The 'rule of thumb' is that voltage shocks, but current kills. But, it depends on a dozen factors, such as duration and timing within heart-beat. Look at De-Fib units. IIRC, they are also used to *stop* heart for surgery. In addition, you have 'dumb luck'. One victim may die of a 'trivial' shock. Another limps away from a lightning strike...
Also, remember how unpredictable tazers and their ilk may be. Don't try it without a CPR-skilled safety-person. Always use correctly 'grounded' and 'breakered' supplies. Always put current limiters in HV. If you have HV bank, Switch off, isolate, dump, earth, then do it again because HV capacitors have a memory and a *vicious* bite...