Pixel Watch 3 won't record ECG over 120bpm

[Anitabrunning]

My cardiologist recommended I but this watch for the ECG function to monitor my atrial tachycardia in case it becomes atrial fibrillation, but the pixel watch 3 won't record my ECG when my heart rate is over 120 bpm (i.e. when I'm having tachycardia).
Why won't it do this?

Moderator Edit: Clarified subject

[LZeeW]

@Anitabrunning   The Pixel Watch records a 30 second single lead (Lead I) ECG.  Its purpose is to look for signs of atrial fibrillation.  It uses a machine algorithm.  This is a medically regulated feature, meaning Fitbit submitted clinical data to the FDA about its accuracy up to, but not beyond 120 bpm.  It can't read any other types of tachycardia.

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