That's like saying construction N95 masks can't be used in the medical setting just because they lack appropriate certification. That old shibboleth has been defenestrated weeks ago.

I bet it can, if FDA is beat over the head with a shovel, which it will be if the need arises. It's a real ECG verifiably capable of detecting irregular hearth rhythm, and it costs a tiny fraction of what a big-ass ECG machine would, and therefore can be deployed at a much larger scale. Just because it could only get approval to detect atrial fibrillation duing "peacetime" doesn't mean it can't be pressed into service for other things.