The Epidemiology of EMS-Witnessed Cardiac Arrest in a U.S. Patient Cohort

Introduction: Out-of-hospital cardiac arrest is fatal without immediate aggressive intervention. Arrests witnessed by EMS personnel are associated with more favorable neurological outcomes, likely because of earlier resuscitation. It is also possible that, if signs of impending arrest are recognized early, some arrests may be avoided. The goal of this study was to describe the epidemiology of EMS-witnessed cardiac arrests.

Methods: This retrospective analysis was conducted using deidentified patient care records from a large national research database maintained by ESO. All adult (18 years and older) arrests from 2018 were included. Descriptive statistics were calculated to describe patient demographics, arrest characteristics, and presence of return of spontaneous circulation (ROSC). 

Results: The data set included 7,574,879 responses from 1,289 distinct agencies. There were 70,746 (<1%) records with documented cardiac arrest. Of these, 62,750 (89%) records were from 9-1-1 responses. Records for 2,207 (4%) patients under 18 were excluded, leaving 60,543 in the analysis population. Of the emergency responses for documented cardiac arrests among adult patients, EMS witnessed 8,014 (13%). Among EMS-witnessed cardiac arrest patients, median age was 65 (IQR 53–76), 71% were white (non-Hispanic), and 60% were male. Presumed etiology of EMS-witnessed arrests included cardiac (54%), followed by respiratory (25%), trauma (12%), and drug overdose (2%). Initial arrest rhythm was shockable in 21% of witnessed arrests, while PEA or asystole was documented in 73% of cases. Common locations where EMS-witnessed cardiac arrests occurred included residences (70%), streets/highways (10%), and nursing homes/assisted living centers (8%). Circulation was restored in 43% of cases. 

Conclusion: In this large national EMS registry data set, EMS witnessed less than 15% of documented cardiac arrests during emergency responses. Most of these EMS-witnessed arrests occurred at a residence, and half of EMS-witnessed arrests occurred in patients younger than 65. About one-fifth presented with an initial shockable rhythm. For all EMS-witnessed cardiac arrests, less than one-half experienced restored circulation.