Preliminary 3D computational analysis of the relationship between aortic displacement force and direction of endograft movement

Abstract

Objective Endograft migration is usually described as a downward displacement of the endograft with respect to the renal arteries. However, change in endograft position is actually a complex process in three dimensional space. Currently, there are no established techniques to define such positional changes over time. The purpose of this study is to determine whether the direction of aortic endograft movement as observed in follow-up CT scans is related to the directional displacement force acting on the endograft. Methods We quantitated the 3D positional change over time of 5 abdominal endografts by determining the endograft centroid at baseline (post-operative scan) and on follow-up CT scans. The time interval between CT scans for the 5 patients ranged from 8 months to 8 years. We then used 3D image segmentation and computational fluid dynamics (CFD) techniques to quantitate the pulsatile displacement force (in Newtons [N]) acting on the endografts in the post-operative configurations. Finally, we calculated a correlation metric between the direction of the displacement force vector and the endograft movement by computing the cosine of the angle of these two vectors. Results The average 3D movement of the endograft centroid was 18 mm (range 9 mm to 29 mm) with greater movement in patients with longer follow-up times. In all cases, the movement of the endograft had significant components in all 3 spatial directions: Two of the endografts had the largest component of movement in the transverse direction, whereas 3 endografts had the largest component of movement in the axial direction. The magnitude and orientation of the endograft displacement force varied depending on aortic angulation and hemodynamic conditions. The average magnitude of displacement force for all endografts was 5.8 N (range 3.7 N to 9.5 N). The orientation of displacement force was in general perpendicular to the greatest curvature of the endograft. The average correlation metric, defined as the cosine of the angle between the displacement force and the endograft centroid movement, was 0.38 (range 0.08 to 0.66). Conclusions Computational methods applied to patient-specific post-operative image data can be used to quantitate three-dimensional displacement force and movement of endografts over time. It appears that endograft movement is related to the magnitude and direction of the displacement force acting on aortic endografts. These methods can be used to increase our understanding of clinical endograft migration.

Altered hemodynamics, endothelial function, and protein expression occur with aortic coarctation and persist after repair

“…While the exact timing of when the coarctation is alleviated in vivo was not precisely determined, the product literature provides an initial strength of ϳ15 lbf and a known strength retention curve based on the number of days since suture implementation. An analysis using this retention curve with our previous CFD results and knowledge of rabbit aortic diameters indicates that the force exerted on the suture used to create the coarctation by integrating the distribution of tractions within this region (22) exceeds the strength indicated by the manufacturer after ϳ21 days. Importantly, this information suggests that the approach of inducing CoA with dissolvable Vicryl suture used for the present investigation provides the stimulus of altered hemodynamic from CoA for 3 wk before restoring BP to normal for Ͼ4 mo (ϳ6 human years) before the experimental end point.…”

Stent graft Surface Movement after Infrarenal Abdominal Aortic Aneurysm Repair: Comparison of Patients with and without a Type 2 Endoleak

“…4,22,23 As an extension of these measurements, in recent studies, stent graft movement in all three spatial directions was explored, which might have an influence on stent graft migration. 9,11,24 Rafii et al 11 showed that, with a mean lateral stent graft movement of 9 mm, the rate of type 1 endoleaks was significantly higher than in patients without lateral movement. The authors assumed that these results represented a clinically relevant predictor of late adverse events.…”

“…Two different working groups reported that pulsatile forces of blood flow, referred to as migration forces, displacement forces, or drag forces, are responsible for the longitudinal movement of the stent graft. 9, 10 Rafii et al 11 focused on the lateral movement of the stent graft, and reported a significantly higher longitudinal migration in patients with a mean 9 mm of lateral deflection. Furthermore, this patient group presented with a significantly higher rate of type 1 endoleaks and the need for secondary interventions.…”

Sideways displacement of the endograft within the aneurysm sac is associated with late adverse events after endovascular aneurysm repair

“…13,14 These investigators found that pulsatile displacement force acting on an endograft is in a sideways direction with respect to the axis of the blood flow rather than in the downstream direction of blood flow. In these patient-specific models, 72% of the total displacement force on the endograft was directed sideways.…”