Sudden Drop in HR During Exercise

For the last couple of months I've experienced a reduction in HR from 120-130 to the lower limit of 60 set on my PM during exercise. It usually happens in the 1 1/2 -2hr range and I have ton stop. My doc and the Boston Sci tech couldn't explain it. Has anyone had this happen and if so do you have an explanation? Thanks


Sudden drop in heart rate

by AgentX86 - 2021-11-17 22:48:32

You don't tell us much about yourself so it's difficult to help much. If your upper rate is set to 130 and you exceed that, under certain circumstances your atria and ventricles will lose synchrony to protect your ventricles.  This could explain your problem.

Or you may have some ectopic (PVCs) going on that, while pacer (SI node or PM) is still functioning, the ectopics will "hide" one of the beats.

I'm sure there are other explations (likely better guesses).  Did they see the EKGs from these episodes?  Any PM records?  Any diagnostics?


Drop in heart rate

by Gemita - 2021-11-18 05:11:50


I am not a settings specialist but it certainly won’t stop me from trying to help you.  I see you have been having these problems since your last generator change and that you have bradycardia which was the reason for your pacemaker?  Did they transfer all your settings over to your new device at your last device change would be my first question?

Do you suffer from sudden blood pressure drops, vasovagal drops perhaps from high vagal tone during exercise, particularly if you become dehydrated?   The pacemaker cannot help with BP drops which may also adversely affect your heart rate, so this may need to be treated separately with extra fluids or medication or other treatments.  

As you will know, some pacemaker settings can specifically help with sudden heart rate drops and there is one feature called Rate Drop Response that can be switched on and adjusted to help with this problem.  Perhaps ask for another treadmill test to get pacemaker settings finely tuned and to check what is happening to your blood pressure, heart rhythm/rate and breathing at the same time.  Have you started getting arrhythmias during exercise as your heart rates increase?  Arrhythmias can certainly cause sudden fluctuations in both heart rate and blood pressure as I well know.

Secondly during treadmill analysis you could ask technician whether you are experiencing a 2:1 block type problem when your heart rate hits higher levels or nears your upper tracking rate.  I have read about this here if my understanding is correct?  As you will know if you are an arrhythmia sufferer, the pacemaker can be set to intervene when it detects high atrial rates and stop tracking these by switching modes (feature is called Mode Switch).  The pacemaker has a sensor to keep us safe during high atrial heart rates.  It will kick in and put the heart in an artificial 2:1 block, so if you are pacing at say around 120 bpm, it could suddenly start to pace at 80 bpm.  A good thing if you have an atrial tachy arrhythmia like Atrial Fibrillation which needs controlling, not so good if you do not have an arrhythmia and you are trying to exercise.  You could check whether this feature is turned on or off or whether the parameters to trigger this response have been set appropriately for you?  I believe our pacemakers can differentiate between high heart rates caused by exercise and high heart rates due to an arrhythmia.

Is some of the above perhaps happening to you as you push your heart rate above the level you can safely pace at?


by Tracey_E - 2021-11-18 08:30:40

If you are suddenly dropping in half, it almost has to be settings. There is a feature where the pacer detects afib and puts us in an artificial 2:1 block, which is great if you are in afib, like hitting a brick wall if you are just trying to work out. 

Is 130 your upper limit? If yes, are they willing to raise it?

Ask if the pacer is dropping your rate artificially, or if the drop is coming from your sinus node. If it's exactly cut in half, my money is on the pacer doing it. If it's your sinus rate tanking, the rate drop response feature Gemita mentiioned can fix it. I use this, too. My rate can come down slowly on its own, but if it drops too quickly the pacer will kick in and keep it level. 

It's odd to me that both the pacer rep and doc have never seen this. Is the rep new, or does the doc only have couch potato patients?? It's not that unusual. 

With Boston

by PacedNRunning - 2021-11-19 03:16:26

Since it's 90-2 hours into the exercise look up Boston Scientific accelerometer/MV sensors. I believe after a this amount of time the sensors reset. Sounds like this is what is happening. 

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