Should Rescuers Give CPR Before Defib?

In the critical moments after a heart stops, should paddle-wielding rescuers shock fast? Or slow?

That's the life-or-death question a new, North America-wide study of nearly 15,000 emergency patients will try to answer. Researchers are examining the benefits of defibrillating victims within 30 seconds of their collapse in cardiac arrest, versus first performing three minutes of cardiopulmonary resuscitation, or CPR, before the shock.

St. Michael's Hospital is one of 43 Ontario hospitals participating in the $15-million undertaking that involves 11 major centres and their myriad emergency-care services.

The mind-boggling logistics involve the co-operation and extra training of about 36,000 emergency medical service workers who will administer one of four combinations of treatment, including the pre-defibrillation 30-second or three-minute CPR. As well, the medical workers will also use a new device designed to increase blood flow during CPR - or a placebo - in the research.

"Most of us who do this kind of research are very excited, because (we'll be able to) answer questions we could never answer before," says Dr. Paul Dorian, a cardiologist at St. Mike's and one of the hospital's key investigators for the study.

Up to 20,000 Canadians suffer cardiac arrests outside of hospitals each year. Only about 5 per cent survive; most die en route to the hospital.

Dorian cites the sheer numbers of study participants, both professionals and patients, as a key factor in the study's success. Ottawa and Vancouver, as well as nine U.S. centres, have signed on to take part in ROC-PRIMED (Resuscitation Outcomes Consortium - Prehospital Resuscitation Using an Impedance Valve and Early Versus Delayed Analysis Trial).

In Ontario, scientists and physicians have joined with emergency workers in Peel Region, Muskoka District and Toronto to launch the trial - a world first.

The motivation for the study is straightforward and dramatic: elapsed time can be as critical as the treatment in saving someone who collapses with a suspected heart problem.

When 74-year-old Mississauga resident John MacLean collapsed during a Leafs-Penguins overtime game at the Air Canada Centre last March, the capacity crowd was silenced and play was halted. Fortunately for MacLean, a nurse sitting nearby leapt to his aid and started CPR. He was resuscitated and taken to hospital, where he underwent triple-bypass surgery.

Traditionally, medical personnel would try to shock a collapsed victim as quickly as possible, sometimes within 30 seconds.

"Now there is research that suggests maybe this isn't the right thing, maybe you shouldn't shock them right away; you should wait three minutes and be doing CPR," Dorian says, indicating recent studies in Seattle and Norway.

"It turns out that when somebody has been unconscious for more than a couple of minutes and you shock their heart right away, the heart may not be ready to receive this electrical shock," he says.

"The way to prime (the heart) is to do some minutes of CPR before you give the shock, so the heart ... will start to beat more effectively.

"But we don't know which is right," Dorian adds.

Small, targeted studies of longer, pre-paddle defibrillation have had surprising outcomes, showing better survival rates. The results have made the large and random effort of PRIMED more important.

All patients will continue to get the best care currently available, researchers promise. New EMS guidelines for cardiac arrest and CPR are already improving survival rates for victims which, after they were treated and released from Toronto hospitals, climbed to 5.6 per cent from 3.8 per cent - and to 19 per cent from 13 per cent for patients with an erratic or disorganized heart rhythm - in 2006 and 2007.

In addition to the pre-shock CPR, the study will test the new Impedance Threshold Device (ITD), which is attached to the face mask and breathing tube used for collapse victims, and increases the vacuum-like effect of CPR.