I see it as: He intentionally put paddle(s) on her and pulled the trigger. Not that he accidentally put the paddle(s) on her and pulled the trigger. Involuntary manslaughter would be that he somehow got the paddles on her by accident and slipped and pulled the trigger. Of course, I am not an attorney. ;-)
Yes, he did. But the question of whether he expected that action to kill her is the key. It's just like a DUI. They are both inherently dangerous, reckless actions not necessarily involving any intent to seriously harm anyone. When he activated the defibrillator, was he really trying to seriously hurt or kill his coworker, or was he exercising stubbornness and very bad judgment in the execution of a prank?
Intent is a very important issue in a criminal trial.