I wouldn't be to sure the Apple watch is even comparable to 1-lead ECG, simply due to the difference of how ECG is attached to you and how the Apple watch is.

Through this doesn't mean the Apple watch can't be a useful addition, just don't rely on it.

I would imagine it is possible the sensor in an Apple watch is more sophisticated than a single ecg lead.

12 lead ECG is just a technology. There could be other techniques. However, the Apple Watch might be comparable to higher number of leads but never be identical to the number of leads.

Except, when you wear additional bracelets at your both legs, the other hand, both shoulders and another 6 on your chest. Then yes ;). And consider the continuous cyborgization of our society, that is not that far away.

The 12 lead ECG is about detecting the electrical impulses of heart beats from different angles of your bodies.

If you found a technology to detect these mV values from a meter away ... tell me ;) We will be rich ;)

You can do only so much with a single signal.

There's a reason ECG probes are attached to multiple points on the body, and you can infer quite a bit of info from just comparing multiple signals alone, including if you have your heart flipped, for some reason. :D You'll not get that from your watch.

Apple state that it is equivalent to a 1-lead ECG.