Time Since Stroke Onset, Quantitative Collateral Score, and Functional Outcome After Endovascular Treatment for Acute Ischemic Stroke

Abstract

Background and objectives: In patients with ischemic stroke undergoing endovascular treatment (EVT), time to treatment and collateral status are important prognostic factors and may be correlated. We aimed to assess the relation between time to CT angiography (CTA) and a quantitatively determined collateral score and to assess whether the collateral score modified the relation between time to recanalization and functional outcome.

Methods: We analyzed data from patients with acute ischemic stroke included in the Multicenter Randomized Controlled Trial of Endovascular Treatment for Acute Ischemic Stroke Registry between 2014 and 2017, who had a carotid terminus or M1 occlusion and were treated with EVT within 6.5 hours of symptom onset. A quantitative collateral score (qCS) was determined from baseline CTA using a validated automated image analysis algorithm. We also determined a 4-point visual collateral score (vCS). Multivariable regression models were used to assess the relations between time to imaging and the qCS and between the time to recanalization and functional outcome (90-day modified Rankin Scale score). An interaction term (time to recanalization × qCS) was entered in the latter model to test whether the qCS modifies this relation. Sensitivity analyses were performed using the vCS.

Results: We analyzed 1,813 patients. The median time from symptom onset to CTA was 91 minutes (interquartile range [IQR] 65-150 minutes), and the median qCS was 49% (IQR 25%-78%). Longer time to CTA was not associated with the log-transformed qCS (adjusted β per 30 minutes, 0.002, 95% CI -0.006 to 0.011). Both a higher qCS (adjusted common odds ratio [acOR] per 10% increase: 1.06, 95% CI 1.03-1.09) and shorter time to recanalization (acOR per 30 minutes: 1.17, 95% CI 1.13-1.22) were independently associated with a shift toward better functional outcome. The qCS did not modify the relation between time to recanalization and functional outcome (p for interaction: 0.28). Results from sensitivity analyses using the vCS were similar.

Discussion: In the first 6.5 hours of ischemic stroke caused by carotid terminus or M1 occlusion, the collateral status is unaffected by time to imaging, and the benefit of a shorter time to recanalization is independent of baseline collateral status.

Figure 1. Flowchart of Patients Through the Selection Process

CTA = CT angiography; DSA = digital subtraction angiography; EVT = endovascular treatment; ICA(-T) = internal carotid artery (-terminus); MR CLEAN = Multicenter Randomized Controlled Trial of Endovascular Treatment for Acute Ischemic Stroke.

Figure 2. Predicted Probability of Poor Functional Outcome According to the Quantitative Collateral Score and Onset to Recanalization Time

Figure is based on a multivariable ordinal logistic regression with the modified Rankin Scale score as an outcome variable. The model was adjusted for potential confounders, and an interaction term was added (ORT ≤249 minutes vs >249 minutes × qCS). ORT was dichotomized at the median for the entire population (249 minutes) for the purpose of this figure only. mRS = modified Rankin Scale score; ORT = onset to recanalization time; qCS = quantitative collateral score.