So, the Cardioversion worked. They shocked him twice and it worked on the second one, so he's back to normal. He fainted afterwards, but that may have been from lack of food, and he faints easily just thinking about anything medical let alone having anything done.
So, apart from his hair (what's left of it) standing on end and smoke coming out of his ears........no, not really........and feeling delicate, he's ok.
Thank you so much for all your help and support, it's been invaluable.