The Flatlining of Cardiac Arrest Survival: Can We Revive the Upward Trend?

Elizabeth D. Paratz; André La Gerche

Disclosures

Eur Heart J. 2022;43(46):4830-4831. 

Graphical Abstract

A range of public health and education strategies resulted in a marked improvement in survival in the decade from 2000. However, there has been a more recent plateau in these gains. More innovative strategies are now required to shorten times to defibrillation.

Sudden cardiac death (SCD) is a leading cause of death for men and women of all ages, with a predominance of inherited heart disease in the young and acquired conditions such as coronary heart disease in older populations.[1] Strategies aimed at reducing the incidence of SCD could address multiple steps in the prevention pathway: better awareness, better risk identification, earlier and more effective resuscitation measures, and optimal post-arrest care.[2] As few as one in 10 victims survive to hospital discharge, suggesting that there is ample opportunity for improvement.[3] Guiding clinical advances is the need for quality research with the potential to identify associations between variations in care and clinical outcomes. In this edition of European Heart Journal, Jerkeman et al. provide insights from the longest-running cardiac arrest registry in the world, by detailing associations in public health measures and resulting changes in arrest outcomes.[4]

The Swedish Cardiopulmonary Resuscitation Registry (SCRR) comprises 30 years of cardiac arrest outcome data among the approximate 10 million residents of Sweden. The most important insight of the paper is that Swedish cardiac arrest survival rates were observed to improve markedly from 1999 to 2011, but then plateaued until current times. It is hypothesized that reasons underlying the initial improvement included the introduction of telephone-assisted cardiopulmonary resuscitation (CPR), a focus on bystander CPR education, increasing public access defibrillator availability, and improvements in coronary revascularization. Certainly, the authors' data demonstrate an impressive leap in bystander CPR rates from 30.9% to 82.2% in 2020, placing Sweden as world leaders in bystander CPR.[5] Improvements in bystander CPR rates may explain the reduction in median time from collapse to CPR from 12 to 2 min over 30 years, and increasing population density and traffic may explain the competing constraints of increasing time from dispatch to ambulance arrival. As the authors conclude, these data are a simultaneous celebration of world-leading implementation of bystander CPR and a call for further innovations to generate the next life-saving leaps.

Following early improvements, the recent plateau in cardiac arrest outcomes raises the question as to whether we are reaching a ceiling in the efficacy of current out-of-hospital cardiac arrest (OHCA) resuscitation treatments? If not, what is a reasonable aspirational target? The SCRR provides an intriguing insight into potential outcomes of 'gold standard' resuscitation, by means of simultaneous data for in-hospital cardiac arrests (IHCAs) against which OHCA outcomes can be compared. IHCAs are frequently witnessed, CPR and defibrillation are very prompt, and advanced resuscitation is immediately available. As a result, more than half of patients aged under 60 years were reported to survive an IHCA in Sweden. These survival statistics may be considered a benchmark of what might be possible with increased resourcing and innovations for OHCA resuscitation efforts. If we could be immediately alerted to community arrests, alert bystanders to CPR, and have novel means of delivering rapid defibrillation, then we might expect the observed plateau in OHCA survival to start shifting favourably towards the benchmark reported here for IHCA outcomes (see Graphical Abstract).

Before fully embracing the sober message of flattening OHCA survival statistics, it is important to consider potential confounders. In the SCRR, cardiac arrest cases were included if resuscitation was attempted; a definition which is shared by some other cardiac arrest registries globally.[6] The number of cardiac arrests increased notably throughout the registry, from approximately 1800 cases per annum at the start of the registry to approximately 5000 cases per annum in recent years. This increase is mainly due to the rolling recruitment of hospital and ambulance units within Sweden. In addition, greater bystander CPR education may have led to greater willingness to initiate CPR and thus an increase in the proportion of OHCA subjects considered eligible. In other words, there may have been a simultaneous increase in both the numerator (OHCA survivors) and denominator (OHCA victims in whom resuscitation was attempted) contributing to the observed plateau in survival statistics. The 4.8-fold increase in bystander CPR, the greater increase in unwitnessed than in witnessed arrests, and the 60% reduction in initial shockable rhythm, all point toward a changing OHCA population: one in which a greater proportion may have arrested some time prior to discovery, with no shockable rhythm, in whom a poor outcome is probable. There are no disadvantages to greater bystander willingness to attempt resuscitation. Without an attempt at CPR, survival outcomes are dismal.[5] However, in future iterations of the SCRR, it would be very interesting to track the proportion of OHCA victims in whom CPR is attempted.

A more granular understanding of the underlying causes of OHCA is another refinement of the registry which could inform future preventive interventions. In the SCRR, cardiac arrests are defined as either 'presumed cardiac', or 'presumed non-cardiac' when accompanied by documentation of precipitants such as drowning or trauma. All cardiac causes of OHCA are therefore limited to a category of 'heart disease'. Collaborations with hospital and forensic services to identify detailed underlying cardiac causes would enable us to interrogate whether there may be changes in the incidence and survival of specific cardiac aetiologies responsible for the cardiac arrest.[7,8] The authors suggest that improvements in the treatment of acute coronary syndrome over the past three decades may have driven a significant proportion of the improvements in observed outcomes. This assertion is supported by the disease-specific data provided from the IHCA arm of the registry, in which there has been a marked reduction in arrests due to myocardial infarction, simultaneously with improved survival in this specific setting. Similarly in the OHCA cohort, the proportion of cardiac arrests with 'heart disease' reduced over time (along with the proportion of shockable cardiac arrests) and survival of these cases increased. It would be extremely helpful to dissect whether these temporal changes are due entirely to advances in the peri-arrest care of acute coronary syndromes or whether improvements have also been realized in patients with cardiomyopathies and other arrhythmic disorders. Disease-specific risk identification and preventive strategies are going to be critical for future advancements in sudden cardiac death prevention, especially when we consider the rapidly evolving era of cardiac genomics.

The strength of Jerkeman et al.'s data is that the relatively large population and consistent definitions enable an excellent snapshot of the trends in cardiac arrest science. The authors propose a range of ambitious initiatives to drive future improvement in arrest survival: wearable technology arrest alerts, mobile phone-initiated recruitment of bystanders, drone-mediated delivery of defibrillators, 'in-the-field' extracorporeal membrane oxygenation, and geolocation assistance to reduce ambulance times. This Swedish collaborative registry deserves praise. High-quality clinical registries such as SCRR enable us to monitor the incremental real-time benefit of each innovation. Informed and systematic implementation of many small steps should enable us to favourably disrupt the current plateau in cardiac arrest survival.

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