Analysis of the Influence of Endograft Geometry on Blood Hemodynamics in Abdominal Aortic Aneurysm by Computational Fluid Dynamics

Chang Hsiang Huang

doi:10.4172/2155-9880.1000340

Abstract

Objectives: Endovascular Aneurysm Repair (EVAR) is considered the treatment of choice for Abdominal Aortic Aneurysm (AAA). However, thrombotic deposits found incidentally in abdominal aortic endografts are common and the deposition of thrombus is reported to be influenced by the geometry of the aortic stent graft. We used computational fluid dynamic techniques to analyze the biomechanical factors associated with different stent graft morphologies Methods and models: Computational fluid dynamic models were constructed to investigate the biomechanical factors affecting both tuburlent flow and the drag force in modular AAA stent grafts. The resultant flow separation and drag force as a net change of fluid momentum were calculated on the basis of varying three-dimensional geometry. Modular AAA stent grafts with four different lengths of graft mani body were compared. Computational fluid dynamic simulations were then performed on each stent graft model according to its geometric parameters to determine the flow separation and the actual change in drag force experienced by the stent graft. Results: In all these simulations, the blood flow created as adverse pressure gradient when blood flow decelerated. Flow separation occurred when the boundary layer velocity gradient dropped almost to zero causing recirculation and vortices to be formed downstream of the main graft body and leading to intraprosthetic thrombosis and endograft limb obstruction. With a shorter length graft main body, it was possible to avoid flow separation, reducing the probability of occurrences of the flow recirculation and vortices. The drag force causing device migration was higher with elevated blood pressure and unchanged with the main body length. Conclusion: Flow separation in modular AAA stent grafts is common and occurs more often in endografts with a longer main body. The shorter main body design of the endograft can be applied without the expense of increasing drag force.

Highlights

Abdominal Aortic Aneurysm (AAA) is a localized dilatation of the abdominal aorta exceeding the normal diameter by more than 50 percent, and is the most common form of aortic aneurysm
The area affected by the recirculation and vortices gradually increases in the frontal plane when the velocity of the fluid field of stent no. 4 is reduced to t/T=0.5, while the fluid field of stent no. 3 started to form recirculation and vortices in the frontal plane at this time (Figure 4A)
The drag force that caused device migration is the sum of the pressure drag force and the friction drag force being applied on the stent wall

Summary

Introduction

Abdominal Aortic Aneurysm (AAA) is a localized dilatation of the abdominal aorta exceeding the normal diameter by more than 50 percent, and is the most common form of aortic aneurysm. The major complication of AAA is rupture, which is life-threatening and mortality of rupture repair in the hospital is 60% to 90% [1,2]. Nowadays Endovascular Aneurysm Repair (EVAR) is considered the treatment of choice for the majority of AAA since it demonstrates improved perioperative morbidity and aneurysm-related mortality, comparing to conventional open repair. Despite the initial technical success and early discharge of the patient, this technique is associated with a unique set of complications, including endoleak, device migration and intraprosthetic thrombosis which mandate ongoing postoperative surveillance [3,4,5,6,7,8,9,10,11]. The hemodynamic changes that the endograft sustains during the follow-up period make it prone to positional changes with subsequent risk for endograft migration and the intraprosthetic thrombus formation, where the geometry of the endograft is one of the most important factors [9]

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Conclusion