Proximal Fixation of Thoracic Stent-Grafts as a Function of Oversizing and Increasing Aortic Arch Angulation in Human Cadaveric Aortas

Abstract

To assess the fixation of 4 commercially available thoracic stent-grafts as a function of oversizing and increasing aortic arch angulation. 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. 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. 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.