SEATTLE — A nationwide push to put portable defibrillators in every school, a response to several high-profile student deaths, may not be worth the cost, a new study concludes.

The survey of emergency response to schools in the Seattle area over 16 years found that students suffered cardiac arrests only 12 times and a third of these children had known heart problems.

Most of the cardiac arrests at schools between 1990 to 2005 involved adults — teachers, volunteers or people just walking on school property. And they occurred much more often in high schools and middle schools than elementary schools.

"I certainly have no objection to AEDs (automated external defibrillators)," said one of the researchers, Dr. Tom Rea, of the University of Washington's Harborview Medical Center. He's also medical director for King County Medic One, the county's emergency medical service.

But not every school has the money for a defibrillator, which cost an average of $1,000 to $3,000 each, not including the cost to train school staff, he said. They decided to do the study after several states mandated the purchase of defibrillators for schools and others were considering similar measures, he said.

Rea said the research, which was published Monday in Circulation: Journal of the American Heart Association, suggests putting AEDs in high schools or pinpointing schools where students and staff have medical problems.

"I'm not trying to make that decision for people," he was quick to add.

The people who do have to make these decisions will find the Seattle study helpful, because it is the first large study of its kind, said Mary Fran Hazinski, a registered nurse who specializes in pediatric emergency medicine at Vanderbilt Children's Hospital in Nashville, Tenn.

Hazinski, who was not involved in the study, said schools are required to identify students with health problems who may require an emergency response. It makes sense to combine that mandate with this study to figure out if defibrillators are needed, Hazinski added.

Hazinski and Rea also emphasized the importance of CPR training and emergency response planning.

"We plan for other emergencies like fire or tornado, and we should plan for medical emergencies," Hazinski said.

She said the American Heart Association recommends putting AEDs in public places where it would take more than five minutes for a paramedic to arrive, such as schools in rural areas or on large campuses. Defibrillators are used to shock the heart back into a normal rhythm.

According to the study, schools are one of the best places for adults to suffer cardiac arrest; 74 percent of those victims were given CPR by a bystander. Hazinski said Seattle and King County have one of the highest rates of CPR training in the nation, but school staff have high training rates everywhere.