A massive Canadian-led study of cardiac arrest patients may lead to changes in international guidelines on how long CPR should be performed before paramedics or other emergency personnel check whether a defibrillator can restart the heart.

The study of almost 10,000 patients across North America has shown that extending the period of initial cardiopulmonary resuscitation, or CPR, to three minutes from roughly one minute makes no difference in how many survive a cardiac arrest. 

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The main public health message is bystanders and citizens all need to know how to do CPR and do it properly, a researcher says. (Stacie Freudenberg/Associated Press)

Principal investigator Dr. Ian Stiell, head of emergency medicine at Ottawa Hospital, said the finding resolves a worldwide controversy about how cardiac arrest should be dealt with in those first crucial minutes after a patient collapses.

The findings are aimed at emergency responders, said Stiell, and in no way change the message of how average Canadians should react upon finding themselves with a relative or stranger suffering cardiac arrest. Bystanders should call 911 and immediately start CPR until paramedics arrive and take over, he stressed.

Every year, more than 350,000 people in Canada and the U.S. suffer a sudden cardiac arrest, in which the heart effectively stops pumping blood. Less than 10 per cent on average survive. A cardiac arrest is not the same as a heart attack, which results from reduced blood flow to the heart, usually because of a blocked coronary artery.

"With cardiac arrest, you collapse, you're unconscious, with no pulse," said Stiell, who noted that in some cases patients having a heart attack can also go into cardiac arrest.

While quickly starting CPR can increase blood flow to the brain and keep the body alive for a short time, for about one-third of cardiac arrest patients, the heart needs to be shocked with a defibrillator to restore normal pumping action. For the remaining two-thirds, jolting the heart would have no effect; instead special drugs and CPR are used to try to restart the heart.

Traditionally, paramedics and firefighters have analyzed heart rhythm as soon as possible after arriving at the patient's side, and provided only brief CPR while preparing a defibrillator. However, several recent studies had suggested it may be better to provide a longer period of CPR — up to three minutes — before hooking up the device and doing that analysis.

'Survival is abysmally low'

Guidelines have not been able to provide clear advice on which approach is better, and standard practice has varied around the world, says the Resuscitation Outcomes Consortium study published in this week's edition of the New England Journal of Medicine.

"Once the patient goes into cardiac arrest, no oxygen is being filtered through the bloodstream to the brain or the heart," said Stiell, explaining that heart muscle begins to deteriorate. "And by four minutes, it's not in great shape. And it may be that applying a shock then won't work very well. The heart may not come back."

It was thought that doing several minutes of CPR would keep blood and oxygen circulating in and out of the heart, making it more responsive to electrical shocks. 

'If you look at this data, you have to say: 'Boy, we really should be investing in automatic external defibrillators in as many public places as possible.' — Dr. Peter Guerra

"The theory, and it was a very good theory, was that you in essence primed the pump, the heart being the pump," he said.

"This was a theory and I think our study proved that it wasn't true, that it didn't help. There's no reason to have guidelines telling you to do two minutes first."

But that doesn't mean CPR should be completely halted. One emergency responder should continue while a partner attaches the defibrillator's electrode pads, stopping compressions only for the few seconds it takes to get a reading on whether the patient can benefit from defibrillation, then resuming the CPR, he said.

"This is one more step in trying to identify what works and what doesn't ... So the next time when they revise the guidelines, they'll know the answer to this question, that prolonged CPR is not helpful."

Cardiologist Dr. Peter Guerra, a heart rhythm specialist at the Montreal Heart Institute, said Wednesday the study is important because it challenges the way cardiac arrest is treated.

"I think one of the important points is that with out-of-hospital cardiac arrest, survival is abysmally low," said Guerra, who was not involved in the study. "So whatever we can do to improve that is important."

To conduct the study, paramedics and firefighters in dozens of cities across Canada and the U.S. were randomly divided into groups and instructed to provide 30 to 60 seconds of initial CPR or three minutes of initial CPR. Partway through the study, the groups were switched.

The study of 9,933 cardiac arrest patients found no difference in survival: about six per cent of patients in each group survived to hospital discharge with satisfactory health. (Worldwide survival rates range from three to 16 per cent.)

However, it also found the chance of survival fell depending on the length of CPR performed by a paramedic in those patients who also had bystander CPR — and a heart rhythm amenable to defibrillation. This subgroup represented about 10 per cent of all patients in the study. There were no differences in other subgroups analyzed.

"The data suggest that patients who received bystander CPR may fare better with the shorter period of paramedic CPR," said Stiell.

"While there is some debate about the significance of this result, I think it is better to be on the safe side and stick with the traditional shorter initial CPR approach."

That doesn't mean bystanders should not react quickly themselves, he said.

"The big public health message is the bystanders and citizens all need to know how to do [CPR] and do it. It's kind of heart-breaking to see so many patients where nobody does anything. It doesn't matter how good the paramedics are if nobody's done anything. It's much more difficult to save the patient."

Guerra agreed, saying the study makes a strong case for bystander CPR and early rhythm analysis and defibrillation.

"If you look at this data, you have to say: 'Boy, we really should be investing in automatic external defibrillators in as many public places as possible.' … It seems to suggest that the sooner we get a rhythm diagnosis and a defibrillation, potentially the better the patients do.

 "And I think one of the issues we have to look at as a Canadian society is access to CPR training for bystanders, and we also should have access and training in automatic external defibrillators."

Manuel Arango, director of Health Policy for the Heart and Stroke Foundation of Canada, said studies by the Resuscitation Outcomes Consortium are essential for refining the science of resuscitation and will help save more lives.

"This knowledge furthers our understanding of optimal resuscitation techniques and will help inform the next Heart and Stroke Foundation Emergency Cardiac Care guidelines."