Ok this is what I found out. The story is that Ryan Church or Erik Timmens or someone else drew a concept painting of Sidious kneeling over Anakin, with his hand on his head. It was meant to echo Obi-wan doing that to Luke in ANH. Lucas liked it and worked it into the film. Matthew Stover and the author of the junior novelization simply said that Sidious was trying to keep Vader from dying.
It's secondary canon. Lucas hasn't confirmed except for when he line edited Stover's work.
I stand corrected. Pass the crow. 😂