Background In the last decade, there has been a rapid increase in the dissemination of automated external defibrillators (AEDs) for prehospital defibrillation of out-of-hospital cardiac arrest patients. The aim of this study was to study the association between different defibrillation strategies on survival rates over time in Copenhagen, Stockholm, Western Sweden and Amsterdam, and the hypothesis was that non-EMS defibrillation increased over time and was associated with increased survival.
Methods We performed a retrospective analysis of four prospectively collected cohorts of out-of-hospital cardiac arrest patients between 2008 and 2013. Emergency medical service (EMS)-witnessed arrests were excluded.
Results A total of 22 453 out-of-hospital cardiac arrest patients with known survival status were identified, of whom 2957 (13%) survived at least 30 days postresuscitation. Of all survivors with a known defibrillation status, 2289 (81%) were defibrillated, 1349 (59%) were defibrillated by EMS, 454 (20%) were defibrillated by a first responder AED and 429 (19%) were defibrillated by an onsite AED and 57 (2%) were unknown. The percentage of survivors defibrillated by first responder AEDs (from 13% in 2008 to 26% in 2013, p<0.001 for trend) and onsite AEDs (from 14% in 2008 to 30% in 2013, p<0.001 for trend) increased. The increased use of these non-EMS AEDs was associated with the increase in survival rate of patients with a shockable initial rhythm.
Conclusion Survivors of out-of-hospital cardiac arrest are increasingly defibrillated by non-EMS AEDs. This increase is primarily due to a large increase in the use of onsite AEDs as well as an increase in first-responder defibrillation over time. Non-EMS defibrillation accounted for at least part of the increase in survival rate of patients with a shockable initial rhythm.
- cardiac arrest
- ventricular fibrillation
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Cardiac disease is the most common cause of mortality in Western countries, with most deaths due to out-of-hospital cardiac arrest (OHCA).1 2 Early defibrillation is the major determinant of survival from OHCA.3 4 To increase early defibrillation rates, many countries have adopted prehospital defibrillation strategies, including traditional first responder automated external defibrillator (AED) programmes (dispatched police officers/fire fighters)5 6 and public access defibrillation programmes with strategically placed AEDs.7–11 In addition, there has been a rapid increase in the dissemination of onsite AEDs. These AEDs are often placed in public areas such as airports, sport facilities and shopping malls and are mainly operated by lay rescuers but are not part of any formal programme.12 On-site AED use has shown to substantially reduce the time to the first shock.13 However, there is insufficient knowledge about how these different prehospital defibrillation strategies contribute to survival.
The objectives of the study were to: (1) evaluate the contribution of different prehospital defibrillation strategies to survival after OHCA; (2) establish whether survival after OHCA is increased in four large Western European regions; and (3) determine whether there was a relationship between the change in bystander AED use over time and survival.
Copenhagen Oslo STockholm Amsterdam (COSTA) group
The COSTA group is a joint research collaboration network in resuscitation science between Denmark, Norway, Sweden and the Netherlands with the aim of improving research in OHCA and early defibrillation. All researchers have extensive interest in the field of early defibrillation. Data from OHCA were merged and analysed in a central research database within the COSTA collaboration.
Setting, study regions and emergency medical service (EMS) systems
This study is an analysis of prospectively collected cohorts of data describing characteristics and outcome of patients who had OHCA in the catchment areas served by four participating registries.
Denmark: central Copenhagen
Central Copenhagen covers 97 km2 and holds approximately 680 000 inhabitants. The EMS of Copenhagen is a two-tiered system comprising ambulances equipped with defibrillators providing basic life support and physician-staffed mobile emergency care units providing advanced life support. Since 2007, if an OHCA is suspected, the dispatcher provides instructions for bystanders to perform cardiopulmonary resuscitation (CPR) and identifies nearby AEDs available for public access defibrillation.14
Sweden: Stockholm County and Western Sweden
Stockholm County covers 6519 km2 and has 2.1 million inhabitants. Western Sweden covers 25 247 km2 and has 1.6 million inhabitants. There is a two-tiered EMS system in Sweden for responses to all medical emergencies. Both tiers consist of EMS units providing advanced life support and AED defibrillation. In 2006, a dual-dispatch first responder system that engages firefighters and police officers in addition to EMS was implemented in Stockholm.15 However, in most parts of Sweden, this system was not implemented until 2011.16 Since 2010, a mobile phone positioning system to dispatch lay volunteers who are trained in CPR has been implemented in Stockholm County.17 Since 1998, dispatchers provide instructions for bystanders to perform CPR and since 2013 to identify nearby AEDs available for public access defibrillation.
The Netherlands: province of North Holland
The province of North Holland covers 2404 km2 and has 2.4 million inhabitants. In response to an OHCA, two ambulances of a single tier are dispatched. In part of the study region, the dispatch centre simultaneously dispatches fire fighters equipped with an AED (since 2005) and, since 2010, also police officers equipped with an AED. Ambulance personnel are equipped with manual defibrillators and perform advanced life support. Since 2009, in part of the region, the dispatcher also sends local lay rescuers, who are trained to perform basic life support and use an AED, to the OHCA site through a text message alert.18
Study population and data collection
The main focus of this paper is to investigate the importance of different defibrillations strategies from the perspective of survivors after OHCA. For the complete picture, we also present in the manuscript the data of all patients with OHCA. Thus, the current study investigated two different selections of patients: survivors who were defibrillated and, in order to study the factors associated with the survival increase over time, all OHCA patients.
OHCA cases were included regardless of the cause, in whom EMS personnel started or continued a resuscitation attempt. We also included patients where EMS did not perform CPR because the patient received an AED shock and had return of spontaneous circulation before EMS arrival. We excluded EMS-witnessed cases and cases in whom resuscitation efforts were aborted due to ethical reasons.
All registries used the Utstein template for collecting data.19 Survival data were collected from the national death registries from each region. For the regions Stockholm County, central Copenhagen and North Holland province, data from 2006 to 2013 were included in the study. For the region Western Sweden, data from 2008 to 2013 were available and included. All data were depersonalised and pooled into the central COSTA database.
In the region North Holland, continuous ECGs from EMS defibrillators and AEDs were analysed to determine the initial rhythm as shockable (ventricular tachycardia/ventricular fibrillation) or non-shockable (asystole or pulseless electric activity). In the other regions, the initial rhythm was derived from EMS case reports. An EMS shock was defined as the first shock provided by EMS personnel using an AED or manual defibrillator. A first responder shock was defined as the first shock provided by an AED from dispatched fire fighters or police officers. An onsite shock was defined as the first shock provided by an AED from an onsite responder or a lay rescuer who was directed to an AED. Time to EMS arrival was the difference between the time of vehicle stop of the first ambulance and the time of the emergency call to the dispatch centre. Survivors were defined as patients who survived at least 30 days after the OHCA.
To study the association between different prehospital defibrillation strategies on survival, we used data of OHCA survivors only. To study if survival has increased and to identify factors that are associated with this increase, we used data of all patients.
To identify the single factor with the strongest association with the survival rate over time, we first examined temporal trends using logistic regression analysis, with ‘year of resuscitation’ as the independent variable. Next, we analysed which variables changed significantly during the study period and were associated with survival. We then individually added such a variable to the regression model to determine whether the OR of ‘year of resuscitation’ would be adjusted towards the 1 (with a non-significant p value). If so, this would indicate that the effect of ‘year of resuscitation’ is (at least partly) explained by that variable. In both analyses, we controlled for the region of resuscitation. In the regression analysis, we used a complete case approach. All cases with missing in at least one variable used in regression were excluded.
The continuous variable ‘age’ was described as mean (SD) and time to EMS arrival as median (25th–75th percentile). To evaluate changes in baseline resuscitation characteristics and survival rates in subsequent years, we calculated a p for trend using a χ2 test (linear-by-linear) for dichotomous data. For continuous variables, we used linear regression in case of normally distributed data. For non-normally distributed data, we used the Jonckheere-Terpstra test. Since the region Western Sweden only had data available from 2008 onwards, all statistical analyses were performed on data from 2008 to 2013. P values of <0.05 were considered statistically significant. All of the data were analysed using the statistical software package of SPSS (IBM SPSS for Mac, V.20.0).
A total of 22 453 OHCA patients with a known survival status were identified, of whom 2957 (13%) survived for at least 30 days postresuscitation (figure 1).
Defibrillation of survivors
Of the 2823 (96%) survivors of whom it was known whether they were defibrillated, 2289 (81%) had a shockable initial rhythm and were defibrillated. A total of 1349 (59%) survivors were defibrillated by EMS, 454 (20%) were defibrillated by a dispatched first responder AED and 429 (19%) were defibrillated by an onsite AED; in 57 (2%) cases, it was unknown who provided the first shock. Baseline characteristics of all survivors are shown in table 1. In addition, the proportion of survivors with a shockable initial rhythm who were shocked by EMS decreased, from 74% in 2008 to 44% in 2013 (p<0.001 for trend) (table 1 and figure 2). Conversely, there was a more than doubling of the proportion of survivors who received a first shock by a first responder, from 13% in 2008 to 26% in 2013 (p<0.001 for trend), or lay rescuer with an onsite AED, from 14% in 2008 to 30% in 2013 (p<0.001 for trend). The proportion of defibrillation from EMS, first responders and onsite AEDs from each region is presented in online supplementary figure 1.
Supplementary file 1
Survival rates over time: all patients
A total of 22 453 OHCA patients with a known survival status were identified.
Baseline data and patient characteristics of all patients with an OHCA are shown in table 2. Between 2008 and 2013, the mean age (from 66 to 67 years, p=0.002), bystander CPR proportion (from 59% to 72%, p<0.001) and time to EMS arrival (from 8 to 9 min, p<0.001) was significantly higher. Between 2008 and 2013, proportions of OHCA at public location (from 33% to 31%, p=0.01), bystander witnessed OHCA (from 68% to 66%, p=0.006) and shockable initial rhythm (from 31% to 29%, p=0.047) significantly decreased. Online supplementary table 1A–D shows the baseline and patient characteristics for each region separately.
Table 2 also shows survival rates over time. In the total study cohort, the survival rate increased from 13% in 2008 to 15% in 2013 (OR 1.04 (95% CI 1.01 to 1.07), p=0.003). Among patients with a shockable initial rhythm, the survival rate increased from 36% in 2008 to 40% in 2013 (OR 1.05 (95% CI 1.02 to 1.09), p=0.004). No significant increase in survival rate of patients with a non-shockable initial rhythm was found (from 3% in 2008 to 4% in 2013, OR 1.05 (95% CI 0.99 to 1.11), p=0.08).
The survival rates of patients defibrillated with the three defibrillation strategies are shown in figure 3.
Factors associated with increased survival rates
To study factors associated with the improved survival rate in patients with a shockable initial rhythm, we analysed which variable changed the crude OR of ‘year of resuscitation’ the most towards a non-significant 1 when added to the logistic regression model. Figure 4A shows the ORs of all statistical significant variables that were associated with survival. Figure 4B shows the ORs of year of resuscitation with each consecutively added variable. Only the variable ‘first shock from any non-EMS AED’ decreased the OR of year of resuscitation to a non-significant level.
Our main finding in this study is that survivors of OHCA are increasingly defibrillated by non-EMS defibrillators. This increase was related to an increase in both onsite and dispatched first responder AED usage and to an increase in survival during the study. During the last decade, there has been a major increase in the dissemination of AEDs for prehospital defibrillation to others than EMS (ie, fire fighters, police officers and lay rescuers). The number of publicly available AEDs is increasing rapidly and programmes for dispatch of first responder and public access programmes are being implemented. These different prehospital defibrillation strategies have developed in recent years, but the association with survival and changes over time are poorly understood. This is a multicentre and multinational study that analysed the survivors after OHCA in relation to different defibrillation strategies. Between 2008 and 2013, the rate of shocks delivered by non-EMS AEDs more than doubled (from 26% to 56%), and the largest increase over time was found among attributed onsite AEDs (from 14% to 30%). The increase in shocks provided by non-EMS AEDs correlated with the increase in survival rate over time of patients with an initial shockable rhythm.
One of the earliest AED programmes was the dual dispatch of AED-equipped first responders, usually police officers or fire fighters, in parallel with standard EMS.15 20 21 Another example of a prehospital defibrillation programme was placing AEDs in casinos,3 airports4 or communities.22 Since then, there has been an increasingly number of AEDs placed at public locations such as shopping malls, stations, sports facilities and public buildings and also in residential areas.13 23 24 In the last few years, AED programmes where the EMS dispatcher plays the key role in guiding lay rescuers have been developed.14 17 18 25 Many of these AED programmes have shown to increase survival.3 4 13 20 24 However, major differences exist in both patient selection, methods and scientific quality. In the current study, we studied the usage of two implementations of non-EMS AEDs: dispatched first responder AEDs and randomly or strategically placed onsite AEDs. We have not performed in-depth analysis of the contributions of the different types of onsite AED defibrillation programmes.
Our study did not explore the relative contribution of each type of AED use to the shortening of time to defibrillation due to lack of reliable time data. This is a major limitation of our study. An earlier study, however, showed that onsite AEDs had shortest time to defibrillation and increased the probability of survival the most, while dispatched first responders was associated with only a modest reduction of time to defibrillation and higher survival.13 15 18 Nevertheless, our study shows that first responder AED use makes up a large and increasing proportion of the survivors with shockable initial rhythm illustrated by the high number of patients who survived after a first responder AED shock (table 1). This ‘epidemiologic paradox’ can be explained by the large number of patients with OHCA in ‘low risk’ areas, such as residential, and unvisited public areas, areas where few onsite AEDs are present, but who can still be defibrillated by dispatched first responders even if shortening of the time to defibrillation interval is modest. Many other factors are important in the context of distribution of public OHCA and AED deployment: population movements and OHCA incidence, risk areas of OHCA incidence26 as well as the potential benefit of AED registries, increased risk assessment and geographically aided identification for optimising AED placement selective placement of publicly available AEDs. Moreover, the importance of widespread CPR training and high bystander CPR rates in this setting should be highlighted. The association between bystander CPR and survival is well established. The increase in survival in our study could also be (partly) explained by increasing bystander CPR rates, although it was not statistically significant following bivariable logistic regression analysis.
Based on the results from our study, two important measures would be to spread and develop programmes for both first responder dual dispatch and onsite AED use, which is also stated in recommendations from a recent Utstein expert meeting.27 One of the most important questions for the future is how to reach residential OHCA patients faster. One large randomised study showed no effect in placing AEDs in private homes of persons with an increased risk of OHCA.28 Another way to increase onsite AED usage and survival could be to dispatch local lay volunteers to retrieve AEDs and respond to patients within the first crucial minutes. Dispatched local lay rescuers with local AEDs have been shown to reduce time to the first defibrillation.18 This is a promising solution, but studies showing increased survival are still lacking.
How can our results be generalised? There are differences between cities and countries in terms of populations. Risk factors and treatment, and logistical and social factors may differ. Also, knowledge of CPR and AED use may be unequally distributed between countries. We report data from four different regions in three countries that are relatively similar in terms of populations and healthcare delivery. In our study, the association with increased survival over time and the contribution of professional first responder AED defibrillation (Copenhagen excluded) and onsite AED defibrillation was consistent for all regions. Even if it might be difficult to generalise the findings from our study to regions in countries with low and middle incomes (where EMS response times may be longer and where bystander CPR and AED use may be different), we believe that it is possible to implement successful prehospital defibrillation programmes to the local settings in most countries.
An analysis from 2015 demonstrates variability in time to defibrillation and survival according to who performed defibrillation (bystander, first responder or EMS).29 This is a plausible explanation to the higher survival rates found in the onsite and first responder group. Very early defibrillation is associated with survival rates of more than 50%.3 4 12 13 Based on previous research and the findings from our study, we recommend the introduction and continuous development of AED programmes involving both dispatched first responder and onsite AEDs aiming at both public and residential areas.
Our study has several limitations. First, our analyses are based on observational data. Therefore, we can only suggest associations and not prove a causal relation between AED strategy and survival. Second, although all regions use the Utstein template to collect data, differences in the measurement of variables still exist, partly because of the variation in the interpretation of the Utstein definitions and partly due to regional differences in the EMS system. Third, time from patient collapse to defibrillation was not analysed in our study due to lack of reliable data. Fourth, missing data occurred for some variables and especially for time to EMS arrival. The reason of missing ‘time’ data was in the majority of cases caused by a failure to send the time stamps from the ambulance dispatch centre and the data registry systems. We assume that this happened randomly and that therefore there is no missing data bias. Fifth, other parameters that may also (partly) explain improved survival rates over time, such as in-hospital management, were not included in the current analyses. Sixth, we have no adequate data on the actual number of AEDs in place during the study period, the change in number over time and the strategy for their placement (individually decided or based on a preconceived plan).
OHCA survivors are defibrillated increasingly by non-EMS AEDs. This increase in non-EMS defibrillation is primarily associated with an increase use of onsite AED defibrillation. Increase in non-EMS defibrillation accounted for at least part of the increase in survival rate of patients with a shockable initial rhythm. We recommend continuous efforts to introduce or extend AED programmes, involving both first responder and onsite AEDs aiming at public and residential areas.
What is already known on this subject?
In out-of-hospital cardiac arrest (OHCA) different prehospital defibrillation strategies have been adopted in addition to dispatch of standard emergency medical services (EMS).
These include dispatch of police/firefighters as professional first responders and dissemination of publicly placed automated external defibrillators (AEDs) for public access defibrillation.
Little is known about how different prehospital defibrillation strategies contribute to survival.
What might this study add?
This study demonstrates that survivors of OHCA are increasingly defibrillated by non-EMS AEDs, primarily due to an increase in the use of public onsite AEDs.
We also show that the striking increase in non-EMS defibrillation is associated with increased survival rates in patients with an initial shockable rhythm.
How might this impact on clinical practice?
Our data strongly support the benefit of early defibrillation from non-EMS AEDs.
These strategies include defibrillation from both dispatched first responders and onsite AEDs reaching both public and residential cardiac arrests.
We are greatly indebted to all participating emergency medical service dispatch centers, regional ambulance services and first responders, as well as all members of the cardiac arrest registries for their cooperation and support as well as their willingness to collaborate and share their data.
Contributors All authors designed the study together. All authors contributed in the planning of intended tables and figures. JAZ, RWK and JH acquired the data. JAZ and MTB were responsible for statistical analysis. JAZ and JH drafted the work, and all authors revised it critically for intellectual content. All authors approved of the version to be published. All authors had full access to all of the data (including statistical reports and tables) in the study and can take responsibility for the integrity of the data and the accuracy of the data analysis.
Funding This work was supported by Laerdal Foundation for Acute Medicine (Denmark). the Swedish Heart–Lung Foundation and Laerdal Foundation (Stockholm), Physio-Control, Zoll Medical, Philips Medical, Cardiac Science and Defibtech, The Netherlands Organization for Scientific Research (NWO, grant ZonMW Vici 918.86.616 and ZonMW 827.11.001), Dutch Heart Foundation (2010T083), the Dutch Medicines Evaluation Board (MEB/CBG) and The Netherlands CardioVascular Research Initiative (Dutch Heart Foundation, Dutch Federation of University Medical Centers, Netherlands Organization for Health Research and Development, Royal Netherlands Academy of Sciences – (CVON2012-10 Predict) (Netherlands)).
Competing interests None declared.
Patient consent Not required.
Ethics approval The medical ethics review boards of all four participating academic institutes approved the study and gave a waiver for obtaining (written) informed consent. All patient identifying information was removed before transferring of data to the COSTA analysis centre.
Provenance and peer review Not commissioned; externally peer reviewed.