Letter to the editor Relationships between age, other predictive variables, and the 90-day functional outcome after intravenous thrombolysis for acute ischemic stroke Dear editor, Prior studies looking at the predictors of outcome in patients treated with intravenous (IV) thrombolysis for acute ischemic stroke have used traditional statistical methods such as regression analysis, which have limited utility in classifying patients into risk categories (1). Further, interactions between predictor variables are often difficult to model using traditional regression methods (1). We thereby used classification and regression trees (CART) (2) to examine the relationships between age, other recognized clinical and radiological outcome predictors, and 90-day outcome following IV thrombolysis among patients presenting with acute ischemic stroke to a tertiary hospital in Australia. Prospectively collected data of 117 consecutive patients (mean age 72·3 ± 13·0, 54% male) presenting at the John Hunter Hospital with acute ischemic stroke and treated with IV thrombolysis between January 2011 and June 2013 were reviewed. Their baseline characteristics, treatment variables, and imaging and outcome data were extracted from the local database. Ethics approval was obtained from the Hunter New England Human Research Ethics Committee, with all patients providing informed consent. There was no upper age limit to the use of thrombolytic therapy. The Alberta Stroke Program Early CT Score (ASPECTS) (3) was used to assess the evidence of early ischemic changes on the noncontrast brain CT images by two blinded reviewers. Cerebral CT angiographic leptomeningeal collateral status Correspondence: Roshan Gunathilake*, John Hunter Hospital, Lookout Road, New Lambton, NSW 2305, Australia. E-mail: [email protected] Conflict of interest: None declared. DOI: 10.1111/ijs.12347

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Fig. 1 Full classification tree containing five terminal nodes for the outcome mRS at 3 months. Each node identifies the most common outcome (first line), the number of people with that outcome and the alternate outcome (second line), and the percentage of the entire cohort in that node (third line). For example, the top node indicates that of the 98 people in this analysis, 51 had a poor outcome (mRS ≥2). Of those 51, 21 had ASPECTS ≤9 and 30 had ASPECTS of 10. Of the 47 who had a good outcome in the first node, only 2 had an ASPECTS ≤9, and 45 had ASPECTS of 10. Another way to read this is that of those with ASPECTS ≤9, 21/23 had a poor outcome (bottom left terminal node).

was assessed using a modified grading system (4). The modified Rankin Scale (mRS) (5) was assessed by Rankincertified personnel at 90 days in the outpatient clinic. Outcome data was unavailable for 19 patients due to loss to follow up. CART analysis was therefore performed in 98 patients to determine which baseline clinical and radiological variables showed dominant influence on the 90-day outcome [dichotomized according to mRS