Computational fluid dynamics of abdominal aortic aneurysm: a

potential diagnostic and prognostic tool

Cristiano Spadaccio, MDCIR – Center of Integrated Research,

University Campus Bio-Medico of RomeDepartment of Cardiovascular Surgery, University Campus Bio-Medico of Rome

c.spadaccio@unicampus.it

Biological SystemsComplex systems

Abdominal aortic aneurysm

Abdominal aortic aneurysm•AAA occurs in about 1% of men who are 60 years of age or less. •The frequency increases to about 6% of men by the age of 80. The incidence is slightly less in women. •TAA is less common, affecting less than 1% of men and women; however, a rupture of a thoracic aneurysm has a greater than 97% fatality rate.

Chaikof EL. et al J Vasc Surg. 2009 Oct;50(4 Suppl):S2-49.

Abdominal aortic aneurysmPathogenesis• Proteolytic

degradation • Inflammatory and

Immunological• Biochemical wall

stress• Molecular

genetics

Abdominal aortic aneurysm

Complications

• Rupture

• Peripheral embolization

• Acute aortic occlusion

• Aortocaval fistula

• Aortoduodenal fistula

Abdominal aortic aneurysm

Operative strategy• Diameter > 5cm• Growth >0,5/year

Chaikof EL. et alJ Vasc Surg. 2009 Oct;50(4 Suppl):S2-49.

•Shear stress

•Turbolence

•Haemodynamics

Abdominal aortic aneurysmRenal Function• >60% of AAA patients

presents with preoperative renal impairment

• Glomerular Filtration rate is a predictor of survival

Stewart R et al. Vasc Endovascular Surg 2007; 41; 225

Abdominal aortic aneurysmPeripheral embolism• Presentation with

acute limb embolism• Presentation with

splancnic embolism

Acute Supramesenteric Thrombosis of Abdominal Aortic aneurysm with deleterious

embolism. Ann Vasc Eugster et al. Ann Vasc Surg 2005 19 (3): 411-413

AIMSAIMS

• To use FEA Finite Element analysis to model biological phenomena related with aortic abdominal with mathematical laws

• Obtain a predictive and prognostic tool

Previous studiesPrevious studies• Stationary models• Simulations on 2D models• Biases on boundary conditions• Non realistic geometries

Endovascular device design in the future: transformation from trial and error to computational design. Zarins CK, Taylor CA. J Endovasc Ther. 2009 Feb;16 Suppl

Image-based computational fluid dynamics modeling in realistic arterial geometries. Steinman DA. Ann Biomed Eng. 2002 Apr;30(4):483-97. Review.

DetailsDetails• Non stationary analysis• Realistic conditions of pulsatile flow• Patient specific 3D model reconstructed from CT scans

Assumptions:Blood was modeled as a newtonian, homogeneous and uncompressible fluid, with given density and viscosity values.

ReconstructionReconstruction

Finite Elements AnalysisFinite Elements Analysis

11929 elements, 59263 dof

Mesh generationFinite Elements AnalysisFinite Elements Analysis

Physical modelPhysical model 2 p

t

u

u u u F

0 u

Navier-Stokes eq.

Continuity eq.

31050 kg m 0.00319 Pa s

Solved with Comsol Multiphysics

Boundary conditionsBoundary conditionsInlet Inflow 0 0 0 0, ,u v w u u 0,0, v t

Physiological pulsed regime (at rest)

0

1 TmRe Re t dt

T

v t dRe t

= ?

From experimental data

Q t*S

*

Q tv t

S

? ?

v(t) was rescaled in order to give Rem = 300, which is a suitable value for rest conditions

InletInlet

1575pRe

v t Re t

300mRe

Profile at the inletProfile at the inlet

Parabolic profile Flat profile

Inlet speedInlet speed

inlet

1 cm

2 cm

3 cm

Source

Wave

guid

e

Boundary conditionsBoundary conditions0u

No slipping boundaries assumption

No slip

Outlet

Outflow

0pT n

0 0p

0p p t

Systemic pressure

1)

2)

SimulationSimulation•Simulation was carried out for 3 cycles

•Results presented for 3rd cycle(1) (2) (3) (4)(1) (2) (3) (4)

1) Systolic acceleration

2) Systolic deceleration

3) Diastole

4) Late diastole

Velocity field (m/s)Velocity field (m/s)t=0.31 s

attached flow patterns

Perturbation in correspondance of a small radius of curvature

t=0.42 s

Velocity field (m/s)Velocity field (m/s)

Vortex extends to the proximal portion of the aneurism

t=0.52 s (flow inversion)

Velocity field (m/s)Velocity field (m/s)

t=1.00 s

Velocity field (m/s)Velocity field (m/s)

Vortex reaches its maximum dimension, before dissolving at the new systole

t=0.20 s

Velocity field (m/s)Velocity field (m/s)

Pressure at walls Pressure at walls (kPa)(kPa)

t=0.20 s

* 12p t kPa

t=0.31 s

* 16p t kPa

Massimo gradiente di pressione

Pressure at walls Pressure at walls (kPa)(kPa)

t=0.42 s

* 15.563p t kPa

Pressure at walls Pressure at walls (kPa)(kPa)

t=0.52 s

* 13.702p t kPa

Pressure at walls Pressure at walls (kPa)(kPa)

t=1.00 s

* 11.667p t kPa

Pressure at walls Pressure at walls (kPa)(kPa)

ResultsResults

• Velocity profiles show the potential for retrograde embolization

• Pressure profile demonstrates higher wall stress on anterior and posterior aortic wall.

The literatureThe literature• The management of abdominal aortic aneurysms in

patients with concurrent renal impairment. Bown MJ, Norwood MG, Sayers RD. Eur J Vasc Endovasc Surg. 2005 Jul;30(1):1-11

• Renal dysfunction and abdominal aortic aneurysm. Losito A, Fagugli RM, Caporali S, Verzini F, Giordano G, Cao PG. Contrib Nephrol. 1994;106:63-7.

• Renal artery stenosis and renal parenchymal damage in patients with abdominal aortic aneurysm proven by autopsy.Nakamura S, Ishibashi-Ueda H, Suzuki C, Nakata H, Yoshihara F, Nakahama H, Kawano Y. Kidney Blood Press Res. 2009;32(1):11-6. Epub 2009 Jan 29.

Renal artery stenosis and renal parenchymal damage in patients with abdominal aortic aneurysm proven by

autopsy. Nakamura et alConclusions: We demonstrated that renal parenchymal damage

and deteriorated kidney function are closely associated in the patients with AAA. Treatment of these patients in view of protection of the kidney is thus relevant.

Kidney Blood Press Res. 2009;32(1):11-6

Acute Supramesenteric Thrombosis of Abdominal Aortic aneurysm with deleterious embolism. Eugster et al

A 55-year-old man was admitted with severe pain, paralysis of both legs and absent femoral pulses. Computed tomographic scan demonstrated a 6 cm juxtarenal abdominal aortic aneurysm (AAA) with thrombosis starting at the level of the celiac trunk. At immediate operation, thrombectomy of visceral arteries was performed and distal neovascularization was achieved with a bifurcated prosthesis. It was revealed that all major arteries were occluded with debris. Embolectomy did restore flow in major vessels, but organ perfusion was not achieved due to occlusion of smaller vessels. The patient died with multiorgan failure. This is the first description in the literature of an acutely thrombosed AAA at the supramesenteric level.

Ann Vasc Surg 2005 19 (3): 411-413

ResultsResults• Results agree with other data

reported in the literaturei• Synthesis of previous works in a

patient specific approach, that migth be merged with physiological blood velocity and pressure

• Might represent an innovative tool for the prediction of aneurism rupture or clot formation

Thanks for your attention

c.spadaccio@unicampus.it