Unexplained up and down of HR after 30 min or HR >= 150

Hello all,
I have a pacemaker because of an AV Block II/III and I am an active runner (several marathons). My cardiologist and I have completely tested the "MEDRONIC Ensura" as far as the limits are concerned. The pacemaker is set to DDD. 
After a certain time or reaching a HR >=150 the system periodically takes me back about 10 beats and after about 6sec again 10 beats up. (in Polar Flow you can see the phenomenon very well). 
Now I suspect that maybe the AV delay (min SAV 90 ms) is the reason for this. MEDTRONIC in DE has no plausible explanation.
Maybe someone has the same problem or even a solution in the PM setting.
Thanks in advance

see Polar Flow Screen in the Galery


What are your symptoms - if any?

by Gemita - 2023-10-29 05:36:28

Hi Peter, I have seen your post remain unanswered and I wish I could help in some way.  Your particular problem of only a 10 bpm drop however is not something that I have seen here before.  I often see posts about upper tracking rate behaviour and heart rate being slashed by half when we hit our upper set rate, but a drop of exactly 10 bpm and then after 6 seconds, the rate going back up by 10 bpm - no, never heard of this “specific” problem. 

What are your symptoms, if any?  Symptoms would suggest a problem that needs fixing.  Which came first, the monitor results or any symptoms you were getting?  Home monitoring isn't always completely accurate and may be affected by pacing or an arrhythmia.

Have you or your team looked into Medtronic Rate Drop Response by chance?   I attach a link which should be copied into your main general browser to open.

All I can suggest is that you continue to work with your team, perhaps during treadmill testing and ask for a Medtronic rep to be present to help with your settings if this has not already occurred.

I also have a Medtronic Ensura pacemaker but for sick sinus syndrome.  My mode is AAI.  I have arrhythmias so various settings are in operation to help with these.  Clearly an arrhythmia can cause fluctuating heart rates at any time and sudden "irregular" drops would not be so unusual, but a specific drop always of 10 bpm and then after 6 seconds, the rate returning to its exact earlier value is not something that I have ever encountered.  Please let us know how this is finally resolved and what might be causing this?


not a big problem, but irritating

by Peter50 - 2023-10-29 06:01:57

Thank you Gemita for your answer.
The problem is physiologically unnatural and inhibits a continuous longer process. (My cardiologist unfortunately doesn't have a treadmill and the Medtronic rep says it's "internal software routines" that can't be changed).
Thanks for the link, I will contact the academy - and report back here.

Oversensing causing an increased blanking period

by Selwyn - 2023-10-29 20:56:13

I would suggest that at highish heart rates, what is happening is that the P waves are falling into the post ventriuclar atrial refractory period ( atrial blanking)  and therefore is being undersensed. The DDD nature of the pacemaker then slows the heart. 

Once this higher rate then settles the P waves fall out side of the PVARP and then the whole effect repeats itself.

You may wish to reduced the PVARP ( risk of looped 'cross talk') to allow for the higher heart rate.


by Peter50 - 2023-10-31 06:48:52

Thanks Selwyn,

we will check the PVARP time again - in the past time we changed the PVARP to avoid a 2:1 block. 


Second what Selwyn said

by PacedNRunning - 2023-11-03 17:32:29

When the P waves get hidden you go into PM wenckebach.  They should adjust your PVARP so that it's higher than your max paced rate. What is your max paced rate? Lets say it's 150.  But your 2:1 block is 160bpm.  Once you go over 150bpm, your PM will put you in wenckebach  up until you reach 160 at which point you will go into 2:1 block. So they have to set your max pace rate above your 2:1 block, which is 160bpm in this example.  Alot of times they miss these calculations. I remember doing research about this and bringing it up to my pacing team and their exact words were "we forget about this!"  especially when we have high max paced rates.  Hope this helps them to figure it out.


by Peter50 - 2023-11-10 09:31:20

Hi Selwyn, that sounds logical - of course we haven't done the calculations. I will also discuss this with the MEDTRONIC representative, as my cardiologist is already a bit annoyed because I keep finding something new :-)

Many thanks - and I´ll come back with the result



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