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Original research
Out-of-hospital cardiac arrests in the young population; a 6-year review of the Irish out-of-hospital cardiac arrest register
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  1. Richard Tanner1,
  2. Siobhan Masterson2,
  3. Joseph Galvin3,
  4. Peter Wright4,
  5. David Hennelly5,
  6. Andrew Murphy6,
  7. Gerard Bury7,
  8. Cathal O'Donnell5,
  9. Conor Deasy8
  1. 1 Cardiology, Cork University Hospital Group, Cork, Ireland
  2. 2 Discipline of General Practice, University College Galway, Galway, Galway, Ireland
  3. 3 Mater Misericordiae University Hospital, Dublin, Ireland
  4. 4 Public Health, University College Galway, Galway, Galway, Ireland
  5. 5 National Ambulance Service, Health Service Executive, Dublin, Ireland
  6. 6 Department of General practice, University College Galway, Galway, Galway, Ireland
  7. 7 University College Dublin, National University of Ireland, Dublin, Ireland
  8. 8 Emergency Medicine Department, Cork University Hospital Group, Cork, Ireland
  1. Correspondence to Richard Tanner, Cardiology, Cork University Hospital Group, Cork T12DC4A, Ireland; richard.tanner{at}umail.ucc.ie

Abstract

Study purpose Out-of-hospital cardiac arrests (OHCA) in the young population have only been examined in a limited number of regional studies. Hence, we sought to describe OHCA characteristics and predictors of survival to hospital discharge for the young Irish population.

Study design An observational analysis of the national Irish OHCA register for all OHCAs aged ≤35 years between January 2012 and December 2017 was performed. The young population was categorised into three age groups: ≤1 year, 1–15 years and 16–35 years. Multivariable logistic regression was used to determine the independent predictors of survival to hospital discharge.

Results A total of 1295 OHCAs aged ≤35 years (26.9% female, median age 25 (IQR 17–31)) had resuscitation attempted. OHCAs in those aged ≥16 years (n=1005) were more likely to happen outside the home (38.5% vs 22.8%, p<0.001) and be of non-medical aetiology (59% vs 27.6%, p<0.001) compared with those aged <16 years (n=290). Asphyxiation, trauma and drug overdoses accounted for over 90% of the non-medical OHCAs for those 16–35 years. Overall survival to hospital discharge for the cohort was 5.1%; survival was non-significantly higher for those aged 16–35 years compared with those aged 1–15 years (6.0%, vs 2.8% p=0.93). Independent predictors of survival to hospital discharge included bystander witnessed OHCA, a shockable initial rhythm and a bystander defibrillation attempt.

Conclusions The high prevalence of non-medical OHCAs and the OHCA location need to be considered when developing OHCA care pathways and preventative strategies to reduce the burden of OHCAs in the young population.

  • paediatric cardiology
  • epidemiology
  • cardiac epidemiology

Data availability statement

Data are available upon reasonable request. Data was sourced from the national Out-of-Hospital Cardiac Arrest Register (OHCAR). Applications for viewing or use of original data are processed on an individual case basis and at the discretion of the Steering group. Further information is available at https://www.nuigalway.ie/ohcar/.Use of data reported in this study will be made available upon reasonable request to the corresponding author.

http://dx.doi.org/10.1136/postgradmedj-2020-137597

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    Introduction

    Out-of-hospital cardiac arrests (OHCA) in the young population (aged ≤35 years) are associated with a poor prognosis and a significant number of years of potential life lost. Survival after OHCA in the young has been reported between 2% and 24%, with notable differences between the regions examined and a paucity of national OHCA outcome data for this patient cohort.1–4

    Understanding key OHCA characteristics such as OHCA location and aetiology for different age groups is important when developing preventative strategies, tailoring resuscitation care pathways and enhancing OHCA training programmes. For OHCA aetiology, previous, largely urban studies have found an increased frequency of non-medical OHCA in young adults (1–35 years) and sudden infant death syndrome (SIDS) to be a significant contributor to infant OHCA (<1 year).1 2 5 It is unclear if these OHCA characteristics can be extrapolated to Ireland.

    The young population has unique challenges associated with improving prearrival care. Basic medical interventions initiated by bystanders prior to trained medical professional contact are, by comparison to older patients, arguably more confronting and challenging to perform for lay bystanders. Many OHCAs occur in the family home for younger patients where family members experience significant psychological stress during the event which can be associated with failure to recognise cardiac arrest and promptly initiate cardiopulmonary resuscitation (CPR).6 Little is known about the emergency medical service (EMS) response times, frequency of bystander CPR and use of automated external defibrillators (AEDs) in the young Irish population.

    The aim of this study is to describe the incidence, characteristics and survival for OHCAs in Ireland over a 6-year period for the young population.

    Methods

    Data source and population

    The Irish out-of-hospital cardiac arrest register (OHCAR) was analysed.7 OHCAR has full national coverage since 2012 and comprises all patients who suffer an OHCA which is confirmed and attended by emergency services with data being collected using the Utstein template. OHCAs where resuscitation is not attempted are excluded from OHCAR. To ensure accurate data entry, missing case identification is undertaken on a quarterly basis to capture cases not directly reported to OHCAR and all cases are validated before being entered onto the OHCAR database.

    In 2016, there were 2 323 959 people aged ≤35 years living in Ireland and 34% of this population lived in rural area (defined as the population residing in all areas outside clusters of 1500 or more inhabitants). The most common forms of accommodation were detached (42%) and semidetached (28%) dwellings.8

    EMS in Ireland

    The National Ambulance Service (NAS) provides a statutory EMS response nationally with Dublin Fire Brigade also providing a statutory response that is concentrated in the greater Dublin area. Dispatcher assisted bystander CPR via telephone is used nationally. In addition, there are community first responder (CFR) groups (n=239 as of June 2019) working in collaboration with the NAS situated across Ireland who receive a text alert from the National Emergency Operations Centre and can corespond to these calls. The Pre-Hospital Emergency Care Council (PHECC) is the regulator for EMS, statutory and voluntary, in Ireland. Paramedics are guided by Clinical Practice Guidelines (CPG) that are produced by the PHECC based on the recommendations of the International Liaison Committee on Resuscitation.9 For a suspected OHCA, the CPG recommends attempting resuscitation unless there are definitive indicators of death (including decomposition, rigour mortis, injuries incompatible with life). It is also advised that consideration be given to cessation of resuscitation if a patient is unresponsive, has no signs of life and remains in asystole after three cycles of CPR.9

    Subjects

    The young population was defined as those aged ≤35 years to allow comparison with previous studies.1 10 This cohort was subdivided into three age groups; aged <1 year, aged 1–15 years inclusive and those aged 16–35 years inclusive. Those aged <16 years were classified as paediatric OHCAs in keeping with the National Clinical Programme for Paediatrics definition of a paediatric case. Furthermore, resuscitation of OHCAs aged <16 years are guided by a separate CPG and are transported to a hospital with designated paediatric facilities.9 OHCAs aged less than 1 year were entered into a separate group given the unique characteristic of SIDS in this group which may distort results for the remainder of the very young population.

    All OHCAs with resuscitation attempted between 1 January 2012 and 31 December 2017 were included. OHCAs witnessed by EMS were excluded in keeping with other similar studies. OHCA aetiology was presumed to be medical unless it was known or likely to have been caused by drug overdose, submersion, trauma, asphyxia, electrocution or any other non-cardiac cause as documented in the patient care report. The presumed aetiology of non-medical OHCAs was analysed in detail for those aged 1–15 years and those aged 16–35 years.

    Statistical analysis

    Analysis of data extracted from OHCAR was completed using the Software package IBM SPSS Statistics V.25. Continuous variables are presented as median with IQR. Categorical data are presented as frequencies and percentages. A Pearson’s χ2 test was used to examine differences between categorical data. Statistical significance was defined at a level of p≤0.05.

    The impact of clinical characteristics on survival to hospital discharge was tested in univariable logistic regression models. Characteristics that reached statistical significance were then entered in a multivariable logistic regression model. Independent variables used in the regression analysis were assessed for multicollinearity and no predictor variable reached a variance inflation factor >1.5. Multivariable logistic regression analysis was undertaken to determine the predictors of the main outcome (survival to hospital discharge) for those aged 1–35 years inclusive with results are presented as adjusted ORs (AORs) with 95% CIs. Age and EMS response times were included as continuous covariates; all remaining covariates were categorical. Those aged less than 1 year were excluded from the regression analysis given the anticipated low rate of survival to hospital discharge for this group.

    Results

    Over a 6-year period (2012–2017), 1295 OHCAs aged ≤35 years were attended to and had resuscitation attempted by EMS in the Ireland. Unadjusted incidence of OHCA for this cohort over the study period was 9.3/100 000 persons per year.

    OHCA characteristics

    Baseline characteristics are shown in table 1. The median age was 25 (IQR 17–31) years and 73.1% (n=946) were male. With increasing age category, the proportion of OHCAs that occurred outside the home increased as did the frequency of OHCA with non-medical aetiology. Compared with those aged <16 years OHCAs were more likely to occur outside the home for those aged 16–35 years (38.5% vs 22.8%, p<0.001). Although those aged <1 year had the highest frequency of OHCA in the home at 91.2%, this group had the lowest rate of witnessed OHCA at 19.3%. For those aged 16–35 years, a subanalysis of OHCAs outside the home (n=304) showed the most common location to be the street (n=183, 60.2%), followed by public buildings (n=45, 14.8%) and recreational centres (n=35, 11.4%), figure 1.

    View this table:
    Table 1

    Utstein-based patient and event characteristics categorised by patient age group

    Figure 1
    Figure 1

    Location of OHCA occurring outside the home for 16–35 years group (n=389). GP, general practitioner; OHCA, out-of-hospital cardiac arrests.

    OHCAs in those aged 16–35 years were more likely to have a non-medical aetiology compared with those aged <16 years (59% vs 27.6%, p<0.001). Further analysis of non-medical OHCA aetiology in the age category 1–15 years (n=71) showed trauma (n=29, 40.8%), asphyxiation (n=24, 33.8%) and drowning (n=13, 18.3%) to be the most prevalent aetiologies, figure 2. In contrast to those aged 1–15 years, the most common non-medical cause of OHCA for those aged 16–35 years was asphyxiation (n=214, 39.3%), while drug overdose was also prevalent (n=147, 27%), figure 2.

    Figure 2
    Figure 2

    Aetiology of non-medical OHCA for the those aged 1–15 years and 16–35 years. OHCA, out-of-hospital cardiac arrests.

    Prearrival care

    Although bystander CPR rates were similar between the three age categories, the frequency of attachment of defibrillator pads before EMS was low and varied between age groups, table 1. For those with a shockable initial rhythm, defibrillation was attempted by EMS (n=96, 70%), a bystander (n=37, 27%) or not attempted (n=4, 3%). The use of defibrillator pads was notably lower for those aged less than 1 year (n=5, 4.4%) and this correlated with the lowest frequency of defibrillator shocks pre-EMS arrival for the three age categories. An increasing use of defibrillator pads was observed for each 2-year increment within the 6-year study period, figure 3.

    Figure 3
    Figure 3

    Change in application of defibrillator pads pre-EMS arrival over time (n=1295).

    OHCA outcomes

    Survival to hospital discharge for the entire cohort (≤35 years) was 5.1%. OHCAs with an initial shockable rhythm had a higher likelihood of survival to hospital discharge than those whose first rhythm analysed was non-shockable (30.5% vs 1.9%, p<0.001). Although those aged 16–35 years had a higher rate of survival to hospital discharge than those aged 1–15 years, it did not reach statistical significance (6.0%, vs 2.8%, p=0.93). The rate of survival to hospital discharge was found to differ based on presumed OHCA aetiology within each age category, figure 4. Within the 16–35 years group, drowning was associated with the highest rate of survival to hospital discharge, whereas a traumatic OHCA was associated with the lowest prognosis.

    Figure 4
    Figure 4

    Survival to hospital discharge based on OHCA aetiology (n=1295). OHCA, out-of-hospital cardiac arrests.

    The association of potential predictor variables with the outcome survival to hospital discharge is summarised for those aged 1–35 years in table 2. A shockable initial rhythm was the greatest independent predictor of survival to hospital discharge (AOR: 11.08, 95% CI: 5.79 to 21.20, p<0.001), followed by bystander witnessed OHCA (AOR: 2.73, 95% CI: 1.42 to 5.23, p<0.003) and a shock being delivered before EMS arrival (AOR: 2.33, 95% CI: 1.02 to 5.29, p<0.044). Presumed medical aetiology, bystander CPR and OHCA outside the home were not significantly associated with survival to hospital discharge in the multivariable analysis.

    View this table:
    Table 2

    Logistic regression analysis of predictors of the outcome survival to hospital discharge in patients 1–35 years (n=1181)

    Discussion

    This study examined the characteristics and outcomes for 1295 OHCAs in the young Irish national population over a 6-year period. Important differences in OHCA location, aetiology and frequency of AED use between age groups were identified.

    A high proportion of non-medical OHCAs were observed in our study, with increasing frequency as age category increased. Non-medical OHCAs were more prevalent than observed in those aged ≥70 years from a previous study on the Irish OHCAR (52% vs 3.3%).11 For the same age group (≤35 years), a 2010 study from London reported a similar frequency of OHCAs having a non-medical cause of OHCA (58.6% vs 52% in London).1 However, a 2017 paper from the Pan-Asian Resuscitation Outcomes Study (PAROS) found a higher rate of non-medical OHCA for those aged 16–35 years (70.1% vs 59%).10 Non-medical OHCAs have unique characteristics that need consideration when developing effective OHCA care pathways. It is notable that non-medical causes were prevalent in those aged 16–35 years and that asphyxiation and drug overdose were the dominant mechanisms causing OHCA; hanging and intentional drug use were the usual settings for these incidents. Central Statistics Office data for 2012–2016 show that 2338 suicides occurred during that period with a reported rate of 30/100 000 among those aged 20–24.12 In the same period, National Drugs Related Deaths Index data show that 1845 poisoning deaths occurred among those receiving methadone treatment for opiate dependence.13 Data from this study show that EMS is significantly involved in the care of patients who attempt suicide and who overdose while using illicit drugs and that the survival rates from these incidents are extremely poor. These EMS data highlight key societal issues requiring better preventive and care strategies in opiate dependent and at risk of self-harm populations. Public health and preventative strategies such as widespread availability of naloxone, crisis intervention services, water safety awareness and increasing psychological support for people with depression and suicidal ideation may reduce the incidence of non-medical OHCAs in this patient cohort.

    Overall survival to hospital discharge for OHCAs in the young population was in keeping with a previous study on the same age group (5.7% compared with 5.1%).1 Having a witnessed OHCA, a shockable initial rhythm and/or a shock delivered before EMS arrival significantly increased the likelihood of survival to hospital discharge. Our rate of survival to hospital discharge for those aged 1–16 years at 2.8% was low in comparison to similar cohorts in London, England (6.5%) and Victoria, Australia (11%).1 14 However, direct comparison of these cohorts is difficult due to differences in OHCA characteristics and demographics such as the population density of each region. It is also plausible that attempted resuscitation for some OHCAs is futile and this may impact on the denominator (the number of OHCAs with resuscitation attempted) used for calculating survival to a greater extent in the younger population cases given the particularly emotionally challenging nature of paediatric OHCA. However, there is no clear definition of medical futility and comparing the impact of attempting futile resuscitation on survival between regions is challenging. A paper from the PAROS study based on 2009–2013 data reported 1-month survival after OHCA in those aged 16–35 years to be 7.8%.10 Although the outcome survival definition for this study is different and EMS witnessed cases were included, this is relatively in keeping with our survival to hospital discharge rate of 6% for those aged 16–35 years. For our youngest age group (≤1 year), there was less than five survivors over a 6-year period. A similarly poor rate of survival to hospital discharge was also seen for OHCAs in those aged ≤1 year in the Resuscitation Outcomes Consortium—Epidemiological Registry (ROC-Epistry) database (3.8%) and Victoria, Australia (4.1%).4 14 SIDS likely makes a significant contribution to OHCAs in this age group, particularly for those aged <6 months. Given that resuscitation is largely unsuccessful in SIDS, resources should be directed to education on preventive measures for SIDS (eg, avoiding smoking in the house, avoiding cosleeping, placing infants in the supine sleeping position).15 16

    Focusing on prehospital care is paramount to improving OHCA outcomes given that survival to hospital discharge is dismal unless return of spontaneous circulation is achieved before reaching the hospital.17 The median time from receiving an OHCA call to EMS being on scene was notable longer in our study (11 min) compared with London (7 min) and Victoria, Australia (8 min).1 2 Improving EMS response times is a key element of the One Life project which is focused on systematically improving outcomes for patients who suffer an out-of-hospital cardiac arrest in Ireland. However, challenges exist in the form of limited resources and delivering an efficient service to a population with a significant proportion of people living in rural areas with a low population density.1 18 CFRs are a fundamental part of the One Life project as they can enable a timelier initiation of resuscitation for OHCAs which is critical given the high frequency of OHCA occurring in the home (>60% in all age categories in our study) and the knowledge that each minute without CPR and defibrillation reduces the chance of survival by 7%–10%.19 20 Furthermore, a recent 17-year review of paediatric OHCA reported survival to be significantly higher if the first shock was delivered by either a first responder or public AED compared with paramedics (83.3% vs 40.0%, p = 0.04).14 Notably, the American Heart Association recommends a call-to-shock time interval of <5 min which it acknowledges cannot be reliably achieved with conventional EMS services.21 The role of CFRs is likely to play a particularly important role in rural areas which are associated with protracted EMS response times.22 23 Encouragingly, an increasing use of AEDs by bystanders was observed over the 6 year period and the benefit of a shock being delivered on the likelihood of survival to hospital discharge can be seen in our multivariable regression analysis. However, significant variation was seen between age groups. The frequency of AED use in OHCA use has been rarely studied but at least one study suggests a lower use in children (aged 1–8 years) compared with adults (16.3% vs 28.3%), this is despite evidence that AEDs improve the chance of neurologically favourable survival in paediatric OHCA (aged 1–17 years).24

    Bystander CPR rates were higher in our study than reported in London (68.4% vs 34.4%) for the overall cohort and the PAROS register (66.7% vs 31.9%) for those aged 16–35 years.1 10 However, bystander CPR failed to reach significance as a predictor of survival to hospital discharge in our regression analysis. This likely reflects the unselected and heterogenous cohort of OHCAs undergoing CPR and is not unique to our study.2 5 Interestingly, a recent study from the All-Japan OHCA Registry on children aged ≤17 years showed that conventional CPR (with rescue breaths) was associated with significantly better neurological outcomes than compression only CPR (7.2% vs 1.6%; OR: 5.54, 95% CI: 2.52 to 16.99) for OHCAs on non-cardiac aetiology with no significant difference between the two CPR methods for OHCA of cardiac aetiology.25

    Limitations

    This study has a number of limitations due to its retrospective nature. The Irish OHCAR only includes patients on whom resuscitation was attempted, hence the true incidence of OHCAs is likely underestimated. Comparison of data with other studies is limited by the lack of published data on the young OHCA population from national OHCA registries. Information on neurological status (cerebral performance score) was incomplete and therefore not included. Finally, the sample size for patients aged <16 years is relatively small and the absolute number of survivors was not reported for those aged less than 1 year to preserve patient anonymity.

    Conclusions

    Important differences in OHCA location, aetiology and survival exist between age categories within the young Irish OHCA population. These OHCAs characteristics should be carefully considered when developing care pathways to improve survival in the young OHCA population. Future studies will need to identify barriers to increasing AED use, improving EMS response times and assess preventative strategies that can reduce the burden of OHCAs in the young population.

    Main messages

    • Out-of-hospital cardiac arrests (OHCAs) in the young population have been examined in a very limited number of regional studies and have unique characteristics.

    • Over 50% of OHCAs within the young Irish population (≤35 years) are of non-medical aetiology with trauma, asphyxiation and drug overdoses being the predominant OHCA mechanisms.

    • The likelihood of survival to hospital discharge was increased when there was an initial shockable rhythm, the event was witnessed and when defibrillation was attempted before the arrival of emergency medical services.

    Current research questions

    • Why is bystander cardiopulmonary resuscitation not associated with an increased likelihood of survival to hospital discharge in the young out-of-hospital cardiac arrests (OHCA) population?

    • What are the barriers to improving survival in the young OHCA population?

    • What preventative strategies can be developed to reduce the burden of non-medical (asphyxiation, drug overdoses, drowning and sudden infant death) OHCAs in the young population?

    Data availability statement

    Data are available upon reasonable request. Data was sourced from the national Out-of-Hospital Cardiac Arrest Register (OHCAR). Applications for viewing or use of original data are processed on an individual case basis and at the discretion of the Steering group. Further information is available at https://www.nuigalway.ie/ohcar/.Use of data reported in this study will be made available upon reasonable request to the corresponding author.

    Ethics statements

    Ethics approval

    Ethical approval for this study was granted by the Clinical Research Ethics Committee of Cork Teaching Hospital (reference ECM 4 (b) 05/03/2019). Results that yielded <5 cases per category were not reported to preserve patient anonymity in accordance with the OHCAR data sharing policy.

    Acknowledgments

    We wish to acknowledge staff of the OHCAR who provided us with original anonymised data.

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    Footnotes

    • Contributors Coauthor contribution. RT: lead author, study design, collection on data, drafted manuscript. SM: study methodology, guided data analysis and edited final draft. JG: analysis of data, expert advice on sudden cardiac death, edited manuscript. PW contributed to study conception, reviewed paper and provided critical review. DH expert advise on national ambulance service, analysed data, approved final manuscript. AM contributed to data acquisition, critically reviewed manuscript. GB critically reviewed paper and provided editing of manuscript. CO’D contributed to data analysis, reviewed paper and approved final draft. CD: study supervisor, contributed to study design, data analysis and critically reviewed final manuscript. All coauthors have approved the final draft.

    • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

    • Competing interests None declared.

    • Provenance and peer review Not commissioned; externally peer reviewed.