I have seen a precordial thump work once. The theory is sound, just like commotio cordis. I also like the idea of percussion pacing from the old school anesthesia literature. When I was a floor nurse I had a patient that kept going asystole on me and every time I did a sternal rub/thump his rhythm would pick back up and he would wake up for a few seconds then slow back down. Pretty cool and worked until the crash cart got there.