Accessibility and Spatial Optimization of AEDs Under Transportation, Temporal and Age Constraints: Evidence from Shenyang, China

Automated external defibrillators (AEDs) represent critical urban health infrastructure for mitigating risks associated with out‑of‑hospital cardiac arrest (OHCA). Multi‑factor evaluation of AED accessibility improves assessment accuracy and provides robust support for time‑constrained emergency rescue responses. Conventional accessibility models seldom simultaneously incorporate travel costs across multiple real‑world travel modes, time‑dependent facility availability, and emergency demand differences among distinct age groups. This shortcoming yields biased estimations regarding the equity and supply‑demand balance of emergency resources. To fill these research gaps, this study develops an enhanced Multimodal Gaussian Two‑Step Floating Catchment Area (Multimodal G2SFCA) framework integrating travel modes, temporal facility availability, and vulnerability among elderly populations. Taking the densely populated, hyper‑aging core area within Shenyang’s First Ring Road as the study area, this research assembles multi‑source, fine‑grained geospatial datasets: age‑stratified population grids, geocoded AED records with venue opening‑hour information, and origin‑destination (OD) travel‑time matrices for walking, driving, and cycling derived from the Amap API. Gini coefficients and bivariate Moran’s I are employed jointly to measure spatial equity and identify supply‑demand mismatches. Results demonstrate that cycling delivers the most comprehensive emergency coverage within the 8‑minute threshold. Walking‑based AED accessibility shows pronounced spatial disparities, with emergency service deserts widespread in ageing residential neighbourhoods on the urban periphery. Only 63.8% of AED sites remain publicly accessible during rest hours, lowering overall regional service capacity by over 30%. The elderly experience cumulative accessibility disadvantages alongside greater resource‑allocation inequality. High‑demand‑low‑supply clusters are prevalent in ageing residential zones. This study advances the spatiotemporal evaluation framework for urban emergency medical facilities and offers practical strategies for AED layout optimisation in densely populated, hyper‑aging cities.