A Randomized Trial of Second-Generation Hydrogel Neurovascular Coils

Several strategies to improve upon bare platinum neurovascular coils have been studied, including coating coils with polymers (eg, polyglycloic acid, lactide, etc) to induce a local inflammatory response and coupling coils with hydrogel that expands upon contact with liquid blood to improve packing density.1 In 2011, the Hydrogel-Coated Coils Versus Bare Platinum Coils for the Endovascular Treatment of Intracranial Aneurysms trial studied first-generation hydrogel coils and found some evidence of benefit of hydrogel over standard, platinum coils.2 However, several technical limitations of the hydrogel coils themselves were noted, and second-generation hydrogel coils that are softer and more slowly expanding were developed to address these limitations. Taschner et al3 performed a multicenter randomized controlled trial to compare second-generation hydrogel coils (experimental arm) with standard bare platinum coils (control arm). The specific hydrogel coils used were HydroFrame and HydroSoft (MicroVention Inc, Aliso Viejo, California) hydrogel neurovascular embolic coils.4 The authors included patients with unruptured intracranial aneurysms (UIA) and also patients with subarachnoid hemorrhage with World Federation of Neurologic Surgeons grades 0 to 3. They excluded aneurysms greater than 12 mm in diameter because the largest commercially available hydrogel coil at the time of the study was 12 mm. Patients randomized to the experimental arm could also receive some bare platinum coils, so long as the second-generation hydrogel coils constituted >50% of the total coil length deployed. Assist devices, including balloons and stents, were allowed in both arms. A blinded, core imaging laboratory analyzed all of the treatment and follow-up radiographic images. The authors created a composite primary endpoint including multiple different unfavorable events including aneurysm recurrence, aneurysm retreatment, and death during treatment or during the follow-up period. The investigators randomized 513 patients from 2009 to 2014, and 484 patients were included in the analysis. The hydrogel and bare platinum arms were well-balanced. Overall, 20% of the hydrogel cohort vs 29% of the bare platinum cohort reached the primary endpoint, meaning that there was a shift in the distribution of unfavorable outcomes towards the bare platinum group. Angiographic outcomes at 18 mo follow-up also favored the hydrogel arm (Table). TABLE. - Angiographic Outcomes at 18-Month Follow-up Randomized treatment Hydrogel Control (bare platinum) No. % No. % Total number of patients with available angiographic follow-up dataa 217 221 Complete obliteration 150 69% 118 53% Residual neck 24 11% 44 20% Residual aneurysm 43 20% 59 27% Missing angiographic follow-up data 26 20 aSix-month instead of 18-mo angiographic controls for 31 (14.3%) patients in the hydrogel arm and 50 (22.6%) patients in the control group.Reprinted by permission from Springer International Publishing AG; Neuroradiology. GREAT—a randomized aneurysm trial. Design of a randomized controlled multicenter study comparing HydroSoft/HydroFrame and bare platinum coils for endovascular aneurysm treatment, Taschner et al. © Springer International Publishing AG, 2015.4 As ruptured and UIA are increasingly treated with endovascular methods, efforts to reduce the incidence of aneurysm recurrence and retreatment are warranted. A systematic review of the 5 previously published randomized controlled trials evaluating bioactive coils showed that bioactive coils (including hydrogel coils) are associated with a higher rate of complete aneurysm occlusion and a lower rate of residual neck filling than bare platinum coils.1 The modest treatment benefit of hydrogel coils seen in these trials—and now echoed in the GREAT trial—will need to be weighed against the added financial costs associated with bioactive coils, and also technical improvements that have occurred in bare platinum coil technology over time. Nevertheless, the authors are to be congratulated for this well-designed and relevant trial. Disclosure The authors have no personal, financial, or institutional interest in any of the drugs, materials, or devices described in this article.