Prognostic Value of Temporalis Muscle Thickness for Predicting Mortality in Patients with Emergency Department Cardiac Arrest.

Background and Objectives: Temporalis muscle thickness (TMT) has emerged as an imaging-based morphometric surrogate associated with reduced muscle mass and frailty; however, its prognostic value in emergency department cardiac arrest (EDCA) remains unclear. This study aimed to evaluate the association between TMT and emergency department mortality in patients with EDCA who had cranial CT imaging available during the same emergency department encounter and to investigate its association with in-hospital mortality. Materials and Methods: This study included 129 adult patients who experienced cardiac arrest in the emergency department between 1 June 2022 and 31 May 2025, and had eligible cranial CT imaging available during the same emergency department encounter. TMT was measured on non-contrast brain computed tomography images. The association between TMT and mortality outcomes, including emergency department and in-hospital mortality, was statistically analyzed. Results: TMT was significantly lower in patients who died in the emergency department compared with survivors (median 3.29 mm [Q1-Q3: 2.63-3.95] vs. 4.69 mm [Q1-Q3: 3.70-5.65], p < 0.001). Similarly, patients who died in an in-hospital setting had lower TMT values than survivors (median 4.06 mm [Q1-Q3: 3.26-5.34] vs. 5.00 mm [Q1-Q3: 4.21-5.85], p = 0.040). ROC analysis demonstrated the moderate discriminative ability of TMT for predicting emergency department mortality (AUC = 0.763, 95% CI 0.671-0.856). Logistic regression analysis identified that, after adjustment for age, sex, and CPR duration, TMT remained associated with emergency department mortality (adjusted OR 0.34, 95% CI 0.133-0.886; p = 0.027). Conclusions: Among patients with EDCA who had eligible cranial CT imaging during the same emergency department encounter, lower temporalis muscle thickness was associated with increased emergency department mortality, whereas its association with in-hospital mortality was weaker. Given the retrospective design and limited number of outcome events, these findings should be considered exploratory and require validation in larger independent cohorts.