I had a routine EKG last week for a pilot medical certificate. Before the EKG, the nurse rubbed a cold gel on my skin, at the places where she then placed the EKG contacts. I'm assuming this gel was to ensure good contact. If doctors have to rub this gel before an EKG, why doesn't the Apple Watch need this, to ensure good contact?
It probably varies by person, but heart monitor chest straps such as those that come with higher-end exercise watches, can benefit from the gel. However, most folks (including myself) either just slap 'em on dry, or with a little spit, and they usually work fine. But at the doctor's office "usually" probably doesn't cut it. If a little gel changes "usually" to "always", then they probably apply as a matter of course.
That's my long-winded way of saying that a little gel on your wrist and finger would help (I guess; I've not seen the watch yet, nor am I a medical professional). But for the not-a-lab-or-medical-office setting, it's good enough.
If you can't use it though, you can't use it. The data may have glitches, anomalous readings, but most of it will be pretty good most of the time, or they wouldn't bother with the feature. I'm also not sure what the apple watch's sensing mechanism is. Is it reading voltage or is it measuring something else that's correlated?
The watch is always running, can throw out large quantities of glitches & anomalous readings, and only produces an alert to seek followup.
The Apple Watch is positioned as a cardiac event monitor. Those are intended for extended wear and only need to take measurements between a single pair of electrodes to function.
For instance, a Zio Patch is a modern version designed to be compact and unobtrusive.
Here's a comparison between a Zio Patch and the old school tech of a Holter Monitor.
https://www.medgadget.com/2014/01/zio-wireless-patch-may-be-...
One of the tech journalists at Ziff Davis who took part in Apple's heart study ended up being dignosed with Afib by his cardiologist. He wrote about the process he went through.
TLDR: The watch flagged that there was a potential problem, he was given a traditional tape on cardiac event monitor to wear for an extended period to confirm the watch data, and was then diagnosed and treated.
https://www.zdnet.com/article/how-apple-watch-saved-my-life/
For me, this was the money quote: "I've had EKGs a number of times, and there was never any indication anything was wrong."
As EKGs go it’s a relatively basic test, is the equivalent of having a single wire.
I’m very curious to see what doctors/etc. make of it once the feature is released.