Sudden cardiac arrest (SCA) denotes instantaneous cessation of the activity of the heart with hemodynamic collapse, and sudden cardiac death (SCD) is a natural death assumed to be caused by the heart that takes place within one hour of initial symptoms if witnessed or within 24 hours of the last time the victim was observed if SCD was not witnessed directly. (1)
SCD is a major public health issue that affects approximately 3.8 million people every year, representing 50% of all cardiovascular deaths and approximately 20% of all deaths, with it being the first manifestation of heart disease in 50% of cases. Most SCDs, 60% to 80%, take place outside the hospital, of which 65-80% take place in a residential setting and 20% in public places. (1-3) The incidence of SCD significantly increases with patient age. It is very low in those aged less than 35 years, comprising <1% of all SCD, of whom at least 5-10% have a normal heart structure, so genetic testing can improve identification of SCD causes. During infancy and childhood, the incidence is 1-2 per 100 000 inhabitants, with the incidence in men being up to 5 times higher, as in other age groups. The incidence is higher at the ages between 15 and 35 (approximately 3.2/100 000), and causes in persons younger than 35 are usually hypertrophic cardiomyopathy (HCM) and other cardiomyopathies, as well as cardiac channelopathies, with coronary heart disease (CHD) being the leading cause of SCD among patients older than 35. (4-6) In middle age, the fifth and sixth decades of life, incidence reaches 50/100 000, and the incidence surpasses 200/100 000 in the eight decade of life, when CHD is the most common cause of SCD. (7,8)
Emergency medical services (EMS) usually successfully treat 50-60% of all SCAs, consequently making incidence assessments uncertain. In Europe, the incidence of SCA is approximately 300 000 patients treated by EMS, i.e. 30/100 000 inhabitants, with a survival rate of 10.7%, (9) whereas in the EuReCa study the incidence was approximately 600 000 (84/100 000 inhabitants, 62/100 000 in Croatia at the time), with 10.3% surviving until hospital discharge. (10) According to the few studies and assessments performed in Croatia, the incidence of SCA is significantly higher than in Europe, with large regional differences. (11-15) In the Split-Dalmatia County, for example, EMS treated 291 patients with SCA (approximately 65/100 000), of whom 21 (7.2%) survived until hospital discharge. (14) In the United States, different explanations have been offered for similar wide ranges in SCA assessments ranging from 250 000 to 400 000 or more. (16)
In athletes, the incidence of SCD is approximately 0.1-2 per 100 000 annually, with a range between 1:40 000 to 1:80 000 or even between 1:3000 and 1:1 000 000, but twice to three times higher than in other non-athlete members of their age group. (17) Current rates of SCD can be significantly higher, especially in men, African-Americans, and basketball players, in part due to Marfan syndrome and aortic dissection, which are more common in these populations. (18) Paradoxically, although moderate physical activity reduces cardiovascular risk factors, strenuous physical activity can be a trigger for SCA, especially in patients with heart diseases. Approximately 90% of SCDs occur during or immediately after strenuous physical activity, especially with HCM or hereditary structural or arrhythmogenic abnormalities, mostly (approximately 90%) in asymptomatic persons engaging in sports recreationally, and not in competitive athletes. (17-20) In 10-15% or more cases, autopsy fails to identify any structural defect as the cause of death, and genetic testing, e.g. molecular obduction, identifies a cause in up to 30% of cases, usually due to channelopathy. (21) In contrast to screening in the general population, the International Olympic Committee and European and US cardiological societies recommend performing screening in athletes, consisting of taking a medical history, performing a clinical examination, performing an ECG and if needed also a Holter ECG, echocardiography, ergometry, etc. (22-24) This screening can reduce the incidence of SCD, primarily by discovering cardiomyopathies, as in the Italian province of Veneto where mortality was reduced by 90% after the introduction of preventive examinations of athletes that included an ECG. (25)
The reversible effects of cardiac arrest, namely ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT), require urgent reestablishment of cardiac and cerebral circulation. Early defibrillation is the most effective measure in such cases, and it significantly increases survival after SCA, but almost exclusively in patients with VF/pVT, the most prevalent cause of SCA (60-85%), with a transformation to asystole developing within several minutes. Expected survival in patients with SCA with VF/pVT who receive successful defibrillation is up to 10 times higher than in cases of asystole. The low survival rates are the consequence of late application of effective defibrillation, since every minute of delay reduced survival by 10-12%. (26-28) Cardiopulmonary reanimation (CPR) is the bridge to defibrillation: it slows down the reduction of the VF amplitude and its transformation to asystole and increases survival by two to three times, even if performed by bystanders with chest compression only before the arrival of EMS. The effectiveness of ventilation in CPR is questionable and is not part of the recommended education for untrained rescuers in the ESC 2021 Guidelines. (29,30) Furthermore, the results of CPR performed by medical professionals are often worse due to interruptions in compression in order to administer injections, intubate the patient, etc. There is no evidence that survival would be improved by advanced resuscitation in comparison with basic resuscitation. (31)
It is important to emphasize the favorable prognosis of patients with SCA after they have been successfully saved from certain death. Their expected lifespan is nearly identical to the general population. One metanalysis conducted by Swiss authors on almost 17 000 resuscitated persons showed that survival after three years was 82.8%, 77.0% after 5 years, and as high as 57.5% after 15 years. (32)
During to the COVID-19 pandemic, resuscitation was performed without artificial respiration since the victim might potentially have COVID-19. In this or similar epidemics, rescuers should only apply compression and defibrillation. Healthcare workers should use personal protective equipment, and defibrillation should be considered even before donning the protective equipment. The resuscitator places a mask on the face of the victim and monitors breathing by observing chest movements. Before administering chest compression, the victim’s mouth should be covered by a piece of cloth or a mask, and the resuscitator should refrain from mouth-to-mouth artificial respiration, using chest compressions only. (33)
Public access to early defibrillation
When and where SCA will happen is unpredictable, and, for most victims of SCA, nowhere in the world can EMS arrive and start the resuscitation within the ideal 3-5 minutes, when reanimation is most successful. (34) In Sweden, EMS arrive in an average of 11 minutes, (27) and in Croatia the goal is to achieve a response time of “approximately 10 minutes in 80% of cases in urban areas, and approximately 20 minutes in rural areas”. (35) It is common for the response time to be half as long in urban areas in comparison with rural areas, (36) e.g. the average EMS response time after the phone call is approximately 7 minutes in urban conditions and over 14 minutes in rural settings. (37) Assistance from bystanders is therefore important, as is the availability of devices for identifying and treating pVT/VF. An automated external defibrillator (AED) is just such a device, with an almost 100% sensitivity and specificity for pVT/VF, and uses speech and text, including the Croatian language, to allow even an untrained person to perform almost risk-free defibrillation. After the device identifies pVT/VF, a shock is delivered either by pressing a button or automatically, although the latter is rarer. (38,39)
The first defibrillation was performed during surgery on an open chest by Claude Beck in 1947, (40) whereas the first closed-chest defibrillation was performed by Paul Zoll and colleagues in 1956. (41) The first defibrillation outside the hospital was performed by Frank Pantridge in an ambulance vehicle in 1966 in Ireland, and AEDs have been widely used by medical staff since the 1980s, gradually becoming more and more accepted by the general population as well.
The Public Access Defibrillation (PAD) program was started in 1990 in the United States with an emphasis on early CPR and early defibrillation using an AED, performed by educated or uneducated bystanders to an SCA before the arrival of EMS. It has been shown that survival of victims of SCA was almost twice as high in groups that received CPR and defibrillation in comparison with those who received only CPR. Previous training in the use of AEDs results in more frequent AED use and a shorter shockable rhythm confirmation time (on average 2.7 minutes faster) and a shorter time to defibrillation. (42)
Four levels of PAD have been defined:
The traditional first responders are police or firefighters equipped by AEDs, who can be directed to less accessible, e.g. rural, areas together with EMS by an EMS dispatcher when SCA is suspected.
The second level of PAD comprises non-traditional first responders, persons with a “duty to respond” (security guards, flight attendants), especially in enclosed spaces (casinos, airplanes, airports).
The third level of PAD comprises persons with training, usually only minimal, in applying CPR and defibrillation, with an AED being available, usually in the family home of an at-risk individual.
The fourth and most common level are bystanders in public places, with or without training in using AEDs. (43-46)
Numerous PAD programs with many trained volunteers and AEDs distributed so that they are available can provide assistance before the arrival of EMS, thus leading to a twice or three times higher survival rate for victims of SCA compared with that achieved by EMS alone. (47-49) The guidelines of the European Resuscitation Council therefore encourage PAD programs in which bystanders, after assessing the patient’s state (not longer than 10 seconds), identifies their loss of consciousness and the lack or irregularity of their breathing as SCA, immediately calls EMS, and begins CPR by employing external heart compression, depressing the sternum by 5-6 cm at a rhythm of 100-120/min. The guidelines from 2021 for basic resuscitation do not recommend artificial ventilation for untrained volunteers and for trained practitioners who do not want to perform it. This kind of CPR is easier to learn and perform, leading to higher resuscitation and survival rates for SCA and less common side-effects. (30,50,51) Therefore, the European Society of Cardiology recommends the use of AEDs, (39) and the European Parliament has issued a declaration calling on member states to establish programs for publicly available defibrillation and urgently pass laws on the conditions for providing publicly available lay resuscitation. (52)
The “Restart a Heart – Save a Life”
Croatian national program
Based on these recommendation, in 2013 and 2020 the Ministry of Health (MH) of the Republic of Croatia passed two Ordinances that addressed the implementation of the public access defibrillation program, conditions for the requisition of devices and for placement and use of the AEDs, mandatory registration and registry maintenance for AEDs as well as a registry for resuscitation involving use of AEDs by trained persons, and methods for training volunteers. (53,54) In the same year, together with the Croatian Institute of Emergency Medicine (CIEM) and the Croatian Institute of Public Health, the MH started a program for public access early defibrillation named “Restart a Heart – Save a Life”, which will, in cooperation with other ministries and the Croatian Red Cross, the Croatian Society for Reanimatology of the Croatian Medical Association, other associations, and the media, conduct a public health education program for citizens, with the goal of improving awareness on SCA and the importance of early CPR and early defibrillation, while also improving access to AEDs in public meeting spaces and training as many citizens in CPR and defibrillation as possible. (55)
At that time, the MH integrated 195 AEDs into the EMS system, and the CIEM has since organized more than 600 courses, training over 5000 volunteers to assist victims of SCA using AED. Additionally, the organization has disseminated educational video materials on its website for the training of potential rescuers. Furthermore, in collaboration with the MH, CIEM has consistently implemented various components of the “Restart a Heart – Save a Life” program for a decade, including maintaining a registry of AED placements on the Croatian AED Network and marking occasions such as World Restart a Heart Day and other anniversaries by installing, at times, the first public AED in various communities, accompanied by volunteer education efforts. (56)
The Croatian Cardiac Society, with the assistance of the StEPP student association and the City of Zagreb, has been implementing the project “Revive Me” through the “Croatian Heart House” foundation since 2014, and this initiative has to date successfully trained over 7500 citizens in modern cardiopulmonary resuscitation for victims of SCA. In addition to emphasizing the importance of swift identification of cardiac arrest and public access to early defibrillation, the Croatian Cardiac Society advocates for the widespread placement of defibrillators and the introduction of a national resuscitation education program into educational institutions, which would, as in northern Europe, allow at least half of the adult population to acquire proficiency in CPR skills. (57)
“Živi bili” (i.e. “Stay Alive”), an association for resuscitated individuals in Split, submitted a similar PAD project to the Ministry of Science, Education, and Sports as early as 2009, modeled after the first European early defibrillation project “Piacenza progetto vita” from 1998. Following a positive review, the project seems to have “vanished”, according to the Croatian Science Foundation. Despite limited response from citizens, the association, with the support of the municipal administration of the City of Split, has trained approximately 220 volunteers (firefighters, security personnel, and volunteers) in CPR and defibrillation over the course of a decade, raising public awareness through media channels on the public health significance SCA and lay resuscitation. (15)
Weaknesses and possible improvements of the public access early defibrillation program
After more than 30 years of the existence of PAD programs, defibrillation before the arrival of EMS has been, despite large regional differences, stagnating at several percentage points worldwide, with a very low effect of survival. The main reasons for this are as follows: most SCA take place in residential settings that are not suited for defibrillation, motivated and trained volunteers are rare, AEDs are very few in number, with existing devices often being unavailable, AED registries are incomplete, and PAD programs are often not included in the local EMS network but are instead run by regional governments, firefighting services, or other organizations. (58-63) In Croatia, support for the “Restart a Heart – Save a Life” has been insufficient, which has resulted in a low number of persons trained in CPR and defibrillation, and the number of available AEDs remains insufficient. Consequently, CPR before the arrival of EMS is rarely applied by bystanders (in 4% to 25% of cases, very rarely more than that), and cases in which defibrillation is applied are even rarer, usually 0% to 14.5%. Data on survival until hospital discharge, particularly data on defibrillation by bystanders, are infrequently reported; more commonly documented are the rates of return of spontaneous circulation prior to hospital admission. (12-15,64) “Survival data should not be based only on survival rates, but also on the number of survivors in a given population, because inclusion bias can influence the survival outcomes”. (65) Based on the estimate that the application of AEDs by bystanders saves 474 lives annually in the USA and Canada (46), in Croatia there would be only up to five such cases per year. Such a low number of lives saved among victims of cardiac arrest raises doubt about the cost-effectiveness and purposefulness of PAD programs. The cost-effectiveness of such programs is estimated at 30 000-50 000 USD per quality-adjusted life year saved. Nevertheless, these costs appear to be in line with other similarly effective healthcare interventions. (66-68) New strategies and equipment for PAD programs will likely improve survival in victims of SCA through more frequent utilization of AEDs, thereby reducing the cost-survival ratio. (69) Improving SCA outcome requires new technologies focusing on improvement across all levels, from preventing cardiac arrest to early defibrillation. Since the majority of SCAs occur in residential settings, where the implementation of PAD programs is particularly deficient, PAD programs must be enhanced primarily in these environments, as well as in rural and other areas, with innovations such as identification and dispatch of the nearest bystander and nearby AED to the location of the cardiac arrest, the use of drones and helicopters for AED delivery, and all other conveniences of new technology, which have already received significant attention across Europe and worldwide. (69-71)
Encouraging early detection of cardiac arrest
Identifying SCA is the first step towards CPR and early defibrillation, especially in residential settings, where SCAs often occur without bystanders and early resuscitation, with death consequently being by far the most frequent outcome. Family members of the victim, who often witness the SCA, should therefore be trained to recognize SCA and immediately call the EMS number directly as well as initiate CPR and defibrillation as soon as possible, with preventing fear from possible harm, legal responsibility, or a feeling of guilt in case of failed resuscitation also being an important factor in the education. (72-74) Early identification of cardiac arrest or imminent SCA can be facilitated by mobile devices such as smartwatches, mobile phones, video devices, or a telemedicine Holter ECG. These devices can discover rhythm and heart frequency disorders for imminent or already present SCA or remotely alert a bystander or EMS when sensors indicate malignant arrythmia, and security cameras can detect stereotypical behaviors of victims of SCA, such as touching the face before falling. Some systems can automatically alert bystanders and EMS. (75) Mobile applications can almost infallibly perform contactless identification of agonal breathing, severe hypoxia, snoring, hypopnea, and central and obstructive apnea during sleep. (76)
Better availability, reliability, and usability of automatic external defibrillators
Successful implementation of a PAD plan requires many AEDs to be publicly available 24 hours a day in visible locations such as cafes, ATMs, etc. Creating a registry for these AEDs is equally important, and this registry should also include private AEDs, in order to assist EMS dispatchers in finding the closes AED to the victim. For example, the Istria County in Croatia provides the Staying Alive mobile phone application that identifies the location of the closest AED. The exact number of registered AEDs in Croatia is not known. Based on the government Ordinances, (53,54) prior to deploying an AED, owners are obligated to train potential rescuers, and they must send a report to the CIEM detailing the date and location of AED placement as well as instances of resuscitation employing the AED, with the goal of forming an AED registry and the registry of resuscitations performed using AEDs. Currently, there are reportedly 647 AED devices, with 45 located in the Split-Dalmatia County. (77) However, the actual number is likely higher due to some owners failing to report their devices to CIEM, and according to AED suppliers in Croatia, which distribute Zoll AEDs, there are currently 764 devices in lay use. (78) Furthermore, approximately an additional 200 installed devices from other manufacturers should be added to this tally, bringing the total to nearly 1000 AEDs or one device per approximately 3800 inhabitants in Croatia. In comparison, the United States has approximately one AED per 300 residents, (46) which is at least ten times more than in Croatia. Therefore, Croatia requires a significantly higher number of available AEDs accessible at all times, especially in the rural and residential areas of our the country! This is because SCA victims near an AED are three times more likely to be defibrillated by bystanders, resulting in a doubling of survival rates. (59) The utilization rate of AEDs prior to the arrival of EMS is poor, often below 3% of SCAs even when the AED is within 500 meters or as little as 100 meters away from a victim of SCA. (59,79,80) Reporting rates on the locations of deployed devices and AED resuscitations in Croatia is very poor, as AED owners lack motivation and incentives, and maintenance of AEDs according to manufacturer instructions often leads to owners “buying” an additional device over a ten-year period in the hope of using it at least once. This must be changed. Resuscitations with an AED are rare and are even more rarely reported, so the registries are incomplete. Defibrillation will soon become simpler and more effective, since some companies are developing smaller and cheaper defibrillators that users will be able to plug as their mobile phones. (69)
Increasing public awareness and the willingness of the majority of the population to use an automatic external defibrillator
Victims of SCA urgently require resuscitation, as every minute of delay reduces the probability of survival by approximately 10%. (26,27) However, public awareness on the importance of CPR and defibrillation, and the willingness of lay bystanders to use AEDs in case of SCA is extremely low. The main reasons for this are neglect of the topic in the media, lack of resuscitation training, and fear of causing harm and suffering legal consequences. Better knowledge on AEDs and resuscitation training would improve bystander awareness on the role of AEDs in treating SCA, while also increasing willingness to employ AEDs in such situations. For example, media coverage of the World Restart a Heart Day with the message “All citizens of the world can save a life” is effective in increasing awareness of a large number of inhabitants on the importance of resuscitation before the arrival of EMS. (81) Most of them need to be motivated and trained in CPR and AED use, which requires educational programs, preferably mandatory, that will involve the majority of the population. Education in schools can significantly increase CPR/defibrillation rates in bystanders, since children are potential rescuers in the long term who are poised to engage in organized learning and capable of acquiring new skills and knowledge. Resuscitation training starting with school education at ages 10 to 11, usually just in chest compression, can have a positive influence on student attitudes towards resuscitation and willingness to resuscitate. (82,83) Several years ago, the World Health Organization approved a training program for schoolchildren (and their teachers) in CPR named “Children Save Lives”. Based on this approval, CPR training has been included in education plans in European primary and secondary schools as a legal obligation in five countries, and as a recommendation in 23 countries. (84,85) In Croatia, the Decision on the Adoption of the Curriculum for the Interdisciplinary Topic of Health in Primary and Secondary Schools (Official Gazette 10/19) has been in effect since 2019. Within this framework, the acquisition of first aid skills is envisioned for students in the 6th and 7th grades of primary schools, as well as the 1st and 2nd grades of secondary schools. Additionally, as part of the “Public Institutions – Friends of Health” project, the Ministry of Health has introduced CPR education into educational institutions. It has also been proposed that, due to the “dramatic increase in SCA and alarmingly low SCA survival rates”, all undergraduate students from all faculties also be enrolled in mandatory CPR courses. (86)
Rapid location of potential rescuers and defibrillators
Utilizing a positioning system, a trained EMS dispatcher can instantaneously locate registered users of mobile phones, whether they are trained or untrained voluntary rescuers or off-duty healthcare professionals, and the dispatcher can then direct them towards the victim of SCA using the AED registry to find the nearest AED, with some smartphone applications, complemented by a video connection with the rescuer, even enabling dispatcher-guided CPR. The smartphone application, activated by the dispatcher, warns its volunteer users of suspected SCA in their vicinity (usually within 500 m) and provides instruction for performing CPR, acquiring the nearest AED, and performing defibrillation. Such a system is very effective, significantly reducing time to intervention before the arrival of the EMS team and thus increasing survival rates. (87-89) Time to bystander defibrillation can also be additionally reduced, especially in residential and rural areas, by having dispatchers send mobile phone messages to guide the nearest volunteers towards the victim of SCA. (90,91)
Faster delivery of automatic external defibrillators to victims of sudden cardiac arrest
The time from the onset of SCA to defibrillation is crucial for successful resuscitation. A new, promising strategy for early defibrillation involves delivering AEDs to the victim via drone, increasing the likelihood of bystander defibrillation before the arrival of EMS and thus improving the survival rates of these victims. In rural and mountainous areas, where EMS response is most often delayed, the potential benefit of such air transportation is the greatest, as the drone reaches the victim significantly before emergency assistance, saving an average of about 20 minutes. Transportation of emergency medical services by helicopter can also be beneficial in managing SCAs and similar emergencies, for instance by delivering epinephrine for anaphylaxis, tourniquets for bleeding control, naloxone for opioid overdose, etc. (92-95)
Prevention of sudden cardiac death by preventing and treating coronary heart disease, cardiomyopathies, cardiac channelopathies, and other causes of sudden cardiac arrest
Sudden cardiac arrest (SCA) is the leading cause of death and the most urgent medical condition that affects around 3.8 million people worldwide every year. (69) Its most common cause is CAD, but overall mortality from CAD has been falling significantly since 1950, with a slightly lower decrease in the incidence of SCA. Over the last 30 years, the incidence of SCA has continued to decline due to the prevention and treatment of coronary and other cardiovascular diseases. (96,97) During this period, mortality rates from myocardial infarction and other cardiovascular diseases in Croatia have also been reduced, primarily due to improved treatment of patients with acute myocardial infarction though the network of primary percutaneous coronary interventions and modern arrhythmia management. (98) However, a large number of SCDs still take place, often as the first sign of CHD, cardiomyopathy, cardiac channelopathy, or other causes. Prevention and treatment of these diseases will continue to have a very important role in preventing SCD, in which genetic testing plays a significant role both globally and in Croatia, as it can quantify the risk of SCD for at-risk persons. If SCA still takes place, the role of public access to early defibrillation with the application of more effective, novel technologies will be even more important and effective. (99) It is therefore crucial to introduce mandatory training in CPR and defibrillation in order to achieve proficiency in at least 50% of the adult population: schoolchildren, students, employees, firefighters, police, and potentially also in other groups such as football fans, while also greatly increasing the number of publicly available, increasingly effective, and ever cheaper and smaller AEDs. All of this is a reason for activating the “Restart a Heart – Save a Life” national program as soon as possible, as this program aims to implement all this in Croatia, thus improving PAD and, hopefully, also significantly improving survival after SCA.