MTR (Max Tracking Rate / Upper Limit

Well, just when I thought I had this figured out.. I have my device set at 150bpm currently. My EP/tech mentioned raising it again if needed.. I haven't needed to as it's been working perfectly for me between that and beta-blockers I've been able to workout comfortably without getting near the 150bpm threshold and getting pushed into 2:1.

Today, I pushed myself cycling up a hill :) I felt great all the way up. Typically, as I approach the 150bpm, I start to feel something probably when the device is getting ready to smack me down, lol. Not today, I looked down at my monitor and my HR was at 161bpm. I felt great! I stopped right away because I know better, but my usual feelings were absent. I'll be more careful....

My question: is my device supposed to let me go that high? I've been at the 150bpm before and that is where it usually stays until the dreaded 2:1 which didn't come today. Is it possible this was my heart, and not the device? I'm 100% HB last I knew.. Maybe the device just sits by and watches if it's my heart?

I know.. not looking for a lecture and I'll be more careful and ask my EP too.. Just curious of your thoughts. Thanks as usual! :)



Yes! It is your own heart

by PacedNRunning - 2023-10-03 18:28:07

Yes! It is your own heart if you can manage to exceed your Max Track.  Heart block can be intermittent and sometimes with exercise the heart wakes up and is able to keep up 1:1.  So this may have been a day your heart is not in block with exercise.  I have my max to 185bpm, only to give me room so that I don't get "smacked down."  I'm usually 150's running and other sports 120-140bpm. I just dread the 2:1 block. Actually my 2:1 block is 220bpm not 185bpm. 185bpm is my max track but my device won't switch into 2:1 block until I exceed 220bpm. Those are 2 different set HR numbers.   They may be offering to raise it because the data the device collects is HR ranges.  They can see how often your HR is in certain ranges.  

That's what I was thinking..

by USMC-Pacer - 2023-10-03 18:33:25

I used to be intermittent so maybe I still am... occasionally. I'll just be more careful as I don't need my HR going that high at 58 years young although it felt great to fly up that hill :) I have a check up coming next week.. we'll see what they see. Thanks for your reply!

The gas pedal

by Lavender - 2023-10-03 18:45:46

A pacemaker is a gas pedal not a brake. It won't stop your heart from beating faster if your heart wants to, as I understand it. 🙃

Help Me Understand MTR

by DoingMyBest - 2023-10-03 23:09:36

I searched through some old threads, but wasn't able to find enlightenment. Apologies if this has already been covered.

Maximum tracking rate. My understanding is this is the maximum rate your PM will pace at, either A, V, or both (depending on your setup and needs). True? If your heart is able to beat faster on its own and your AV conduction will support it, I assume your heart can go as fast as it wants and the PM would just sit there and watch (1:1, A and V). Surely it's not trying to continue to pace at the MTR rate if the heart is running faster (assuming a normal rhythm, not an arrhythmia). Is this (pacing vs sensing-only with respect to MTR) a PM "feature" that can be selectively enabled?

Is the 2:1 block you mention also an enableable PM feature? Does that only apply to people with a total AV block requiring 100% ventricle pacing? Or can it also apply to people with functional or semi-functional AV nodes? Why would we want it?

In my case 1st degree AV block, RBBB and LAFB are the primary problems (slow and uncoordinated conduction), with infrequent 2nd and 3rd degree AV block. When exercising I am generally A-sensed, V-paced. If I surpass my MTR of 150, I expect things to keep going at whatever rate the SA node decides to go (without further V pacing). Do I have to worry about the PM throwing up some kind of 2:1 thing? I can't imagine the effect or what that would feel like.

For those who are curious about my PM setup, rather than a biventricular CRT-P device, I received a conventional dual-chamber device. The ventricular lead is purposefully placed to stimulate the left bundle branch in the septum. Natural conduction left to right occurs in the ventricles and apparently does as (acceptably) well or better than a three-lead CRT setup without some of its drawbacks. So I was told.

Long story short.. :)

by USMC-Pacer - 2023-10-03 23:31:24

Historically, my PM would always put me in 2:1 block when I hit my MTR of 150bpm with all the unpleasantness that comes with it. Today, that didn't happen. I felt great at over 160npm. Until I see my EP (or speak to him) I'm going to avoid it. 

My MTR is @ 150bpm. My max sensing rate is at 140bpm. Usually, I feel a change in pacing at around 140bpm which tells me I'm getting close so I look at my monitor, I see 140-145bpm and slow down.. Today, for the first timeI didn't feel any of that, got to the top of that hill, looked at my monitor and was at over 160bpm. 

DoingMyBest 2:1 Setting

by Penguin - 2023-10-04 05:40:35

DoingMyBest - There is a 2:1 setting on the Abbott Assurity pacemaker which specifies a heart rate. I'm still unclear on exactly what it does.

Perhaps it would help to drill down into what this does? 

My h/rate also exceeds the max tracking rate.  My techs have confirmed that my own heart is doing this and that it is functioning without the device. 

Abbott Assurity settings

by Selwyn - 2023-10-04 06:11:04

I must say Penguin, when I had a look at the Abbot Assurity settings ( as shown on the above site)  I could not find  your 2:1 setting. 

The only concept for 2:1 I am familiar with is the saftey ratio concept for capture where the programmed voltage/ threshold voltage is usually set to 2:1. I suspect that for the Abbot Assurity this is fixed.

Lightbulb moment!

by Repero - 2023-10-04 07:10:32

So this 2:1 smack-down must be what happened to me last week: I didn't know it existed.

I was monitoring my heart rate during a Morris dance. I got up to 130 bpm (my MTR) when it suddenly dropped to about 69 bpm. I didn't feel anything as the dance was just finishing, but it looked dramatic on the trace.

Can anyone point me towards a description of this feature? What is the feature actually called? I have a Biotronik Enitra 8 DR-T and complete heart block.


by Penguin - 2023-10-04 08:32:41

I do have this setting on my device - under Rates.  It says 2:1 Block Rate. 

I'll PM you about it rather than disturb this thread further.  

2:1 block settings

by Selwyn - 2023-10-04 08:46:56

Thanks to Penguin, as to where this setting is to be found, I have noted the following:

'The 2:1 block rate is a function of the total atrial refractory period (TARP), which is composed of the SAV interval and the postventricu- lar atrial refractory period (PVARP. In this device the nominal PVARP setting is "Auto* with a minimum PVARP of 250 ms. The automatic PVARP feature shortens the PVARP  to maintain 1:1 tracking, while prolonging it at lower rates to prevent tracking of retrograde P waves conducted from the previous ventricular paced VP)  beat, which may trigger pacemaker-mediated tachycardia.

Therefore at  atrial rates above the upper limit  threshold every second P wave will fall in the PWARP and hence it is not tracked.'

This would then be a safety feature of the pacemaker when your are exceeding the upper rate limit for exercise.

MTR & 2:1 Effects TBD

by DoingMyBest - 2023-10-04 11:44:16

Selwyn and Penguin, a big thanks. This helps a lot. I had been unable to find that Abbott datasheet in my searches and you've cleared up a lot of the mystery about MTR and 2:1 block.

I still don't know quite what to expect will happen when I exceed MTR provided my intrinsic conduction keeps things going. It's possible I may not even get there. They recently restarted me on a beta-blocker that is suppressing my HR somewhat. My last vigorous exercise topped at 135.

The good news is that I am in cardiac rehab and intend to push myself to see if I can get it up there in a controlled environment. I'll let you know of any interesting development.


by USMC-Pacer - 2023-10-04 18:44:58

Wow, I got an email saying I got 6 messages.. too bad none of them were related to my thread. Thankfully, I got my answer from my EP... talk about derailed! 


by Vtl.3 - 2023-10-09 01:36:49

By "smack down" do you mean when your pacemaker reasches it's set maximum rate, and once you each it, it shocks your heart rate back down to a lower rate?

You know you're wired when...

Your signature looks like an EKG.

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