Abstract 2481: Day 7 NIHSS is a Sensitive Outcome Measure for Exploratory Clinical Trials in Acute Stroke: Evidence from the Virtual International Stroke Trials Archive (VISTA)

Abstract

Introduction: Clinical trials in stroke typically measure outcome after 90 days. Earlier outcome assessment would reduce costs and may increase power. Aim: To compare the sensitivity of 4 outcome measures (mRS at 30 and 90 days, and NIHSS at 7 and 90 days, analysed as ordinal measures) to the established treatment effect of r-tPA. Methods: We undertook a controlled comparison of r-tPA treated patients versus untreated controls from VISTA. A multiple re-sampling approach was used. From our total sample 10,000 random samples of independent patients were drawn, each of the same size. In each sample ordinal logistic regression (adjusted for age and baseline NIHSS score) was used to test for the r-tPA treatment effect as measured by each of the 4 outcome measures. The percentage of samples yielding significant results approximates the power of each endpoint at a given sample size. This process was repeated across a range of sample sizes. Results: Our data included 4712 patients of whom 1934 (41%) received r-tPA. r-tPA treated patients were younger, and had more severe strokes. For our 4 outcome measures of mRS at 30 and 90 days, and NIHSS at 7 and 90 days the smallest sample sizes required to generate statistical power >80% were 620, 480, 370, and 420 respectively, making 7 day NIHSS the most sensitive endpoint. These results were supported by dichotomised analyses. Conclusions: 7 day NIHSS score appears a sensitive endpoint that should be validated in a randomised trial dataset for use in exploratory stroke trials.