Cryonicist Ben Best has put a lot of effort into studying and testing personal alarm gadgets you can wear which signal cardiac arrest to try to reduce the incidence of these unattended deanimations and long delays before cryopreservation. I plan to look into those myself.

Ironically, I've noticed that cryonicists talk a lot about how much they believe in scientific, medical and technological progress, but then they don't seem to want to act on it when you present them with evidence of the correctable deficiencies of real, existing cryonics.

Reference:

Personal Alarm Systems for Cryonicists

http://www.benbest.com/cryonics/alarms.html