Public access defibrillators, alongside CPR, can provide immediate life-saving support when someone is in cardiac arrest and waiting for an ambulance.
The new call handling system, called NHS Pathways, was first introduced by YAS for 999 calls in May 2025 and is currently used by more than half the ambulance services in the UK.
YAS said it changed the way calls were “handled and coded”, which meant patients might receive different advice based on the information gathered during the assessment.
The trust said the previous system used to prompt the allocation of a defibrillator “more often” and this was done as a precautionary measure when “in many cases” they were not needed.
It said defibrillators were now only advised when “it’s clear someone is having a cardiac arrest and CPR instructions are being given over the phone”.
Firth, who founded Public Access Defibrillators UK 13 years ago and has seen his devices help save 33 lives, said he believed the changes could “unnecessarily cost lives”.
“At one time it would be deployed as a precaution for a potential life-threatening condition, such as a stroke or a heart attack,” he said.
“Now, that action is delayed until the patient actually stops breathing.”
Firth said his defibrillators used to be accessed 30 or 40 times a month, but since last September that had dropped to an average of once a month.
“Now that they’re not being deployed as a precaution, you’re taking away the advantage of it being available during that first three to five minutes of a cardiac arrest, which is reducing their chances of survival,” he said.
YAS said its deployment rates were now “at similar levels” to most of the other ambulance services using NHS Pathways as their telephone triage system.