues and was wondering if anyone has faced something like this before. 

My resting HR is set to 70 bpm and the upper limit for the "Activities of Daily Living" setting is set to 120 bpm. The top limit of the "Exercise" setting is 155 bpm. I understand that the pacemaker will go into the Exercise mode once it detects running motion. The problem is that as soon as I start running, it goes to 155 immediately...I might not even have run 100 feet. There does not seem to be a gradual increase in HR as I start running slowly. The doctors have been playing with the setting to no avail yet. The best run I have had so far as been a 3 mile run at 13 min/mile pace.

My questions are:

- Can they somehow modify the pacemaker so that it gradually increases the HR?

- Should the upper limit of my Exercise setting be say 135 or 140 bpm? Because that was my comfort zone before the implant.

- Say, I wanted to sprint, will the pacemaker allow the HR to exceed the max setting for a few min or seconds?

- During one of the sessions, the lab technician who was changing the settings told me that this pacemaker gathers data and then modified its behavior. Not sure if anyone has any experience with this.

- When it comes to cycling, the problem is opposite. The pacemaker seems to be stuck at 120 bpm even though I need a little more juice. I understand that's because the pacemaker is not detecting upper body motion. What's the solution to this? I have tried to tap on it manually today but it seemed to make no change.

- Does anyone know what it will do to my swimming?

I wonder how the body regulates its HR in a normal person. Because of the pacemaker implant, is some sort of feedback loop now broken? Is the pulmonary function entirely dependent or independent on the HR? I guess I have forgotten my high school classes...

BTW, all data is collected on my Apple Watch 4.


Appreciate any help/thoughts anyone can provide. Thank you in advance...if there is additional information you need, let me know.



Lotsa questions

by AgentX86 - 2019-08-18 20:48:14

With a complete heart block and without the atrial lead you're likely to have a number of the isues you report here.  I'm in a similar situation because of an AV ablation (an intentional heart block) needed to stop A-flutter caused by a Maze procedure gone wrong.  I'm also paced ventrically only, though in both ventricles.  What this means, for us, is that the atria and ventricles are no longer synchronized.  Instead of an "atrial kick", improving the efficiency of the heart, the atria actually impede the filling of the ventricles.

To your questions:

- Can they somehow modify the pacemaker so that it gradually increases the HR?

That shouldn't be a problem.  Most of us have exactly the opposite problem - our pacemaker doesn't change rate fast enough for us.  I suggest that you find a pacemaker technician who you can work with and keep him/her close.  This is a conservative bunch and they don't like making big changes.  It will probably take several visits before you're happy with the changes.  You may never be happy with your swimming or cycling performance.

- Should the upper limit of my Exercise setting be say 135 or 140 bpm? Because that was my comfort zone before the implant.

- Say, I wanted to sprint, will the pacemaker allow the HR to exceed the max setting for a few min or seconds?

These are questions to ask your EP.  It may be that, due to your AV dyssynchrony, your heart can no longer beat as fast as it once did.

- During one of the sessions, the lab technician who was changing the settings told me that this pacemaker gathers data and then modified its behavior. Not sure if anyone has any experience with this.

Yeah, I have experience with this.  In my experience, it's great marketing material but doesn't work out in the real world.  That was one of the first feechurs to be shut off.  It was doing exactly the opposite of what I wanted.

- When it comes to cycling, the problem is opposite. The pacemaker seems to be stuck at 120 bpm even though I need a little more juice. I understand that's because the pacemaker is not detecting upper body motion. What's the solution to this? I have tried to tap on it manually today but it seemed to make no change.

Yes, that's a real problem.  The only thing they can do is turn up the accelerometer sensitivity.  It's going to be a tough balancing act.  Cycling is a problem.  BTW, tapping on mine makes no difference, either.

- Does anyone know what it will do to my swimming?

You're not going to be happy.  Cycling doesn't give enough motion to the accelerometer to control the rate response appropriately.  Swimming will give it even less, though you need even more output from your heart.  Sorry, but this isn't going to work out well.  The "solution" may be a Boston Scientific pacemaker with the "Minute respiration" sensor. 

Theory of operation: The body's natural system measures CO2 in the bloodstream and uses a "closed loop" to regulate the heart's rate.  The more energy the body uses, the more CO2 is injected into the bloodstream by the muscles.  The "SI node" detects this increased CO2 and increases its rate accordingly.  The faster heart rate pumps more blood through the lungs, which exchange more oxygen for the CO2.  As the CO2 partial pressure stabilizes the heart rate likewise stabilizes.  This is a "closed loop".  Since we've broken that loop with a damaged AV node, other means of "regulation" are needed.  Our Medtronic pacemakers sense motion and try to guess how much energy we're using.  Running and swimming are going to put a lot different motion on our upper body (thus pacemaker), so it's pretty tough to set the pacemaker to recognize both.  Boston Scientific pacemakers also have a "Minute respiration" sensor to attempt to measure the lung's activity. This may be a better measure across all exercise types but that's not one of our choices.  EPs should be very sensitive to their patient's lifestyle but apparently they aren't all well tuned in.

Thank you!

by SNORTINGDONKEY - 2019-08-19 22:42:19

AgentX86 - Appreciate you taking the time to write this all up. Thank you!

Sometimes I suppose ignorance is really bliss...oh well...I guess this is what fate has in store for me.

I did realize a couple of things while running today - looks like if I tread/run softly, the HR does not hit the roof as bad...I am a heavy runner and so I guess I'll have to ask the tech to reduce the sensitivity.

From what I understand my SI node is working ok. The doctor did say that the capsule-like pacemaker from Medtronic is the perfect device for me because supposedly it will take away the dyssychrony.

I do have one question - why can we not use the Boston Scientific device? 

Also, will a SpO2 oxygen monitor tell me anything? 

Cycling is not horrible at 120 bpm, and if I were to take something positive out of this, cycling at this pace will only continue to build my base?


More questions

by AgentX86 - 2019-08-19 23:03:08

Seems none of us are well prepared for life with a pacemaker.  If I'd known then what I know now...  In all fairness, PMs are very technical devices and most people don't want to get into the nitty gritty.  EPs don't know how much control each person wants or is capable of managing.  Understanding, of course, that we aren't normally on our sharpest when we find out we need a PM.

You can't use the Boston Scientific device because your EP implanted the Medtronic device.  ;-)

I don't fully understand the Medtronic Micra.  I don't understand how you  could not have AV dyssynchrony with this pacer.  It has no atrial lead (it sits in the ventricle) so doesn't know when the SI node fires. Particularly since you have complete heart block, it can't know what the atrium is doing. 

A pO2 monitor might tell you something but I've never seen a number lower than 98%.  I'm not a runner or swimmer, though.



by SNORTINGDONKEY - 2019-08-21 16:07:14

To be quite frank, I am not sure why the doc said the Micra is the device for me. I have an appointment with the doc tomorrow and am going to ask him all these questions.

There are changes that can be made that can help.

by Mike417 - 2019-08-24 14:56:41

So, I have the same PM implanted last Dec. for SSS/bradycardia, and have been struggling ever since.

The first change you may need is to have adjusted daily living turned off.  If you take a week off exercise it will adapt the response to that activity. Not what you want.

The second change is is the UR setting - not the upper rate set point - this setting changes the ramping up of your heart rate. It sounds like yours is at the factory setting of 20-30.  The larger the number the slower the ramp-up to your max. A setting of 60-70 (My setting) may work best for you given the activities you describe.

The third change is the delay in response; factory setting is 30, meaning that you PM does not kick in until after 30 sec after activity initiation. I was having syncope when climbing stairs due to my HR not changing fast enough to get my BP up by the time I got to the top of the stairs.

The medtronic PMs detect motion from side to side or perpendicular movement to the direction of travel. Tapping on the PM will not do anything.  The Boston PM detects forward motion, as well as breathing rate. Tapping on that PM should work, as well as breathing faster.  That is why it is harder to get you PM to increase the HR when bicycling.

Even with those changes my Azure PM is not working all that well for me. The EP nurses pointed out this PM works very well for their patients (major medical university hospital), but they are older sedentary patients who don't exercise that much. The EP doc stated had he known how active I was (I am 66, do 6-8 mi. walks 5 days a week, go backpacking and day hikes). he would have put in the BS PM.  And he offered to swap out the Medtronic PM for the BS PM in a few months.  I will take him up on that, but not sure how the insurance will work.


by SNORTINGDONKEY - 2019-08-25 22:49:21

Hi Mike417,

Thank you for your response but I am not sure I understand what you are saying fully. Why do you think daily living should be turned off? I don't know what my UR is set at. I just know that I am paced at 70 and the upper limit of the daily living is 120. My cardiologist did not have any answers (he is not the EP) but I have an appointment to see a tech on Wednesday. I will ask him.

Following is what I was thinking about asking him to do...everyone, please blow holes in this.

The PM is not going past 120 while cycling by design. I am thinking that I will ask him to bump up the upper limit of daily living to 130 and also reduce the sensitivity a little bit...because right now, I am at 120 right away as soon as I start walking. I don't know if I really need that much oomph while simply walking. At 130, I think I should be able to bike okay.

For exercise, I am hitting the top limit of 150 almost right away. I noticed that if I tread really softly, the HR hovers in the high 140s. So I am thinking of asking him to either reduce the sensitivity or bring down the upper limit to 140 because I can sustain that.


I will definitely enquire about the BS PM. I am in Tampa Bay but if I don't see results, am thinking of going to the Cleveland Clinic. Not sure if anyone has had any experience there.

UR setting.

by Mike417 - 2019-08-26 09:22:47

The Azure PM, like all medtronic PM, ramps up your HR at a given speed. If you plot out the speed/rate it forms a curve.  The steepness of the curve is determined by the UR setting. The lower the UR setting the steeper the curve; i.e., your PM gets your HR going higher with a little bit of effort. Likewise the higher the UR setting the shallower the curve - it is slower to increase your heart rate to max, and you have to work harder for the HR to go up.  This is a little bit of a botched explanation, but I hope it makes sense. Your UR setting is probably too low and accelerates your HR too quickly. I would walk/stroll a block and my HR would go up to my max of 155 . (BTW, I am 66, and do a lot of hiking and walking for exercise.)

It took me several visits to convince the EP lab to contact the local rep and have her recommend adjusting the UR. If your PM keeps ramping up your HR with little effort you will quickly get tired out and fatigued.

The EP nurses (major medical center) told me that their patients are older with other medical issues, and more sedentary. So they had no experience with a patient like me.


UR setting...

by SNORTINGDONKEY - 2019-08-26 16:18:41

Thank you! Actually, you reminded me to look for the manual for the PM which I found online. They had a graph that illustrates how it responds. This is good info and as I was looking at the graph a number of questions popped in my mind. I am not sure anyone knows the answers and perhaps the answers are in the manual already but I just haven't taken the time to go through it completely. See page 73.


1. The X-axis is the weighted activity counts. What EXACTLY is/are "weighted activity counts"? Is it counting number of steps taken? The manual does not explain this.

2. The ADL setpoint is inclusive of moderate exercise. I guess what does "moderate" mean? Is it aerobic exercise in zone 3, which is something you can sustain for long periods?

3. The UR setpoint is the "pacing rate during vigorous exercise." To me that implies zone 4. 

I am an endurance athlete...and so if I were to applying the above taxonomy to myself:

- My Lower Rate is currently 70 and that's where it should stay.

- My ADL setpoint is 120 right now. There are a couple of problems I see one is that it's hitting it too soon and secondly if ADL is inclusive of moderate activity, it should be higher for me. I can sustain myself at 130 - 135 when I am running easy (zone 3) and so I would think that the ADL setpoint should be 130 or 135 but the activity counts needs to be relooked at as I'd like it to raise slower.

- If the UR is all about zone 4, where you are in anaerobic zone and it's tough, the upper limit can be what it is now (I think 155 or 156.)

OF COURSE, if my definition of "moderate" is not correct, the above logic will all change.

BTW, I am 53 years old and so I were to plug in my age, following is what I get as far as different HR zones are concerned.

Zone 5 (90-100% of maximum) 150–167 bpm

Zone 4 (80-90% of maximum)  134–150 bpm

Zone 3 (70-80% of maximum)  117–134 bpm

Zone 2 (60-70% of maximum)  100–117 bpm

Zone 1 (50-60% of maximum)  84–100 bpm


Here is another reference about HR zones:

Medtronic limitations

by JWren - 2019-09-02 19:14:30

If I may, I will jump in on this.  I have very similar timing and experiences.  I had a Mentronics device done in December for SSS and was very unhappy with it at first.  My EP told me in December that rate response would work by sensing respiration and motion.  We were very clear about my lifestyle and activity level. Then he ended up not being the one to do the implant due to a "mix-up."  After a number of adjustments, I had what they called a "problem clinic" with the original EP and the head tech person.  At that time (April) he said he did not remember telling me about respiration but he definitley did.  They got on the phone with Medtronics and after some additional setting changes, I am better, not great.  I have been preparing for a Rim to Rim one day hike in Grand Canyon, in less than a month now.  I now get a decent response when going uphill, although it takes a little time to kick in.  I'm even a little better with cycling and the HR gets right up there when I run-which is just a little.

The swimming has not gotten any better at all.  I top out at about 110 in the pool.  I have been a swimming coach for almost 50 years, so I know what's going on in there-and what's not.  I've been enjoying open water swimming this summer because it feels OK and I don't know how slow I'm going.  That will end soon, I'm in Maine.

I think I should have had a differnt device.  Where I left it last with the EP was that I would see how the last adjustments would work and if my life was sufficiently compromised, he would talk with the insurance complany about a possible change of device.  The health care system in Bangor, ME has a deal with Medtronics which is why they use those almost exclusively.

I have an appointment with a new cardiology group in Portland in November.  I am pretty fed up with the locals.



UR setting...

by SNORTINGDONKEY - 2019-09-02 20:56:56

@JWren - I am curious which Medtronic model you have.

@AgentX86, @Mike417: I did go back to see the tech last Wednesday. PRIOR TO Wednesday, following were my settings:

Rate Response = ON

ADL Rate = 120

ADL Response = 9

Upper Sensor Rate = 150

Exertion Response = 2

Activity Threshold = Medium-High

Activity Acceleration = 30  sec

Activity Deceleration = Exercise

With the above settings I was able to run/walk 5 miles at 13 min/mile pace. As far as cycling goes, I couldn't get my HR above 120 because it was not able to figure out I was actually doing a vigorous exercise.

After telling all the above to the tech, they called some Medtronic person and modified the following when compared to the list above:

ADL Rate = Reduced to 100 

Upper Sensor Rate = Reduced to 140

Activity Acceleration = Increased to 60 sec

(Rest of the settings are the same as before.)

I tried to run, bike, play tennis over the past few days and things are a little WORSE than before. I was short of breath while running, and while cycling of course I could not get my HR beyond 100. The one parameter that threw me off and which I do not see in the pacemaker manual is the UR Setpoint (which is what Mike417 is referring to.) For me that is set to 101. I don't really know what that means...does it mean that once I have taken 101 steps while jogging it will put me 140? It looks like typically it is set automatically (although seems like the tech can override it.) I wish I knew what is the min and max range of UR Setpoint.

Medtronic Exercise Settings

by frankmcw - 2019-09-03 19:33:52

I received an email from you, but was unable to find it when I logged onto this website, so I am posting a comment. It looks like you are asking all the right questions regarding changes to you PM settings. I have had a PM since 2015 but was having the same problems you are until I (luckily) found a Med Tech in the Phoenix area, who works with athletes, give me an adjustment that works for all forms of exercise. I have done quite a bit of research and have put together a 3 page pdf I will send you if you want. (This applies to anyone else reading this post.) I have learned from some of the more knowledgeable posters here, but there is also much misunderstanding about how the PM should be set for exercise. Contrary to many posters here, the Medtronic PM with an accelerometer can be set to respond well to biking, running, hiking, swimming, and any form of exercise that involves even a light degree of body movement. Let me know if you would like the pdf. Also, I will post a simplified version of the settings needed to make your PM work better on this thread when I have more time.

Medtronic pdf

by JWren - 2019-09-03 20:35:58



I would love to see the pdf you

Jeff Wren

Medtronic Settings

by frankmcw - 2019-09-04 00:19:06

It is unfortunate that there is so much confusion regarding settings to optimize the Medtronic pacemaker for exercise. I believe it is because a high percent of patients are sedentary or elderly and the overall medical field is trying to save the most  lives they can. But, that leaves us, (the 10% of all pacemaker recipients who are trying to seriously maintain our exercise level), with few resources for optimizing our pacemakers. After much study, and some good input from posters on this blog, I was fortunate to find a Medtronic Technician In the Phoenix area who had been working with a number of athletes in our situation. Since his adjustment 18 months ago, I have been totally satisfied with the way it performs, and I believe my settings would apply to most Medtronic patients that are trying to get their pacemaker to pace them better during exercise. The settings are listed on the “Parameters” sheet from an interrogation you would have done when your technician. Here is the exact printout from my latest remote reading:

Rate Response:

ADL Rate-115 bpm (important)

Optimization-Off (important)

Activity Threshold-MedLow

Activity Acceleration-30sec

Activity Deceleration-Exercise

ADL Setpoint-10 (important)

UR Setpoint-120 (important)

My lower rate is set to 50 bpm and upper rate is set to 160 bpm but every person would be different on that. The above Rate Response settings are simply configuring the PM to begin pacing after a certain number of “accelerative movements” and then maintain pacing based on the continuation of those movements. This is the pure science of the pacemakers algorithm and it will function according to the physical movements of the accelerometer regardless of the patients medical situation. All of the Rate Response settings must be made at once or it will not perform properly. If anyone needs further explanation please post a question or contact me via a message on this blog.



by SNORTINGDONKEY - 2019-09-04 00:45:28

Thank you so much for your response. You’re giving me a lot of hope...In fact the settings I was suggesting last week to the my tech were pretty much the same as what your settings are. Like I said, what threw me off was UR Setpoint. I will take you up on your offer for the PDF if you don’t mind sending it to me. Thanks again!

Few more questions for Frank

by SNORTINGDONKEY - 2019-09-04 09:36:34


As I was reading through your post again, I was curious about the "important" comments that you have. Can you provide some context?


BTW, Frank, very curious about your UR of 160...I am 52, so if you use the formula for zone training, my max HR (zone 5) should be 167. But my tech has been gradually bringing it hindsight, I think that was the wrong thing to do. I think that it is more important to move (increase) the UR Setpoint so that the the max HR will take a long time to reach.


Hello. Question about your device

by 24-7Pacer - 2019-09-04 10:43:01

Just wondering if the Medtronic Azure device you have, and the implant procedure is HIS-Bundle. 


by SNORTINGDONKEY - 2019-09-04 11:29:57

I have the Azure XT SR MRI SureScan. I am sorry but don't know the implant procedure. I will ask the doc next time.


Heart Rate During Exercise

by packrat1 - 2019-09-14 00:32:15

I see all these comments about a person's HR during different types of exercise and I'm wondering what device/devices everyone uses so that they know what their HR is at any given point in their workout.

My PM is a dual lead Boston Scientific K173 I received in 2014 for bradycardia. The lower rate is 50 but I don't know if there is an upper limit. I'm 80 but still in pretty good shape - treadmill 5 - 7 times a week and a home gym occasionally. I track my HR with a Fitbit Ionic but on the treadmill it shows my HR occasionally bouncing around from 138 to 107 to 90 to 115 very quickly. I haven't been able to find whether this is normal or not.

I'd appreciate any insight.

HR during exercise and follow-up from the doctor visit...

by SNORTINGDONKEY - 2019-09-14 18:29:27


I use Apple Watch 4 to track my HR and it matches the HR taken at the doctor's office. Also, I recently bought a Garmin HR wrist monitor because I wasn't sure I could wear the ones with the strap on your chest (I bought it because it syncs with my Garmin cycle computer and the Apple Watch does not.)

Regarding the HR bouncing around, I can say that my HR goes up pretty quickly. In my PM, there is a activity decelaration parameter that you can set...mine is set to "Exercise" and it decreases the HR gradually I think. I don't think I have seen such drastic ups and downs such as yours.


On a side note:

I did go to see the tech a week ago and while they resisted making all the changes I was suggesting to them (after reading Frank's write up), following is what I ended up with:

Rate Response = They left it ON...I wanted it OFF but tech did not agree. They specifically did not agree to change the UR setpoint.

ADL Rate = Brought up from 100 to 120 (I wonder what will happen if I bump up to 130? Is there anyone out there with ADL = 130?)

ADL Response = 9 (Stayed same)

Upper Sensor Rate = Changed to 150 from 140.

Exertion Response = 2

Activity Threshold = Changed to Medium-Low from Med-High. I think this has made a difference in cycling for the better!!

Activity Acceleration = Changed back to 30 sec from 60 sec.

Activity Deceleration = Exercise (Stayed same)

In general, I am better, but of course, not where I was before. For running, I intend to ask them to change Exertion Response from 2 to 1 to see if will make any difference.

Ionic HR

by SNORTINGDONKEY - 2019-09-14 18:33:10


The HR rate that you mention - is that from the treadmill's built-in HR tracker on the handle/safety bar OR is the Ionic HR syncing to the treadmill?

Is your Ionic HR snug on your wrist? If not, this can cause the probs you are describing. 

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