Rapid action by bystanders plays a crucial role in cardiac arrest

If you collapse from cardiac arrest outside a hospital, your chances of survival are significantly higher if people already present start resuscitation immediately. This is shown in a new Danish registry-based study from the University of Southern Denmark, based on data from more than 21,000 cases of cardiac arrest between 2018 and 2023.

Patients who received chest compressions from a bystander had more than double the likelihood of surviving both after 30 days and after one year. This is based on the researchers’ comparison with patients whose treatment was started later.

- The most important thing we see is that it makes a big difference whether someone present takes action straight away, says Søren Mikkelsen, professor and head of research at Prehospital South and the Department of Regional Health Research, University of Southern Denmark.

- Cardiac arrest requires immediate action. Even a delay of just a few minutes can affect survival, says Søren Mikkelsen.

In the study, the researchers examined who provided the initial resuscitation in cases of out-of-hospital cardiac arrest. They distinguish between three groups: people already present at the scene, so-called volunteer responders or other first responders, and ambulance personnel.

No difference between volunteer responders and ambulance personnel

That early resuscitation increases the chance of survival has also been shown in previous studies.

The new study shows that people on site can make a decisive difference. However, the study does not find a difference in survival between patients who received initial resuscitation from volunteer responders and those whose treatment only began when the ambulance arrived.

– In our data, we cannot see a difference between whether a volunteer responder or a paramedic initiates resuscitation. However, not seeing a difference is not the same as saying that volunteer responders have no effect. We simply cannot demonstrate it in this study, says Søren Mikkelsen.

He notes that the study reaches the same conclusion as a similar Swiss study from last year. That study also did not find increased survival associated with volunteer responders. The researchers explained the result by noting that first responders are typically only dispatched once the emergency call centre has been contacted about a cardiac arrest, which may cause a delay.

Implications for future initiatives

According to Søren Mikkelsen, the results highlight that time to first treatment is crucial.

– It suggests that what makes the difference is how quickly resuscitation is started. There may therefore be potential in strengthening both the public’s ability to act and the telephone guidance provided by emergency call centres, he says.

At the same time, he points out that survival after out-of-hospital cardiac arrest has remained largely unchanged over the past nine years. Despite the widespread deployment of defibrillators and the introduction of first-responder schemes, roughly the same number of people survive each year.

This suggests a need for greater focus on teaching the general public how to respond to cardiac arrest.

Results should be interpreted with caution

The study is based on registry data and is therefore an observational study. This means that the researchers cannot establish causality. There may be differences between patient groups that are not fully accounted for, such as medical history or the quality of the treatment provided.

For example, the researchers did not have data on the quality of resuscitation or on patients’ comorbidities, both of which may influence outcomes. They also did not have information on brain injury or functional status after cardiac arrest, only on survival.