• cardiac arrest
• health care delivery

Out-of-hospital cardiac arrest (OHCA) is a major cause of mortality in industrialised countries and an emerging public health challenge in developing countries as the burden of non-communicable chronic disease—specifically cardiovascular disease—increases. Although efforts aimed at risk stratification and prevention are key, OHCA is often the first clinical manifestation of heart disease, making prevention only part of a comprehensive solution.

As a consequence, there is a need for effective treatment in the form of resuscitation. What are the public health implications of improving survival from ventricular fibrillation OHCA? Current international estimates are that there are ~12 treated ventricular fibrillation arrests per hundred thousand persons of population.1 Extrapolated to North America, Europe and Australia, this incidence translates to nearly 150 000 such arrests each year. Estimates of incidence are less certain for Asia, Africa, Central and South America, but undoubtedly ventricular fibrillation OHCA collectively strikes hundreds of thousands of lives each year in these geographies as well.

Survival is variable across communities. Aggregate estimates for survival among mature, resourced emergency response systems range from 15% to 30% for ventricular fibrillation OHCA and yet there are examples of survival consistently exceeding 50% in particular systems or circumstances, indicating a real opportunity to advance survival and in turn improve public health if we could achieve consistent best practices across systems.1 Importantly, if resuscitation is successful and an OHCA victim survives to be discharged from the hospital, the survivor experiences on average an excellent prognosis that rivals age-matched counterpart without OHCA. Most survivors return home, resume work and enjoy a satisfactory quality of life.2 Hence, strategies that can increase survival following OHCA have important personal and societal benefits.

High-yield strategies to improve resuscitation should derive from our understanding of the pathophysiology of OHCA. Scientific investigation has provided for important discovery that has defined effective resuscitation care. Collectively, these strategies are termed the links in the chain of survival and are composed of early OHCA recognition, early CPR, early defibrillation, expert advanced cardiac life support and expert post-resuscitation care. The links of the chain highlight the predominant and relentless effects of time. Time is the great enemy in OHCA; estimates are that the chances of survival decline by 5%–10% for each additional minute of delay between the onset of arrest and initial defibrillation. Professional response systems typically provide an initial shock 10 or more minutes after collapse, consequently the survival of 15%–30% in most systems. Importantly, early CPR can slow the adverse march of time, but ultimately the best recourse is to provide defibrillator shock in the first few minutes after collapse.

If provided early, the shock often achieves defibrillation, an organised cardiac rhythm, and mechanical myocardial contraction that produces clinical circulation, and in turn limits the ischaemic insult to heart, brain and other organs. If delayed, the shock may result in defibrillation but is less likely to produce organised rhythm and spontaneous circulation. In cases where shock is applied in the early moments following collapse, survival can approach 75%. Such an achievement across systems would multiply survival and translate to tens of thousands of additional well-functioning survivors each year. Hence, we understand both the challenge and the solution but cannot yet successfully achieve consistent early defibrillation. Put simply, we have effective treatments that are thwarted by operational realities of community implementation.

As a potential real-world solution, one approach to achieve early defibrillation is to strategically locate automated external defibrillators (AEDs) accessible to the public so that they may provide defibrillation prior to professional response. This strategy—termed public access defibrillation or ‘PAD’—is based on physiological understanding and supported by observational and interventional research.3 Yet, estimates suggest that less than 5% of ventricular fibrillation OHCA receive early defibrillation with a public  access AED indicating that the strategy in its current implementation form has a modest and incomplete public health benefit.4

The investigation by Deakin et al in this edition of Heart is an interesting and provocative investigation on how to leverage the PAD resource more effectively.5 The investigation maps suspected cardiac arrests identified by the dispatch centre against the geocoordinates of the AED registry for the South Central Ambulance Service region of England. The mapping study smartly leverages the two data platforms to investigate the potential to incorporate PAD in cases of suspected OHCA. The study finds that a PAD was available within 100 m of the event in almost 6% of arrests during daytime hours and fell to less than 2% during overnight hours. The study determined that a PAD might theoretically be retrieved prior to professional rescuer arrival in about 25% of suspected OHCA.

The work advances the field by using techniques that incorporate realistic assumptions in modelling the potential of PAD involvement. The investigators do their best to account for day and night-time events and the reality that some AEDs are not accessible outside daytime hours, an assumption that reduced the availability of AEDs by two-thirds. The study used advanced mapping techniques that plotted the real pedestrian distance to the AED as opposed to the straight-line, ‘as-the-crow-flies’ distance. The model used realistic assumptions with regard to retrieval: 2 min for emergency dispatcher communication, 1 min at the (AED) site to locate the AED and 4 mph average walking speed. These logistics will ultimately have real implications for the success of such a strategy.

And yet the study has some acknowledged limitations that are generalisable to all systems considering how this strategy might impact OHCA outcome. The investigation appropriately uses dispatch-suspected arrest, though dispatch inevitably fails to identify some OHCA in a timely manner. The model presumes that the AED registry is accurate and robust. The investigators assume that the circumstances of each event support attempted AED retrieval. This assumption typically would require multiple rescuers. Even if multiple rescuers are available, there is the question of whether bystander CPR might suffer if an ‘extra’ rescuer left the scene for several minutes instead of staying on scene to assist with CPR or at least provide encouragement. Finally, only a fraction of OHCA presents with ventricular fibrillation, so that AED retrieval will often not have direct benefit for the patient. These limitations highlight the theoretical simulated nature of the current study—as smart as it is. The reality is that there are other very real obstacles and challenges to layperson AED use that may become evident only when such a strategy ‘goes live’.6

Importantly, the investigation assumes that all events—public and residential (private)—are eligible for this strategy. The approach has persons leave and return to a private residence—where the majority of arrests occur—to apply the AED prior to professional rescuers. The strategy thus transforms the term ‘public access defibrillation’, which was borne primarily of the idea that AEDs be accessible for public setting OHCA. Indeed, we should challenge the paradigm of PAD beyond the conventional public setting use. The AED is agnostic to the location of the arrest.

The investigation pushes us towards a new paradigm where we connect rescuers and potentially lifesaving technology to OHCA victims regardless of their physical location through smart technologies.7 These models include mobile community rescuers, potentially equipped with AEDs or directed to AED locations, who are dispatched simultaneously with professional response to suspected OHCA. This social media strategy can potentially recruit and mobilise a just-in-time cohort of rescuers to provide early CPR and AED prior to professional rescuer arrival. The approach could include private in-home response, a strategy that has seen some early success in Europe. Such an all-access response in North America is largely theoretical, though survey of public safety personnel suggests initial interest and support.8 The enlistment of human responders for all-access CPR and defibrillation may even be supplemented by AED delivery via drone or other modes of delivery in a select subset of OHCA victims.

Finally, we should consider whether we can achieve a low-cost technology that serves as a bridge for the OHCA victim until the industrial-strength AED arrives. Current AEDs are designed and engineered to operate correctly 99.9% of the time, deliver tens of shocks and be reusable. Although speculative, a bridge device likely could be engineered for far less though may only serve a single event and not achieve the same near-perfect operational proficiency. What if the bridge device was a personal or home safety item that would be standard in a consistent location so that the emergency dispatcher could highlight in a suspected OHCA call? Analogous to the home fire extinguisher, the bridge device may provide definitive, lifesaving therapy that could circumvent the need for advanced resuscitation of professional rescuer. Moreover, the bridge would not delay professional response while fast-tracking access to early defibrillation.

The take-home is that we should think creatively about how to deliver a proven therapy to the right place at the right time. A multifaceted early defibrillation model may ultimately prevail—and should consider the realities of a given community as effective implementation relies on local factors that can accelerate ‘public access’ towards ‘all-access’ defibrillation.