Can i.m. administration of narcan (naloxone) in a cardiac arrest victim be helpful?

IM not so much: Narcan (naloxone) can reverse respiratory depression caused by opiate overdose, but if that has lead to a respiratory arrest causing cardiac arrest, the IV form would be much more useful, and only useful then when circulated by chest compressions.

In opiate overdose: But that is often late in the game, as your brain is much more sensitive than your heart to the lack of oxygen, and the arrest is likely to go poorly.