Authors: Bernard R. Bendok, MD, FAANS; Karl Abi-Aad, MD; Jennifer Ward, MBA; Jason Kniss; Mary Jeanne Kwasny; Rami James Aoun, MD, MPH; Tarek El Ahmadieh, MD; Samer Zammar, MD; Salah Aoun, MD; Najib El Tecle, MD; Rudy Rahme, MD; Matthew Welz, MS (Phoenix, AZ)

Introduction: The Hydrogel Embolic System (HES) coil (Microvention, Aliso Viejo, CA), which is a hydrogel coated platinum coil, was designed to improve packing density and long-term obliteration rates of intracranial aneurysms. The first-generation HES demonstrated lower recurrence rates than bare platinum coils (BPC); however, its use was limited by technical difficulties. A second-generation HES was designed to withstand longer working times and reproduce the ease of use of BPC. The New Generation Hydrogel Endovascular Aneurysm Treatment Trial (HEAT) compares the second-generation HES with BPC in 600 subjects, over a period of 2 years. Methods: HEAT is a multicenter randomized controlled clinical trial that enrolled subjects 18–75 years of age with 3–14 mm ruptured or unruptured brain aneurysms eligible for endovascular treatment. Randomization occurred in a 1:1 fashion across 46 sites in the US and Canada. Subjects assigned to the Hydrogel arm received 90% second-generation HES, at least. The primary outcome of the study was aneurysm recanalization. Secondary outcomes were initial occlusion, packing density, hemorrhage, retreatment, mortality, and aneurysm recanalization assessed by other scales. Results: Enrollment began in 2012 and ended in 2016. 86.2% of the 600 enrolled subjects had at least one follow-up angiogram or MRA evaluation. Recanalization rates were 4.4% for HES and 15.4% for BPC (p<0.001). In terms of secondary outcomes, there were no differences in adverse events (p=0.498) mortality (p=0.641), retreatment (p=0.162), and rehemorrhage rates (p=0.297) between both arms. Conclusion: In the HEAT trial, the second-generation Hydrogel Coil was found to be superior to the bare platinum coil in reducing aneurysm recurrence rates. Adverse events and Clinical outcomes were similar between both arms of the study. The findings of this trial suggest that second-generation hydrogel coils are associated with greater durability of treatment when compared to bare platinum coils without any increase in morbidity.