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September 1, 2011
Canadian study: Longer CPR little benefit after heart attack
By Sheryl Ubelacker
TORONTO — A huge 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 cardiac arrest patients across North American has shown that extending the period of initial cardiopulmonary resuscitation from one minute to roughly three minutes provides no benefit. However, several other recent studies have suggested it may be better to provide a longer period of CPR — up to three minutes — before analyzing heart rhythm or using a defibrillator.
Principal investigator Dr. Ian Stiell, chairman 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.
Every year, more than 350,000 people in Canada and the U.S. suffer a sudden cardiac arrest, in which the heart suddenly stops pumping. Less than 10 per cent 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.
While quickly initiating CPR can increase blood flow to the brain and keep the body alive for a short time, for cardiac arrest patients, the heart can only be restarted by providing an electrical shock with a defibrillator.
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.
Guidelines have not been able to provide clear advice on which approach is better, and standard practice has varied around the world, Stiell said.
"The theory, and it was a very good theory, was that you in essence primed the pump, the heart being the pump," he said. "Once that patient goes into cardiac arrest, no oxygen is being filtered through the bloodstream to the brain or the heart."
Stiell said the heart muscle starts 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."
The theory was 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, 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 that CPR should be halted - one emergency responder should continue chest compressions while a partner attaches the defibrillator's electrode pads to get a reading on whether the patient can benefit from having the heart jolted, he said.
To conduct the study, published in this week's issue of the New England Journal of Medicine, paramedics and firefighters 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 6 per cent of patients in both groups survived to hospital discharge with satisfactory health.
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."
But he stressed that these findings in no way change the message of how average Canadians should react upon finding themselves with a relative or stranger suffering cardiac arrest.
"The big public health message is the bystanders and citizens all need to know how to do (CPR) and do it," he said. "It's kind of heartbreaking 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."
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