Changes in Stroke Care Regionalization in California Associated With Evolving Evidence of Benefit for Endovascular Thrombectomy: A Network Analysis

BACKGROUND: The 2015 demonstration of the benefit of endovascular thrombectomy (EVT) led to increases in interhospital transfer of patients with large vessel occlusion stroke. We sought to characterize the associated evolution in stroke care regionalization. METHODS: We used comprehensive California statewide all-payer administrative data from 2010 to 2021 to identify ischemic stroke encounters and transfers (using recorded disposition and adjacent claims). We applied network analysis methods to create the interhospital transfer network, examine access to EVT-capable hospitals (time-varying, based on performance of ≥2 EVT cases that year), and used block models to identify clusters of hospitals closely connected through transfer by year and pre- versus post-2015. We used regression modeling with a linear spline and knot at 2015 to examine changes in network characteristics over time. RESULTS: We identified 19 244 transfers between 338 hospitals. Pre-2015, 7 of 11 clusters had ≥1 EVT-capable hospital. Post-2015, 24 of 26 clusters had ≥1 EVT-capable hospital. More hospitals had EVT capability over time (21.6% [70/324] to 33.7% [106/315]). EVT-capable hospitals consistently received more transferred patients relative to noncapable hospitals (mean number of received transfers/y pre-2015: 55.2 versus 15.6; post-2015: 97.3 versus 13.8). Initially, transfers for EVT increased from 10.7% of EVT cases having an interhospital transfer in 2010 to 36.0% by 2016. After 2016, the trend reversed, decreasing to 21.7% by 2021. CONCLUSIONS: The California stroke system of care became less regionalized for EVT access from 2010 to 2021. Although we expected increased consolidation with fewer clusters centered around EVT-capable hospitals, we instead observed an increased number of EVT-capable hospitals with more clusters around them and less need for transfer to access EVT. More work is needed to examine the relative trade-offs of regionalization patterns in stroke systems of care, given recognized benefits of more regionalized care around higher-volume centers in other conditions.