Pauline and Phillip Loyley believe the St John Ambulance volunteers who administered medical aid at the scene of their daughter's death in March repeatedly ignored alarms - triggered by a resuscitation machine - to administer an electric shock.
After an inquest into Miss Loyley's death held in Bath last week, Mr and Mrs Loyley say the coroner's summing-up of the case let their daughter down.
They accept the verdict of death by natural causes, but both parents wish that highly sophisticated technical evidence they submitted, commissioned at their own expense, had been given more weight.
"We fought to have the data that had been recorded by the AED, or automatic external defibrillator, admitted into evidence, and it should have become one of the few indisputable facts of the case," said Mrs Loyley, 55.
A defibrillator is the device used to administer a therapeutic electric shock to a patient whose heartbeat has "fibrillated", or broken up.
Mr Loyley, a 53-year-old Bath businessman, added: "The whole point of making these machines simple and portable is to get a shock to patients as soon as possible."
The state-of-the-art portable machine was used by members of the St John Ambulance to shock Miss Loyley's heart back into normal action.
Yet the machine's self-recording facility later revealed it had requested those in attendance to "Check Patient" (the instruction that appears in immediate preparation for administering an electric shock) on at least six separate earlier occasions, and possibly as many as nine.
The St John Ambulance service has 60,000 volunteers nationally, aged between 16 and 65, all of whom receive at least 40 hours' training.
Those who are qualified to use a portable defibrillator receive more training and are also given regular refresher courses. Mr John Slater, general manager of Avon St John Ambulance, was at the inquest. Later he said he still believed his team had done all they could at the time and the medical methods they used were appropriate.
"All four witnesses treating the patient saw no sign that the defibrillator was calling for a shock and they all testified on oath that Miss Loyley had a pulse," he added. "But we need to thank the Loyleys for the work they have put into this.
"Their energy resulted in the coroner's important recommendation that race organisers should give runners comprehensive heart checks."
Mr Slater said that in the light of the clash between the human and the mechanical evidence about Miss Loyley's condition during her last moments, the St John Ambulance had impounded the defibrillator concerned and now planned to have it independently checked.
Richard Lazar, an American expert on the AED who flew to Britain for the inquest, said: "The machine is attached to the patient and detects vital signs.
"It is designed to be portable and easy for anyone to use in order to save lives moments after an attack.
"It gives a vocal instruction and an on-screen display which carries the message 'Check Patient' when there are no signs of life."
Miss Loyley, who was an extremely fit and experienced runner, died as a result of a heart attack brought on by a previously undetected condition that predisposed her to arrhythmia, or an uneven heartbeat.
Although the attack itself was unavoidable in the circumstances, Miss Loyley's parents and her fiance, Nick Raggett, a 32-year-old television actor from London, are now haunted by the idea that if the defibrillator had been used earlier, she might have lived.
The St John Ambulance were paid to attend the race, on 8 March, and one of their training officers was involved in Miss Loyley's treatment. Two doctors, including one who had just run the race himself, also came forward to help.
Miss Loyley's heartbeat was temporarily revived by an electric shock after eight minutes, but at that point she would already have been likely to have been mentally impaired, even if she had regained consciousness. She was in Bath Spa Hospital after only 16 minutes, but staff there were unable to save her.
Mr Raggett said that, like Miss Loyley's parents, his aim was still to improve emergency provisions for all marathon runners.
"While we were gathering all the evidence together for the inquest some friends said to me, 'Why are you doing all this? It won't help Anna now.'
"But the thing has snowballed. We just kept on finding out more and more that did not hang together.
"Neither Anna's parents or I were ever interested in any sort of negligence claim. We were happy to waive all that, we just wanted to know what had happened."Reuse content