January 31, 2011

Survive ‘shockable’ cardiac arrest? Chances excellent in big venues

Astudy of more than 14,000 men and women whose hearts suddenly stopped suggests that the chances of survival are very high if such cardiac arrests are witnessed in large public venues, including airports, sports arenas or malls.

The reasons, researchers say, are that almost four out of five such cases appear to be due to a survivable type of heart rhythm disruption and that big places with lots of people are more likely to have an automated external defibrillator, or AED device, handy, along with those who can apply it as well as CPR.

“Our research clearly shows that the chances of surviving a shockable cardiac arrest are best when someone publicly witnesses it happening, a bystander uses CPR to keep blood flowing to the brain and other key organs, and an AED can be applied to electrically restart the heart,” said Johns Hopkins cardiologist Myron “Mike” Weisfeldt. “The best outcomes have all been followed by prompt arrival of trained emergency medical personnel and a trip to the hospital,” said Weisfeldt, director of the Department of Medicine at the Johns Hopkins University School of Medicine and physician in chief at The Johns Hopkins Hospital.

Among the team’s key findings, reported in the Jan. 27 edition of the New England Journal of Medicine, was that 79 percent of such victims had the kind of disrupted heart rhythm that could be corrected by an electrical shock from an AED device placed on them in public by a bystander. Among those who actually were shocked, 34 percent survived, recovering well enough to be discharged from the hospital.

The frequency of such shockable rhythm disturbances—known by the acronym VT/VF for ventricular tachycardia, ventricular fibrillation—was much less among those stricken at home, at 36 percent. If a relative or bystander witnessed the arrest there and used an AED, 11.6 percent survived to leave the hospital.

Weisfeldt, the study chair for a large network of emergency medical services systems, speculates that patient demographics and severity of their heart disease likely explain why VT/VF rates are different between those whose hearts stop pumping at home and those who suffer an event in public, with people at home being older and more likely to have underlying chronic disease than those who are active and attending major sports events. He points out that many who suffered a cardiac arrest at home had no remaining electrical activity in the heart.

Weisfeldt emphasizes that people at risk of sudden cardiac death and who have an AED at home may still benefit. “But the survival rate is really not that much different than with a bystander practicing CPR without an AED and quickly calling 911,” he said.

Researchers at Johns Hopkins and other large medical institutions involved in the report say that their latest study is believed to be the largest and most comprehensive VT/VF analysis to date in the United States and Canada. Conducted in 10 major cities from December 2005 through April 2007, the study helps explain the difference in survival rates between those who arrest in public and those who do so at home.

“The likely next best step to maximize people’s chances of surviving VT/VF is the placement of more AEDs in big, popular public venues, along with uniform and prominent AED location signs so that people can easily find one,” Weisfeldt said. He recommends that all public places and businesses that can accommodate more than 1,000 people at a time should have the laptop-size AEDs on site and in well-marked locations.

Every year, experts say, more than 300,000 Americans of all ages die from sudden cardiac death, many of them elderly.

For the study, researchers closely monitored the circumstances surrounding thousands of incidents of cardiac arrest reported to 911 emergency lines. The researchers checked for survival, discharge from hospitals and more than 200 “unique observations” about each cardiac arrest, its location and the use of CPR and AEDs. Emergency medical personnel in all 10 cities recorded the details, which were then sorted by study team members at the University of Washington in Seattle.

“Fortunately, the chances nowadays of getting bystanders to help with CPR and using an AED in public are pretty good,” said Weisfeldt, a past president of the American Heart Association, who notes that more than 10 million Americans, many of them health care workers, are trained or retrained in CPR each year. “A lot of people are trained in basic lifesaving techniques, and now we have to give them the tools, including an AED, to make sure they can make the best use of their skills.”

The latest study is part of a landmark series of research projects known as the Resuscitation Outcomes Consortium, designed to reveal the best lifesaving techniques for cardiac emergencies. The research, which is set to continue through 2017, was funded by the National Heart, Lung and Blood Institute.

Related websites

Johns Hopkins Department of Medicine

Resuscitation Outcomes Consortium

‘New England Journal of Medicine’