How Unexpected Is Out-of-hospital Sudden Cardiac Arrest? A Retrospective Cohort Study

Approximately 100,000 suffer from sudden arrest (CA) in The causes for CA are in 75% of these The present study aims to investigate the prehistory of patients who suffered from (OHCA) in a with inhabitants and how


Abstract Background
Approximately 100,000 patients suffer from sudden cardiac arrest (CA) annually in Germany. The causes for CA are cardiac in 75% of these cases. The present study aims to investigate the medical prehistory of patients who suffered from out-of-hospital cardiac arrest (OHCA) in a town with 250,000 inhabitants during 5 years and how many of these patients had already been previously treated at the local cardiac arrest center (CAC).

Case presentation
All resuscitations due to OHAC were retrospectively analyzed for the cause of OHCA, preexisting cardiac conditions and treatment, lay resuscitation, and outcome from January 1, 2012, to December 31, 2016, in Aachen, Germany. Data analysis was based on the resuscitation protocols and data from the CAC clinical information system. More than 50% of the patients with CA from cardiovascular origin were already known at the receiving respective CAC. Almost 60% of all patients already had cardiac preexisting conditions. Nevertheless, lay resuscitation occurred in only 34.1% of all cases. It was not performed in more than 60% although the probability of discharge can be signi cantly increased by lay resuscitation.

Conclusion
The rate of lay resuscitation is relatively low although many patients suffering from CA have cardiac preexisting conditions. These ndings show the importance of better priming their relatives for emergencies to improve lay resuscitation and improve the chances for a better outcome.

Background
More than 350,000 patients suffer out-of-hospital cardiac arrest (OHCA) in Europe annually (1), and more than 100,000 in Germany alone (2). Estimates suggest that only about 10% of all patients survive an OHCA despite the recent advances and improvements in the standard of care for periarrest patients (3,4).
The EURECA One study also showed a 10.3% survival rate for at least 30 days (5). Those few patients surviving OHCA are often discharged with increased morbidity and poorer quality of life (6, 7) after a lengthy and costly hospital stay (8-10).
The majority of adult cardiac arrests (CA) occurs because of cardiac reasons (11)(12)(13). About half of all cardiovascular mortalities worldwide are caused by sudden cardiac death (14). In most cases, patients suffering from sudden cardiac arrest had coronary heart disease before cardiac arrest (15). Therefore, it is likely that the majority of patients who suffer from OHCA have already been suffering from preexisting cardiac disease. The outcome after OHCA is poor. Thus, this study aims to nd out how many patients with OHCA had preexisting conditions and have already been hospitalized before the onset of circulatory arrest. This knowledge could offer the possibility of identifying risk patients more easily and may offer the chance for an intervention to increase the probability of survival. In Germany, for example, OHCA is witnessed by laypersons in about 55% when not occurring in the presence of medical professionals.
However, the rate of lay resuscitation by witnesses is still as low as 42% (16,17). Moreover, several campaigns, e.g., the German "Resuscitation Week," have tried to encourage the population to perform su cient lay resuscitation (18,19).
The primary aim of this study was to estimate the proportion of patients with OHCA who were already known to the responsible cardiac arrest center (CAC) beforehand. The secondary aims were to measure the proportion of lay resuscitations and the outcomes of these patients. Therefore, a retrospective analysis of OHCA cases treated by the Aachen Emergency Medical Service (EMS) was conducted and the clinical data from the responsible CAC were matched.

Patients
The appropriate ethics committee waived the requirement for informed consent and granted permission to the EMS Medical Director to retrospectively analyze patient data (EK109/15). All out-of-hospital cardiopulmonary resuscitations (CPRs) between January 1, 2012, and December 31, 2016, conducted by the City of Aachen (Germany) EMS were eligible for inclusion.
All patients suffering OHCA in Aachen are usually hospitalized in the University Hospital of Aachen as the only local CAC. Patients who were resuscitated owing to noncardiac causes were excluded from the study.

Data sources and variables
As a member of the German Resuscitation Registry (www.reanimationsregister.de), the City of Aachen EMS collects data of all out-of-hospital resuscitation patients in the requested standardized format based on the Utstein template. For this analysis, the respective data were used and complemented with data from the original emergency mission protocols and hospital records abstracted by using the names, dates of birth, dates of resuscitation and admission times, and patient data from the local CAC, including administrative data, diagnoses codes, previous medical history, discharge letters, and neurological outcome (cerebral performance category [CPC]). Information about medical history was also taken from emergency mission protocols to complete existing hospital records or only as data source. The reason for OHCA and its compatibility with preexisting conditions were also evaluated. All of the aforementioned sources were used to complete the preresuscitation information of the patients concerning their medical history of preexisting conditions. Using the above data sources, the number of previous hospital admissions, admission reasons, and preexisting conditions were categorized at the discretion of the investigator.

Statistical methods
All analyses were exploratory. Data were analyzed with GraphPad Prism 8 (GraphPad Software, San Diego, CA, USA). Categorical and continuous data were compared using the exact Fisher's test and Student's t-test. The probability of a type I error < 0.05 was considered statistically signi cant.

Patients
During the study period, 904 patients were resuscitated by the EMS of the City of Aachen. After excluding 309 cases of OHCA due to noncardiac reasons and 67 cases with missing data (patients unidenti able), 528 cases of cardiac-related OHCA were analyzed (Fig. 1). Patients were mostly male (65.5%) and had a median age of 74 years (interquartile range [IQR], 61-82). Return of spontaneous circulation (ROSC) could be established in 42.3% of the patients (n = 226). The characteristics of the study population are depicted in Table 1.

Discussion
This retrospective analysis of 528 OHCA cases between 2012 and 2016 from the EMS of Aachen, Germany, found that (1) almost half of these patients had been admitted to the respective CAC before OHCA; (2) three-quarters of the OHCA patients already had preexisting conditions, most commonly cardiopulmonary diseases; (3) the rate of lay resuscitation was only one-third of all OHCA patients, but patients receiving lay resuscitation were more often admitted to the hospital and were more often discharged from the hospital; and (4) only one-third of the previously hospitalized patients received lay resuscitation.
This study has several strengths. As a participant and provider of data to the German Resuscitation Registry, the current study has good data quality of all OHCAs within the purview of the City of Aachen EMS. With only one (university) CAC in the vicinity, a high follow-up of successful OHCA resuscitations exists. However, data quality is limited by the accuracy or haziness of the documentation by the attending physicians, which is usually poorer compared to the structured prospective data collections, because this study only conducted a retrospective chart review. Both sample size and generalizability results are limited because this is the analysis of a single EMS and a single CAC.
Half of the OHCA patients had prior admission to the CAC due mostly to cardiac diagnoses. Although not surprising, no study exists that has yet quanti ed this proportion of prior hospitalizations and admission diagnoses. Moreover, the most common preexisting conditions were coronary artery disease and myocardial infarction. These results are similar to other studies (e.g., an analysis of 40,000 patients from a 20-year registry found that patients with OHCA were more likely to have diabetes mellitus and myocardial infarction) (21). In addition, a systematic review analyzing the relationship between comorbidity and OHCA found that that prearrest comorbidities are associated with reduced survival and poorer neurological outcomes (22). Although the systematic review is limited by the high heterogeneity of the included studies, diabetes mellitus and myocardial infarction were especially demonstrated to be associated with poorer outcomes in OHCA patients. Nearly all of the patients with OHCA treated by the City of Aachen EMS are subsequently hospitalized in the local CAC. Available data may be incomplete if patients were treated in other hospitals or doctor's o ces. Thus, patients with preexisting conditions may not have been known at the UKA and are mistakenly listed as without prior hospitalization and without preexisting conditions in this study. This could have led to an underestimation of the number of patients with prior hospitalizations and preexisting conditions.
In the current sample, a good neurological outcome, de ned as CPC 1 or 2, was 9.1% higher with than without lay resuscitation. Referring to the latency time, the discharge rate decreases in inverse proportion to the latency time in the current study except for those cases that were latency free. These results are consistent with another study from 1997. This study showed that the survival probability decreases by 10% on average per minute until the start of resuscitation measures in the context of resuscitation (23).
A striking feature of the current study was the low discharge rate in patients who collapsed in the presence of the EMS/emergency personnel (EP). The potential reasons for this are symptoms existing over a longer period and resulting in greater damage, which is why the EMS/EP were alerted already before the collapse occurred in these cases. Furthermore, the comparability between the EMS/EPwitnessed resuscitations and the other cases must be questioned. Cardiac arrest observed by EMS/EP occurred in only 55 of 522 cases (10.5%) wherein the resuscitation was initially started. In addition, all patients who did not receive lay resuscitation and were discharged were nevertheless resuscitated by the EMS/EP.
The average discharge rate in the current study could have been theoretically increased by 39 patients (7.5%) to an overall discharge rate of 137 patients (from 18.6-26.1%) if lay resuscitation would have been performed in 100% of the cases and similar success rate as in the current group with lay resuscitation would have occurred. Although the rate of lay resuscitation is increasing, the discharge rate was not. Thus, lay resuscitation seems not to be su cient. Therefore, identifying high-risk patients is especially important. Moreover, these patients, as well as their relatives, must obtain better training in resuscitation measures and recognition of emergencies to effectively increase the rate of lay resuscitation.
Further studies are needed referring the cause of cardiac-caused OHCA and better detection of high-risk patients as well as further campaigns for better education for CPR especially for these patients and their relatives.
Lay resuscitation was rather low with one-third in patients with OHCA and OHCA with prior hospitalization. This is within the European and internationally reported proportion of lay resuscitation in OHCA. Wnent et al. found that lay resuscitation was much more frequent if the collapse had been observed (25.2% vs. 8.0%) and that ROSC was signi cantly more frequent with lay resuscitation than without (50% vs. 41.5%) (24). A signi cant increase in lay resuscitation was noted in Germany from 2008 to 2013 (23.4-36.9%) (25). OHCA patients in the current sample who were resuscitated by lays were more often admitted to the hospital and survived more often. The higher survival rate has also been shown by previous multiple studies (26, 27).
The low rate of lay resuscitation may offer a possibility to improve the outcomes of patients with OHCA.
Effective lay resuscitation has been shown to signi cantly improve the likelihood of survival (28). As previously described, the frequency of lay resuscitation tremendously differs between countries. This is most likely because bystanders often have to overcome barriers as fear of harming the patient or the feeling of being at risk (29). However, the more bystanders are present, the higher the probability of a lay resuscitation (30). Moreover, lay resuscitations are signi cantly more frequent in public (24,31,32). This is despite the generally strong discrepancy existing between the general willingness of the population to perform lay resuscitation and the actual measures taken (24). Malsy et al. showed in a study with 303 subjects aged between 9 and 89 years that although almost everyone considered helping in an emergency, about 50% never participated in resuscitation training and more than 46% had their last training more than 20 years ago and never had a refresher (18). Therefore, measures such as annual CPR education of schoolchildren should be conducted because it improves performance effectiveness as well as self-e cacy (33).
Against the background of the current ndings that most OHCA patients have prior been hospitalized for cardiopulmonary diagnoses or had cardiopulmonary comorbidities, this may offer a unique possibility to increase lay resuscitation rate and, therefore, patient survival. Moreover, the need for improving the lay resuscitation rate in the general public, focusing on CPR training and educating the spouses and family members of patients with cardiopulmonary hospitalizations and comorbidities, is imperative. Future research should develop scores for early OHCA risk detection and measure the effectiveness of family education and training.

Conclusions
This retrospective analysis demonstrates that half of the patients with OHCA have prior been hospitalized because of cardiopulmonary diagnoses. Furthermore, three-quarters of OHCA patients suffered from comorbidities, especially cardiopulmonary diseases. However, the lay resuscitation rate was as low as only one-third in all patients and risk patients, i.e., previously hospitalized or suffering from relevant comorbidities. Offering education and training to spouses and family members of risk patients may increase the lay resuscitation rate and ultimately the outcome of OHCA patients. Availability of data and materials

List Of Abbreviations
The datasets used and/or analysed during the current study are available from the archive of the emergency physician protocols of the professional re brigade Aachen Figure 1 Flowchart showing the composition of the study cohort. Discharge rate depending on age and initial resuscitation Above Discharge rate depending on patients' age. In the 50-to 59-year-old age group, the discharge rate was signi cantly increased (p < 0.05) by lay resuscitation compared with no lay resuscitation. The other values did not differ signi cantly from each other. Below Discharge rate depending on by whom initial resuscitation was performed. The discharge