Due to battery life, anyone should have a pacemaker designed to handle it. Furthermore, they even say that even if something interferes getting away from the interference will return normal operation. Medical devices like this are highly tested and designed to be highly reliable against random and environmental interference (deliberate hacking is a different concern starting to come into its own light - many modern devices have wireless settings that are NOT well secured and one particularly terrifying example I've seen is remote controlling an insulin pump to inject a lethal dose in someone).

Sorry, this story just doesn't add up. While best to avoid out of an abundance of precaution, there's just no way this makes any sense. The worth thing even remotely likely to happen is that a pacemaker will set off the metal detector, so it's useless anyway.

That said, this is an argument for AIT - there's zero risk from MMW scanning since it's so far outside of the operational range and so easily blocked by the pacemaker housing.