Heart Rate Precision with Irregular Heart Rate

[munulu]

I have Afib, i.e. my heart beat is pretty fast and jumps all over the place. I was hoping the Charge 5 can give me some idea and alerts when I go over a certain heart beat rate. However, while it can detect my Afib with the 30s test function it doesn't measure my actually heart beat properly. It always shows significantly lower values then what it really is. Do others have similar experiences? Can the Charge 5 just not measure irregular heart beats within a reasonable error range? 

[LZeeW]

@munulu   My background is physiology and a bit of biomedical engineering.  I'm not going to give you a detailed explanation, but this is a limitation of EVERY brand of fitness tracker that uses optical heart rate monitoring.

[munulu]

Why can't this be done with optical sensor?

[LZeeW]

@munulu   Optical heart rate sensors look for pulsations in microscopic blood vessels just below the skin.  When someone has a normal heart rhythm, these pulsations are very similar from one heartbeat to the next -- your heart pumps about the same amount of blood with every heartbeat.  This doesn't happen in atrial fibrillation.  An irregular heart rhythm doesn't pump out the same amount of blood with each heartbeat.  So you get some strong microscopic pulsations and some that are below the level of detection.  Fitness trackers don't have medical grade senors.  Medical grade sensors are better.  Even medical grade optical sensors, like a finger clip SpO2, give a different heart rate than an ECG.

[Gabbee]

I suggest you download and look at your AF ECG. You'll see a jagged mountain range of peaks of varying height. The software in the fitbit tries to decide which of these peaks is a genuine pump cycle and has some difficulty in so doing. If you measure your HR with various other devices (including a pulse oximeter as suggested or a blood pressure monitor), you'll get different results as the software struggles to do its job. I had the same problem when I had AF intermittently, and the best indication of whether I had AF or not was my actual HR which was measured as significantly higher in AF by some devices.

So my best advice is to get a device which specialiases in AF detection, rather than a 'fitness tracker' which mainly takes educated guesses about the state of your body, and often gets it wrong in

Similarly, you wouldn't get a fitness tracker to measure your SPO2 reliably, because it doesn't really have the information needed at the time you need it.