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How common are “shockable” cardiac arrests in public versus at home?

If you see someone collapse in public or in another setting, you should consider the likelihood of sudden cardiac arrest (SCA). A new study funded by the National Heart, Lung, and Blood Institute (NHLBI) shows that SCAs that can be treated by electric shock are more common in public than at home. When bystanders used automated external defibrillators (AEDs) to treat individuals who had suffered SCA in public, more than one-third of the individuals survived to hospital discharge.

Sudden cardiac arrest

Sudden cardiac arrest occurs when the heart unexpectedly stops beating. Blood flow to the brain and other vital organs is stopped, and death can result in minutes without treatment. Most cases are due to ventricular fibrillation (v-fib), or to other arrhythmias (irregular heartbeats), such as pulseless ventricular tachycardia (VT). These arrhythmias are lethal if left untreated.

SCA is different from a heart attack, in which blood flow to part of the heart muscle is suddenly blocked. During a heart attack, the heart usually doesn't suddenly stop beating. Although people who have heart disease are at increased risk for SCA, SCAs also happen in people who appear healthy and have no known heart disease or other risk factors for SCA.

Between 250,000 and 450,000 Americans have SCA each year. SCA occurs most often in people in their mid-thirties to mid-forties, and appears to affect men twice as often as women. Ninety-five percent of people who have SCA die from it—most within minutes unless promptly treated. Rapid treatment of SCA with a defibrillator can be lifesaving.

What was the study?

The study, "Ventricular tachyarrhythmias after cardiac arrest in public versus at home," was published in the New England Journal of Medicine, January 27, 2011.

  • The study involved more than 14,000 patients who were assessed or treated by one or more of more than 200 emergency medical services (EMS) agencies in 10 North American communities. These patients were entered into the EMS registry as part of the Resuscitation Outcomes Consortium (ROC) research activities. This is the world’s largest registry of prehospital SCA and life-threatening trauma.
  • SCAs occurred between December 1, 2005, and March 31, 2007, and took place in either a public or private setting.
    • A public location was defined as a street or highway, public building, place of recreation, industrial place, or other public property. Health care facilities (such as hospitals and medical clinics) were excluded.
    • A private setting was defined as a home, a residential institution (such as a nursing home), or another nonpublic setting (typically a rural farmland location). Study results focused on the home environment only.
  • Participants were 19 years of age or older and had experienced nontraumatic, out-of-hospital SCA under one of several scenarios:
    • Bystanders (non-EMS personnel) witnessed the SCA.
    • Bystanders witnessed the SCA and used AEDs to treat patients.
    • EMS staff witnessed the SCA.
  • Data collected included patient characteristics, circumstances of the SCAs, characteristics of care, and the survivor status as measured by hospital discharge.

What did the study find?

  • Of 12,930 out-of-hospital SCAs, 2,042 occurred in public and 9,564 occurred at home.
  • Of the SCAs that occurred in a public setting, the incidence of lethal arrhythmias such as v-fib or pulseless VT was:
    • 38 percent when the SCA was witnessed by EMS personnel
    • 60 percent when the SCA was witnessed by a bystander
    • 79 percent when a bystander used an AED
  • Of the SCAs that occurred in a home setting, the incidence of v-fib or pulseless VT was:
    • 25 percent when the SCA was witnessed by EMS personnel
    • 35 percent when the SCA was witnessed by a bystander
    • 36 percent when a bystander used an AED
  • Put another way, of the 12,930 patients:
    • 39 percent had SCAs that were witnessed by a bystander in a home or public location
    • 2 percent were treated with an AED by a bystander before the arrival of EMS personnel
    • 9 percent had SCAs that were witnessed by EMS personnel
  • The rate of survival to hospital discharge was 34 percent for SCAs in public settings when bystanders used AEDs. In comparison, the survival rate was 12 percent for SCAs that occurred at home and were treated with an AED.

What are the take-home messages?

  • The use of AEDs saves lives. More than one-third of people who had an SCA in public and were treated with an AED survived.
  • The proportion of SCAs with “shockable” arrhythmias (v-fib or pulseless VT) is much greater in public settings than in the home. This may be because individuals who tend to spend more time in public places, such as at airports and office buildings, are typically younger, more active, and have fewer chronic diseases, thus making them more likely to suffer an SCA that is treatable with an AED.
  • Individuals who suffered an SCA in a home environment may have been older, more likely to have one or more chronic illnesses, on medications that may have altered the incidence of lethal arrhythmias, or have suffered an SCA that was not “shockable.” The lower survival rate was not due to a lack of witnesses or to the absence of a nearby AED.
  • The findings underscore the benefits of putting AEDs in public locations and in using them promptly. They highlight the importance of raising awareness about the devices, as well as the importance of administering cardiopulmonary resuscitation (CPR) and immediately calling 9–1–1 in both public and private settings.
  • AEDs don’t require training to use. The lightweight, battery-operated devices will automatically detect abnormal heart rhythms and will guide users with voice prompts to let them know if and when a shock should be delivered. AEDs are safe to use. There are no reports of AEDs harming bystanders or users, and there are no reports of AEDs delivering inappropriate shocks.

Where can I learn more?

  • Weisfeldt, M.L., Everson-Stewart, S., Sitlani, C., Rea, T., Aufderheide, T.P., Atkins D.L., et al. (2011). Ventricular tachyarrhythmias after cardiac arrest in public versus at home. New England Journal of Medicine, 364(4), 313–321.
  • Bardy, G.H. (2011). A critic’s assessment of our approach to cardiac arrest. New England Journal of Medicine, 364(4), 374–375.
  • Resuscitation Outcomes Consortium (ROC)
  • “Sudden Cardiac Arrest” From the NHLBI Diseases and Conditions Index (DCI)
  • "Arrhythmia" From the NHLBI DCI
  • Researcher Profile: Meet Dr. John Wikswo, Ph.D., who is studying metabolic abnormalities that underlie many cardiac electrical problems, such as SCA.
  • Shockable cardiac arrests are more common in public than home (news release)

Additional information on the study

  • ROC is the first and only large-scale effort to conduct clinical trials focusing on the very early delivery of lifesaving interventions by EMS teams in the field. This has the potential to optimize patient survival and have a large impact on public health. ROC consists of 10 regional clinical centers with 268 EMS and fire services providers. It involves more than 36,000 EMS personnel who serve a combined population of nearly 24 million persons from diverse urban, suburban, and rural regions. The 10 North American communities include seven U.S. sites (Alabama; Dallas, Texas; Iowa; Milwaukee, Wisconsin; Pittsburgh, Pennsylvania; Portland, Oregon; and Seattle–King County, Washington) and three Canadian sites (Ottawa, Toronto, and British Columbia).
  • EMS response times were under 7 minutes for more than 75 percent of the patients in both public and home locations. The median time from the 9–1–1 call to the arrival of an EMS vehicle was 5 minutes for SCAs that were witnessed by bystanders in public locations, and 5.6 minutes for SCAs that were witnessed by bystanders in the home.

April 2011

Archived page, reproduced from a 2011 copy. It is reference material, not current guidance.