Almost a third of patients who suffer cardiac arrest in hospitals don’t get a defibrillator-delivered shock to make the heart beating again within two minutes how the American Heart Association recommends, a new study revealed.

This delay, the researchers say, significantly reduces patients’ chance of survival. More than a half a million patients suffer cardiac arrest inside a U.S. hospital each year.

"The longer the delay, the less likely it is you'll survive," says lead author Paul Chan of St. Luke's Mid America Heart Institute in Kansas City, Mo and of University of Michigan.

The study used data from 369 hospitals that volunteered in a Heart Association program to track defibrillator usage. The study included 6,789 cases of cardiac arrest caused by abnormal heart rhythm, the kind most responsive to getting shocked back to a normal heartbeat. The researchers included only the cases that happened in intensive-care units or regular units, not those on the emergency room or during surgery.

The study revealed that between 2000 and 2005, only 70 percent of patients received a shock within the two minutes recommended by the American Heart Association. Of those, 39 percent survived to leave the hospitals compared with only 22 percent of those whose treatment was delayed past the two minute recommendation.

Delayed defibrillation was more likely to happen in hospitals with fewer than 250 beds or in hospitals where patients were not continuously monitored or patients admitted with diagnosis other than heart disease. The problem occurred during “off hours” (nights and week-ends) or in case of black people, the study showed.

"It may very well be the case that black patients are more likely to go to smaller community hospitals that have no academic affiliation," Chan said.

"We might make external defibrillators available to more units. That is one potential solution that might have a significant impact over time. And hospitals might set up emergency teams to intervene when there is a cardiac arrest code," Chan suggested as a solution to the problem.

He also suggested that nurses should be allowed to administer shocks within manual defibrillators or installing automated defibrillators that anybody can use. However, he said more study is needed to establish which steps would be the most cost-effective.

"We still have a lot to learn as to how to deliver treatment in an effective way," he said.

The results of the study are published in the January 3 issue of the New England Journal of Medicine.