In Simple Terms
When someone’s heart suddenly stops, the people nearby may be able to help before an ambulance arrives. A large North Carolina study found that an intensive training program did not clearly increase survival over five years. Denmark’s experience suggests that training far more people, and keeping it up for years, may matter.
When the Heart Stops Outside the Hospital
Sudden cardiac arrest happens when the heart stops pumping blood effectively, cutting off the supply to the brain and other organs. It is not the same as a heart attack, although the two are often confused. A heart attack usually involves a problem with blood flow to the heart muscle. Cardiac arrest means the heart has stopped doing its job of pumping blood, and it can happen for a range of reasons.
The figures from the United States show the scale of the challenge: about 350,000 people experience cardiac arrest outside a hospital each year. Only about one in 10 survives. Saving someone in those moments depends on a sequence of actions: recognizing what is happening, calling emergency services, starting cardiopulmonary resuscitation (CPR), and using an automated external defibrillator (AED), if one is available.
In this situation, time is critical. According to figures cited in the study, the chance of survival falls by about 10% for every minute CPR is not started. A person in cardiac arrest generally cannot wait for medical professionals to arrive without help. That means someone at the scene—even someone who does not work in health care—may be a crucial link in saving a life.
A Large Trial Tested a Multi-Part Plan
To find out whether improving community readiness and emergency response could make a difference for patients, researchers randomly assigned 60 counties in North Carolina to two groups, beginning in 2021. Counties in the first group received an intensive public-awareness and training program for responding to cardiac arrest. The other counties continued with usual practices.
The program did more than teach CPR to members of the public. It trained emergency call handlers to quickly recognize a possible cardiac arrest and guide callers through CPR. It also trained first responders to use defibrillators before emergency medical services arrived. In addition, CPR sessions were offered to people in a range of settings, including workplaces, religious communities, government offices, and other locations.
The aim was to improve several links in the response, rather than rely on a single person’s initiative. An emergency call handler could help a caller start CPR; someone near the patient could perform it; and a defibrillator could provide an additional intervention before an ambulance arrived. But the most important test was not simply how many training sessions took place. It was whether people in the program counties lived longer and had better brain function than those who received usual care.
More Than 22,000 Cases, but No Clear Rise in Survival
The participating counties had a combined population of about 8.5 million. Over the five-year study period, researchers recorded 22,459 out-of-hospital cardiac arrests among adults. The patients’ median age was 64, meaning about half were younger and half older. Women accounted for 37% of cases, Black people for 33%, and 29% of patients lived in rural areas.
There were 11,615 cases in counties assigned to the intensive training program and 10,844 in counties that continued with usual care. A comparison of the results did not show that the program led to more people surviving. Nor did it demonstrate an improvement in the outcome the researchers focused on: survival with a favorable neurological outcome, meaning the person lived without severe brain injury.
The result may be disappointing after so much effort went into training responders and communities. But it highlights a distinction that matters: increasing the use of interventions such as CPR or defibrillators is not the same as increasing the likelihood of survival. Programs may make CPR more common without, by themselves, ensuring that more people survive or recover with better brain function.
Amrish Deshmukh, a cardiac electrophysiologist at the Frankel Cardiovascular Center at University of Michigan Health, described the findings as discouraging but not surprising. Previous studies, he noted, have found that phone alerts, volunteer training, and greater access to defibrillators can increase the rates of CPR or device use. But improvements in those actions have not always translated into a confirmed improvement in survival or neurological outcomes.
A Late Signal Worth Following
The trial did not produce results that were entirely without promise. In an exploratory analysis of data from the fourth year, the share of patients who received CPR from a bystander increased. Lead researcher Carolina Malta Hansen also observed what appeared to be an improvement in this measure during the final year. That is encouraging, but it does not, on its own, show that the program increased survival. Bystander CPR is an intermediate outcome; whether it ultimately helps more patients survive still needs to be assessed.
Hansen, a cardiologist and associate professor of clinical research at Herlev and Gentofte Hospital and the Copenhagen Emergency Medical Services, believes the study period may have been too short to reveal the effects of some parts of the program. Community habits do not necessarily change after one course or campaign. People may need more time to learn a skill, feel confident using it, and act quickly when faced with a real emergency.
About 5% of the population in the counties received training during the trial. At that level, researchers began to see a difference in the delivery of CPR between counties in the program and those in the comparison group. But that was not enough to produce a clear difference in survival. The gap is between training a particular group and reaching a level at which immediate help is likely to be available in many places, from a diverse range of people, at any time.
What Does the Comparison With Denmark Show?
Hansen points to Denmark, where about 80% of the population has received CPR training, compared with roughly 5% in the North Carolina program. The data she presented show that 75% of cardiac arrest patients in Denmark receive rapid care. Defibrillators are used in 11% of cases there, compared with 2% in the United States. Survival is about 16% in Denmark, versus 10% in the United States.
This comparison does not, by itself, prove that training is the only reason for the differences between the two countries. Observational figures do not automatically separate the effect of each part of a health system. But they raise a practical possibility: limited training coverage may not be enough to make early CPR familiar and widely available. In Denmark, the share of people trained rose from about 20% in the early 2000s to 80% today—a gradual change built over many years, not a short campaign.
One way Denmark has helped bring training to large numbers of people is by making CPR certification part of the requirements for getting a driver’s license. Rather than relying on individual interest or scattered workplace initiatives to provide training, this creates an organized opportunity to reach a broad section of the population. That step alone cannot guarantee that patients will be saved, but it shows how public policy can make a skill more widely and consistently available.
The difference is not just in the numbers; it is also about how deeply preparedness becomes part of everyday life. Where more people know how to perform CPR, there is a greater chance that someone able to help will be near a patient. If a defibrillator is available too, it may be used before emergency services arrive. Turning these possibilities into better outcomes, however, requires a fast, coordinated network—and training that remains a usable skill, not just information someone once learned.
Why Might Training Take Time to Make a Difference?
The timing of the trial is an important factor. It began in 2021, when the COVID-19 pandemic was disrupting educational activities and gatherings. Brahmajee Nallamothu, an interventional cardiologist and editor-in-chief of a journal affiliated with the American Heart Association, raised the possibility that the pandemic affected how the training was delivered or how well the program reached the population as planned. He also posed a broader question: Was the training delivered in the best way to ensure that people would remember what they learned and use it under pressure?
Knowing the steps of CPR in theory does not necessarily mean someone will begin performing them in an emergency. A person must recognize the situation quickly, act without delay, and manage the fear and confusion surrounding a sudden crisis. People may also need reminders or repeated practice to keep the skill from fading. The study did not settle how best to build and maintain this kind of readiness.
The trial also illustrates how difficult it can be to turn a health intervention that seems sensible into a measurable improvement across an entire population. Training may help some people and increase CPR use, but survival depends on a whole chain of events: how quickly the arrest is recognized, whether someone calls emergency services, whether a trained person is nearby, whether a defibrillator is accessible, and how quickly response teams arrive. If one or more links fail, the effort may not show up in the final outcome.
The Next Step: More Time and a Lasting Network
Hansen’s team plans to follow North Carolina residents for at least one additional year. During the trial, the researchers built a structure for collaboration and a local working network, and they hope to continue working with the participating communities. Further follow-up will show whether the rise in CPR identified in the later analyses continues—and whether it may eventually be associated with better chances of survival.
Continuing the program does not mean the path forward is simple or certain. As Deshmukh cautioned, putting health interventions into practice on a large scale is a challenge in itself, even when their value is clear. What may make a difference is improving how the program is delivered: reaching more people, repeating training, strengthening emergency call centers’ ability to guide callers, and making defibrillators accessible and ready to use. These are directions suggested by the trial and the international comparison, not guarantees that any one measure will necessarily increase survival.
The central lesson is that rescue begins before an ambulance arrives. In an out-of-hospital cardiac arrest, the people nearby may have to act during the first few minutes, while the emergency system guides them and carries the response forward. Yet in this trial, intensive training that reached only a small share of the population did not clearly improve survival. Changing outcomes may require widespread, sustained preparedness—and further testing to find out whether it truly saves lives and protects the brain.
The Bottom Line
A randomized study across 60 North Carolina counties tested a program that trained emergency call handlers, first responders, and community members to respond to cardiac arrest outside the hospital. Among 22,459 cases recorded over five years, the program did not clearly increase survival compared with usual care, although bystander CPR rose later in the trial. Denmark’s higher training coverage—80% of the population—suggests that broad, long-term efforts may matter more than a limited program. Longer follow-up and further evidence are needed to determine whether wider access to training and better delivery can improve survival.