"Save or Die" effects in GURPS.

[Cato the Elder]

Being a relatively new convert to GURPS (from D&D), I have put a lot of effort into adapting the GURPS ruleset to a D&D-like campaign. One place where I have trouble, however, is building "save or die" effects with the rules. It's easy to ad-hoc these effects as something like "roll HT -3 or die", but I'd like to know how one could create such an effect from the rules as written.

One option that seems promising is a Cyclic effect that would continue to damage a person until it killed them, but I'd like to see a way to kill a person instantly, preferably in a way other than inflicting tremendous amounts of damage on them.