It may not be possible for a cryonics team to be standing by at the moment the heart stops, because cardiac arrest may be unanticipated, and/or may also require investigation by the local coroner or medical examiner.
Studies exist showing retention of brain cell structures after long periods of clinical death. Only future physicians using more advanced medical technology will be able to determine whether a person injured in this way is really still recoverable.
Outcomes of medical procedures usually provide prompt feedback for the people involved. Clear feedback of this type does not exist in cryonics. The final outcome of cryonics procedures will not be known definitively until far in the future.
The lack of formal medical or legal recognition of the cryonics means that cryonics patients are considered legally dead, and often requires the cooperation of funeral industry professionals and facilities in addition to medical professionals.