Changes in collateral status during transfer for thrombectomy are predictive of functional outcome in large vessel occlusion stroke

Collateral circulation that determines infarct progression in large vessel occlusion (LVO) is implicitly regarded as stationary. We investigated collateral circulation changes during interfacility transfer for endovascular thrombectomy (EVT) and its association with functional outcome in anterior circulation LVO stroke. Seventy consecutive patients with middle cerebral artery occlusion transferred for EVT from January 2017 to December 2018 within a regional stroke network underwent repeated CTA at the comprehensive center allowing longitudinal assessment of collateral status, quantified by the Tan score, and AI-derived collateral percentage. Demographics, NIHSS, intravenous thrombolysis, blood pressure, stroke-to-reperfusion time, recanalization status, and 90-day mRS were recorded. Ordinal logistic regression was used to identify predictors of outcome. Collateral status was dynamic rather than stationary, with changes observed in 51/70 (73%) patients (median = -3.69% (IQR = - 22.28-4.83)). Collateral change emerged as a significant independent predictor of 90-day functional outcome (OR = 0.98, p = 0.008), with patients showing improvement in collaterals having better outcomes. Additionally, older age (OR = 1.04, p = 0.030), higher baseline NIHSS (OR = 1.20, p = 0.001), and longer stroke-to-reperfusion time (OR = 1.01, p = 0.014) were each significantly associated with worse 90-day functional outcome. Patients with improved/stable collaterals had significantly better 90-day functional outcomes compared to decliners (median mRS 2[IQR 0-4] vs. 4 [1.25-6], p = 0.008). Collateral status is not stationary during a stroke event, and its improvement independently predicts good functional outcome, highlighting the importance of therapeutic efforts to improve collateral circulation.