Abstract WMP1: Factors Influencing Differential Outcomes in Stent Retriever Trials: Comparison to a new Outcome Model Based on Percent Utilization of rt-PA
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Background: While stent-retriever randomized clinical trials (RCTs) were uniformly positive, their designs differed. Here, we assessed whether trials also differed in the magnitude of improvement and if factors could be identified that distinguished the best performers. Because % utilization of rt-PA in the control arms varied, we developed a multi-dimensional outcome model from the control arms of all IV tPA RCTs treating various % of subjects and their baseline stroke severity (NIHSS). This model was used to compare each trials functional outcome (mRS < 2) and mortality at their own baseline without need for statistical manipulation. We assessed factors that potentially distinguished the best performers. Methods: The model was developed from 54 RCT control arms representing >11,000 subjects treating between 0-100% with IV rt-PA. 3-D non-linear functions were fit to the 90-day mortality and mRS 0-2. This model includes 95% statistical interval surfaces to assess whether a trials outcomes surpass the variability inherent in a sample of RCT subjects (Neurology 85:274-83, 2015). 6 stent retriever RCTs were compared. Results: The models showed excellent fit: mRS 0-2 (r 2 =0.83, p<<0.001) and mortality (r 2 =0.65, p<<0.001) Figs 1a, 1b. All stent retriever arms exceeded mRS 0-2 +95% surface indicating better than expected efficacy, but the degree of improvement varied: 30-40% absolute improvement over expected outcome was seen in EXTEND and SWIFT-PRIME, compared to 12% for SWIFT and REVASCAT. The 2 top performers had a 75 minute shorter treatment time. Both treated 100% with IV rt-PA compared to SWIFT (33%) and REVASCAT (68%). Conclusion: A new outcome model based on stroke severity and % IV rt-PA permitted analysis of stent-retriever therapy compared to a large population. Best outcomes were related to shorter treatment time and higher utilization of rt-PA, suggesting a treatment interaction between these modalities. Factors influencing mortality are being analyzed.
