Distinguishing Subtypes of Unwitnessed Out-of-Hospital Cardiac Arrest by Estimated Last Seen Alive Time

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.

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.

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).

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.