First, there was cardiopulmonary resuscitation (CPR). A group of doctors led by cardiologist Leonard Scherlis started the American Heart Association (AHA) in 1963. One of the association's earliest actions was to endorse CPR, a form of external chest compressions and mouth-to-mouth rescue breathing. AHA has been studying and tweaking CPR ever since.
"Clear!"Then, there was defibrillation. Shocks are delivered to victims in ventricular fibrillation, hoping to defibrillate the heart (hence the term defibrillators). Early on, initial shocks were delivered in groups of three called "stacked shocks."
The first shock was always delivered at a strength of 200 joules. If the first shock didn't work, the rescuer would quickly follow-up with another shock at 300j, and then another at 360j. Each one was stronger because the ability of body tissues to conduct electricity gets worse with each shock. When automatic defibrillators - officially, automated external defibrillators or AEDs - became available, the 3-shock protocol was programmed into the new devices because - well - it had always been done that way. The 3-shock protocol didn't work very well for AEDs. The problem wasn't really the protocol, it was how long the AED took to apply the protocol.
Reading Between the LinesAEDs use computers to interpret the lines on the EKG screen - cardiac rhythms - to determine if a victim's heart is in ventricular fibrillation. When all defibrillators were manual, human caregivers interpreted the cardiac rhythms.
Humans, it turns out, are faster than computers at reading those little squiggly lines. CPR was often delayed while the AED's computer brain carefully determined whether victims needed to be shocked or shocked again, up to three times. Touching a victim while the AED tries to analyze the heart will confuse the machine and cause it to start over. Sometimes, the victim would go without CPR for nearly a minute while the AED made up its computer mind.
Since rescuers were always waiting for the computer to make a decision about shocking the victim, it seemed that defibrillation was much more important than CPR. The necessity of well-performed CPR took a back seat to the much more dramatic and sexy defibrillation.
Back to BasicsThere is renewed interest in performing CPR now, thanks in part to a slew of research published in 2005 and 2006. In one study, emergency responders in Seattle started mixing CPR and defibrillation differently a year before the American Heart Association made the recommendations public. Seattle's results are very promising.
AEDs aren't going to read the rhythm any faster, so the decision was to cut out the AED as much as possible.
"After the initial shock," said Dr. Thomas Rea, principle author of the study, "our experience supports starting/continuing CPR as soon as possible" rather than re-analyzing the rhythm or even checking a pulse, even for rescuers using manual defibrillators - the ones without the computer brain.
These protocols are for professional rescuers, a group accustomed to checking for pulses after shocking victims. The new protocols took some getting used to. "Each year (rescuers) receive training regarding resuscitation," Dr. Rea said, "just that for implementation this time, they trained on a different protocol. Clearly a team effort on this one." According to Dr. Rea, three of the coauthors of the study are paramedics in Seattle.
Dr. Rea said emergency medical service providers in Seattle liked the new protocol better than the way they were delivering shocks before. "We are encouraged by the results," he said. "We have continued the 'new' protocol" even after the study was finished.
Retraining lay rescuers to use public access defibrillation (PAD) may not be as easy to change, he cautioned. "Reprogramming devices outside of the EMS system, i.e. PAD, is a challenge that we are considering."
Look for changes coming soon to an AED near you.
References:"2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care Part 5: Electrical Therapies." Circulation. 28 Nov 2005
Marenco, JP, et al."Improving survival from sudden cardiac arrest: the role of the automated external defibrillator." JAMA. 7 Mar 2001
Rea, Thomas, et al."Increasing use of cardiopulmonary resuscitation during out-of-hospital ventricular fibrillation arrest: survival implications of guideline changes." Circulation. 19 Dec 2006
van Alem, AP, BT Sanou and RW Koster. "Interruption of cardiopulmonary resuscitation with the use of the automated external defibrillator in out-of-hospital cardiac arrest." Ann Emerg. Med. Oct 2003