Invalid Low Heart Rate Notifications

[Bill_209]

My wife has been getting many low heart rate notifications on both her Inspire 3 and Charge 6 devices over the last several months so she recently completed a 2-week, continuous heart rate test prescribed by her doctor.

The test results showed that her sinus rhythm range was (56 - 131) bpm, with an average of 85 bpm, so absolutely no heart rate measurements lower than 56 bpm over a two week period.  However, she does have frequent PACs (39.6% burden).

My wife's Charge 6 gave her 19 low heart rate notifications during the same period of time that the heart monitor test was being performed and they were all between (40 - 45) bpm, so it appears that the PACs are not being handled well by the heart rate measurement algorithm, resulting in reporting much lower heart rates (approx. a factor of 2) than actual, for 10 minutes or longer.

[Bill_209]

Can someone tell me if this is a known bug that is currently in the queue for resolving?

[Bill_209]

Just contacted Customer Support about this issue and they instructed me to add the Charge 6 device to the App again, so we'll see if that resolves the issue or not.

[Bill_209]

Well, adding the Charge 6 back to the App again did not resolve the invalid low heart rate notification issue (just got another notification  this morning), but that isn't too surprising because the same thing was happening with a previous Inspire 3 device.

[LZeeW]

@Bill_209   I'm going to try and explain the physics and physiology of your wife's experience with an optical heart rate monitor (OHRM)  This isn't specific for Fitbits.  An OHRM looks for pulsations in very tiny blood vessels under the skin.  That's the physics part.  Now I'll try to explain the physiology part.  The 'strength' of pulsation from a sinus rhythm pulse is greater than the 'strength' of a pulsation from a PAC.  The timing is off compared to a normal sinus beat (hence the premature part).  The heart doesn't pump out as much blood as a normal sinus beat.  That heartbeat's strength (and the shape of its waveform if you were recording it) will be less than a normal, fully coordinated beat.  It might not be enough for the OHRM to sense it.

IMO, this isn't a bug that can be fixed as it is a result of your wife's altered physiology.  You and you wife might want to ask her doctor if you should continue to use this feature or change the low heart limit to something different.

[Bill_209 · Accepted solution]

@LZeeW , thank you very much for the detailed response.  If you are saying that the resolution and accuracy of the optical heart rate sensor used in most fitness trackers isn't as good as the electrical heart rate sensor that was used for the 2-week heart rate test the doctor used, then I accept that as being true.

Based upon what I have read, I was hoping that the Charge 6 would work a little bit better than the Inspire 3 did for measuring the heart rate, but apparently not.  Instead of eliminating the invalid low heart rate notifications, we'll probably just leave them active and just look at the depth, duration and frequency of those events to see if the trends change over time going forward.

[LZeeW]

@Bill_209   I like to use this analogy.  Your heart is a machine with wiring and plumbing.  The ECG monitor measures using the wiring part of your heart.  The OHRM measures using tiny blood vessels, the plumbing part of your heart.

You wrote that she has frequent PACs.  If you use the ECG app, frequent PACs can give an inconclusive result.

[Bill_209]

Yes, we used the ECG App on the Charge 6 to run an ECG test and the result was 'Inconclusive', but we were not able to view the sinus rhythm trace result from the test because the ECG PDF download function still doesn't work on the Charge 6 either.

[LZeeW]

@Bill_209   Android users seem to be having an ongoing problem download ECG reports.  It works fine in iOS.  Your Fitbit model isn't the issue here.

[Bill_209]

@LZeeW , understood that the ECG PDF download problem with Android devices is not a Charge 6 hardware issue, because the ECG PDF download function reportedly worked just fine with Fitbit App 4.25 and then it stopped working with App 4.26. 

Google has apparently confirmed that this problem is due to a bug in the Fitbit App software, with a 'fix' coming at some point in time, but it is still not working a few months and 6 App software versions later, so the Android users are still patiently waiting for the 'fix'.