Endovascular aneurysm sealing system (EVAS)
Endovascular aneurysm sealing system (EVAS) was developed with the intention to expand beyond the anatomic limitations of endovascular aneurysm repair (EVAR) devices, as well as to decrease the rates of re-intervention secondary to graft migration and type II endoleaks.
EVAS was designed by Endologix with the Nellix device and first implanted in 2012. It is a dual lumen balloon expandable PTFE alloy stent surrounded by two separate endobags that are inflated with polyethene glycol to create aneurysmal seal surrounding the patent alloy stents.
- abdominal aortic aneurysm (AAA)
- ruptured/symptomatic AAA
A number of relative contraindications are recognised 1.
- proximal neck diameter of 18-32mm, neck angulation <60%
- maximum Aneurysm flow lumen <70mm
- iliac arteries luminal diameter 9-35mm
CT is essential pre-operatively to measure aneurysmal neck diameter and length, distance from the renal arteries, aneurysm maximal flow diameter, and iliac artery diameter length. Imaging and measurements are reviewed and summarised by Endologix sizing report (produced by the company) to determine optimal stent length, landing zones and predicted polymer fill volumes. The patient is also assessed for suitable access anatomy via femoral arteries.
Important note: This article is not intended to be a step by step instructions set, nor does it replace the need to refer to the manufacturer's instructions.
General or regional anaesthesia. Sterile prep and drape. Bilateral percutaneous access or cut down to femoral arteries. Guidewire insertion, followed by bilateral Nellix catheter insertion. Angiography may be undertaken prior to catheter insertion to confirm proximal neck anatomy and identify landing zones.
Both Nellix catheters inserted into common femoral arteries and stents deployed immediately. The polymer is removed from ice and submerged in room temperature normal saline externally. The bilateral endobags are then pre-filled simultaneously with 0.9% NaCl through the Nellix console until target pressures are achieved, volume recorded then saline is aspirated. The same volume of polymer fill is then inserted simultaneously through the console, pressures reviewed and allowed to cure for 3-5 minutes. A secondary fill may be undertaken if a complete seal has not been achieved. Post insertion angiogram if required, catheters removed, arterial and skin closure.
Post procedural care
There is no consensus at present as to imaging modality and optimal time frame for follow-up. Current trials suggest 30-day and 1-year CT and/or ultrasound to assess for endoleaks 2-4.
Early trials still require long-term follow-up studies to assess endoleak and re-intervention rates, as well as long-term morbidity and mortality statistics. Initial studies show a 30-day mortality rate of 32% in ruptured AAA EVAS 4.
- 1. Endologix. Nellix Safety Information: Endologix; 2017 [10/04/2017]. Available from: https://endologix.com/safety-information-nellix/.
- 2. Holden A, Savlovskis J, Winterbottom A, van den Ham LH, Hill A, Krievins D, et al. Imaging After Nellix Endovascular Aneurysm Sealing: A Consensus Document. J Endovasc Ther. 2016;23(1):7-20.
- 3. McWilliams RG, Fisher RK, England A, Torella F. Observations on surveillance imaging after endovascular sealing of abdominal aortic aneurysms with the Nellix system. J Endovasc Ther. 2015;22(3):303-6.
- 4. Reijnen MM, de Bruin JL, Mathijssen EG, Zimmermann E, Holden A, Hayes P, et al. Global Experience With the Nellix Endosystem for Ruptured and Symptomatic Abdominal Aortic Aneurysms. J Endovasc Ther. 2016;23(1):21-8.