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Commentary: The Unsupported Nitinol Main Body of the Ovation Device: Blamed More Often Than Deserved?

The most common complication after EVAR remains type II endoleak, with an incidence of 15% to 44%. According to the literature, 75% to 80% resolve spontaneously, with the rest following a rather benign course; rupture rate secondary to an isolated type II endoleak is <1%, but more than a third occur in the absence of sac expansion. However, a persistent endoleak with sac growth necessitates an intervention. Moreover, endoleaks in several cases evolve with recruitment of additional vessels over time, making successful obliteration of type II endoleak most challenging. The commonest approaches for embolization of type II endoleak include transarterial, translumbar, or direct vessel puncture to deliver embolizing agents such as metallic coils, Amplatzer vascular plugs, thrombin, liquid glues, or ethylene vinyl alcohol copolymer (Onyx). According to Hajibandeh et al, the translumbar approach has the highest technical success. Still, no embolizing route can ensure a durable effect, with a 5-year recurrence rate reported to be 25% to 80% following successful intervention. Although its major application is considered treatment of arteriovenous malformations, glue embolization alone or in combination with coils has been also reported for the treatment of type II endoleak. N-butyl-cyanoacrylate (NBCA) is mixed with iodized oils to gain opacity and alter polymerization time, that is, the polymerization rate increases when it comes in contact with anions in blood. Mixing the glue with lipiodol results in a homogeneous solution that increases in viscosity, density, and interfacial tension with the proportion in lipiodol. The polymerization rate, front propagation speed, and volume reduction also increase with the glue concentration. NBCA is mixed with iodized oil in a ratio varying from 1:1 to 1:5, although there have been reports of successful use even at concentrations of 10%. The Ovation Abdominal Stent Graft System (Endologix, Irvine, CA, USA) is a trimodular endoprosthesis that uncouples the stages of stent-graft fixation and sealing seen with suprarenal fixation and replaces them with a long, rigid anchored stent and a pair of inflatable polymer-filled rings to seal onto the neck. While the lack of a nitinol skeleton enables adaptation to lower profiles, which ensures greater flexibility and easier navigation through stenosed and tortuous iliac anatomies, it renders the unsupported main body of the endograft prone to kinking and collapse if pushed externally. Moreover, the inflated pair of rings pose a technical challenge to management of central endoleaks when it comes to catheter-directed embolization from above. In the April 2018 issue of the JEVT, Ni et al report collapse of the Ovation endograft during glue embolization of 2 type II endoleaks after injecting 8 mL of 10% glue. Since there was no preliminary injection of contrast agent to estimate the endoleak volume, it could be that the volume of delivered glue was higher than needed, presumably in the authors’ attempt to drive the glue into the lumbar feeders. Since outflow was sealed with coils, the complication may have occurred due to a combination of chemical and mechanical factors. The volume injected in a closed space probably displaced the unsupported Ovation limbs while at the same time the low concentration reduced the polymerization and thus the shrinkage effect of the volume injected. Another interesting scenario would be that although NBCA and lipiodol are miscible, solution concentrations lower than 25% in a vertical plane may have caused a 761049 JETXXX10.1177/1526602818761049Journal of Endovascular TherapyGeorgakarakos and Koutsoumpelis research-article2018