Collaterals Predict Outcome Regardless of Time Last Known Normal

Recent studies suggest that patients with large-vessel ischemic strokes (large-vessel occlusion [LVO]) with favorable imaging may benefit from mechanical thrombolysis even when treated outside the standard 6-hour window. However, many patients in these studies presented with unknown times of onset. We compare outcomes in thrombectomy patients treated at less than versus greater than 6 hours from last known well (LKN), and evaluate whether "unknown time of onset" alters prognosis.

We retrospectively reviewed patients at 2 comprehensive stroke centers. Student's t and chi-square tests evaluated the association between predetermined clinical and radiographic variables, including unknown time of onset, and outcome (discharge and follow-up National Institutes of Health Stroke Scale score and modified Rankin Scale [mRS] score) for LVOs treated after greater than 6 hours versus 6 hours or less from LKN. Multivariable logistic regression was used to determine the odds of good outcome (mRS score 0-2).

A total of 113 patients were treated over 2 years; 31 were treated at greater than 6 hours. Those who were treated at greater than 6 hours and experienced poor outcomes were more likely to have large-artery atherosclerosis (P = .033). There was no difference in outcome for patients outside the window with known (39.1%) versus unknown (60.9%) time of onset. mRS scores at discharge were higher among those outside the window (odds ratio 3.78; 95% confidence interval 1.20-11.89) but not at follow-up. After multivariable regression, favorable collaterals alone were associated with a mRS score of 0-2.

When imaging is favorable, the mRS score at follow-up is comparable regardless of time LKN. Functional outcomes appear to be driven most significantly by the presence of collaterals.