Background and purpose: Recombinant tissue plasminogen activator (rtPA) has been demonstrated to improve outcomes in acute ischemic stroke when delivered within 3 hours of symptom onset. However, the Alteplase Thrombolysis for Acute Noninterventional Therapy in Ischemic Stroke (ATLANTIS B) trial, in which patients were treated mostly between 3 and 5 hours after symptom onset, found no overall benefit from rtPA. We hypothesized that a subgroup of patients at low risk for thrombolysis-related intracranial hemorrhage, identifiable on the basis of pretreatment clinical variables, may benefit even when treated after 3 hours, despite the overall results of the trial.

Methods: Using an independently derived multivariate model that predicts the risk of thrombolysis-related intracranial hemorrhage in patients receiving tPA for acute myocardial infarction (based on 6 easily obtainable clinical characteristics), we stratified patients in the ATLANTIS B trial into low-, intermediate-, and high-risk tertiles. We examined outcomes in the prespecified low-risk subgroup using a global test of significance across 4 outcome scales.

Results: Despite having a similar average baseline stroke severity and median time to treatment (270 minutes), patients in the prespecified low-risk group (n=194) were significantly less likely to have a symptomatic intracranial hemorrhage than other patients in the trial (2.2% versus 9.2%, P=0.03). Although there was no treatment effect for rtPA in the overall trial, a consistent trend favoring rtPA therapy (a 5% to 12% absolute treatment benefit) was found across 4 different stroke scales in the prespecified low-risk group (P=0.10). The treatment-benefit-by-risk interaction was significant (P=0.03).

Conclusions: Use of a multivariate index based on clinical variables is a promising approach to assist in the selection of patients with a favorable risk-benefit profile for thrombolytic therapy beyond 3 hours.