Ah, thank you. Still, 10 microamps? Really?
Yes, 10-20 uA will fibrillate a heart if it passes across the muscle. I recall being shocked 
it was so low. As i said everyone involved in designing ecg DAS front ends were amazed we hadn’t killed someone. Oops forgot to mention most important part- for years clinicians would run across the odd patient that said they could feel the ecg but everyone dismissed that as some fear effect. Certain medicines significantly affect skin condition.
They call it poke-yoke now but in the real early days they used ecg terminals that were a bladed terminal design. Had been that way for some time. That is until someone plugged them into a power extension cord laying on a patient’s bed. That led to big changes in connector design for uniqueness based on function. You think 12 volts is bad…
Also spent time designing defibs. DFMEAs were excrutiatingly detailed but quite necessary.
I worked in a high tech electronics factory. We not only had some fantastic equipment, we had some of the sharpest engineers in the world, and we had a lot of technicians very near it.
Not just because of personal ability, but because when people work together in a cooperative manner, they tend to elevate the whole group to a very high level. And, sometimes a really top individual will motivate his entire team to very high levels. Our new engineers and technicians weren’t much above average when they hired in, but after 5 years, they were way up the ladder.
(I digress here, but our top techs who raised us all up by their abilities did not lightly suffer fools, and because we had a union they could not be fired because they thought management drones were idiots, and this was a major factor in our high level of performance. All you hear about is unions protect the lazy and incompetent, it apparently occurs to no one they also protect the super competent. Our smartest technician would have been the first one fired if the union collapsed.)
We spent a lot of time on these issues, because our lives were at stake. Skin resistance not only varies widely, but from day to day. Which is why in my company, the smart techs never wore rings, ever.
So, what some of you “believe” means nothing to me. I know what we found. A few men here got it, for example, the one who said skin resistance can vary widely between individuals and at different times. He is absolutely correct.
Surgeons discovered some years ago some of the deaths on the operating table were from static electricity, the same sort you get sliding out of a car seat. When they are working with metal instruments inserted into a patient’s body, it doesn’t take much of a jolt to stop that heart. I am told (I don’t work in OR’s) that it is standard to have anti-ESD equipment when operating on patients.
The thing is, such incidents are very rare. It takes a whole bunch of things happening just right (or wrong) but when it does, look out. Anecdotes and data are not the same thing, so I would expect most people to handle 12 v batteries for their entire lives without a major shock. And, when it does happen, you can be sure most people will say, “Um, you imagined it.”