As per AHA standards... If you witness the arrest than the thump is used (at least that's how protocols go here in NYC).

Vfib and Asystole are being treated the same as far as the CPR goes. Both require compressions and ventilations. Difference comes into play when defiblirator is involved. Vfib is a shockable rythm (AED will shock) while you don'r really shock asystole (AED will not shock). Vfib shows on the screen as a really crazy zig zag line with no pattern while asystole is a straight line. There is a belief in the field that sometimes asystole may be a very fine vfib and you can shock it. Doesn't really hurt since being is asystole is as dead as you are going to get. Does it make any difference if the patient is in asystole or vfib? Not really from cpr point of view.