Spatiotemporal disparities in automated external defibrillator access: identifying national deficits.

Background: Timely defibrillation is vital for survival after out-of-hospital cardiac arrest (OHCA), yet the availability of automated external defibrillators (AEDs) at critical moments remains uncertain. Placement guidelines emphasize high-traffic public sites, but most OHCAs occur at home and outside business hours, raising questions about accessibility. Few national studies address both geography and temporal availability. Switzerland's decentralized system without placement standards provides a critical test case. This study applies a spatial-statistical framework to analyze clustering, assess links between AED presence and population or employment density, and quantify accessibility deficits and affected populations. Methods: We analyzed over 14,000 devices from the Swiss AED registry under two scenarios: those with 24-h access and all devices hypothetically available 24/7. Clustering was tested with Ripley's L and Moran's I. Associations with population or employment density were estimated using Bayesian spatial logistic models (BYM2), separating demographic effects from residual spatial structure. Accessibility deficits were defined as the gap between modeled and observed AED presence, weighted by demographic counts, and expressed as population-weighted risk scores. Results: AEDs were significantly spatially clustered, with deployment more strongly aligned with employment than with residential population. Strong residual spatial structuring persisted beyond demographic effects. The 5 % of grid cells with the highest accessibility deficits contained between 16 % and 42 % of the national population or workforce. Conclusion: AED deployment in Switzerland reflects historical and institutional patterns rather than risk-based planning. This study provides a framework for identifying spatial and temporal accessibility deficits and guiding more equitable AED placement.