Endotension Distribution in Fluid-Structure Interaction Analysis of Abdominal Aortic Aneurysm Following Endovascular Repair

Zeinab Hooshyar, Hadi Fakhrabadi, Somayeh Hooshyar, Alireza Mehdizadeh

Department of Medical Physics, School of Medicine, Shiraz University of Medical Sciences (SUMS), Shiraz, Iran.
Department of Midwifery, Shiraz University, Shiraz, Iran.
Mechanical Engineering, Shiraz University, Shiraz, Iran.

DOI: 10.4236/jbise.2014.710084                

Abstract

Endovascular aneurysm repair is a new and minimally invasive repair for patients with abdominal aortic aneurysm (AAA). However, endotension is one of the post-operative compliances of endo-vascular aneurysm repair in abdominal aortic aneurysm. Typically, endotension is mainly a result of pressure transmitted to the aneurysm sac through endovascular implanted graft (EVG) by intermediary of the stagnant blood filled aneurysm cavity. Focusing on a representative AAA with an EVG, a fluid-structure interaction (FSI) solver has been employed to provide physical insight for evaluating the blood flow dynamics, maximum AAA-stresses and deformations. Although implanting an EVG can reduce the sac pressure, mechanical stress and wall deformation in AAAs significantly, they remain non-zero. These magnitudes depend on multi-factors including blood flow conditions such as velocity and pressure, as well as EVG and aneurysm geometries. In this study, it was found that blood flow velocity deceleration occurs on the graft due to the curvature of its neck, so greater curvature of the graft neck can contribute to vortex formation in this area and exert load on the graft wall. In the iliac bifurcation region, divaricating of the flow leads to a large net flow momentum change. It results in additional stress on the implant graft and may lead to graft migration. One of the peak wall stress points is in the neck region where the stent-graft is in contact with the aneurysm wall. This necessitates considering adequate graft fixation to withstand the stresses of blood flow through the implanted graft. Also, maximum deformation of sac wall occurs in around the large diameter of the sac, and deformation during the systole phase is higher than that during the diastole phase.

Keywords

Endotension, Fluid-Structure Interaction, Endovascular Repair, Endovascular Implanted Graft

Conflicts of Interest

The authors declare no conflicts of interest.

References

[1]	Nordon, I.M., Hinchliffe, R.J., Loftus, I.M. and Thompson, M.M. (2010) Pathophysiology and Epidemiology of Abdominal Aortic Aneurysms. Published Online 16 November 2010.
[2]	Legs For Life (2013) National Screening for Vascular Disease. http://www.legsforlife.org/
[3]	Drury, D., Michaels, J.A., Jones, L. and Ayiku, L. (2005) Systematic Review of Recent Evidence for the Safety and Efficacy of Elective Endovascular Repair in the Management of Infrarenal Abdominal Aortic Aneurysm. The British Journal of Surgery, 92, 937-946. http://www.ncbi.nlm.nih.gov/pubmed/16034817
[4]	Magennis, R., Joekes, E., Martin, J., White, D. and McWilliams, R.G. (2002) Pictorial Review Complications Following Endovascular Abdominal Aortic Aneurysm Repair. Departments of Radiology and Vascular Surgery, Royal Liverpool University Hospital, Liverpool.
[5]	Gilling-Smith, G.L., Brennan, J.A., Harris, P.L., Bakran, A., Gould, D.A. and McWilliams, R.G. (1999) Endotension after Endovascular Aneurysm Repair: Definition, Classification and Strategies for Surveillance and Intervention. Journal of Endovascular Surgery, 6, 305-307. http://dx.doi.org/10.1583/1074-6218(1999)006<0305:EAEARD>2.0.CO;2
[6]	Jackson, R.S., Chang, D.C. and Freischlag, J.A. (2012) Comparison of Long-Term Survival after Open vs Endovascular Repair of Intact Abdominal Aortic Aneurysm among Medicare Beneficiaries. JAMA, 307, 1621-1628.
[7]	Di Martino, E.S., Guadagni, G., Fumero, A., Ballerini, G., Spirito, R., Biglioli, P. and Redaelli, A. (2001) Fluid-Structure Interaction within Realistic Three-Dimensional Models of the Aneurysmatic Aorta as a Guidance to Assess the Risk of Rupture of the Aneurysm. Medical Engineering Physics, 23, 647-655. http://dx.doi.org/10.1016/S1350-4533(01)00093-5
[8]	Finol, E.A., Di Martino, E.S., Vorp, D.A. and Amon, C.H. (2003) Fluid-Structure Interaction and Structural Analyses of an Aneurysm Model. Proceedings of the ASME 2003 Summer Bioengineering Conference, Key Biscayne, FL, 25-29 June 2003, 75-76.
[9]	Li, Z., Kleinstreuer, C. and Farber, M. (2005) Computational Analysis of Biomechanical Contributors to Possible Endovascular Graft Failure. Biomechanics and Modeling in Mechanobiology, 4, 221-234. http://dx.doi.org/10.1007/s10237-005-0003-0
[10]	Molony, D.S., Callanan, A., Kavanagh, E.G., Walsh, M.T. and McGloughlin, T.M. (2009) Fluid-Structure Interaction of a Patient-Specific Abdominal Aortic Aneurysm Treated with an Endovascular Stent-Graft. BioMedical Engineering OnLine, 8, 24. http://dx.doi.org/10.1186/1475-925X-8-24
[11]	Molony, D.S., Kavanagh, E.G., Madhavan, P., Walsh, M.T. and McGloughlin, T.M. (2010) A Computational Study of the Magnitude and Direction of Migration Forces in Patient-Specific Abdominal Aortic Aneurysm Stent-Grafts. European Journal of Vascular & Endovascular Surgery, 40, 332-339. http://dx.doi.org/10.1016/j.ejvs.2010.06.001
[12]	Thubrikar, M., Al-Soudi, J. and Robicsek, F. (2001) Wall Stress Studies of Abdominal Aortic Aneurysm in a Clinical Model. Annals of Vascular Surgery, 15, 355-366. http://dx.doi.org/10.1007/s100160010080
[13]	Chong, C.K. and How, T.V. (2004) Flow Patterns in an Endovascular Stent-Graft for Abdominal Aortic Aneurysm Repair. Journal of Biomechanics, 37, 89-97. http://dx.doi.org/10.1016/S0021-9290(03)00236-7
[14]	Volodos, S.M., Sayers, R.D., Gostelow, J.P. and Bell, P. (2003) Factors Affecting the Displacement Force Exerted on a Stent Graft after AAA Repair—An in Vitro Study. European Journal of Vascular & Endovascular Surgery, 26, 596-601. http://dx.doi.org/10.1016/j.ejvs.2003.08.002
[15]	Di Martino, E.S., Bohra, A., Scotti, C.M., Finol, E.A. and Vorp, D.A. (2004) Wall Stresses before and after Endovascular Repair of Abdominal Aortic Aneurysms. AAA Pre- and Post-EVAR, IMECE2004-61556. ASME IMECE, Advances in Bioengineering, Anaheim, CA, 13-19 November 2004, 325-326.
[16]	Ganong, W.F. (1988) Review of Medical Physiology. Appleton & Lange, California.
[17]	Lai, W.M., Rubin, D. and Krempl, E. (1999) Introduction to Continuum Mechanics. Elsevier Science, Burlington.
[18]	Johnston, B.M., Johnston, P.R., Corney, S. and Kilpatrick, D. (2006) Non-Newtonian Blood Flow in Human Right Coronary Arteries: Transient Simulations. Journal of Biomechanics, 39, 1116-1128. http://dx.doi.org/10.1016/j.jbiomech.2005.01.034
[19]	Cho, Y.I. and Kensey, K.R. (1991) Effects of the Non-Newtonian Viscosity of Blood in Flows in a Diseased Arterial Vessel. Part 1: Steady Flows. Biorheology, 28, 241-262.
[20]	Johnston, B.M., Johnston, P.R., Corney, S. and Kilpatrick, D. (2004) Non-Newtonian Blood Flow in Human Right Coronary Arteries: Steady State Simulations. Journal of Biomechanics, 37, 709-720. http://dx.doi.org/10.1016/j.jbiomech.2003.09.016
[21]	Giannakoulas, G., Giannoglou, G., Soulis, J., Farmakis, T., Papadopoulou, S., Parcharidis, G. and Louridas, G. (2005) A Computational Model to Predict Aortic Wall Stresses in Patients with Systolic Arterial Hypertension. Medical Hypotheses, 65, 1191-1195. http://dx.doi.org/10.1016/j.mehy.2005.06.017
[22]	Suzuki, K., Ishiguchi, T., Kawatsu, S., Iwai, H., Maruyama, K. and Ishigaki, T. (2001) Dilatation of Stent-Grafts by Luminal Pressures: Experimental Evaluation of Polytetra-fluorothylene (PTFE) and Woven Polyester Grafts. CardioVascular and Interventional Radiology, 24, 94-98. http://dx.doi.org/10.1007/s002700000388
[23]	Taylor, C.A., Hughes, T.J. and Zarins, C.K. (1998) Finite Element Modeling of Three-Dimensional Pulsatile Flow. Annals of Biomedical Engineering, 26, 975-987. http://dx.doi.org/10.1114/1.140
[24]	Molony, D.S., Callanan, A., Morris, L.G., Doyle, B.J., Walsh, M.T. and McGloughlin, T.M. (2008) Geometrical Enhancements for Abdominal Aortic Stent-Grafts. Journal of Endovascular Therapy, 15, 518-529. http://dx.doi.org/10.1583/08-2388.1
[25]	Li, Z., Kleinstreuer, C. and Farber, M. (2005) Computational Analysis of Biomechanical Contributors to Possible Endovascular Graft Failure. Biomechanics and Modeling in Mechanobiology, 4, 221-234. http://dx.doi.org/10.1007/s10237-005-0003-0