Use of Liquid Embolic Agents

In a presentation at The International Symposium on Endovascular Therapy (ISET) that took place February 4 – 7, 2018 in Hollywood, Florida, Marcelo Guimaraes, MD, FSIR, of the Medical University of South Carolina, provided a brief overview of liquid embolic agents, including N-BCA (N-Butyl Cyanoacrylate), Onyx, and sclerosants, and their applications in peripheral embolization procedures. During his talk, Dr. Guimaraes devoted his time to discuss embolic agent selection and preparation as well as best-practice techniques. Additionally, he presented several cases in which embolization therapy with liquid embolic agents were successfully utilized.

Tips for Choosing Embolic Agents

When embolic agents are chosen, a factor that is important to understand is the location of the occlusion that’s being treated, according to Dr. Guimaraes. Additional factors to consider when choosing embolic agents include the level of occlusion, blood vessel diameter, flow dynamics (eg, fast or slow), whether the patient is or is not hemodynamically stable, whether it is an emergency, and whether or not coagulopathy is present. Typically, liquid embolic agents are used in microaxial systems in a microcatheter. Glue, such as N-BCA, is a liquid embolic agent that polymerizes quickly via an anionic mechanism, or upon contact with fluid or tissues in the body. Mixing glue with ethiodol will reduce the polymerization time, he noted.

Management Techniques

To prevent polymerization of the glue inside the microcatheter, Dr. Guimaraes suggests priming the catheter with 5% dextrose as a means for preventing ion contact with fluid or tissue. Saline should never be used to prime the catheter, since this solution contains ions and will facilitate the polymerization process and result in solidification of the glue in the catheter.

While some interventionalists may have a “recipe” for glue, Dr. Guimaraes notes that his use of glue isn’t standard and primarily depends on the level of embolization. For instance, if embolization occurs proximally and you can only advance the microcatheter proximally, it may be better to use a diluted glue of low concentration.
 

Diluted, low-concentration glue will take longer to polymerize, and the glue will go deeper into the tissue. If the catheter can be advanced more proximal to the target, a 50% N-BCA glue with 50% ethiodol may be appropriate. If it is necessary to have the glue polymerize quickly, it’s best to use a higher concentration of glue and a lower concentration of ethiodol (eg, 70% and 30%, respectively).

The “pull back” technique allows interventionalists to delve deeper into the tissues via injecting into the tissues while slowing “pulling back.” This technique enables clinicians to have a better view of several vessels, which may be important in trauma cases where multiple branches have sites where bleeding originates.

Onyx Liquid Embolic Agent

Onyx, a spongy, foam-like agent comprised of ethylene-vinyl alcohol copolymer with DMSO (dimethyl sulfoxide) solvent and micronized tantalum powder, was developed and approved by the FDA in 2005 for treatment of cerebral AVMs. The agent is non-adhesive, liquid, and is a permanent embolic for large/small vessels. Solidification occurs in contact with ionic materials, but the agent does not precipitate or solidify to the same extent as glue. Dr. Guimaraes emphasized that Onyx is less adhesive than cyanoacrylate and can be injected over a long duration without the risk of catheter adherence.

Onyx is similar to a volcano lava, forming a cast on the exterior and a liquid-like consistency in the interior. Once injected, the agent begins to expand and occupy space. To create an Onyx preparation, vials should be shaken for a total of 20 minutes. The catheter should be flushed and primed with DMSO. Injection should be performed slowly, otherwise the patient will complain of pain. Additionally, fluoroscopy should be used during injection. Dr. Guimaraes suggests that clinicians can allow Onyx to bounce back 1 cm to the microcatheter, but beyond this point the microcatheter might get stuck. When embolization of a large area is required, road mapping may be helpful to “map” the location of Onyx.

Overall, Dr. Guimaraes adds that both glue and Onyx liquid embolic agents are effective and safe to use in most cases. These agents can be used off-label for several applications in peripheral embolization, are relatively simple to use, and are cost-effective.

- Brandon May