Three patients lost their lives after St John's life-saving defibrillators failed in a blunder linked to the ambulance service's poor record keeping.
Documents show the patients died last year in emergency responses in which St John staff reported the defibrillators they were using failed to work properly.
Read more from David Fisher's special report into St John's:
Emergency for St John
Defibrillators are a critical tool for ambulance services and work by delivering an electric shock to restore a normal rhythm to an irregularly beating heart.
St John now has a programme to replace batteries on its defibrillators inside their two-year lifespan.
The incidents emerged in a Herald investigation into St John which revealed the ambulance service was struggling to meet the basic requirements laid out by the Government.
The investigation found staff were over-worked, the organisation was struggling to make ends meet and that the Government is preparing a major funding boost to help improve performance.
Issues facing St John are as simple and critical as maintenance of equipment used every day. A March audit by Verification NZ, which approves St John as meeting its contracted quality standard, found there was no planned system for checking whether blood pressure gauges or pulse monitors were working accurately. Visits to ambulance stations found "there was either no ongoing maintenance check of equipment or if there was it was inconsistently being carried out".
In the case of defibrillators, the Herald found there were four failures between January and September last year. In three of the cases, patients had died.
St John chief executive Peter Bradley said an inquiry had been done to find whether patients had died because of the defibrillator failure. "No patient's death can be directly attributed to the failure of one of our machines.
"We didn't have a proper system in place. It's fair to say we didn't have the proper battery replacement system in place. We do now."
A St John spokeswoman said families of those who had died were not contacted about equipment faults because the St John clinical review - which wasn't independently checked - found those who died could not have been saved.
Ministry of Health group manager for ambulances services Joy Cooper said it had copies of the clinical reviews and had confidence in St John processes.
Documents released through the Official Information Act show how the ambulance staff were let down by the defibrillators as they fought to save lives.
A report on the first incident recorded stated: "Patient in cardiac arrest was defibrillated 20 times but only 12 were recorded on the code summary with the other eight shocks shown as no shock delivered. The patient did not survive."
In the next reported case, ambulance staff were forced to wait four minutes for the arrival of a second ambulance after their defibrillator malfunctioned. Again, the patient died.
The third incident noted the "defibrillator powered off three times" but when needed worked properly - although didn't save the patient.
In the fourth case, paramedics believed the defibrillator was working because the patient gained a pulse despite the machine not recording the delivery of any shocks.
Clarification & correction
Three people who lost their lives in cases in which defibrillators failed did not die as a result of the equipment failures, St John Ambulance has reiterated. While this finding was reported on May 12, St John has taken exception to the headlines: 'Three deaths as defibrillators fail' and 'St John gaffe: 3 end up dead'. In another case, a headline on May 13 was incorrect, when it stated a North Shore woman had battled St John for information on faulty gear, after the death of her mother. In fact, the woman had sought legal advice on other matters arising from the case. The Herald regrets that error and is happy to reiterate St John's findings on the other cases.