Dichotomized efficacy end points and global end-point analysis applied to the ECASS intention-to-treat data set: post hoc analysis of ECASS I.

BACKGROUND AND PURPOSE

It is not yet known which end points are the most suitable for evaluation of the effects of acute stroke intervention. The European Cooperative Acute Stroke Study (ECASS) I study used 2 primary end points. The study was powered to detect a 15% improvement of the median of each primary end point. The study failed to show this effect and was negative in the intention-to-treat analysis. The National Institute of Neurological Disorders and Stroke (NINDS) study used 4 dichotomized end points and applied a global end-point analysis. This study was positive and led to FDA approval of thrombolytic therapy for acute ischemic stroke. This study was undertaken to answer the question of whether a different statistical design may have shown a positive results of the ECASS I trial.

METHODS

We performed a retrospective analysis of the ECASS I intention-to-treat data set (615 randomized and treated patients, rtPA treatment versus placebo) and post hoc application of the NINDS trial statistical methodology (global end-point analysis). The scores of the modified Rankin Scale (mRS), Barthel Index (BI), and the National Institutes of Health Stroke Scale (NIHSS) were dichotomized according to the criteria used in the NINDS trial. Favorable outcome was defined as a score of 0 or 1 on mRS, a score of 95 or 100 on BI, and a score of 0 or 1 on NIHSS.

RESULTS

The number of patients reaching favorable outcome were higher in all 3 end points in the rtPA-treated group. The effect sizes were 8% for mRS, 6% for BI, and 14% for NIHSS, respectively. The differences are statistically significant for the mRS (P=0.044; odds ratio [OR], 1. 4; 95% confidence interval [CI], 1.0 to 2.0) and the NIHSS (P=0.001; OR, 1.9; 95% CI, 1.4 to 2.8), while for the BI significance was missed (P=0.102; OR, 1.3; 95% CI, 0.9 to 1.8). The global end-point statistics, however, shows a significant increase (P=0.008; OR, 1.5; 95% CI, 1.1 to 2.0) of favorable outcome in the rtPA-treated patient group.

CONCLUSIONS

Using the global end-point analysis, ECASS is positive in the intention-to-treat analysis. This may indicate that the time window for thrombolysis may be as long as 6 hours. Looking at the 3 dichotomized end points, the effect sizes for 2 end points, mRS and BI, are smaller in the ECASS 6-hour intention-to-treat population compared with the NINDS trial, whereas the effect size for the NIHSS is larger. While in the NINDS trial all 3 end points reveal statistically significant results, in ECASS only 2 of the 3 corresponding end points, mRS and NIHSS, were statistically significant. This finding underlines an important difference of a global end-point approach: it may show a positive overall result although one of the end points is not positive.