But the researchers, whose report appeared in the journal Resuscitation, said that there was no survival advantage to having multiple rescuers for cardiac arrests suffered at home, which is where most take place.

"An increased number of rescuers improves the outcomes of out-of-hospital cardiac arrests," wrote study leader Hideo Inaba of Kanazawa University Graduate School of Medicine.

"However, this beneficial effect is absent in out-of-hospital cardiac arrests that occur at home."

The American Heart Association (AHA) and other groups say that everyone should learn cardiopulmonary resuscitation, or CPR, which generally means "hands-only," or just chest compressions without any mouth-to-mouth breathing.

Studies have shown this is just as effective as the traditional way when it comes to helping adult cardiac arrest victims.

The Japanese study found that among more than 5,000 adults who went into cardiac arrest outside of a hospital, the odds of surviving were up to two-times higher when more than one person tried to help.

Six percent of victims were alive one year later when three or more "rescuers" were there, versus 3 percent when only one person came to their aid. When two people responded, the survival rate was 4 percent.

The researchers did not know if all of those rescuers performed CPR. Some may just have tried to help in some way, the researchers noted.

Still, the findings do show that the more bystanders who jump into action, the better, said Michael Sayre, an associate professor of emergency medicine at Ohio State University in Columbus, who is also a spokesman for the AHA.

"The study confirms the importance of bystanders responding to cardiac arrest, and the importance of early CPR," he told Reuters Heatlh.

Inaba's team found no clear reason why there was no survival advantage to having multiple rescuers when a cardiac arrest occurred at home, and Sayre agreed that many factors could be at work. Among others, those who are out and about when cardiac arrest strikes may be relatively healthier.

Cardiac arrests in the elderly and frail are very likely to happen at home.

CPR alone cannot restart the heart when it stops, but it can keep the flow of blood and oxygen moving until medical help arrives. So along with performing CPR, bystanders need to immediately call for emergency help.

According to the AHA, more than 380,000 people in the United States go into cardiac arrest outside a hospital each year, but most people have either not learned CPR at all or their training has lapsed.

"Hands only" CPR is easily learned, with or without a class, Sayre said. The AHA website has a teaching video at: bit.ly/LhVoQl.

The basic instruction is to give strong, steady chest compressions at a rate of 100 per minute. Experts have pointed out that humming the Bee Gees' 1970s disco song "Stayin' Alive" will help rescuers find the 100-beat-per-minute rhythm.

"Learning CPR is something people often feel that they can put off," Sayre said. "But you never know when you'll be called upon to act." SOURCE: bit.ly/LjRENu

(Reporting from New York by Amy Norton at Reuters Health; editing by Elaine Lies and Bob Tourtellotte)

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