Displacement forces in iliac landing zones and stent graft interconnections in endovascular aortic repair: an experimental study.

ABSTRACT

OBJECTIVES: Stent graft migration influences the long-term durability of endovascular aortic repair. Flow-induced displacement forces acting on the attachment zones may contribute to migration. Proximal fixation of aortic stent grafts has been improved by using hooks, while distal fixation and stent graft interconnections depend on self-expansion forces only. We hypothesized that flow-induced displacement forces would be significant at the distal end, and would correlate with graft movements. METHODS: As part of an experimental study, an iliac limb stent graft was inserted in a pulsatile flow model similar to aortic in vivo conditions, and fixed-mounted at its proximal and distal ends to strain gauge load cells. Peak displacement forces at both ends and pulsatile graft movement were recorded at different graft angulations (0-90°), perfusion pressures (145/80, 170/90, or 195/100 mmHg), and stroke frequencies (60-100 b.p.m.). RESULTS: Flow-induced forces were of the same magnitude at the proximal and distal end of the stent graft (peak 1.8 N). Both the forces and graft movement increased with angulation and perfusion pressure, but not with stroke rate. Graft movement reached a maximum of 0.29 ± 0.01 mm per stroke despite fixed ends. There were strong correlations between proximal and distal displacement forces (r = 0.97, p < .001), and between displacement forces and graft movement (r = 0.98, p < .001). CONCLUSIONS: Pulsatile flow through a tubular untapered stent graft causes forces of similar magnitude at both ends and induces pulsatile graft movements in its unsupported mid-section. Peak forces are close to those previously reported to be required to extract a stent graft. The forces and movements increase with increasing graft angulation and perfusion pressure. Improved anchoring of the distal end of stent grafts may be considered.