Public Access Defibrillation by Activated Citizen First-responders - The HeartRunner Trial
Phase: NA
Conditions: Out-Of-Hospital Cardiac Arrest
Sponsor: Emergency Medical Services, Capital Region, Denmark

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Public Access Defibrillation by Activated Volunteer Citizen 
Responders - the HeartRunner Trial 
ClinicalTrials.gov number: NCT03835403 
 
General Information 
Primary Investigator and sponsor: Fredrik Folke, MD, PhD, Professor, Head of Research, 
Copenhagen Emergency Medical Services, Copenhagen University and Herlev Gentofte Hospital, 
Department of Cardiology. 
 
Responsible Investigator: Fredrik Folke, MD, PhD, Professor 
 
Investigators: 
Carolina Malta Hansen, Copenhagen Emergency Medical Services, Ballerup, and Herlev and 
Gentofte Hospital, Division of Cardiology, Capital Region of Denmark, Denmark.  
Linn Andelius, Copenhagen Emergency Medical Services, Ballerup, Denmark 
Mads Tofte Gregers, Copenhagen Emergency Medical Services, Ballerup, Denmark 
Annette Kjær Ersbøll, National Institute of Public Health, University of Southern Denmark, 
Copenhagen, Denmark 
Professor Christian Torp-Pedersen, Department of Clinical Investigation and Cardiology, North 
Zealand Hospital, and Department of Cardiology, Aalborg University Hospital  
Professor Gunnar Gislason, Department of Cardiology, Herlev Gentofte Hospital, and the Danish 
Heart Foundation, Denmark. 
Professor Lars Køber, Department of Cardiology, Rigshospitalet, Copenhagen, Denmark 
Freddy Lippert, Copenhagen Emergency Medical Services, Ballerup, Denmark 
This is an investigator-initiated study. 
 
This study will be conducted in accordance with this protocol. The study will comply 
with regulatory and ethical requirements. 
 
The study will initiate in 2019 and run for up to 8 years. 

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Table of contents 
 
1. SCIENTIFIC SUMMARY ............................................................................................................ 4 
2. RATIONALE ................................................................................................................................. 6 
3. STUDY AIMS ................................................................................................................................. 8 
4. STUDY METHODS ....................................................................................................................... 9 
5. STATISTICS AND POWER CALCULATIONS ..................................................................... 18 
6. STUDY QUALITY ....................................................................................................................... 22 
7. ETHICAL ASPECTS .................................................................................................................. 22 
8. SAFETY MANAGEMENT ......................................................................................................... 23 
9. DATA MANAGEMENT ............................................................................................................. 24 
10. PATIENT, CAREGIVER AND HEARTRUNNER ENGAGEMENT TEAM .................... 25 
11. DISSEMINATION OF RESULTS ........................................................................................... 25 
12. FINANCING AND INSURANCE ............................................................................................ 25 
13. RELATION BETWEEN TRYGFONDEN AND INVESTIGATORS .................................. 26 
14. TRIAL ORGANIZATION ........................................................................................................ 26 
 
 
 
 
 
 

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Abbreviations: 
AED 
Automated External Defibrillator 
CPC 
Cerebral Performance Category 
CPR 
Cardiopulmonary Resuscitation 
EMD 
Emergency Medical Dispatch 
EMS 
Emergency Medical Service 
ERC 
European Resuscitation Council 
OHCA  
Out-of-hospital cardiac arrest 
ROSC 
Return of Spontaneous Circulation 
PAD 
Public Access Defibrillation 
VF/pVT  
Ventricular fibrillation/pulseless ventricular tachycardia 
 
 
 

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1. Scientific summary 
A large proportion of out-of-hospital cardiac arrest (OHCA) patients have an initial cardiac rhythm 
that can be treated by means of defibrillation. As the chance of survival decreases by 10% per 
minute from collapse to first defibrillation,1, 2 efforts to decrease the time to first shock are crucial. 
Whereas the overall survival rate following OHCA is 12% in Denmark, 7 out of 10 may survive if 
defibrillated by an automated external defibrillator (AED) within the first minutes after collapse.3  
In 2007, an AED registry was implemented in Denmark to make AEDs easier to locate 
(www.hjertestarter.dk/english). In 2010, the AED registry became nationwide and linked to the 
emergency dispatch centres in Denmark allowing the dispatchers to direct OHCA bystanders to the 
nearest available AED.4 In May 2017, the registry held approximately 16,000 publicly available 
AEDs but despite these initiatives, AEDs are only used in 3-4% of all OHCA in Denmark.5, 6 
7Therefore, new strategies aimed to increase public AED use are warranted. The aim of the 
“HeartRunner Trial” is to evaluate a unique logistical model for instantly identifying and recruiting 
nearby volunteer citizen responders (called ‘heart runners’) through a smartphone app to retrieve an 
AED in case of nearby OHCA with the purpose of increasing OHCA survival.  
 
At any time, a mobile phone can be geographically positioned with an accuracy of 0-100 m in urban 
areas. Using this information, volunteer citizens that are located within 1800 m distance of the 
OHCA and can be alerted from the emergency dispatch center to retrieve the nearest AED and bring 
it to the cardiac arrest location. The volunteer citizen responder receives a digital map on the 
smartphone and a description of where the AED is located as well as the closest way to the site. 
Such a smartphone application has already been developed and tested in Sweden.8, 9 For all OHCAs 
meeting the activation criteria explained in the Method section, the dispatcher will always 
“activate” the HeartRunner mobile positioning system, and then randomization (1:1) will be carried 
out within the computer system thus blinded for the emergency dispatchers. Accordingly, only in 
50% of the cases will there be an actual dispatch of citizen responders by means of smartphone 
activation. Data on all OHCAs (both those where citizen responders were activated or not by their 
smartphones) are collected at the EMS in Copenhagen to compare the effect of citizen responder 
activation.  
 
In addition, it is unclear whether it is physically and mentally safe for the activated citizen 
responders to quickly find and bring an AED to the cardiac arrest location and begin 

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cardiopulmonary resuscitation (CPR) before ambulance arrival. No studies have investigated the 
risk of physical damage when citizen responders are activated to move as quickly as possible 
through traffic to the cardiac arrest victim. Similarly, there are very few studies investigating the 
mental burden and stress that lay persons might experience when attending in a resuscitation 
attempt. Studies on a lay-responders experience in resuscitation attempts reports that up to 40% 
experienced mild/tolerable psychological effect whereas 10% had severe psychological effect.10-12 
Accordingly, the HeartRunner Trial will examine whether it is safe both physically and 
psychologically to activate citizen responders to find an AED, bring it to the OHCA patient, and 
initiate CPR and defibrillation before EMS arrival. All citizen responders who receive an alarm and 
either accept or decline the alarm will receive a short questionnaire 90 minutes after the alarm. The 
questionnaire will include questions about the resuscitation attempt as well as psychological distress 
and physical harm for the citizen responder.  
 
The HeartRunner Trial will be implemented and tested in the Capital Region of Denmark 
comprising 1.8 million inhabitants with approximately 1400 OHCAs per year. It is expected to run 
for approximately 8 years and include approximately 4200 cases of suspected out-of-hospital 
cardiac arrests.  
 
The primary aims of the HeartRunner Trial are: 
1) To test whether activating volunteer citizen responders can improve 30-day survival after out-of-
hospital cardiac arrest. 
2) To examine the potential physical or psychological risk involved for the activated citizen 
responders when alerted to a suspected cardiac arrest to start resuscitation before EMS arrival. 
 
As the chance of successful resuscitation is very dependent on the time from collapse to first 
defibrillation, the HeartRunner trial (including randomization) will be conducted in 3 predefined 
strata according to expected time from activation to arrival of a citizen responder: <3 minutes 
(group 1), 3-9 minutes (group 2), and >9 minutes (group 3). The study is powered to test difference 
in survival in groups 1 and 2.  
The study is designed to randomize activation of citizen responders vs no activation of citizen 
responders for incoming calls to the emergency dispatch center which are ‘suspected cardiac arrest’. 
Standard treatment including dispatch assisted CPR, guidance to a nearby AED, if feasible, and 

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dispatch of ambulance and a physician manned ambulance will be carried out in all cases of 
suspected cardiac arrest regardless of citizen responder randomization.  
The Ethics Committee’s responsibility is to assess medical research projects. The Ethics Committee 
has evaluated the study protocol and deemed the study is not a medical research project as defined 
in the Ethics Committee’s § 2. The study is therefore deemed not notifiable and can be initiated 
without further approval from the Ethics Committee (Journal nr.: 17018804).  
The study is registered by the Data Protection Agency via The Capital Region of Denmark (journal 
nr.: 2012-58-0004, VD-2018-28, I-Suite nr.: 6222) and data will be stored in accordance to Danish 
data legislation. The study has also been registered with the Danish Patient Safety Authority (3-
3013-2721/1, 31-1522-14, and R-20051145) and will adhere to Danish law regarding handling og 
personal data for patients.  
 
 2. Rationale 
 
This study is a comparison of activation of volunteer citizen responders and usual care for patients 
with out-of-hospital cardiac arrest.  
 
Scientific Background 
Out-of-hospital cardiac arrest (OHCA) is a major health problem, accounting for approximately 
4000 OHCAs in Denmark,13 and more than 700,000 annual OHCAs in the United States and 
Europe.14 CPR and early defibrillation have been shown to be the most significant factors for 
improving OHCA survival.15 Though CPR is unlikely to eliminate ventricular fibrillation and 
restore a perfusing rhythm,16-18 CPR can prolong the time until the brain cells are damaged and can 
increase the probability for a successful defibrillation and survival.1, 2 Early CPR has been shown to 
triple the chances of survival,15, 17, 19, 20 as well as the quality of CPR performed is relevant for the 
chance of survival. Efforts to decrease the time to first shock are crucial as the chance of survival 
decreases by 10% per minute from collapse to first defibrillation.1, 2 In cases where defibrillation is 
performed within five minutes, more than 50% of all patients can be saved.3, 21, 22 For optimal 
survival benefit, AEDs need to be used within minutes of the event and, thus, be close to the victim, 
easily locatable and accessible to bystanders. Several studies have shown a significant increase in 
OHCA survival when AEDs are placed in public locations where the above mentioned criteria are 
met like airports,21 on aeroplanes,23, 24 and in casinos,3 with reported survival rates as high as 49% 

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to 75%.3, 21, 23, 24 These findings have led to a more widespread AED deployment in public locations 
with positive effect on OHCA survival.22, 25-27  
Since 2010, a national AED registry has been set up as an initiative from the Danish foundation 
TrygFonden to collect the geographic location of all AEDs in Denmark 
(www.hjertestarter.dk/english). The rationale behind this is that a national registry enables lay 
people to find the closest AED and increase awareness among the public of AED placement in the 
community. A great effort has been made with regards to quality control and every AED in the 
registry is checked every 12th month for functionality, location, and confirmed opening hours. By 
the end of 2018, the registry held more than 19,000 AEDs throughout the entire country. In 2010, 
the AED registry was linked to the emergency dispatch centres in Denmark allowing the dispatchers 
to direct OHCA bystanders to the nearest available AED. Despite increased AED dissemination and 
public awareness, AEDs are only used in 3-4% of all OHCA in Denmark.5, 13 
There are several reasons for low AED use: a) AEDs are not dispatched by conventional alarm 
systems, b) AEDs must be transported to the cardiac arrest site within few minutes, c) AEDs might 
not be accessible at the time of OHCA, and d) only few cases of cardiac arrests occur in high-
incidence places where an on-site AED is located. Furthermore, the vast majority of all cardiac 
arrests (65-80%) occur in residential areas,28-30 where stationary on-site AEDs are rarely 
available,28, 31 and the chance of bystander defibrillation is very low (1-2%). 5, 13, 31, 32   
To benefit optimally from AEDs, both public and residential areas are in need of early first-
responder activation. Such a responder needs to be closer to the cardiac arrest patient than 
traditional first responders (police or firefighters) and/or EMS and must be alerted by the dispatch 
center. One solution implemented by several regional dispatch centers in Europe is a text message, 
or smartphone alert system.8, 33, 34 Such systems alert local citizen responders to perform CPR and 
directs them to a nearby AED before EMS arrival. In case of a suspected OHCA, the dispatcher 
manually activates the alert process and a software program then automatically identifies nearby 
available volunteer citizen responders as well as nearest accessible AEDs and sends text/push 
messages to citizen responders in proximity of the OHCA location. Such systems have been tested 
and implemented in several regional dispatch centers in Europe.8, 33, 34 Experiences from Holland 
and Sweden showed that not only did activated citizen responders shorten the time from collapse to 
first defibrillation,33 and increased bystander CPR rate,8 but these responders also reached OHCA 

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victims in residential areas normally not reachable with public access defibrillation (PAD) 
programs. 
Using new smartphone technology renders a possibility of activating citizen responders to help 
improving efficacy of public AED use as a compliment to the existing EMS system.8, 35 Thus, 
engaging the society at large using volunteer citizens that can be dispatched to nearby OHCAs to 
recruit the closest defibrillator hold the potential to increase AED use, bystander CPR, and 
ultimately OHCA survival.  
3. Study aims 
Patient Outcomes 
The overall aim of the HeartRunner Trial is to test whether activating citizen responders can 
improve survival after out-of-hospital cardiac arrest and to assess whether it is safe, psychologically 
and physically, to dispatch citizen responders to resuscitation attempts. As the chance of successful 
resuscitation is very dependent on the time from collapse to first defibrillation, the HeartRunner 
trial will be conducted in 2 predefined strata according to expected time from call to arrival of a 
citizen responders: <3 minutes (group 1) and 3-9 minutes (group 2). Data from our pilot study 
shows only 4% of all cases would be classified as group 3 (> 9 minutes) and for this reason, the 
study was not designed to test outcomes in this group. Nevertheless, data and outcomes will be 
reported for this group as well. 
 
Feasibility 
The trial will also examine a unique logistical model for instantly identifying and recruiting nearby 
volunteer citizen responders to retrieve an AED in case of nearby OHCA using new smartphone 
technology with the purpose of increasing OHCA survival. 
 
Citizen Responder Outcomes 
For safety outcomes, the trial aims to examine the risk of physical injuries as well as psychological 
stress or anxiety among activated citizen responders.  
  
3.1 Outcome Measures 
Primary outcome:  
1. 30-day survival in OHCA patients included in the HeartRunner trial.  

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Secondary outcome measures: 
1. Bystander defibrillation prior to EMS arrival 
2. Bystander cardiopulmonary resuscitation prior to EMS arrival 
3. Return of spontaneous circulation at hospital arrival 
4. Neurological intact survival at hospital discharge (cerebral performance category score of 1-
2)36  
5. 1-year survival 
 
The study is powered to independently address primary outcomes in 2 time strata according to 
expected time from activation to arrival of a citizen responder who can assist with resuscitation: <3 
minutes (stratum 1) and 3-9 minutes (stratum 2).  
 
For safety outcomes the secondary outcomes are: 
1. Physical injuries or accidents among activated citizen responders  
2. Psychological stress or anxiety among activated citizen responders  
Physical injuries and psychological stress will be assessed through an electronic survey sent out 
90 minutes after activation. Non-responders will be followed up by phone call, text message or 
e-mail.  
 
4. Study methods 
 
4.1 Study design 
The study is an investigator initiated, investigator-blinded, prospective, randomized controlled trial, 
comparing the number of OHCA patients who survived 30 days between patients with activation of 
citizen responders vs. no activation of citizen responders (usual care). The estimated project period 
will run over 8 years in the Capital Region of Copenhagen, beginning May 2019. As indicated 
below the study is planned to include 4200 patients. 
 
4.2 Study settings 
The study will take place in the Capital Region of Denmark (covering approximately 2 559.4 km2 
and with a resident population of ≈ 1,8 million). There are approximately 1400 cardiac arrests 
annually in the Capital Region of Denmark. The Danish AED network is a nationwide registry of 

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publicly accessible AEDs, linked to all emergency medical dispatch centers. Approximately 5700 
AEDs are currently registered in the Capital Region of Denmark, 37.8% of which are accessible 
24/7. The registry has previously been described in detail.4, 37 The emergency medical dispatch 
center in the Capital Region of Denmark covers the entire study area with one single activation 
number (1-1-2) and will be the only dispatch center involved in the HeartRunner study. The system 
is public, and users are free of any charge. Emergency Medical Dispatchers are trained in a 
standardized manner, including training in recognition of cardiac arrest. All dispatchers use a 
medical index computer system to aid dispatchers in emergency call handling. This system includes 
standardized questions to determine whether there is a suspicion of cardiac arrest. The EMS in the 
Capital Region of Denmark is a two-tiered system comprising advanced life support provided by 
physician-manned ambulances and basic life support provided by ambulances equipped with 
defibrillators. In all cases of suspected cardiac arrest, both tiers of response are dispatched 
simultaneously. In case of a suspected cardiac arrest, the medical index system recommends the 
dispatcher to choose a pre-specified response plan for cardiac arrest: 1) Activation of the EMS 
system (dispatching an ambulance and a physician-manned ambulance), 2) Guiding bystanders to 
perform CPR (dispatch-assisted CPR), 3) when feasible, guiding bystanders to retrieve the nearest 
accessible AED.  
 
The HeartRunner system has been running as a pilot study since September 1, 2017. The system has 
been successfully implemented in the Capital Region of Denmark and modified as necessary. 
Integration of the software with the emergency medical dispatch center has been completed and the 
app is fully functional. Until randomization begins, emergency medical dispatchers activate the 
system for all consecutive cases of suspected cardiac arrests, following the inclusion and exclusion 
criteria described below.  
 
4.3 Patient Population 
A cardiac arrest will be defined as the absence of consciousness and no normal breathing, identified 
by dispatcher at the emergency dispatch center. The emergency medical dispatch center does not 
activate the HeartRunner system in case of an OHCA of traumatic origin, in children under eight 
years of age, when the caller is not in direct contact with the victim, or when an AED is not 
indicated, e.g. in nursing homes where trained personal is already present (as described in exclusion 

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criteria). Accordingly, the patient population for this study only includes patient where the 
HeartRunner system has been activated.  
 
4.4 Volunteer Responder Population – Citizen responders 
Citizen responders are individuals who have volunteered and registered through the HeartRunner 
app. The only requirement for registration is age ≥ 18 years. Prior training in CPR skills and AED 
use compliant with contemporary European Resuscitation Council (ERC) guidelines is 
recommended but not mandatory. Citizen responders are recruited through advertisements in 
newspapers, TV, radio, social medias, CPR instructors, etc. Contact information (name, age, 
county, e-mail, cell-phone number) as well as information about completed CPR training is 
registered online in a database. At registration, citizen responders are asked whether they are 
professional healthcare workers, police/firefighter/ambulance personnel, student, or “other”. 
 
4.5 Inclusion criteria 
All EMS-treated OHCAs within the Capital Region of Denmark in whom the HeartRunner system 
was activated through the emergency dispatch center.  
 
4.6 Exclusion criteria 
Emergency medical dispatchers are instructed not to activate citizen responders in case any of the 
exclusion criteria below. However, since it can be challenging for emergency medical dispatchers to 
gather sufficient information about the patient within the first few minutes, citizen responders will 
admittedly be activated even though they should not have been. Since randomization will occur for 
all cases in which the HeartRunner system is activated, cases with any of the exclusion criteria 
below will be secondarily excluded.38  
 
OHCA-related 
- 
Not true cardiac arrest (suspected, but not verified by the Danish Cardiac Arrest Registry) 
- 
EMS-witnessed OHCAs 
- 
OHCAs due to trauma, intoxication, or suicide 
- 
OHCAs not treated by the EMS due to ethical reasons or obvious signs of death 
- 
OHCAs under the age of 8 
- 
OHCAs in nursing homes or health care facilities  
- 
OHCAs with no citizen responders within 1800 meters 

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These cases will be accounted for but not included in analyses of outcome. Our pilot study showed 
approximately 64% of suspected cardiac arrests were true cardiac arrests. Therefore, we expect 36% 
of cases for which citizen responders were dispatched not to be true cardiac arrests.  
 
4.7 Study procedure 
When the emergency medical dispatcher receives a call, the geographical location of the incoming 
call is already determined. As explained above, in case of a suspected cardiac arrest the medical 
index system recommends the dispatcher to choose a specific response plan for cardiac arrest. 
During the HeartRunner Trial, the cardiac arrest response plan will always include the usual OHCA 
care including dispatch of an ambulance and a physician manned ambulance, CPR instructions to 
the caller and if feasible, instruct bystanders to retrieve a nearby AED. In addition to activating 
usual care, activation of citizen responders will be carried out through a mobile phone positioning 
system for citizen responders. The location of the incoming emergency call will be compared to the 
geographical mapping of mobile phones connected to the HeartRunner app. The app sends out new 
locations whenever citizen responders changes their positions according to the “significant change 
of location service”39 and the latest updated position is stored as coordinates and used to identify 
citizen responders nearby a cardiac arrest. If a position is over 72 hours old, the citizen responder is 
considered inactive and not included. The HeartRunner software will identify all citizen responders 
(mobile phones) within a radius of 1800 meters (configurable) from the suspected cardiac arrest and 
up to 20 citizen responders (configurable) closest to the site of cardiac arrest will receive an alarm 
as a notification on their smartphone requesting whether they are able to respond. When the citizen 
responders accept the alarm, they will send out a new, updated, position and the software will 
confirm that the updated position is within 1800 meters. If the citizen responder is >1800m of the 
cardiac arrest, the citizen responder will be informed they are now too far from the cardiac arrest 
and their help will therefore not be required. The system will not find a new replacement for this 
citizen responder. The system will recruit the remaining citizen responders to either go directly to 
the site of arrest and begin CPR or go fetch a publicly accessible AED. An algorithm will be used 
for allocation of the citizen responders who accept an alarm. Starting from the first citizen 
responder who accepts the alarm, the first four citizen responders will be instructed to fetch the 
nearest accessible AEDs and then go to the cardiac arrest location. Based on the updated position, 
the citizen responders are directed to the closest accessible AED at the time of alarm. The fifth 
citizen responder is instructed to go directly to the cardiac arrest location and perform CPR. This 

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algorithm is performed up to 4 times dependent on how many citizen responders are located close to 
the OHCA location. If a citizen responder aborts the alarm, the assignment (AED or CPR) is 
reassigned to the next citizen responder accepting the alarm. If there are no publicly available AEDs 
close to the OHCA, all citizen responders who accept the alarm will be directed to start CPR. The 
software includes the total distance from citizen responder to AED and then to cardiac arrest to 
select the 20 nearest citizen responders. The OHCA location is displayed on a map through the 
HeartRunner app including OHCA address. If the citizen responder is directed to an AED, that 
location and address is also shown on the map, including additional accessibility information. A 
map showing the route from citizen responder to location of cardiac arrest is also provided. The 
HeartRunner app is linked to the Danish AED-Network and only takes accessible AEDs into 
account, at time of alarm.  
 
4.8 Randomization method 
During the study period, in all cases of suspected cardiac arrest, the dispatcher will follow the same 
dispatch procedure and activate the advanced medical response system for OHCA described 
previously, as well as activating the HeartRunner system in every OHCA that meets the activation 
criteria described above. However, the HeartRunner system will be randomized to operate in 50% 
of the cases (the intervention arm). Therefore, randomization is blinded to both dispatchers and 
investigators. All cases of suspected cardiac arrest will routinely be assigned a unique incident-ID at 
the dispatch center. This number will then be the intervention key, and allocation is blinded to 
dispatchers and to investigators until randomization code is broken at final analysis.   
The HeartRunner randomization will be run in the 3 independent strata. The HeartRunner server 
will identify citizen responders who will likely be able to arrive <3 minutes (0-359 meters), 3-9 
minutes (360-1080 meters), and ≥9 minutes (> 1080 meters) after being alerted based on calculated 
distance from the citizen responder to the nearest accessible AED and from there to the location of 
the OHCA. Distance is calculated as straight line and default speed is set to 2 m/s (4.47 mph). This 
probability estimation will be performed automatically at the HeartRunner server (Appendix 1) for 
every suspected cardiac arrest alarm providing 1:1 randomization to citizen responder activation or 
no citizen responder activation. The alarm is assigned to one of the 3 predefined time strata 
accordingly.  
 

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Randomization will take place independently in the 3 predefined strata. For each stratum, 
randomization ensures that allocation is random, maintains balance between the treatment arms, and 
ensures that the randomization procedure is unpredictable. Randomization will occur prior to any 
interaction with citizen responders and thus before the citizen responders accept the alarm and 
update their position. Therefore, the allocation to stratum is based on assumed location (latest 
updated position). To reduce the chance randomizing cases for which no citizen responders 
accepted the alarm, randomization will only be activated when at least 4 potential citizen responders 
have been identified in a given strata (< 3min, 3-9 min, > 9 min). Thus, to activate randomization in 
stratum 1 (<3 min), at least 4 citizen responders must be identified in stratum 1. This limit was set 
based on data from our pilot study showing that only 25% of all citizen responders who were 
alerted actually accepted the alarm. Thus, to increase the chance that at least 1 citizen responder 
accepts the alarm in a given stratum when randomized to be activated, at least 4 citizen responders 
need to be identified within the given stratum prior to randomization. When an alarm is sent to the 
HeartRunner server from the emergency dispatch center, this alarm will then undergo 
randomization at the server based on a simple algorithm based on the estimated straight-line 
distance between cardiac arrest location, nearest accessible AEDs, and the individual citizen 
responders:  
 
1). Stratum 1: Are there at least 4 (≥4) citizen responders within 3 min (0-359 meters) straight-line 
distance from the suspected OHCA? 
- 
If ‘yes’, this alarm is then categorized as a ‘Stratum 1’ response and randomization occurs 
(either ‘control’=no activation or ‘active’ alarm=sending a mission to all potential citizen 
responders within the maximum distance of the OHCA)  
- 
If ‘no’, then the algorithm continues to question 2: 
 
2). Stratum 2: Are there at least 4 (≥4) citizen responders not included in Strata 1 and within 9 
minutes (<1080 meters) straight-line distance from the suspected OHCA? 
- 
If ‘yes’, this alarm is then categorized as a ‘Stratum 2’ response and randomization occurs 
(either ‘control’=no activation or ‘active’ alarm=sending a mission to all potential citizen 
responders within the maximum distance of the OHCA)  
- 
If ‘no’, then the algorithm continues to question 3: 
 
3). Stratum 3: Are there at least 4 (≥4) citizen responders not included in Strata 1 or 2 and within 
15 minutes (<1800 meters) straight-line distance from the suspected OHCA? 
- 
If ‘yes’, this alarm is then categorized as a ‘Stratum 3’ response and randomization occurs 
(either ‘control’=no activation or ‘active’ alarm=sending a mission to all potential citizen 
responders within the maximum distance of the OHCA)  

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- 
If ‘no’, then this alarm is categorized as a ‘Stratum 3’ response if there is at least one citizen 
responder within 1800 meters and randomization occurs (either ‘control’=no activation or 
‘active’ alarm=sending a mission the potential citizen responder within the maximum 
distance of the OHCA).  
- 
If no (zero) citizen responders are within 1800 meters, then no randomization will occur, 
and the case should be marked in data to make it possible to trace how many of these cases 
we have.  
 
The strata are mutually exclusive.  
 
OHCAs for which there are no potential citizen responders within 1800 meters will be excluded. 
During the pilot phase of the trial, only 11 out of 433 cardiac arrests had no citizen responders 
within 1800 meters, so this number is expected to be low. Further, approximately half of citizen 
responders were in stratum 1 and half in stratum 2 and only few in stratum 3.  
 
 
All activated citizen responders are therefore assigned to either strata 1, 2, or 3 with corresponding 
assumed arrival time from received alarm to location of the cardiac arrest.  
 
Calculations of distance according to walking pace: 
We have used the assumption that the walking pace for a citizen responder is 2.0 meters/second, 
which was recently found in a Swedish citizen responder population40. This may be slower than 
most people’s walking pace but takes probable delays, such as time from receipt of alarm to 
acceptance of alarm and beginning to move towards the cardiac arrest, time to retrieve an AED, find 
the cardiac arrest location and so on. We have also assumed citizen responders only need to walk a 
one-way distance. Finally, the estimated time from potential citizen responders to the location of the 
cardiac arrest calculated by the HeartRunner server (based on an average speed of 2 m/s) is based 
on a straight-line distance, not taking the local infrastructure into account. Based on previous 
experiences looking at the correlation between straight-line and real walking-route distances, real 
walking-route distances are approximately 1.5 times longer than straight-line distances.  
 
4.9 Randomization process at the HeartRunner server 
Using a simple random allocation scheme each participant has equal likelihood of being assigned to 
treatment versus reference groups. However, by chance an unequal number of individuals may be 
assigned to each arm of the study and thus decrease the power to detect statistically significant 
differences between groups. Additionally, an imbalance of treatment groups within confounding 

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factors may occur. This is especially true for small sample sizes. We therefore intend to use block 
randomization, a commonly used technique in clinical trial design to reduce bias and achieve 
balance in the allocation of participants to treatment arms, especially useful when the sample size is 
small.  
Random permuted block randomization will take place independently in the 3 strata planned. 
Blocking ensures the treatment groups are balanced at the end of every block. By using blocking 
within strata, important prognostic characteristics (the stratification factors) are balanced between 
the treatment groups and ensure that allocation is random. 
The randomization process is described in detail in Appendix 1.  
 
4.10 Implementation period 
The first 20 months (From September 2017 through April 2019) were used to test whether the 
HeartRunner system was operational, to ensure technical stability, and to recruit approximately 
30,000 voluntary citizen responders in the Capital Region of Denmark. Also, this period was used 
to set up the HeartRunner server to estimate the citizen responder transportation time from location 
of smartphone alert to arrival at the OHCA location.  
 
4.11 Trial period 
The HeartRunner trial period is scheduled to start May 15, 2019. The 3 time strata will run in 
parallel and stratum 1 and 2 will be evaluated separately (group 3 will not be evaluated during the 
trial period). The HeartRunner trial is planned to run for 8 consecutive years, but each stratum can 
be terminated by the independent safety committee if significant improvement in survival is 
obtained or if serious adverse events are experienced.  
 
4.12 Data collection 
All incoming 1-1-2 calls are registered at the EMD center. The process of OHCA identification is 
supported by the criteria-based, nationwide Emergency Medical Dispatch System (Danish Index for 
Emergency Care).41 Six data sources will be used.  
 
1. HeartRunner App – HeartRunner (mission) server: the mission server registers all cases 
where the HeartRunner system is activated. Every time a dispatcher activates the system, 
the mission server produces a unique mission ID. For each mission ID, a unique 

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HeartRunner ID for each citizen responder identified within a radius of 1800m of 
cardiac arrest is recorded. For each HeartRunner ID detailed information is collected 
(see table).  
 
 
2. The Emergency Medical Services, electronic dispatch system (CAD): each 1-1-2 call 
generates a unique incident ID. From the Incident ID the following data is collected: 
time of incoming call, patient unique social security number, exact incident address (GIS 
location), type of EMS response, time of ambulance dispatch, time of citizen responder 
dispatch, time of EMS arrival (vehicle stop at scene). 
 
3. Danish Cardiac Arrest Registry  
Data from all cardiac arrests are routinely and systematically collected and entered into 
the Danish Cardiac Arrest Registry. The Danish Cardiac Arrest Registry has existed 
since 2001 and has previously been described in detail.13 The National Cardiac Arrest 
Registry follows the Utstein template for reporting cardiac arrest.42 The following 
information is collected through the Danish Cardiac Arrest Registry: witnessed status, 
location of arrest, first recorded rhythm, whether bystander performed CPR and/or 
defibrillation, EMS CPR and/or defibrillation, whether the arrest was EMS treated, time 
of EMS first shock, return of spontaneous circulation, time to return of spontaneous 
circulation, patient status at hospital admission (terminated at the scene, ongoing CPR, 
return of spontaneous circulation but comatose, or alive).  
 
4. Patient Charts 
For neurologic outcome data will be obtained from patient charts from in-hospital 
treatment and patient’s performance at discharge. Neurological outcome will be 
categorized using the Cerebral Performance Category (CPC) score. The CPC score 
ranges from 1 to 5 where 1 equals good cerebral performance, 2 equals moderate 
Mission ID 
x 
HeartRunner 
ID 
Notified time 
(1/0), including 
time, date and 
HeartRunner 
position 
Alarm 
confirmed by 
HeartRunner 
app (1/0), 
including time 
and date  
Alarm accepted 
or declined by 
HeartRunner 
(1/0), time and 
date. Updated 
position if heart 
runner accepted 
the alarm. 
Alarm 
cancelled by 
HeartRunner 
(1/0/), time, and 
date  
AED position 
and ID (if 
HeartRunner 
was guided to 
retrieve AED) 

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cerebral disability, 3 equals severe cerebral disability, 4 equals coma or vegetative state, 
and 5 equals brain death. We will classify good neurological outcome as 1-2.  
 
5. Questionnaire: 
All citizen responders who have accepted or declined an alarm will receive a text 
message with a link to a short questionnaire within 90 minutes after the alarm. The 
questionnaire will obtain information about 1) The cardiac arrest: whether the citizen 
responder reached the scene of arrest, whether they arrived prior to EMS, performed 
CPR and/or defibrillation and 2) Psychological impact and physical injury. Physical 
injuries will be classified as ‘serious’ defined as requiring hospital admission, ‘minor’ 
injuries defined as not requiring hospital admission, or risk of been injured or close to 
get injured on the way to the cardiac arrest or during the resuscitation attempt.   
Citizen responders who report significant psychological distress will be contacted and 
offered debriefing by phone by healthcare personnel. The full questionnaire is displayed 
in appendix 2. A text message reminder will be sent to citizen responders that have not 
completed the questionnaire within 24 hours. A second text message reminder will be 
sent to citizen responders who have accepted an alarm and not completed the 
questionnaire within 1 week. In case of no reply after the second reminder, citizen 
responders will be contacted by phone, text message or email. 
 
6. Danish Civil Registry: 
Information on whether the patient is alive or dead after 30 days will be retrieved from 
the Danish Civil Registry.  
5. Statistics and power calculations 
5.1 Statistical analyses 
Eligibility, allocation, inclusion and exclusion are displayed in a trial diagram (Figure 1). Analysis 
will be performed following an intention-to-treat principle (patients for whom the HeartRunner 
system was activated vs. not activated). Baseline characteristics will be summarized as means and 
standard deviations, medians and interquartile ranges, or percentages. 

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The primary outcome will be reported as proportion of patients surviving 30 days with and without 
the intervention. The comparison will be by Fischer’s exact test. Survival during the first 30 days 
will be presented using Kaplan-Meier estimates. 
 
Analysis of bystander defibrillation, bystander cardiopulmonary resuscitation, return of spontaneous 
circulation on hospital arrival, and neurological intact survival at hospital discharge (cerebral 
performance category score of 1-2) will be reported as proportions and compared within 
intervention groups using Fischer’s exact test. Survival during the first year will be presented using 
Kaplan-Meier estimates and compared with the log-rank test.  
 
All tests will be performed independently in the 2 time strata of the study. As a secondary analysis, 
data from stratum 1 and 2 will be combined. 
 
Additional Statistical Analysis 
In addition to the standard frequentist analysis, to aid interpretation of the results, we will also 
perform a Bayesian analysis. If the assumptions underlying the design of the trial are found to be 
substantially incorrect (for example, the proportion of survivors may be lower than was 
anticipated), the precision of the trial’s results may be reduced, which would reduce the chance of 
any treatment difference reaching the conventional threshold for statistical significance. In this 
situation, interpretation of the results by clinicians and decisionmakers will be helped by producing 
a quantitative summary of the probability that activation of HeartRunners is beneficial, taking into 
account existing evidence and the trial’s results.  

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Figure 1. Trial Diagram 
 
5.2 Power calculations 
There was an overall survival of approximately 15% in 2018 in Denmark. Based on prior studies 
from Stockholm and Holland time to arrival of bystanders decreased by 2.5 minutes with 
introduction of activated lay persons. Experiences from Sweden have shown that volunteer citizen 
responders can be recruited and arrive before all dispatched units in 25% of the cases. 8, 33  
 
This is a superiority trial and sample size and power calculations are based on an assumed effect 
size using a binary outcome (30-day survival). Data from Danish OHCA cases without introduction 
of a HeartRunner program showed a decreased chance of survival with increasing EMS response 
times (30-day survival for all OHCA cases were 12%, 8%, and 4% for EMS response times of <5 
minutes, 5-10 minutes, and >10 minutes, respectively).15 Similarly, the chance of having a 
shockable heart rhythm (ventricular fibrillation/pulseless ventricular tachycardia) decreased from 
50% within 5 minutes, 30% within 5-10 minutes, and below 20% for EMS response times above 10 
minutes.15  
Estimated 30-day survival chances according to citizen responder response times are: 25% within 3 
minutes, 25% within 3-9 minutes, and 4% after 9 minutes.  

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Power calculations estimated by Fisher’s exact test according to time groups are then (using a 
power (1-beta) of 0.80 and a significance level (alpha, two-sided test) of 0.05): <3 minutes: 536 
patients (increase from 15 to 25%) and 3-9 minutes (increase from 15 to 25%): 536 patients.  
 
Data from the pilot study showed approximately 64% of suspected OHCA were real OHCA. 
Further, in approximately 40% of cases for which the HeartRunner system was activated, at least 1 
citizen responder arrived prior to EMS. It is thus necessary to account for these conditions when 
calculating power for this study. Thus, for group 1 and 2, 536 cases of true OHCA would be 
identified among 838 cases of suspected OHCAs. To achieve at least 838 suspected OHCAs where 
at least one activated citizen responder arrived prior to EMS, it would require 2094 suspected 
OHCAs. Thus, in total, 2094 suspected cardiac arrests in stratum 1 and in stratum 2 are estimated to 
be included in the study. Power calculations were performed using the procedure Power (with the 
twosamplefreq statement based on Fisher’s exact test) in SAS version 9.4 (SAS Institute, Cary, NC, 
USA). 
 
5.3 Subgroup Analysis 
Since time from cardiac arrest to defibrillation is the most powerful determinant of survival, there 
may be heterogeneity of the intervention effect between subgroups that inherently differ in time 
from cardiac arrest to citizen responder intervention due to practical circumstances.43 Differences in 
the primary outcome are therefore anticipated in the following groups: 
1. Witnessed OHCA defined as someone (not EMS) sees or hears the person collapse with a 
cardiac arrest.  
2. According to ambulance response time (< 5 minutes, 5-10 minutes, >10 minutes) defined 
as time from emergency call to arrival of EMS at the OHCA location, not at the patient’s 
side. 
4. Cardiac arrests occurring in public settings. Public OHCA will be defined as a cardiac 
arrest occurring in public buildings, sport facilities, airports, work/office buildings, outdoor 
locations, and in public transport. 
5. Cardiac arrest in residential setting. Residential OHCA will be defined as a cardiac arrest 
occurring in private homes or in nursing homes. 
6. Distance from OHCA to nearest AED (0-250m, 251-500m, 501-1000m, >1000m). 
Distances will be calculated as straight-line. 

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A test for interaction in subgroups in relation to the intervention effect (citizen responder activation) 
will be performed for the primary outcome for the above-mentioned groups. This study is not 
powered to detect differences in primary outcome between intervention and control arm in the 
subgroups. 
6. Study Quality 
The study will be conducted according to principles of Good Clinical Practice, apply to ethical 
principles, and regulatory requirements. 
The study will be monitored according to a monitoring plan, according to principles of Good 
Clinical Practice for clinical studies.  
The study will be subject to audit as required by authorities. 
 
7. Ethical Aspects 
 
7.1 Scientific aspect 
Overall survival following OHCA was 15% in Denmark in 2018 but 7 out of 10 may survive if 
defibrillated by an AED within the first minutes after collapse.3 The AED registry in the Capital 
Region of Denmark currently holds nearly 6000 AEDs, but AEDs are only used in 3-4% of all 
OHCA.5, 13, 44 Bystander defibrillation is not only crucial for survival, but also survival with 
favourable neurologic outcome and chance of returning to work.45, 46 Activating citizen responders 
may increase rates of bystander CPR and defibrillation, and consequently, survival. If citizen 
responder activation indeed increases survival, it is necessary to understand how many persons need 
to be activated to save a life and consider the extent of physical injury or psychological stress for 
the citizen responders. Given this background we find that the risks involved with the study are 
justified by a good chance of improving outcomes. 
 
7.2 Legal aspects 
The Ethics Committee’s responsibility is to assess medical research projects. The Ethics Committee 
has evaluated the study protocol and deemed the study is not a medical research project as defined 
in the Ethics Committee’s § 2. The study is therefore deemed not notifiable and can be initiated 
without further approval from the Ethics Committee (Journal nr.: 17018804).  

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The study is registered by the Data Protection Agency via The Capital Region of Denmark (journal 
nr.: 2012-58-0004, VD-2018-28, I-Suite nr.: 6222) and data will be stored in accordance to Danish 
data legislation. The study has also been registered with the Danish Patient Safety Authority (3-
3013-2721/1, 31-1522-14, and R-20051145) and will adhere to Danish law regarding handling og 
personal data for patients.  
 
7.3 Patient information and informed consent 
Patients: The study is designed to randomize activation of citizen responders (activation of citizen 
responders vs no activation of citizen responders) for incoming calls to the emergency dispatch 
center which are ‘suspected cardiac arrest’. Standard treatment including dispatch assisted CPR, 
guidance to a nearby AED if any, and dispatch of ambulance and a physician manned ambulance is 
carried out in all cases of suspected cardiac arrest regardless of citizen responder randomization.  
 
Citizen responders: To complete the registration through the HeartRunner app all volunteer citizens 
must sign the terms of agreement. These include not to disclose any details about suspected cardiac 
arrests that could lead to identiﬁcation of individual patients. Citizen responders also sign a 
confidentiality agreement ensuring personal information about the patient or resuscitation attempt is 
not to be disclosed. Citizen responders agree to be geographically located when they are logged on 
to the app, including before receiving alarms and to be contacted by the research team. Citizen 
responders can delete their app end withdraw from the HeartRunner program at any given time.  
 
8. Safety Management 
 
8.1 The Safety Committee and Monitoring Board 
A Data Safety and Monitoring Board with statistical, cardiological and prehospital 
expertise will follow the study. Formal interim analyses are not planned. This 
committee is composed of members otherwise independent of the study. They can 
recommend the steering committee to discontinue the study, but it is the only body 
which during the course of the study received unblinded results grouped by treatment. 
The Safety Committee and Monitoring Board will form its own guidelines. The major events to be 
considered by the safety committee are survival rates (effect) and serious physical injuries or 
psychological stress among citizen responders (safety). The primary tracking of safety uses a 

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research computer linked directly to the HeartRunner mission server. Using this system, responses 
can be tracked continuously, and reports can be prepared for the study Data Safety and Monitoring 
Board. Further, events that come to the attention of study staff and which are not covered by 
tracking of citizen responder responses and which are either fatal, life threatening, causes 
hospitalization or lengthening of hospitalization, results in significant or lasting 
disability or leads to a congenital defect will be reported as well. 
 
8.2 Practical reporting of safety 
For the purpose of this trial all citizen responder hospitalizations and deaths in relation to 
responding as citizen responders are considered serious adverse events. These events will be 
tabulated on a biannual basis for the whole trial based on citizen responder survey responses. In 
order to monitor adverse events, we will follow-up on non-responders by email, text-messages and 
phone call. Further, events that are serious according to the above definition and not in the listings 
from surveys will be reported as well. 
 
8.3 Risks and side effects of trial procedures 
Prior studies have activated volunteer citizens to respond to OHCA and have only reported mild 
psychological stress. Physical injuries have not been reported.8, 10 During our pilot study, 1% of 
citizen responders reported moderate or severe psychological stress and one case of serious physical 
injury was reported (a foot fracture). 
 
9. Data management 
9.1 Data access 
Data for this study are derived from the Danish Cardiac Arrest Registry, the HeartRunner Mission 
Server, the citizen responder survey, the Danish Civil Registry, and the emergency dispatch center 
as previously described.  
Data managers at the Copenhagen EMS has access to the study data during the course of the trial 
and can provide listings and calculations for the Data Safety and Monitoring Board. When the study 
closes as scheduled, or prematurely, the code is made available to further study staff. 
 
9.2 Data storage and security 
Data is stored in accordance to Danish data legislation. 

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Personal data will be treated with the usual secrecy in compliance with current regulations and 
legislation in the Capital Region of Copenhagen, Denmark. Personal Identifier numbers such as 
social security numbers and all other data that may lead to identification of subjects included in the 
study will be coded and keys for decoding will only be accessible to key persons in the project. 
Data will be stored on a dedicated and secure server at the Emergency Medical Services 
Copenhagen, Capital Region of Denmark. Only few people in the research group have access with 
data logging and a code to access data. Data will be stored for 10 years after closing of the study. 
 
10. Patient, Caregiver and HeartRunner Engagement Team 
Since this trial will be conducted in the community including patients, caregivers and citizen 
responders, an engagement team consisting of a cardiac arrest patient, a caregiver and citizen 
responders with different backgrounds will be formed to participate in planning, conducting, and 
disseminating the results of our study. The team will provide feedback on the study protocol and the 
follow up questionnaire to citizen responders. The team will also oversee the implementation and 
conduct of the trial, with special focus on ethical issues.    
 
11. Dissemination of results 
The study will be presented as a manuscript following CONSORT guidelines.47 Regardless of the 
result of the study the main result will be published in an international peer reviewed journal and 
presented at relevant congresses. The protocol will be made publicly available as the study starts 
and will be registered as required for proper publication. 
 
12. Financing and Insurance 
The study is financed by an unrestricted research grant from TrygFonden. Provision of this 
support is provided with a contract signed by TrygFonden, the principal investigator and the 
head of the Emergency Medical Services in Copenhagen. This is an investigator initiated trial and 
Danish patients are in general covered by rules that ensure coverage of patients when exposed to 
adverse events during the course of a treatment. 
 

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13. Relation between TrygFonden and Investigators 
The principal investigators have previously received grants from TrygFonden to perform 
epidemiological studies of out-of-hospital cardiac arrest. The investigators are otherwise 
independent of TrygFonden.  
 
14. Trial organization  
Principal investigator 
Fredrik Folke, MD, PhD, Professor 
Herlev and Gentofte Hospital, Department of Cardiology, 
Copenhagen University Hospital, 
Hospitalsvej 1, 2900 Hellerup  
Denmark 
 
Head of Research, Copenhagen Emergency Medical Services, University of Copenhagen, 
Telegrafvej 5, opgang 2, 3.sal 
2750 Ballerup 
Denmark 
Fredrik.Folke@Regionh.dk 
0045-28182978 
 
Executive scientific steering committee: 
Professor Christian Torp-Pedersen, Department of Clinical Investigation and Cardiology, North 
Zealand Hospital, and Department of Cardiology, Aalborg University Hospital, Denmark 
Professor Lars Køber, Department of Cardiology, Rigshospitalet, Denmark 
Professor Gunnar Gislason, Herlev and Gentofte Hospital, Hellerup, Denmark and the Danish 
Heart Foundation, Denmark 
Dr. Freddy Lippert, Copenhagen Emergency Medical Services, Ballerup, Denmark 
Dr. Carolina Malta Hansen, Copenhagen Emergency Medical Services, Ballerup, and Herlev and 
Gentofte Hospital, Division of Cardiology, Hellerup, Denmark  
Dr. Linn Charlotte Andelius, Copenhagen Emergency Medical Services, Ballerup, Denmark 
Dr. Mads Tofte Gregers, Copenhagen Emergency Medical Services, Ballerup, Denmark 

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Professor Annette Kjær Ersbøll, National Institute of Public Health, University of Southern 
Denmark, Copenhagen, Denmark 
Professor Fredrik Folke, Copenhagen Emergency Medical Services and Herlev and Gentofte 
Hospital, Division of Cardiology, Hellerup, Denmark (chair) 
 
The steering committee is responsible for study conduct. All decisions regarding 
management of the study will be made by the steering committee. During the study the steering 
committee will remain blinded to study outcome, but the committee will be continuously informed 
of study progress. This ensures that the steering committee has sufficient information to handle any 
problems with study progress. The steering committee will regularly be provided with updates by 
the Safety Committee and Monitoring Board. These updates are restricted to a recommendation to 
either continue or discontinue the study. No further information can be given by the Safety 
Committee and Monitoring Board during the course of the study. 
 
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Appendix 1:  
Randomization 
Functionality 
Randomization is configurable in the HeartRunner MissionServer. For the HeartRunner trial, 
randomization is activated and divides each incident into two groups by random: Intervention group 
and control group. The ratio in which the incidents are divided is configurated to 1:1 randomization 
during the whole study period.  
 
Intervention group: 
1. Perform standard missions 
Control group: 
1. Abort mission, i.e. do nothing meaning that the incident is invisible to all candidates. 

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Random allocation 
The process of deciding if an incident is an intervention incident or a control incident need 
to follow certain statistical rules in order to satisfy scientific requirements. 
 
Block randomization 
Block randomization is used to ensure that the same number of incidents fall into each group 
even with small sample size. Simply speaking, block randomization means that for certain 
block size, for example 6, every 6th subsequent incidents will have 3 incidents in control 
group and 3 incidents in intervention group. Then the next 6 incidents will also have 3 of 
each. Within each block the pattern is random. Instead of the simple approach of using fixed 
block size, MissionServer will use a variable block sizes of 4, 6 and 8, meaning that for each 
new block the next block is randomly selected to have size 4, 6 or 8. 
Note that the intervention/control ratio must match every block size used. 
Example of variable block size with 24 incidents using 1:1 ratio. Here, these 24 incidents 
make up 4 entire blocks: 
 
Incident # Block size Group 
1 
8 
Control 
2 
8 
Control 
3 
8 
Intervention 
4 
8 
Control 
5 
8 
Intervention 
6 
8 
Intervention 
7 
8 
Control 
8 
8 
Intervention 
9 
4 
Control 
10 
4 
Intervention 
11 
4 
Intervention 
12 
4 
Control 
13 
6 
Intervention 
14 
6 
Control 
15 
6 
Intervention 
16 
6 
Control 
17 
6 
Control 
18 
6 
Intervention 
19 
6 
Intervention 
20 
6 
Intervention 
21 
6 
Control 
22 
6 
Control 
23 
6 
Intervention 
24 
6 
Control 
 
Stratified randomization 
MissionServer will support stratified randomization based on candidate-proximity. The idea 
behind stratified randomization is to ensure that important baseline variables (like candidate 
proximity in this case) thought to be associated with the outcome, are evenly distributed 

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between groups. Each incident is grouped into one proximity group depending on how far 
the four nearest candidates (citizen responders) are located. Then separate block randomization lists 
are applied to each group. 
 
Proximity group Criteria 
Stratum list 
1 
At least 4 candidates with TVP < 180 sec List 1 
2 
At least 4 candidates with TVP < 540 sec List 2 
3 
At least 4 candidates with TVP < 900 sec List 3 
4 
At least 1 candidate with TVP < 900 sec  List 3 
Rest 
No candidate with TVP < 900 sec 
No alert (no randomization) 
 
Note these criteria are evaluated in the specified order. 
 
Note that if the incident does not match any of the proximity groups there will be no alarm. 
 
 
Appendix 2: 
Survey 
Survey sent to all citizen responders whose app has confirmed the alarm. The original survey is in 
Danish and here translated to English.  
 
Start question 
 
Q0 
Did you accept the alarm?  
 
Yes (Go to Q1) 
 
 
No (Go to Q50) 
 
Accept questions: 
 
Q1 
Did you try to retrieve a defibrillator?  
 
Yes (Go to Q2) 
 
 
No (Go to Q3) 
 
 
Q2 
Did you succeed in retrieving a defibrillator?  
 
Yes (Go to Q4) 
 
 
No (Go to Q3) 
 
Q3 
Why did you not succeed in retrieving a defibrillator? 
 
The alarm did not include enough information   
 
The defibrillator was not accessible 
 
The defibrillator I was directed to was already taken 
  
There were technical problems with the app 
 
I was not directed to a defibrillator 
 
Other reason 

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1 (Go to Q4) 
 
2 (Go to Q4) 
 
3 (Go to Q4) 
 
4 (Go to Q4) 
 
5 (Go to Q4) 
 
6 (Go to Q4) 
 
Q4 
Did you try to reach the cardiac arrest location?  
 
Yes (Go to Q6) 
 
 
No (Go to Q5) 
 
 
Q5 
Why did you not try to reach the cardiac arrest location? 
 
I was unavailable to help 
 
I noticed the alarm too late 
 
It was too far away 
 
There were technical problems with the app 
 
Other reason 
 
 
1 (Go to Q17) 
 
2 (Go to Q17) 
 
3 (Go to Q17) 
 
4 (Go to Q17) 
 
5 (Go to Q17) 
 
Q6 
Did you succeed in reaching the victim? 
 
 
Yes, by foot (Go to Q8) 
Yes, by bike (Go to Q8) 
Yes, by car (Go to Q8) 
Yes, with other transportation (Go to Q8) 
 
No (Go to Q7) 
 
Q7 
Why did you not succeed in reaching the victim? 
 
The alarm did not contain sufficient information 
 
I aborted the alarm when I saw the emergency personnel    
 
There were technical problems with the app 
 
Other reason 
 
 
1 (Go to Q17) 
 
2 (Go to Q17) 
 
3 (Go to Q17) 
 
4 (Go to Q17) 
 
Q8 
Did you reach the victim before the emergency personnel?  
 
Yes (Go to Q9) 
 
 
No, I arrived after the emergency personnel (Go to Q9) 
 
Q9 
Was cardiopulmonary resuscitation initiated when you arrived? 
 
Yes (Go to Q11) 
 
 
No (Go to Q10) 
 

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Q10 
Did you initiate cardiopulmonary resuscitation? 
 
Yes (Go to Q12) 
 
 
No (Go to Q12) 
 
 
Q11 
Who performed cardiopulmonary resuscitation? 
 
Emergency personnel 
 
Other bystander 
 
 
1 (Go to Q12) 
 
2 (Go to Q12) 
 
Q12 
Did you or any other citizen responder attach a defibrillator to the patient?  
 
Yes (Go to Q13) 
 
 
No (Go to Q14) 
 
Q13 
Did the defibrillator deliver a shock to the patient? 
 
Yes (Go to Q14) 
 
 
No (Go to Q14) 
 
Q14 
Did you perform cardiopulmonary resuscitation? 
 
Yes (Go to Q15) 
 
 
No (Go to Q16) 
 
Q15 
What kind of cardiopulmonary resuscitation did you perform?  
 
Only chest compressions 
 
Only ventilations 
 
Both chest compressions and ventilations 
 
1 (Go to Q17) 
 
2 (Go to Q17) 
 
3 (Go to Q17) 
 
Q16 
Why did you not perform cardiopulmonary resuscitation? 
 
The patient was not in cardiac arrest 
 
The patient was awake  
 
Someone else performed cardiopulmonary resuscitation  
 
Other reason 
 
 
1 (Go to Q17) 
 
2 (Go to Q17) 
 
3 (Go to Q17) 
 
4 (Go to Q17) 
 
Q17 
Did you suffer any physical injuries or were you at risk of physical injuries on your 
way to the cardiac arrest location? 
 
Yes 
 
No 
 
 
1 (Go to Q20) 
 
2 (Go to Q18) 
 
Q20: 
On your way to the cardiac arrest location: 

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Were you at risk of physical injuries or close to getting injured? 
 
Did you suffer minor injuries without need for treatment/hospitalization? 
 
Did you suffer severe injuries with need for treatment/hospitalization? 
 
Other? 
 
 
1 (Go to Q18) 
 
2 (Go to Q18) 
 
3 (Go to Q18) 
 
4 (Go to Q18) 
 
Q18: 
It can be stressful to participate in cardiac arrest resuscitation.  
 
What impact did the experience have on you? 
1.     I was not affected 
2.     Only minor distress 
3.     Moderately distress 
4.     Severe distress, but no need for follow-up by healthcare personnel 
5.     Severe distress, with need for follow-up by healthcare personnel 
 
 
1 (Go to Q19) 
 
2 (Go to Q19) 
 
3 (Go to Q19) 
 
4 (Go to Q19) 
 
5 (Go to Q19) 
 
Q19: 
Do you want to continue as a citizen responder? 
1. Yes 
2. No 
3. In doubt   
 
 
1 (Go to END) 
 
2 (Go to END) 
 
3 (Go to END) 
 
END 
If you need debriefing or follow-up by healthcare personnel, please send an e-mail to  
 
hjerteloeber.den-praehospitale-virksomhed@regionh.dk 
Please be aware that we cannot reveal any information or outcome about the cardiac arrest 
patient. 
 
Thank you for your participation. 
 
Decline questions: 
 
Q50: 
We ask you to answer two short questions to help us improve the citizen responder system.  
  
What was the reason you did not accept the alarm? 
1.     I was unavailable to accept the alarm 
2.     I did not feel comfortable to help 
3.     I expected the emergency personnel to get there before me 
4.     Technical problems 
 
 
 
1 (Go to Q51) 
 
2 (Go to Q51) 

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3 (Go to Q51) 
 
4 (Go to Q51) 
 
Q51: 
Do you want to continue as a citizen responder? 
1. Yes 
2. No 
3. In doubt   
 
 
 
1 (Go to END2) 
 
2 (Go to END2) 
 
3 (Go to END2) 
 
END2 
If you want to contact us, please send an e-mail to  
 
hjerteloeber.den-praehospitale-virksomhed@regionh.dk