Modeling Affiliated Interhospital Stroke Transfers for Endovascular Therapy and Stroke Network Analysis in Two Large US Cities

Introduction: Interhospital transfers of stroke patients with large-vessel occlusions for endovascular treatment (EVT) are common and transfer times may drastically impact the time to reperfusion. We sought to model and compare the efficiencies of intra- and extra-health system stroke transfers in two major cities, Chicago and New York City (NYC).

Methods: We identified EVT-capable centers (defined as comprehensive [CSC] and thrombectomy-capable [TSC] stroke centers) and their affiliated health-system hospitals for each city. For each affiliated hospital, we modeled travel times on various dates and times to its system EVT-capable center as well as the nearest non-system EVT-capable center. Using a Monte Carlo simulation (10,000 runs per pair) we modeled and compared intra- and extra-health system transfers by ambulance. This information was used in a network analysis of overall stroke network community structures.

Results: Overall, Chicago had 9 affiliated transfer pairs and NYC had 25 affiliated transfer pairs. The average travel time (mean [SD], minutes) for affiliated transfers was significantly greater for Chicago (41.6 [10.1]) compared to NYC (25.0 [4.8]) (p < 0.01). The median extra time for affiliated vs nearest unaffiliated transfers was 23.0 minutes (IQR 10.6-34.3) for Chicago and 7.9 minutes (IQR 1.07-17.3) for NYC (p < 0.01). In a network analysis, transfers that favored the closest CSC or TSC had a stronger community structure (modularity), with the increase more pronounced in Chicago. Prolonged affiliated transfer time was not associated with the certification level of either the transferring or receiving facility.

Conclusion : The stroke networks of Chicago and NYC vary considerably with the density of EVT-capable centers and are not optimized based on travel time. These results have implications for stroke transport policy and identifying potential centers within a health system that would further optimize transfers if certified for EVT.