It would be theoretically possible to get a tracing with accurate wave morphology between 2 limbs with an Apple Watch, but it could be inverted if the polarity is switched. Please dont try this though, it can only serve to stress you out more. As long as the watch says sinus rhythm, you are probably good. Ask your physician for a standard EKG is you are concerned.
Thats exactly what I did. I was told you could use it on that area and even on the ankle to replicate different ECG (EKG?) leads. Thank you for the info!! Phew!