Heart Rate Monitor Inaccuracy

This is what was happening. I would bike on my trainer and at certain points my heart rate would drop, and I would be out of breath. I thought what was happening was my pacemaker was malfunctioning and that I was experiencing the same 2:1 AV block phenomenon that got me to get it in the first place. 


So, this morning I spent about an hour on my bike at the hospital with my electrophysiologist, his nurse/tech, Matt from Medronic (my brand of PM) and a couple of other people. I biked at different levels of exertion. They stuck about 7 or 8 electrodes on me. I also was wearing my heartrate monitor (Polar H10).


Here’s what I learned. My HRM is a bullshit liar. I bike significantly harder than it indicates. At times it would show half or less than what was true. The takeaway is that I should pay attention to the Rate of Perceived Exertion not the readout from my HR monitor. 

Anyway, that’s the story. My pacemaker and I are fine and longing for summer. Ride on!


Polar OH1

by McFlatters - 2020-01-29 14:38:11

I had problems with my garmin chest HRM which didn't give any sort of reading after I had my pacemaker fitted, which apparently blocks the signal from the HRM. I bought a Polar OH1 + Waterproof Optical Heart Rate Sensor which works fine. I also bought a CooSpo Heart Rate Armband Monitor which I use when swimming. They are both worn on the forearm and solved my problem.

My ANT+ Garmin chest strap HR monitor works fine with my PM

by crustyg - 2020-01-29 18:03:05

While I was having my BostonSci PM tuned for me for biking I was watching my Garmin-reported HR (along with the EP tech and the BostonSci rep) and the data from the BSci PM interrogation unit (using Zip telemetry - can't use the wand as it messes up the Minute Ventilation).  Beat for beat identical.

No reason why it shouldn't be: it's a quality device that monitors Lead I - exactly as the EKG machine in the Doc's office.  There's no logical reason why having a PM would affect a good chest strap these days - otherwise the Doc's EKG wouldn't work either.

Early PMs using uni-polar pacing leads produced quite a large pacing artefact which could affect the QRS detection that the chest strap depends on, but most PMs these days use bipolar leads which produce a tiny pacing artefact - you have to look quite carefully to spot it.

This probably doesn't apply to you, Donniederfrank, since you've just been through the exercise lab testing, but one possible cause of odd, or incorrectly low reported HR from a chest strap during exercise would be a burst of an atrial tachy (usually AFib) - this will make QRS detection more difficult for the strap.  Any HR monitoring device that depends on all heart beats being of roughly the same power (all pulse-oximeters, and some devices like automatic sphygmomanometers) may produce incorrect HR results if some beats are strong and others weak (perhaps caused by AFib or AFlut - which can be a paroxysm and not sustained).

I had stopped using my older Garmin chest strap with my Forerunner years ago because it seemed to produce so many odd results.  Turns out that I was having bursts of AFlut and the chest strap was accurately reporting something that I should have been smarter to understand.  But that's hindsight.

lots of posts

by dwelch - 2020-01-31 01:45:31

There are lots of posts on this site related to off the shelf monitors.  We are not electrically normal, so there is that.  And they are not ekg machines they all have some warning about what they are and are not. 

With or without a pacer these things are crappy at best, so why waste time even trying to use one. 

Find a different metric, get in tune with your body, it will tell you how the workout is going.  Or buy an EKG machine and get it calibrated per the manufacturers recommendations.


by DonNiederfrank - 2020-01-31 09:30:40


"Find a different metric, get in tune with your body, it will tell you how the workout is going."

This is exactly what my electrophysiologist said. Well, not exactly. He nodded at the Percieved Exertion chart and said, "Use this."

Besides, when I get outside this spring (I live in WI), not having a HRM on will liberate my vision from my **** phone to look around while I ride.

Don who is now going down the basement and Zwift away.

Chest HR monitors with PM

by ar_vin - 2020-02-05 21:59:47

As noted above by crustyg, chest HR monitors work fine with or without PMs. 

Of course if you have AF or AFIB you might see some strange results.

I have a PM for bradycardia and I always use my Polar H10 chest HR monitor for all my hikes and runs (almost every single day). I've never seen any weird numbers.

I even "calibrated" the chest HR monitor while in the hospital; it was very close.

But my experience with optical HR monitors has been rather mixed.


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