Ischemic Stroke Systems of Care in California: Evolution in the Organization During the Mechanical Thrombectomy Era.

Background: Optimized stroke systems of care enable access to timely care, including endovascular thrombectomy (EVT). Stroke systems have likely evolved after publication of EVT benefit (2015). Our objective was to map the stroke patient transfer network in California in terms of EVT access and patient transfer patterns, and to examine changes after 2015. Methods: In this observational study, we identified all ischemic stroke encounters, transfers, alteplase use, and EVT procedures in California from 2010 to 2017. An established connection between any hospital pair was defined as the transfer of ≥2 patients between them. A 2-level logistic regression model assessed whether encounters were more frequently transferred to EVT-capable hospitals post-2015, adjusting for patient- and hospital-level factors. Linear regression examined trends in key network characteristics over time, and interrupted time series regressions examined for changes post-2015. Results: Among 336 247 encounters, 3.4% were transferred, 9.3% received alteplase, and 2.3% underwent EVT. From 2010 to 2017 the proportion that were EVT treated increased (1.0%-4.3%; Conclusion: The California stroke network has been dynamic over time. Although most changes have been incremental, after the release of EVT trial data in 2015 changes in transfer patterns did lead to increased access to EVT.