Distinguishing Subtypes of Unwitnessed Out-of-Hospital Cardiac Arrest by Estimated Last Seen Alive Time.
Prehospital emergency care · 2025-07-11 · Registry study
Abstract
OBJECTIVES: Approximately one-half of all out-of-hospital cardiac arrests (OHCA) are unwitnessed and have a very low survival rate. Our objective was to assess if use of a bystander estimated last-seen-alive (ELSA) time could predict a subset of unwitnessed OHCA patients with outcomes resembling those with witnessed OHCA. METHODS: This is a registry-based retrospective analysis of adults presenting with emergency medical services (EMS)-treated, non-traumatic OHCA from 2018 to 2023, in the Portland Cardiac Arrest Epidemiologic Registry. We excluded EMS-witnessed arrests, patients with do-not-resuscitate orders and records with incomplete data. Our primary outcome was survival with a favorable neurologic outcome at hospital discharge (Cerebral Performance Category score ≤2). We compared bystander witnessed arrests to unwitnessed arrests with ELSA times <5 min, 5-10 min, 10-15 min, ≥15 min, or unknown. ELSAs were abstracted from EMS charts using bystander estimates of when the patient was last seen, with values averaged if a range was given. We used multivariable mixed effects regression analysis to adjust for potential confounding variables. In the subset of patients where no-flow time (NFT) could be calculated, using the interval from estimated time of arrest (using ELSA and 9-1-1 call time) to initial EMS cardiopulmonary resuscitation, we performed propensity score matching by NFT and potential confounding variables. RESULTS: There were 2067 bystander witnessed and 2755 unwitnessed patients meeting inclusion criteria. Patients with an unwitnessed arrest and an ELSA <5 min had similar adjusted favorable neurologic survival (absolute difference (95% confidence interval)) relative to witnessed arrests (-1.4%, (-6.9%, 4.2%)). Compared to witnessed arrests, neurologically favorable survival was significantly lower in unwitnessed arrests with ELSA 5-10 min (-5.3% (-9.5%, -1.2%)), 10-15 min (-6.8% ((-10.7%, -2.9%)), ≥15 min (-9.2% ((-12.7%, -5.7%))), or unknown (-5.2% ((-7.0%, -3.4%))). In our propensity matched group by NFT and covariates, there was no differences in favorable neurologic survival for unwitnessed arrests (11.4%) and bystander witnessed arrests (10.0%, p = 0.785). CONCLUSIONS: OHCA patients with unwitnessed arrests with an ELSA under 5 min or using ELSA to match by NFT displayed similar neurologically favorable survival as witnessed arrests. These findings suggest that the use of ELSA may help better characterize unwitnessed OHCAs.