PROJECT ABSTRACT Rural Americans face disproportionate cardiovascular disease burden, yet they must travel farther to reach hospitals that can provide effective, guideline-concordant treatment for acute myocardial infarction (AMI). Transfer networks play a crucial role in care for rural ST-Elevation Myocardial Infarction (STEMI), the most severe form of AMI, moving patients from rural hospitals to hospitals that can perform primary Percutaneous Coronary Intervention (PCI), the preferred treatment for STEMI. Of the 925 hospitals have closed or been acquired in rural areas since 2007, 75% may have been part of a STEMI transfer network. Although closures and acquisitions of hospitals may disrupt STEMI transfer network, the impact on STEMI patients has not been explored. Existing research on hospital closures finds conflicting results on AMI mortality. Failure to account for networks disadvantages previous research in 3 ways. 1) Time to PCI depends on the geographic location and the transfer relationships of hospitals within STEMI transfer networks. 2) Disruptions can cause spillover effects to patients not directly affected by closures and acquisitions but in the same transfer network. 3) The characteristics of network affect time to PCI after disruption. Although not previously explored, disruptions in rural STEMI networks could worsen rural-urban disparities in AMI mortality rates and reverse reductions in rural cardiovascular mortality over the past four decades. This project will draw upon novel data resources collected by the research team including validated data on hospital closure status and timing and validated data on hospital-level PCI capabilities. Leveraging the expertise of the research team in innovative network analysis techniques, invasive cardiology, emergency medicine, rural health, Medicare claims data, and biostatistics we will estimate STEMI transfer networks using Medicare claims data from 2007-2021 and link networks to hospital closure and acquisition data collected and validated by the research team. We will leverage connections to stakeholders in STEMI systems of care and rural health as well as expertise in survey design and implementation to develop a survey of EMS agencies to collect information on the emergency medical services involvement in STEMI networks. We propose the following aims: 1) estimate the association of STEMI network disruption with through0network time to PCI; 2) estimate the association of STEMI network disruption with STEMI treatment and mortality; 3) identify network-level factors associated with changes in patient mortality after STEMI network disruption; and 4) quantify the role of STEMI transfer network disruption in rural-urban STEMI disparities. We will disseminate information on STEMI networks and their characteristics via a web-based app. Our findings will identify a previously unknown access barrier for rural patients and can inform policymakers and clinicians about how to improve the health ...