> probably contains some subpatterns in beats that are hard for humans to appreciate Not really, no... As you said, AFib is one of a very small number of cause

> probably contains some subpatterns in beats that are hard for humans to appreciate Not really, no... As you said, AFib is one of a very small number of causes of irregularly irregular heart rates (and is by far the most common). AFib is pretty easy to spot, even just by feeling someone's pulse with your fingers.