Large vessel occlusions of milder severity show better collaterals and reduced harm from thrombectomy transfer delays

Background and PurposePatients with large vessel occlusion (LVO) stroke of milder baseline clinical severity are often missed by pre-hospital severity-based triage tools. We examined whether these patients had differences in 1) markers of collateral circulation and 2) the relative harm of transfer delays on outcome, compared to patients with clinically more severe baseline deficits. MethodsRegistry data from two large Australian thrombectomy centers was used to identify all directly presenting and transferred LVO patients undergoing endovascular thrombectomy, divided into those with milder baseline deficits (NIHSS <10) and severe baseline deficits (NIHSS [&ge;]10). Baseline CT-perfusion markers of collateral circulation and the association between transfer status and functional outcome (using the 90-day modified Rankin Scale) were compared. ResultsOf 1210 included LVO patients, 273 (22.6%) had milder severity. Milder LVO patients showed smaller median ischemic core volumes (12.6 [IQR 0.0-17.9] vs 27.5 [IQR 6.5-37.1] mL, p<0.001)), higher median perfusion mismatch ratio (148.3 [IQR 5.0-500.0] vs 66.2 [IQR 3.6-17.2], p<0.001) and lower median hypoperfusion intensity ratio (0.25 [IQR 0.18-0.38] vs 0.40 [IQR 0.22-0.57], p<0.001). Transferred patients had a lower odd of excellent outcome than primary presenters, when deficits were severe deficits (aOR 0.759 [95% CI 0.576-0.999]) but not when deficits were milder (aOR 1.357 [95% CI 0.764-2.409], pinteraction=0.122). ConclusionsPatients with LVO stroke of milder clinical severity have significantly better imaging markers of collateral circulation compared to high-severity patients. Despite high rates of thrombolytics, secondary transfer to thrombectomy-center was only associated with poorer 90-day functional outcomes in higher-severity patients. Failure of pre-hospital screening tools to detect lower-severity LVO patients for immediate pre-hospital bypass to a thrombectomy center may not deleteriously affect their outcome.