I dont think current gamers know what a defibrillator is, given its use in video games currently. It really annoys the hell out of me when games so ignorantly add defibrillator, not knowing what they are or do.
A defibrillator will NOT work if there is no electrical rhythm. If the heart is not beating and has no electrical activity at all (Asystole) then contrary to what happens in the movies, using a defibrillator would be pointless. In this situation, the only thing that can possibly "bring the patient back" is full life-support and cardiac drugs.
If chunks of your heart are outside your body, inside your lungs, and in various other places after taking a C4, fragmentation grenade, or a load of buckshot to the chest, its safe to say there isn't a whole lot of electrical activity going on there.
Or general trauma for that matter, really.
Even for what defibrillators are used for, they rarely work.