Aneurysm Recurrence Reduced by Hydrogen Coil in HEAT Trial

Caroline Helwick

April 17, 2019

SAN DIEGO — Final results of the randomized New Generation Hydrogel Endovascular Aneurysm Treatment (HEAT) trial show the second-generation hydrogel coil was superior to the bare platinum coil in reducing aneurysm recurrence rates.

A number of secondary endpoints were also improved with the hydrogel coil, Bernard R. Bendok, MD, chair of the department of neurologic surgery at the Mayo Clinic in Phoenix, Arizona, reported.

As Bendok pointed out, recurrence after aneurysm treatment continues to be a problem. A number of measures have been attempted but most have failed. "Anything we can do to improve that would be a good thing," he told Medscape Medical News. "It's my hope to show that hydrogel coils have started to address this problem."

Findings from HEAT trial would suggest that to be the case, as second-generation hydrogel coils were associated with greater durability of treatment when compared to bare platinum coils without an increase in morbidity, he reported here at the American Association of Neurological Surgeons (AANS) 2019 Annual Scientific Meeting.

Hydrogel Coils

The Hydrogel Embolic System (HES) coil (MicroVention) is a hydrogel-coated platinum coil designed to improve the 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 and the device was not widely adopted. A second-generation HES was designed to withstand longer working times (ie, repositioning time) and reproduce the ease of use of BPC, Bendok explained.

The HEAT trial compares the second-generation HES with BPC in 600 subjects over a period of 2 years. The investigators hypothesized there would be no difference in recurrence between BPC and HES in treating brain aneurysms of 3 to 14 mm, with follow-up up to 24 months posttreatment.  

HEAT was a multicenter randomized investigator-initiated clinical trial conducted in the United States and Canada between 2012 and 2018. The study assessed 3971 patients for eligibility, ultimately enrolling 600 subjects ages 18 to 75 years with 3- to 14-mm ruptured or unruptured brain aneurysms. All patients were considered eligible for endovascular treatment, without comorbidities. Baseline characteristics were well matched.

Patients were randomly assigned to HES or a BPC of physician's choice. Assist devices (balloons and/or stents) were allowed. Only 45 patients in the BPC group and 44 in the HES group discontinued or were lost to follow-up. Patients were followed for up to 2 years, which is about 1 year longer than occurs in most trials, Bendok pointed out.

The primary outcome of the study was aneurysm recurrence (recanalization), defined as any progression by Raymond–Roy occlusion classification at any time during follow-up. Secondary outcomes included a number of imaging and clinical endpoints: initial complete occlusion, packing density, aneurysm occlusion stability, major vs minor recurrence, aneurysm hemorrhage, retreatment, morbidity and mortality, and modified Rankin score. The imaging correlate was blinded to treating site and coil type.

Hydrogel Coil Superior for Most Endpoints

"We tried to look at this from every possible angle," Bendok said. By most of these "angles," the HES yielded better outcomes, he reported.

Rates of recurrence, the primary endpoint, were 4.4% for HES and 15.4% for BPC (P < .001), a highly significant difference that held true for both unruptured aneurysms and ruptured aneurysms.

The same was observed when outcomes were evaluated according to the Meyers scale, considered a "more sensitive" measure of recurrence, he said. The differences were statistically significant, as well, for major recanalization and for minor recanalization.

Table. Outcomes with Hydrogel Coil and Bare Platinum Coils


Hydrogel (%)

Bare Platinum (%)

P Value

Recurrence rate (overall)



< .001

Recurrences in unruptured aneurysms




Recurrences in ruptured aneurysms




Recurrences by Meyers scale



< .001

Major recanalization




Minor recanalization




Packing density



< .001

Incomplete occlusion, initial




Incomplete occlusion, 12-14 months








Adverse event





Packing density (the fraction of aneurysmal volume occupied by a deployed microcoil) was "interestingly" higher with HES "although less coil was used," Bendok reported. "This could have cost implications."

There were no differences in retreatment and rehemorrhage rates, a finding that will be further explored, Bendok added. Adverse events and mortality rates were also similar, as were quality of life measures.

"We did have 3 reported cases of hydrocephalus with hydrogel coils. In all cases, these occurred after more than 1 year of follow-up in patients whose aneurysms were in the posterior circulation," he said. "I am not personally convinced these are related [to treatment choice] but we are reporting them."

Well-Designed Trial Shows Benefit

Invited discussant Adam S. Arthur, MD, of the Semmes Murphey Clinic and the University of Tennessee Department of Neurosurgery in Memphis, welcomed the findings and lauded the quality of the trial.

"This is a randomized controlled trial with blinded adjudicated outcomes that shows a definitive difference," he said. "I am heartened to see that this sort of study is becoming more common in our field as we see improvements in the level of evidence in vascular neurosurgery."

Arthur noted that embolization of aneurysms, both ruptured and unruptured, is a proven and widely available treatment. Embolization has a "favorable safety record" though it is susceptible to angiographic recurrence. While angiographic recurrence rate at 1 year is the generally accepted surrogate for efficacy, "it's important to note that this trial looked at recurrences up to 2 years, which would be expected to be a little more rigorous bar."

He also emphasized the importance of having blinded adjudication, especially for research "in a field that is filled mostly with self-adjudicated outcomes" that can reflect physician bias.  

Frederick Barker, MD, of Massachusetts General Hospital, Boston, further validated the design and analysis of HEAT from a statistical point of view, concluding, "We can have confidence in the results of the trial."

This study was funded by MicroVention. Bendok has no financial relationships with MicroVention. Arthur has consulted for Terumo-MicroVention and a number of other manufacturers. Barker has disclosed no relevant financial relationships.

American Association of Neurological Surgeons (AANS) 2019 Annual Scientific Meeting: Abstract 200. Presented April 15, 2019.  

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