Background: Intravenous thrombolysis is beneficial in, even very elderly, acute ischemic stroke patients. However, while the relation between treatment benefit and treatment delay (onset time to treatment) in patients younger than 80 years is well known, it is uncertain in the very elderly. Aims: This analysis aims at examining this relationship in the elderly, and to provide a comparison with the derived relationship in younger patients as a check of validity. Methods: We assessed the interaction between age, onset time to treatment, and thrombolysis exposure by analyzing the modified Rankin scale score distribution or mortality rate at 90 days, among patients registered in a trials archive. We established whether the effect of alteplase changes with onset time to treatment, by treating onset time to treatment as a continuum in a multivariate logistic regression model. Results: Data were available for 3063 patients, of whom 2341 were thrombolysed. Five hundred ninety-seven patients were aged >80, of whom 352 were thrombolysed. Among patients aged >80, no significant interaction of outcome with onset time to treatment was observed (P = 0·4650), but the estimated slope of the decay in benefit with onset time to treatment was comparable with that established for younger patients. Analyzing the entire dataset, there was an interaction between onset time to treatment and alteplase treatment (P = 0·0159), but neither between age and onset time to treatment (P = 0·7098) nor between age and alteplase treatment (P = 0·0755). Conclusions: In this nonrandomized comparison, the relationship of benefit and safety with thrombolysis across onset time to treatment in very elderly stroke patients was comparable with that in their younger counterparts. Across the investigated time span of 3·5 h, we can safely treat with the same time window as we use for younger patients
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