Endovascular Stent-Anchored Aortic Grafts: A Comparison between Self-Expanding and Balloon-Expandable Stents in Minipigs

Improvement in Proximal Aortic Endograft Fixation: An Experimental Study Using Different Stent-Grafts in Human Cadaveric Aortas

Purpose:

To compare the proximal fixation characteristics of different types of stent-grafts (SG) and the adjunctive effect of a proximally placed Palmaz stent.

Methods:

Human cadaveric aortas were obtained at autopsy and cut into 30 aortic segments. Appropriately oversized (10% to 20%) commercial stent-grafts (Zenith, Ancure, Excluder, Talent) and 4 configurations of homemade Palmaz-based stent-grafts (polytetrafluoroethylene or polyester coverings each with no uncovered proximal edge or a 20-mm bare section of stent) were implanted 20 mm into an aortic segment and balloon dilated. Each segment was placed in an experimental apparatus to measure the dislodgment force. Bare Palmaz stents were used to reinforce the proximal fixation of the commercial stent-grafts, and the measurements were repeated. Manual anastomoses were made and their dislodgment force tested for comparison.

Results:

The median dislodgment force ranged from 6.5 N for the Excluder to 26.5 N for the Zenith (8.0 N for the Talent, 11.8 N for the Ancure, and 8.1 to 10.7 N for the various Palmaz stent-graft designs). There was no significant difference between the Zenith and the Ancure groups or between the Excluder and the Talent groups. However, the Zenith and Ancure devices required significantly higher (p = 0.0004) force (∼25%) to displace them than the other stent-grafts tested. With the Palmaz stent added to the proximal attachment site, the median dislodgment force for the different commercial endografts was significantly improved for all devices (p < 0.03): 34% for the Zenith device, 69% for the Ancure, 73% for the Talent, and 80% for the Excluder endoprosthesis.

Conclusions:

The Zenith stent-graft had the best resistance to dislodgment. An additional Palmaz stent placed at the proximal attachment site greatly improves endograft fixation regardless of the type of stent-graft. For complex aneurysm necks or for intraoperative type I endoleak management, an adjunctive Palmaz stent could be used.

How to design the optimal stent graft--what have we learnt?

It is now more than 20 years since the first report of stent graft insertion in the human arterial system was published. The first "homemade" devices proved that the technique was possible but could not show any durability. Using these devices, it was possible to get a good seal but not a good anchorage. Not even the first generation of commercially available stent grafts proved to be durable. First after gaining knowledge about the forces acting on the stent graft, it was realized that attachment was important for the durability and the hooks and barbs or a longitudinal stability are needed to minimise the risk for distal migration. Not much of a difference in the overall performance is noticed between the ePTFE graft or the polyester graft or when comparing stainless steel stents with those made out of nitinol. The systems are made much more flexible and hydrophilic leading to a better performance and a greater chance of percutaneous approach. The optimal stent graft is not out on the market yet, but hopefully will come with further development.