WEDNESDAY, Jan. 26 (HealthDay News) -- The odds of surviving cardiac arrest are greater if it is caused by a "shockable" arrhythmia and if bystanders can give CPR and a shock from a nearby automated external defibrillator (AED), a new study finds.

That's why one is more likely to survive if a cardiac arrest occurs in a busy public place, where there are people to witness and respond to the emergency and AEDs are available, the researchers noted.

"Patients who have a cardiac arrest in a public location -- airports, public buildings, sporting events or exercise facilities -- most often have a cause for the cardiac arrest that responds to a shock from an AED to save their life," explained lead researcher Dr. Myron L. Weisfeldt, director of the Department of Medicine at the Johns Hopkins School of Medicine in Baltimore. "People who have an arrest at home have a much lower frequency of this type of heart irregularity that responds to a shock from an AED."

AEDs placed and used in public places will save lives if they are easy to find and a bystander is willing to use them, Weisfeldt added.

"AED use in the home will benefit some patients but not nearly as consistently as in public places," he added. "In the home, it is even more important to call 911 to get the EMS activated and to perform CPR."

The report is published in the Jan. 27 issue of the New England Journal of Medicine.

For the study, Weisfeldt's team collected data on 12,930 cardiac arrests. Of these, 2,042 happened in a public place and 9,564 occurred at home.

Of these arrests, 79 percent were so-called shockable arrhythmias -- ventricular tachycardia or ventricular fibrillation. In these arrhythmias, the lower chambers of the heart, known as the ventricles, are contracting chaotically and too fast. The result is that blood is not being circulating throughout the body.

Shocking the heart with an AED can, in many cases, return the heart's rhythm back to normal.

In fact, among these types of arrests, 34 percent of those who were treated with an AED used by a bystander in a public venue survived and were able to get out of the hospital, the researchers found.

Far fewer patients (36 percent) suffered ventricular tachycardia or ventricular fibrillation at home. Among those who were shocked with an AED by a bystander or family member, 11.6 percent were able to leave the hospital, the authors noted.

"Despite an overall decrease in frequency of shockable cause for cardiac arrest, AEDs are potentially of great value in a public place. In the home, as well as in public, calling 911 and performing CPR will help to save lives," Weisfeldt said.

Dr. Gregg Fonarow, an American Heart Association spokesman and a professor of cardiology at the University of California, Los Angeles, said that "between 250,000 to 350,000 Americans have out-of-hospital sudden cardiac arrest each year with over 90 percent of these individuals not surviving."

This new study found that shockable rhythms are much more frequent when sudden cardiac arrest occurs in public locations than when it happens at home, he said.

"This difference in frequency in shockable rhythms between home and public locations likely reflects differences in age and underlying disease in individuals sustaining sudden cardiac arrest in these locations," Fonarow said.

"These findings suggest that AEDs placed in public locations will provide greater value than those in the home. This research also highlights that more needs to be done to prevent and successfully resuscitate those with sudden cardiac arrest," he added.

Another expert, Dr. Gust H. Bardy, a clinical professor of medicine at the University of Washington and founding president of the Seattle Institute for Cardiovascular Research, thinks AEDs should be widely available, but believes CPR is ineffective.

"I am one of the few people on the planet that thinks CPR is not useful. If it were so great, why are people dying at the same rate that they have been dying since the onset of CPR," said Brady, who wrote an accompanying journal editorial.

It's a "pretend therapy," he said. "You wouldn't tolerate a pretend therapy in breast cancer. You wouldn't tolerate a pretend therapy in stroke. Why are we tolerating a pretend therapy in cardiac arrest?"

The only thing that has made any difference in survival is the AED, and they need to be more readily available, he said.

"The manufacturers need to slash their prices so they are less than an iPhone and move to a widespread personal distribution," Brady said. "Why don't we all have AEDs clipped to our belts? Why don't we have a disposable AED?"

A Japanese study in last March's issue of the New England Journal of Medicine also found that the availability of AEDs in public places saved lives, and often with little neurological damage afterwards.

More information

For more on cardiac arrest, visit the U.S. National Library of Medicine.