From the Stroke Outcomes Research Unit (G.S.), Division of Neurology, Department of Medicine, and Li Ka Shing Knowledge Institute (G.S., M.M.), St Michael's Hospital, University of Toronto, Toronto, Ontario, Canada; the Institute for Clinical Evaluative Sciences (ICES; G.S., J.F., M.K.K., J.V.T., M.M., P.A.), Ontario. Canada.; the Division of General Internal Medicine and Clinical Epidemiology (M.K.K.), Department of Medicine, University Health Network, Toronto, Ontario, Canada, and the University Health Network Women's Health Program Toronto, Canada; the Institute of Health Policy, Management and Evaluation (G.S., M.K.K., J.V.T., M.M., P.A.), University of Toronto, Toronto, Canada; the Applied Health Research Center (G.S., M.M.), and the Clinical and Translational Science Institute (S.C.J.) and the Department of Neurology, University of California, San Francisco, CA.
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Background and Purpose—Tools to predict the clinical response after intravenous thrombolytic therapy (tPA) are scarce. The iScore is an existing validated tool to estimate outcomes after an acute ischemic stroke. The purpose of this study was to determine the ability of the iScore to predict clinical response and risk of hemorrhagic transformation after tPA.Methods—We applied the iScore (www.sorcan.ca/iscore) to patients presenting with an acute ischemic stroke at 11 stroke centers in Ontario, Canada, between 2003 and 2009 identified from the Registry of the Canadian Stroke Network. A cohort of patients with stroke treated at 154 centers in Ontario was used for external validation. We compared outcomes between patients receiving and not receiving tPA after adjusting for differences in baseline characteristics using propensity-score matching. Patients were stratified into 3 a priori defined groups according to stroke severity using the iScore.Results—Among 12 686 patients with an acute ischemic stroke, 1696 (13.4%) received intravenous thrombolysis. Higher iScores were associated with poor outcomes in both the tPA and non-tPA groups (P<0.001). Among those at low and medium risk based on their iScores, tPA use was associated with a benefit in the primary outcome (relative risk, 0.74 for those with low-risk iScores; 95% CI, 0.67–0.84; relative risk, 0.88 for those with medium risk iScores; 95% CI, 0.84–0.93). There was no difference in clinical outcomes between matched patients receiving and not receiving tPA in the highest iScore group (relative risk, 0.97; 95% CI, 0.94–1.01). Similar results were observed for disability at discharge and length of stay. The incident risk of neurological deterioration and hemorrhagic transformation (any or symptomatic) with tPA increased with the iScore risk. Results were similar in the validation cohort for risk of poor outcome with tPA by iScore level.Conclusion—The iScore may be used to predict clinical response and risk of hemorrhagic complications after tPA for an acute ischemic stroke. Patients with high iScores may not have a clinically meaningful benefit from intravenous tPA at the time of carrying a higher risk of hemorrhagic complications.