Abstract W P9: SAMMPRIS, WASID, and the Non-Linearity of Stroke Risk: Is There Room for Further Trials of Intervention for Intracranial Stenosis?

Background: SAMMPRIS concluded that aggressive medical management (AMM) was superior to early percutaneous transluminal angioplasty and stenting (PTAS) plus AMM for patients with symptomatic severe intracranial stenosis. WASID and SAMMPRIS have shown that the risk of recurrent stroke after the initial event is early, non-linear, and markedly diminishes over one year irrespective of treatment. We therefore investigated the feasibility of demonstrating benefit for a new endovascular intervention (nEI) for these patients within this narrow time window. Methods: We compared 1-year stroke/death rates in patients treated with AMM versus a hypothesized nEI. The 1-year stroke/death rate for AMM was derived from the SAMMPRIS trial. A minimal 30-day stroke/death rate for a nEI was set to 3% using data from endovascular treatment of unruptured intracranial aneurysms. The subsequent stroke/death rate over the ensuing 11 months was varied above and below the rates achieved in SAMMPRIS, and the sample size for a future 1-sided superiority trial was calculated at 0.05 alpha and 80% power. Results: For a nEI with the same 31-365 days stroke/death rate as SAMMPRIS AMM (5.3%) but an improved 30-day stroke/death rate of 3%, a total of 1,484 subjects would be required to show significant benefit over AMM. At the SAMMPRIS recruitment rate of 187 patients/year, it would take 7.9 years to recruit 1,484 patients. Varying the 31-365 days stroke/death rate for nEI from 3% to 8%, and keeping 0-30 days stroke/death rate constant at 3%, (1 year total nEI stroke/death rate ranging from 6% to 11%), the total sample size required to show significant benefit at 1 year over AMM (1 year stroke/death rate of 12.2%) would be 518 and 17,600 respectively. This trial would take approximately 2.8 years and 94.1 years to recruit the eligible subjects at the SAMMPRIS rate, respectively. Conclusion: Identification of higher-risk subgroups, demonstration of decreased 30-day endovascular complication rates, and enhanced recruitment strategies will be necessary before institution of trials of new endovascular interventions for symptomatic intracranial stenosis.