My daughter is in a wheelchair and can't stand, so she can't go thru the metal detector and the wand just goes off with the metal.
They patted her down instead when she was chosen at Disney World for screening in October 2016 (which is what they do at the airport for her, although the airport pat down is much more involved). WDW is currently selecting people for detector screening, not having everyone go thru the scanners. I have heard they will be switching soon to 100% screening, but don't know just when (rumor is April 3, 2017). We are at WDW now, but none of us have been chosen for the metal detector - yet.
In his case, he would just say he can't go thru the metal detector or have a scanner used on him because of a medical device. He will probably need to point out the places with metal and the 'critical' points, like where the driveline comes out.
If you would feel better contacting Disney, I would contact by email and not call.
If you call you will get a call center, not necessarily someone who can answer your question. Answers people have gotten from calling have not necessarily been the same answer as in the parks.
This is a link to the email contact for Walt Disney World:
https://disneyworld.disney.go.com/help/email/
Chose 'Disability Services' as your subject.
The hospital I work at cares for LVAD patients who are past the point of surgery, but are waiting for a heart transplant or are still too unstable to be home or in a nursing home. They are too ill to go anywhere, but I found a nice website that seems to have good travel information (it appears to be a British site)
https://www.mylvad.com/content/lvad-travel-tips
That site lists LVAD Centers around the world and does show one in Florida:
Florida Hospital Transplant Institute
2414 N. Orange Ave
Orlando, FL 32804
United States
+1-407-303-2474