Proximal fixation of thoracic stent-grafts as a function of oversizing and increasing aortic arch angulation in human cadaveric aortas.

PURPOSE: To assess the fixation of 4 commercially available thoracic stent-grafts as a function of oversizing and increasing aortic arch angulation. METHODS: A benchtop pulsatile flow model was devised to test stent-graft anchorage in a 2-cm-long proximal landing zone at varying landing zone angles (70 degrees to 140 degrees ) and stent-graft oversizing (5% to 37%). The experiments were performed using 15 human thoracic cadaveric aortas and 4 stent-grafts with different proximal anchoring mechanisms: TAG, Zenith TX, Valiant, and Relay. The lack of device-wall apposition was measured as a function of landing zone angulation and oversizing during static and dynamic (60 pulses/min, 300/150 mmHg) tests; stent-graft collapse was also investigated. RESULTS: The Valiant stent-graft remained apposed to the aortic wall at each increment of neck angulation and degree of oversizing. Lack of apposition of the proximal anchorage segment (Relay: bare spring; TAG: scalloped flares) was observed with the Relay above 80 degrees landing zone angulation (1-7 mm) and with the TAG above 90 degrees angulation (1-6 mm). The lack of device-wall apposition was greater with Relay than TAG (p = 0.009), but the "body" of these devices always remained well apposed. Lack of "body" apposition (1.0-7.5 mm) was first observed with the Zenith stent-graft above 70 degrees angulation (p<0.001). No stent-graft collapse was seen. An increase in stent-graft oversizing significantly (p<0.01) increased the lack of device-wall apposition for the TAG, Zenith, and Relay devices. CONCLUSION: In the face of severe aortic arch angulation, stent-grafts with hooks do not improve fixation. Major factors in stent-graft design that contribute to secure proximal anchorage seem to be radial force and the presence of a proximal open stent segment.

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 (approximately 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.