Unpredictable emergency department cardiac arrest: clinical features and the limits of early warning scores and triage acuity

BACKGROUND: Emergency department cardiac arrest (EDCA) is a distinct clinical entity for which early identification remains challenging. A clinically important subset may occur in patients initially classified as low acuity or low physiological risk, potentially delaying evaluation and treatment. We compared characteristics of predictable versus unpredictable EDCA and assessed whether low-acuity Korean Triage and Acuity Scale (KTAS) and low-risk National Early Warning Score 2 (NEWS2) at triage are associated with unpredictable EDCA among EDCA cases. We also explored potential phenotypes within low-acuity/low-risk strata. METHODS: A single-center retrospective study of adult patients (≥ 18 years) who experienced their first cardiac arrest after arrival in the ED was conducted between January 2018 and October 2023. Predictable EDCA was defined as cardiac arrest occurring in the resuscitation room or during transfer after deterioration had already been recognized, whereas unpredictable EDCA referred to events occurring in non-monitored areas. KTAS was dichotomized as high acuity (1–2) versus low acuity (3–5). NEWS2 was dichotomized as high risk (≥ 5 or any single parameter score of 3) versus low risk (< 5). Multivariable logistic regression identified KTAS/NEWS2 strata associated with unpredictable EDCA. Exploratory analyses summarized chief complaints and presumed etiologies by KTAS/NEWS2 strata. RESULTS: Among 242 EDCA events, 98 (40.5%) were predictable and 144 (59.5%) were unpredictable. Unpredictable EDCA occurred later after ED arrival than predictable EDCA (median 242.5 vs. 41.5 min; p < 0.001). Rates of return of spontaneous circulation, 30-day mortality, and favorable neurological outcome at 30 days did not differ significantly. In multivariable analysis, low-acuity KTAS (adjusted OR 10.60; 95% CI 3.90–28.81) and low-risk NEWS2 (adjusted OR 2.06; 95% CI 1.06–4.01) were independently associated with unpredictable EDCA. Exploratory analyses suggested that chest pain presentations and hyperkalemia-related etiologies may represent potential missed-risk phenotypes within low-risk strata. CONCLUSIONS: Among EDCA cases, unpredictable EDCA was associated with low-acuity KTAS and low-risk NEWS2 at triage. These findings suggest a potential process vulnerability during prolonged ED stays and generate hypotheses that dynamic reassessment and targeted diagnostics may be beneficial for selected presentations despite initially reassuring triage-time labels.