The date of your suspension will usually start from the date that you have any remedial work or get a formal diagnosis of a condition, not necessarily the date of your cardiac arrest.
For example, if you have a cardiac arrest and 2 weeks later get an ICD implant, then the suspension will start from the date of the implant, not the arrest.
If you have a heart attack as the cause of your cardiac arrest, the problem is often looked at and dealt within a short time frame (same day) so the suspension will start from that day.