Effect of Curvature on Displacement Forces Acting on Aortic Endografts: A 3-Dimensional Computational Analysis

Abstract

¤ ¤Purpose: To determine the effect of curvature on the magnitude and direction of displacement forces acting on aortic endografts in 3-dimensional (3D) computational models.Method: A 3D computer model was constructed based on magnetic resonance angiography data from a patient with an infrarenal aortic aneurysm. Computational fluid dynamics tools were used to simulate realistic flow and pressure conditions of the patient. An aortic endograft was deployed in the model, and the displacement forces acting on the endograft were calculated and expressed in Newtons (N). Additional models were created to determine the effects of reducing endograft curvature, neck angulation, and iliac angulation on displacement forces. Results: The aortic endograft had a curved configuration as a result of the patient's anatomy, with curvature in the anterolateral direction. Total displacement force acting on the endograft was 5.0 N, with 28% of the force in a downward (caudal) direction and 72% of the force in a sideways (anterolateral) direction. Elimination of endograft curvature (planar graft configuration) reduced total displacement force to 0.8 N, with the largest component of force (70%) acting in the sideways direction. Straightening the aortic neck in the curved endograft configuration reduced the total force acting on the endograft to 4.2 N, with a reduction of the sideways component to 55% of the total force. Straightening the iliac limbs of the endograft reduced the total force acting on the endograft to 2.1 N but increased the sideways component to 91% of the total force. Conclusion: The largest component of the force acting on the aortic endograft is in the sideways direction, with respect to the blood flow, rather than in the downward (caudal) direction as is commonly assumed. Increased curvature of the aortic endograft increases the magnitude of the sideways displacement force. The degree of angulation of the proximal and distal ends of the endograft influence the magnitude and direction of displacement force. These factors may have a significant influence on the propensity of endografts to migrate in vivo.

Computational Fluid Dynamics Modeling of Redundant Stent-Graft Configurations in Endovascular Aneurysm Repair

“…A recent study by Figueroa et al has highlighted the fact that the important displacement forces are not entirely in the downward direction, but that a significant component is in the 'lateral' direction [18]. Since the geometry created in our study lay entirely in a horizontal plane, there was no lateral force in the z-direction (which was the direction of significant proximal anterior angulation in their study).…”

“…Morris et al have further characterized analytical studies of stent-graft flow by adding pulsatile flow and graft compliance [7]. Other studies have pursued patient-specific geometries [14,15] and comparisons of pre-and post-EVAR scenarios [16][17][18]. In a recent review of biomechanical behavior and performance of stent-grafts, Corbett et al noted that as the technique of EVAR matures, the focus of research is moving from feasibility studies to assessments of failure mechanisms [19].…”

“…It is becoming increasingly clear that evaluating the simple downward (y-direction) force acting on the device is not sufficient, and that the out-of-plane forces play an important role [18,40]. Our group is presently evaluating the out-of-plane configuration of crossed-limb stent-grafts.…”

Studying the Flow Dynamics Within Endografts in Abdominal Aortic Aneurysms

“…The latter constitutes a rather common incidental finding, occurring more frequently that previously assumed (Wu et al, 2009). Finally, the study and understanding of the hemodynamic alterations and the parameters that influence them, could lead to better designs of endovascular grafts, in order to eliminate the factors that predispose to endograft migration as well as to generation of endoleaks (Figueroa 2009and 2010, Liffman 2001, Mohan 2002). …”

Functional assessment of thoracic aortic aneurysms – the future of risk prediction?

“…Whereas 4D flow MRI is limited to only acquiring live data from patients, CFD has the capacity to simulate proposed changes in anatomy and physiological parameters which may be the result of medical, surgical or pharmacological interventions, in order to see the effect that these may have on haemodynamics and biomechanics. [34][35][36] This allows simulating interventions and procedures to see their effects, without putting patients at the risks of the intervention. Nevertheless, CFD and 4D flow MRI can be used together to further improve understanding of hemodynamics in aortic disease.…”