Exploring Temporal Dynamics in No-Reflow Assessment.

Background: For acute ischemic stroke (AIS) patients, successful endovascular thrombectomy (EVT) may not recover functional independence. One potential mechanism driving this disparity is no-reflow, a lack of perfusion despite recanalization of the large vessel occlusion (LVO). None of the published methods for assessing no-reflow have gained acceptance, and debate persists about isolating no-reflow from upstream hemodynamic anomalies as well as the temporal dynamics no-reflow assessment. This work conducts an exploratory analysis of the effect of time since EVT on the performance of different methods for assessing no-reflow. Methods: We identified a cohort of UCLA Health patients with successful LVO recanalization (≥ mTICI 2b) of a thrombus located in M1 or ICA. Patients were stratified into 'early' and 'follow-up' cohorts of < 24 and < 48 hours since EVT. A set of published methods using perfusion imaging for no-reflow detection were adapted to run semi-automatically for both cohorts. Results: We compiled 83 imaging studies from 64 patients. No-reflow rates varied from 4 . 2 % to 51 . 4 % by method, time since EVT, and mTICI. Follow-up no-reflow rates more closely match the original literature across all methods. mTICI 2b patients likely inflated no-reflow, as rates dropped approximately 50 % for mTICI 2c/3 cases. Early cohort inter-method agreement shows kappa scores as low as - 0 . 017 , but improved up to 0 . 72 in the follow-up cohort. Conclusion: No-reflow exhibits substantial dependence on time across all no-reflow detection methods studied. Inter-method agreement is good for methods using the same perfusion parameters, but each method is subject to confounding influences, motivating an aggregate method for robust evaluation. The temporal dynamics of no-reflow detection raises questions about imaging timing post-EVT for detection within the intervention window.