Have Outcomes After Out of Hospital Cardiac Arrest Improved Over Time?

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In this issue of Circulation: Cardiovascular Quality and Outcomes, Waldmann et al[1] describe a 5-year population-level study of patients identified as having out of hospital cardiac arrest (OHCA) in pre-coronavirus disease (COVID) Paris, France. The objective of this analysis was to assess temporal trends in patient characteristics and resuscitation outcomes among this population while applying special consideration to those in whom resuscitation was not attempted. Others have previously demonstrated that there is a large variation in outcomes after experiencing this condition across broad geographically dispersed regions.[2] Understanding and improving these outcomes is important given the high global public health burden of OHCA.

Previously, the Utstein template was developed and promoted to try to standardize reporting of outcomes after OHCA in different communities.[3] Many have applied this template to focus on outcomes after bystander witnessed ventricular fibrillation based on the rationale that such patients are treatable. Outcomes in this subset are generally regarded as a measure of the efficacy of treatment by emergency medical services (EMS). But a minority of patients with OHCA have a first rhythm that is shockable. EMS responds to OHCA without prior knowledge a patient is indeed in cardiac arrest, whether the first recorded rhythm is shockable, or whether treatment will be initiated. Thus, outcomes after resuscitation attempt or identified cardiac arrest are likely a better measure of the effectiveness of treatment by EMS. Which denominator is used has a significant and important impact on the proportion of patients reported as having a favorable outcome.[4]

In their longitudinal analysis, the Parisian investigators reported that the overall incidence of OHCA and of those without resuscitation attempted—but not those with resuscitation attempted by EMS—increased over time. As a consequence of these secular changes in the burden of OHCA, survival to discharge significantly increased among patients treated for OHCA but not among all patients with OHCA.

Why did the incidence of OHCA increase? The authors report no change throughout the study in case definition, proportion of cases reported by fire, EMS or medical examiner, or incidence of OHCA attributed to opioid use. It appears as though the most likely cause for the increased incidence was aging of the population. It is plausible that ongoing changes in EMS-based decision making may have contributed to the change in incidence, given the consistent temporal trend in changes in witnessed status overall and within the untreated group.

Does the lack of significant change in survival among those with or without resuscitation attempted suggest that improving overall outcomes is a Sisyphean task? No. Effective therapies that appear to have been relatively underused in this study include bystander cardiopulmonary resuscitation and lay use of automated external defibrillator. As well, no information is provided about use of implantable or wearable defibrillators in those identified as moderate or high risk for OHCA, training family members of those at risk of OHCA in early recognition, use of hospital-based postresuscitation care including early coronary angiography in those suspected of having acute coronary occlusion as a cause of OHCA, induced hypothermia or targeted temperature management to reduce brain and heart injury, and deferred prognosis assessment and withdrawal of life sustaining treatment. The Parisian investigators and others should continue to focus on improving outcomes in their community after OHCA.

What are the implications of this study for application of the Utstein template to compare the process and outcome of care between communities? Focusing on those patients who have bystander witnessed ventricular fibrillation could give an inflated sense of EMS performance. As well, the likelihood that the first recorded rhythm will be found to be shockable depends in part on the EMS response time interval,[5] so analyses restricted to those with a shockable rhythm can be confounded by differences in response time. Although the resuscitation community often focuses on those with a shockable rhythm, outcomes can also improve over time among those with pulseless electrical activity or asystole.[6] Since the majority of patients with OHCA have either of the latter as their first recorded rhythm, developing a better understanding of what causes these rhythms and how to prevent or treat them could hold the greatest promise for reducing the overall burden of OHCA.

If adequate resources are available, registries should collect data on all patients identified as having OHCA by EMS providers, regardless of whether treatment is initiated by bystanders or EMS providers in the field. This would provide additional insight into how much regional differences in decision to treat impact on regional differences in outcome after OHCA, and whether outcome is indeed improving over time. Note that this does not include patients who die in the field but are never assessed by EMS, as outcomes in such patients are not likely to be impacted by resuscitation attempts.

OHCA remains a common, high-impact clinical problem, which can be modified by EMS care. Ongoing efforts are warranted to understand and reduce this burden.

Disclosures

Dr Nichol reports salary support from Leonard A Cobb~ Medic One Foundation Endowed Chair in Prehospital Emergency Care, University of Washington; position as a consultant and research contract, ZOLL Circulation Inc. San Jose, CA; consultant position, Acute Care Program, General Electric Health Care Inc, Chicago, IL and Roche Inc, Chicago, IL; consultant position, Kestra Medical Technologies, Kirkland, WA; research contract from ZOLL Medical Inc, Chelmsford, MA; research contract from Abiomed Inc, Danvers, MA; research contract from General Electric Health Care Inc, Chicago, IL. Dr Salcido reports a research contract from ZOLL Medical (LifeVest), Pittsburgh, PA.