Some defibrillators in public places offer step-by-step voice instructions to help lay bystanders deliver a shock to cardiac arrest victims if needed. ((CBC))

Placing portable defibrillators in public places such as schools and workplaces has helped people survive cardiac arrest, Japanese researchers say.

The devices, known as automated external defibrillators or AEDs, should be more widely available to the public, the researchers suggest in a study published Thursday in the New England Journal of Medicine. 

Defibrillators shock the heart to restore its normal rhythm. AEDS are portable and are designed to automatically analyze the heart's rhythm and instruct the user to deliver a shock if needed.

The researchers looked at the cases of 12,631 Japanese adults who suffered cardiac arrest outside of a hospital in front of witnesses between 2005 and 2007.

One year before the study began, Japan made it legal for any citizen to use an AED. During the study period, the availability of the devices in public places such as schools, transit stations, malls, offices and sports venues increased from fewer than one per square kilometre of inhabited area to four or more.

The overall rate of survival after one month with minimal brain damage was 14.4 per cent. Among the four per cent of victims who received an AED shock from a lay bystander, the figure jumped to 32 per cent surviving with little to no brain damage one month after their cardiac arrest.

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Researchers suggest the improvements were due to bystanders who witnessed a collapse calling quickly for emergency help, asking where the AED was and using it.

"This study underscores the importance not only of shocks administered early after a cardiac arrest but also of bystander-initiated cardiopulmonary resuscitation [CPR], irrespective of the type of CPR," Dr. Tetsuhisa Kitamura of the Kyoto University Health Service and colleagues concluded.

"The time from a patient's collapse to the initiation of CPR was reduced because of the increase in bystander-initiated CPR, and both early shock and early initiation of CPR contributed to a better outcome."

It's estimated that a victim's chances of survival drop 10 per cent for each minute defibrillation is delayed, but using CPR to keep the person's blood circulating improves those odds.

In Canada, more AEDs are being placed in public places such as ice rinks and other recreational facilities. The devices cost about $2,500 to $3,000 each.