My observation is that his brain, brainstem in particular (which controls breathing) and spinal cord are all intact so even with heart ripped out all these cells are still alive and able to conduct impulses from the dying brain and there are obviously still electrochemical reactions in the nerves even for just a twitch.
We've seen it in decapitated heads when they move their mouth and try to draw breath it is rare and unique thing to see.
There is no real research into this we are bordering on what is currently known to science and there may be additional explanations to this.
I will let you know if I find.