• Cardiac arrest

Until a few decades ago, nearly no one survived out-of-hospital cardiac arrest.1 A recently published meta-analysis of 79 outcome studies from around the world reported an overall survival rate of 7.6% that had not changed throughout the past three decades.2 Recent data are more optimistic and several studies have reported survival rates above 10%.3–6 The increasing number of patients surviving to hospital discharge have directed focus towards long-term outcomes of survival and function following cardiac arrest.7 8

In their Heart manuscipt Andrew et al 9 focused on very long-term survival among 3449 patients discharged alive after out-of-hospital cardiac arrest in the years from 2000 to 2014. The setting was Victoria State, Australia, with a population of approximately 5.9 million people and an area of 2 27 000 km². With a mean follow-up time of 12 years, Andrew and colleagues demonstrated that 8 out of 10 discharge survivors were alive after 5 years, 7 out of 10 after 10 years and 6 out of 10 after 15 years. The study reports a more than fivefold increased risk of death compared with the background population during the first year but similar relative risk at 5 years and beyond. The survival curve is steep during the first year, after which flattening occurs and the line is almost perfectly linear for the remaining years. It is expected that cardiac arrest survivors should have an increased mortality risk related to the reason for their cardiac arrest, but it is surprising that it stabilises so quickly. The observational nature of the study does not allow distinction between stabilisation of risk factors and depletion of a high-risk subpopulation.

Andrew et al examined factors related to long-term survival. A multivariable Cox regression model of survival stratified by the initial arrest rhythm including age at the time of arrest, gender, arrest aetiology, witness and bystander CPR status, EMS response time, arrest location, metropolitan versus rural region and transport to a PCI-capable hospital indicated little impact of peri-arrest factors, whereas transport to a PCI-capable hospital was associated with increased long-term survival. Also, the ability to return to home from hospital was associated with longevity, and so were return to work and quality of life measures within 1 year after cardiac arrest in a separate model including 1-year survivors only.

The study by Andrew et al provides evidence that out-of-hospital cardiac arrest survivors can live a long life after cardiac arrest, and this was most prominent for patients with a favourable functional outcome within 1 year after cardiac arrest. The authors conclude that further investigation of in-hospital clinical practices and postarrest rehabilitation initiatives that optimise a patient’s recovery is needed, given the association between favourable recovery and long-term survival. In the study by Andrew et al, only direct transport to a PCI-capable facility among many investigated baseline and peri-arrest variables was related to long-term survival. This observation may reflect a value of procedures performed or it may reflect a group of patients where the willingness to perform additional procedures was high. While it may be that witness status and bystander CPR are of less importance once discharge survival is achieved, bystander-witnessed patients and patients who received bystander CPR may be more likely to be transported directly to a PCI hospital. Similarly, bystander-witnessed patients and patients who received bystander CPR may also be more likely to return to their own home rather than a care facility or rehabilitation centre, as well as these patients may be more likely to return to work and/or have favourable physical/functional recovery.7 As such, although the authors note that direct transport to a PCI-capable facility, return to own home and return to work and/or other favourable physical/functional recovery were the only factors associated with longevity, it may be that peri-arrest factors such as witness status and bystander CPR influenced short-term survival and thereby potentially also long-term survival.

In resuscitation science, peri-arrest factors are often correlated and statistical model building can be subject to multicollinearity issues, where ‘the winner takes it all’. This may be an explanation as to why bystander CPR and other peri-arrest factors had little impact in this study by Andrew et al. In continuation, analyses in the study by Andrew et al were stratified according to the initial heart rhythm to satisfy the proportional hazards assumptions. It is commonly seen that patients with bystander-witnessed arrest and in whom bystanders initiated CPR are more likely to have an initial shockable rhythm relative to their counterparts. This may be because the no-flow or low-flow time is shorter in witnessed arrests, where the emergency medical services in most cases are alerted immediately following recognition of cardiac arrest, as well as the no-flow or low-flow time is even shorter, where bystanders also initiated CPR.

In conclusion, irrespective of above methodical speculations, the study by Andrew and colleagues demonstrates a very high long-term survival after out-of-hospital cardiac arrest if the patients had survived to hospital discharge. The study inspires to a series of new questions. First, further insight into factors that are important for obtaining long survival are necessary to improve the outlook for these patients. Second, the marked result that survival quickly approached the background population should inspire to studies of whether there is early depletion of a high-risk group of patients such that few interventions are necessary after a certain time. Third, and finally, because a larger number of people survive out-of-hospital cardiac arrest and remain alive in long-term outcome assessments, further insights are needed into the long-term quality of life and other indicators of functional status.