EKG Heart Rate Accuracy vs. Fitbit Heart Rate Accuracy

[JohnDH]

So, I have been using the EKG feature of Fitbit and I am finding something very confusing. 

The EKG only works if your heart rate is below 120. Well, for example, my Fitbit was just telling me that my heart rate was 73 and I tried it. According to the EKG, my heart rate was 147, so it didn't work. I have tried measuring my heart rate with an oximeter and it was closer to the 73 than the 147, so I am kind of confused. Why is there such a huge gap? Which one is right and which one is wrong? Can anyone provide some guidance?

[LZeeW]

@JohnDH   My background is human physiology, so this might be the explanation.  The first thing I noticed is that the Fitbit ECG said your heart rate was almost exactly double you actual heart rate.  The ECG trace for a single heartbeat is a series of spikes and bumps.  I suspect there is something about the shape of your spikes and bumps such that the algorithm reads one heartbeat as two.  I see this from time to time in the lab.  This is usually the difference between an algorithm analyzing something and a pair of trained eyes looking at something.  You can always forward a copy of the results to your doctor and have a pair of trained eyes look at it.

My resting heart rate is almost always under 50, so my results are also inconclusive.

[JohnDH]

I double checked it just now. Resting heartbeat of 91 on the Fitbit
regular. 130 on the EKG. So, I'm sorry if I gave the impression that it's
always doubled.

[LZeeW]

@JohnDH   Please make sure your arm is at rest on a table and don't squeeze too hard with your finger and thumb.  This makes muscle movement "noise" and can cause an erratic reading.  If you still have this difference between the two numbers, then I think you should send a trace to your doctor to get a pair of trained eyes.