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TABLE 38.2 Stent-Graft Devices Used for Endovascular Abdominal Aortic Aneurysm Repair (EVAR)
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Endurant II
(Medtronic)
Excluder
(Gore)
Device Features
Modular bifurcated
design
Barbed suprarenal
fixation
Modular bifurcated
design polytetrafluoroethylene (PTFE)
fabric, nitinol frame
Barbed infrarenal
fixation
Proximal Neck
Proximal Neck
Diameter (mm)
19–32 ≥10 ≤60 18
19–32 ≥15 ≤60 18
Proximal Neck
Length (mm)
Angulation
(degrees)
Main Body
Introducer Sheath
Size (French)
Zenith Flex
(Cook Medical)
Zenith Fenestrated
(Cook Medical)
AFX
(Endologix)
Modular bifurcated
design
Polyester fabric, stainless steel frame
Barbed suprarenal
fixation
Modular bifurcated
design
Customized fenestrations and scallops
allow suprarenal graft
placement for short
aortic necks
Unibody design
Anatomic fixation
at the aortoiliac
bifurcation
ePTFE fabric is
external to the cobaltchromium frame,
allowing expansion
and coaptation with
the aortic wall
18–32 ≥15 ≤60 18
19–31 ≥4 ≤45 20
18–32 ≥15 ≤60 17
Continued
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TABLE 38.2 Stent-Graft Devices Used for Endovascular Abdominal Aortic Aneurysm Repair—cont’d
Ovation
(Trivascular)
Aorfix
(Lombard)
Device Features
Modular bifurcated
design
PTFE fabric, nitinol
frame
Inflatable proximal
rings filled with polymer provide seal
Barbed suprarenal
fixation
Modular bifurcated
design
Polyester fabric, nitinol frame
Barbed infrarenal
fixation
Proximal Neck
Proximal Neck
Diameter (mm)
16–30 ≥13 ≤60 14
19–29 ≥15 ≤90 22
Proximal Neck
Length (mm)
Angulation
(degrees)
Main Body
Introducer Sheath
Size (French)
Incraft
(Cordis)
Nellix
(Endologix)
Modular bifurcated
design
Polyester fabric, nitinol frame
Barbed transrenal
fixation
PTFE fabric, cobalt
chromium frame surrounded by endobag
Polymer in the endobag seals the actual
aneurysm sac
17–31 ≥15 ≤60 14
18–32 ≥10 ≤60 17
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4. An infrarenal neck diameter less than 32 mm, based on the largest available stent-graft device.
5. Proximal neck angulation less than 60 degrees. More angulated necks increase the risk of endoleaks.
6. Access vessels should have at least 6–8 mm luminal diameter.
PREOPERATIVE IMAGING
Adequate preoperative imaging of the descending aorta, its major abdominal tributaries, the iliac vessels, and the femoral
arteries are required for procedural planning and proper stent-graft selection. Contrast-enhanced computed tomography
(CT) is the imaging modality of choice, ideally with three-dimensional reconstruction. High-resolution CT angiography
allows accurate measurement of all the dimensions required for appropriate graft selection and sizing. Image rotation along
three axes enables superior examination of vessel tortuosity, as well as the precise location, size, and disease state of the
pertinent branch arteries (celiac, superior mesenteric, inferior mesenteric, renal and internal iliac) as well as the access vessels (femoral, external iliac). CT also permits adequate evaluation of mural thrombus and wall calcification.
In instances where contrast-induced allergic reaction or nephropathy is a concern, magnetic resonance angiography
(MRA) is an alternative imaging modality. With MRA, exposure to ionizing radiation is avoided. Like CT, MRA allows for
three-dimensional reconstruction and multiaxial evaluation of structures. Overall spatial resolution, however, is inferior to
CT imaging, and MRA is unable to adequately demonstrate vessel calcification.
Catheter angiography may also be used for preoperative imaging and planning, especially with the use of new threedimensional rotational angiography technology that permits acquisition of CT-like volumes. However, catheter angiography is avoided for this purpose as it is invasive, it is unable to adequately detect the presence of mural thrombus, and the
overall information obtained is not as robust as that of CT.
VASCULAR ACCESS
Adequacy of the iliofemoral access vessels has historically been the primary determinant for EVAR eligibility. Small
caliber (<6 mm luminal diameter), significant stenosis, severe circumferential calcification, and extreme tortuosity of the
access vessels significantly increase procedural complications and are among the most common reason for exclusion from
EVAR or for conversion to open surgical repair [12].
Surgical cutdown of the iliofemoral artery is the most common approach to obtaining vascular access for EVAR,
accounting for nearly 75% of cases. An oblique incision is made close to the inguinal ligament, which may be dissected
and partially divided to expose the external iliac artery. The common femoral or external iliac artery is punctured using an
18-gauge needle, through which a 0.035″ guidewire is advanced into the aorta. The introducer sheath is then inserted over
the wire, after predilation of the arteriotomy using dilators of increasing diameters.
Percutaneous vascular access through the common femoral artery is rapidly gaining popularity as it is the least invasive
approach to EVAR. The percutaneous approach affords a shorter procedural time, shorter length of stay, and fewer wound
complications compared to surgical cutdown [13]. Using fluoroscopy and real-time ultrasound guidance, the common
femoral artery is accessed via micropuncture technique using a 22-gauge needle, 0.018″ introducer wire, and 4-French
microsheath. With the direct ultrasound visualization, needle entry through the anterior wall of the vessel is ensured, and
puncture into a heavily calcified vessel wall segment can be avoided (these factors are crucial to vascular closure device
success and hemostasis after the procedure). Femoral angiography can be performed through the microsheath to confirm
location of the arteriotomy. If the puncture site is suboptimal, the microsheath can be pulled out because trauma to the vessel is minimal, hemostasis should be achieved after a few minutes of compression, and another attempt at vascular access
is made with the micropuncture needle. The proximal segment of the common femoral artery (owing to its larger diameter)
is utilized in EVAR and so the puncture site is typically higher than that of other femoral catheterization procedures that
use smaller-bore sheaths. Alternatively, the common femoral artery may be accessed “blindly” with palpation using a standard 18-gauge needle via modified Seldinger’s technique. A 0.035″ guidewire is passed through the femoral artery and a
6-French introducer is used to predilate the arteriotomy. Preclosure of the arteriotomy is made using two Perclose Proglide
closure devices or a Prostar XL device before the large-bore introducer sheath is inserted.
Although the choice of access strategy is mostly subjective, the percutaneous technique hinges heavily on the adequacy
of the common femoral artery. If the vessel is significantly diseased, has severe diffuse calcification, or has borderline luminal size, surgical cutdown is generally preferred as it allows utilization of the external iliac artery. The cutdown approach also
provides more controlled and more complete hemostasis and repair of the arteriotomy after the procedure. If the iliofemoral
vessels are inadequate for either percutaneous or cutdown access, EVAR using an iliac conduit [a polytetrafluoroethylene
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(PTFE) tube is sutured directly into the iliac artery after retroperitoneal exposure] or through alternative access sites (e.g.,
subclavian artery, common carotid artery, thoracic aorta) may be considered. However, EVAR utilizing nonfemoral access
is associated with high mortality and morbidity rates that may actually exceed that of open surgical repair [14].
THE EVAR DEVICE
All clinically available stent grafts are composed of a self-expanding metallic stent frame (nitinol, cobalt-chromium, or
steel) covered by impermeable fabric (PTFE or polyester/Dacron). There are three possible stent-graft configurations: tube,
bifurcated, and aorto-uniiliac (Fig. 38.1).
Most stent-graft devices are of a modular bifurcated design. Modular devices are composed of two or more parts: the
main body, the iliac limb/s, and extensions. The main body, which is deployed first, usually has proximal anchoring wires
with transmural barbs that serve to fix the superior portion of the stent graft to the aorta to prevent it from migrating.
The EVAR device is composed of the self-expanding stent graft, which is crimped inside a catheter-based delivery system. Modern delivery devices are low-profile (14- to 22-French outer diameter), tapered, and highly trackable to facilitate
advancement through tortuous iliac arteries, as well as to reduce incidence of vascular and bleeding complications.
STENT-GRAFT DEPLOYMENT
The EVAR procedure is performed in an operating room with a C-arm fluoroscopic system, or in a hybrid catheterization
laboratory, with a sterile environment to minimize risk of infection. This setting also allows the ability to rapidly convert
to an open surgical AAA repair or other simultaneous vascular surgery whenever required. General or regional anesthesia
is most commonly used, but more and more EVAR procedures are now utilizing local anesthesia and conscious sedation
(monitored anesthesia care). The patient is prepped and draped for both femoral-based exposure and laparotomy.
Each EVAR device has its own specific IFU for device delivery and stent-graft deployment, but most devices require a
primary femoral access site (typically the larger, less tortuous, less calcified, and less diseased vessel) where the large-bore
introducer sheath is inserted. The contralateral femoral artery becomes the ancillary access site that is cannulated with a
smaller sheath and where the marker pigtail catheter (which is used for aortography and contrast injections during stentgraft deployment) is inserted.
A digitally subtracted abdominal aortogram is obtained using the pigtail catheter with 15–20 mL of contrast delivered
by a power injector at a rate of 15 mL/s. The tip of the catheter is placed just above the renal arteries. The aortogram should
FIGURE 38.1 Possible configurations of endovascular abdominal aortic aneurysm repair stent grafts.
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adequately show the suprarenal abdominal aorta segment, the ostia of the renal arteries, the infrarenal abdominal aorta, and
the iliac arteries, including the iliac bifurcation.
An exchange-length 0.035″ stiff wire (e.g., Amplatz Super Stiff, Lunderquist) is inserted through the primary access vessel and into the thoracic aorta. The stiff wire straightens some of the vessel tortuosity and enhances the trackability of the
delivery system. Unfractionated heparin is given intravenously to achieve an activated clotting time (ACT) between 250 and
300 s. Bivalirudin intravenous (IV) bolus followed by a drip had also been used as an alternative anticoagulant, especially
for patients with heparin-induced thrombocytopenia.
The large-bore introducer sheath is advanced over the stiff wire to the proximal neck of the AAA. The proximal
edge of the stent graft is positioned just inferior to the ostium of the lowest renal artery. Contrast injections through the
pigtail catheter during this process permit visualization of the pertinent landmarks for optimal device positioning. The
stent graft is carefully deployed according to the manufacturer’s IFU. The pigtail catheter is removed before the device
is fully deployed and is subsequently reinserted through from the primary access site to the graft lumen for completion
angiography.
For modular devices, deployment of the contralateral iliac limb requires the passage of a wire from the ancillary femoral
vessel to the main body of the stent graft. This requires cannulation of the main body’s contralateral gate using a singlecurve catheter (e.g., Bernstein, right Judkins, multipurpose glide) with a 0.035″ angled glidewire. This maneuver is sometimes technically challenging, so alternatively, the wire is passed from the primary access vessel through a curved catheter
(e.g., RIM, Contra, Omni Flush) to the lumen of the main body, up and over the graft bifurcation, and into the contralateral
iliac artery. The wire is captured using a snare and externalized from the ancillary access vessel, where appropriate wire
exchange is made through a suitable catheter. A stiff 0.035″ wire is passed from the ancillary access site through the lumen
main body and into the thoracic aorta. The contralateral iliac limb or extension is then deployed according to the device
IFU.
For unibody stent grafts, contralateral wire externalization into the ancillary access site using the snare method is made
early on in the procedure prior to the deployment of the stent graft. After the stent graft and associated limb/extensions
are deployed, a completion aortography is obtained to evaluate device placement, endoleaks, suboptimal stent expansion,
or injury to the access vessels. Although the stent grafts are self-expanding, “touch-up” balloon dilatation (with a Coda or
similar balloon catheter) of the device is frequently performed, particularly at the proximal and distal attachment sites, as
well as junction sites of the modular components to ensure an adequate seal.
After the procedure, heparin anticoagulation is reversed using protamine if ACT is above 150 seconds (bivalirudin does
not have a specific reversal agent, but has a short 10–90-min half-life). If surgical cutdown was performed, the sheaths and
wires are removed and the arteriotomy is closed with running sutures. A patch closure of the arteriotomy may be performed
if the access vessel is diseased. For percutaneous access, the sheath is removed but 0.035″ guidewire is left in place. Closure
of the arteriotomy is achieved by cinching the preclosed Proglide or Prostar XL sutures. If adequate hemostasis is achieved,
the wire is removed. If there is still residual spurting or oozing, the guidewire in place allows the deployment of additional
closure devices.
ENDOLEAKS
There are four types of endoleaks (Fig. 38.2). A fifth type (endotension) is proposed where the sac pressure is elevated
without demonstrable leak of imaging, but this is controversial.
Type 1 endoleaks arise from either the proximal (type 1a) or distal (type 1b) attachment sites due to suboptimal seal.
Type 1 endoleaks require treatment, except in cases where the channel is tiny such that it is expected to thrombose and seal
itself with time. For type 1a endoleaks that are caused by underexpansion of the stent frame, touch-up angioplasty of the
proximal attachment site may be done with a large balloon (e.g., Z-Med). Deployment of a large stent (e.g., Palmaz) may
be helpful in improving apposition of the proximal segment to the aortic wall if the leak is persistent. If the type1a endoleak
is caused by low placement of the graft, deployment of another proximal cuff or extension may be required. Touch-up
angioplasty is also the initial treatment for type 1b endoleaks; if persistent, deployment of an additional limb extension is
considered.
Type 2 endoleaks retrogradely fill the aneurysm sac from the lumbar or internal iliac arteries. This is generally not clinically significant, and observation is sufficient for most cases. However, if there is evidence of enlargement of the aneurysm
sac, the treatment is indicated with embolization of the feeding vessels.
Type 3 endoleaks are caused by mechanical failure of the graft component/s, such as a tear in the fabric or separation of
a limb module from its joint attachment site. If the leak is at a suitable location, deployment of additional cuff or extension
may resolve the issue.
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Ty
Ty
pe 1b
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Type 1a
pe 2
pe 4
FIGURE 38.2 Types of endoleaks.
Type 3
Ty
Type 4 endoleaks occur because of the porosity of the fabric wall, usually with thin polyester materials. Treatment is
generally not indicated as the endoleak resolves with thrombosis of the aneurysm sac.
In general, type 1 and type 3 endoleaks require treatment. Conversion to open AAA repair is recommended for type 1
and type 3 endoleaks that do not resolve with endovascular interventions, or for sac-expanding type 2 endoleaks that failed
endovascular or laparoscopic treatment.
POST-EVAR SURVEILLANCE IMAGING
Although the long-term durability of AAA stent grafts is well established, reintervention rate for EVAR is significantly
higher than open surgical repair. Up to 30% of EVAR patients may need some form of graft-related treatment after 5 years
[15]. Periodic surveillance imaging is, therefore, mandatory after EVAR to prevent late aneurysm rupture by monitoring for
aneurysm growth, endoleak, device migration, or mechanical failure. Contrast CT imaging is traditionally obtained at 1, 6,
12 months after EVAR, and then annually thereafter. Frequent CT imaging does increase the risks associated with radiation
and contrast exposure, so the 6-month scan may be omitted if the initial CT was unremarkable.
Noncontrast CT imaging of the entire aorta is recommended at 5-year intervals after AAA repair. For patients with renal
insufficiency, contrast CT imaging may be substituted with Color Duplex ultrasonography and a noncontrast CT for postEVAR surveillance. In fact, if neither endoleak nor AAA expansion is noted during the first year following EVAR, Color
Duplex ultrasonography may replace contrast CT for annual surveillance.
REFERENCES
[1] American Heart Association Statistics Committee. Heart disease and stroke statistics–2016 update: a report from the American Heart Association.
Circulation 2016;133(4):447–54.
[2] ACC/AHA Task Force on Practice Guidelines (Writing Committee to Develop Guidelines for the Management of Patients With Peripheral Arterial
Disease). American Association for Vascular Surgery; Society for Vascular Surgery; Society for Cardiovascular Angiography and Interventions;
Society for Vascular Medicine and Biology; Society of Interventional Radiology; ACC/AHA Task Force on Practice Guidelines Writing Committee
to Develop Guidelines for the Management of Patients With Peripheral Arterial Disease; American Association of Cardiovascular and Pulmonary
Rehabilitation; National Heart, Lung, and Blood Institute; Society for Vascular Nursing; TransAtlantic Inter-Society Consensus; Vascular Disease
Foundation. ACC/AHA 2005 Practice Guidelines for the management of patients with peripheral arterial disease (lower extremity, renal, mesenteric,
and abdominal aortic). Circulation 2006;113(11):e463–654.
[3] Karthikesalingam A, Holt PJ, Vidal-Diez A, et al. Mortality from ruptured abdominal aortic aneurysms: clinical lessons from a comparison of out-
comes in England and the USA.. Lancet 2014;383(9921):963–9.
Endovascular Stent-Graft Repair of Abdominal Aortic Aneurysms Chapter | 38 431
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[4] Dutch Randomized Endovascular Aneurysm Management (DREAM)Trial Group. A randomized trial comparing conventional and endovascular
repair of abdominal aortic aneurysms. N Engl J Med October 14, 2004;351(16):1607–18.
[5] Balko A, Piasecki GJ, Shah DM, et al. Transluminal placement of intraluminal polyurethane prosthesis for abdominal aortic aneurysm. J Surg Res
1986;40(4):305–9.
[6] Volodos NL, Shekhanin VE, Karpovich IP, et al. A self-fixing synthetic blood vessel endoprosthesis [in Russian]. Vestn Khir Im I I Grek
1986;137(11):123–5.
[7] Lazarus HM. Intraluminal graft device, system and method. United States Patent number 4,787,899; November 29 1988 (filed December 10, 1986).
[8] Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5(6):491–9.
[9] American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines. Management of patients with periph-
eral artery disease (compilation of 2005 and 2011 ACCF/AHA guideline recommendations). Circulation April 2, 2013;127(13):1425–43.
[10] Society for Vascular Surgery. The care of patients with an abdominal aortic aneurysm: the Society for Vascular Surgery practice guidelines. J Vasc
Surg 2009;50(Suppl. 4):S2–49.
[11] Speziale F, Sirignano P, Setacci F, et al. Immediate and two-year outcomes after EVAR in “on-label” and “off-label” neck anatomies using different
commercially available devices. analysis of the experience of two Italian vascular centers. Ann Vasc Surg 2014;28(8):1892–900.
[12] Murray D, Ghosh J, Khwaja N, et al. Access for endovascular aneurysm repair. J Endovasc Ther 2006;13(6):754–61.
[13] Buck DB, Karthaus EG, Soden PA, et al. Percutaneous versus femoral cutdown access for endovascular aneurysm repair. J Vasc Surg 2015;62(1):16–21.
[14] Nzara R, Rybin D, Doros G, et al. Perioperative outcomes in patients requiring iliac conduits or direct access for endovascular abdominal aortic
aneurysm repair. Ann Vasc Surg 2015;29(8):1548–53.
[15] The DREAM Study Group. Long-term outcome of open or endovascular repair of abdominal aortic aneurysm. N Engl J Med 2010;362:1881–9.
Chapter 39
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Risk of Thrombosis in Downstream
Flow of Mechanical Aortic Valves:
A Computational Approach
Yee Han Kuan1, Foad Kabinejadian2, Vinh-Tan Nguyen3, Hwa Liang Leo
1
National University of Singapore, Singapore, Singapore; 2University of Michigan, Ann Arbor, MI, United States; 3Institute of High Performance
Computing, A∗STAR, Singapore, Singapore
Chapter Outline
Background on Computational Approach 433
Comparison of the Effects of Bileaflet and Trileaflet Mechanical
Aortic Valve Design on Downstream Flow Patterns and
Blood Shear 434
Effect of Implantation Angles of Mechanical Aortic Valves on
Flow Patterns and Blood Shear 439
Summary 442
References 442
1
BACKGROUND ON COMPUTATIONAL APPROACH
Different types of artificial prosthetic heart valves have been implanted to replace defective heart valves since the 1960s.
The first successful artificial heart valve was designed and implanted in human patients by surgeons Dr. Robert Starr and
Dr. M. L. Edwards in 1961 [1]. Their device, the Starr–Edwards valve, is now a standard in heart valve replacement field.
Mechanical heart valves, especially bileaflet mechanical heart valve (BMHV) designs, remain the most prevalently used
due to their strength and durability compared to others. However, there is always a risk of blood clot formation after a
mechanical heart valve is implanted. As such, patients are required to take anticoagulation medication for life. Additionally,
complications such as hemolysis, chronic platelet activation, and initiation of thrombus formation associated with mechanical heart valve implantation have resulted in ischemic attacks and strokes [2–4]. Besides material properties and contact
activation, hemodynamics performance and shear stress are believed to be the main causes for the complications [5,6].
During the valve design process, virtual valve prototypes are computer designed and tested in the early stage. In the
recent years, computational fluid dynamics (CFD) simulation has become a potentially useful tool to predict the hemodynamic performance of these newly designed heart valves. The earliest CFD works used two-dimensional simulations
or symmetrical three-dimensional models due to limited computational power. Two-dimensional and three-dimensional
simulations provide insights into the flow pattern near peak systole Reynolds number. A major computational challenge
is to develop a computational model with physiological conditions and anatomically more accurate model that can look
into the flow hemodynamics through mechanical heart valve designs. The numerical simulation acted as a tool for thromboembolic potential characterization to observe the physical viscous stresses experienced by the blood elements and the
capability to refine the analysis to a level of spatial details that would be hard to achieve experimentally. This chapter looks
at the use of an Arbitrary Lagrangian–Eulerian (ALE) method with moving mesh technique using an open source software,
OpenFOAM. The effects of downstream flow and blood shear on the widely used BMHV and the trileaflet mechanical heart
valve (TMHV) design are compared. Also, the effect of implantation angles of mechanical aortic valves on flow patterns
and blood shear is discussed, along with how to minimize the risk of thrombosis through valve designs.
In the computational model, the incorporation of leaflet motions by simulating the flow dynamics in a mechanical heart
valve is important. This has been done by constructing an ALE model using solid body motion technique to investigate the
flow hemodynamics. Specifically, an open source code has been developed and tailored to incorporate the leaflet motion by
simulating the flow dynamics in mechanical heart valve model. This method is a more accurate approach to investigate the
New Approaches to Aortic Diseases from Valve to Abdominal Bifurcation. http://dx.doi.org/10.1016/B978-0-12-809979-7.00039-0
Copyright © 2018 Elsevier Inc. All rights reserved.
433
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flow through the valve in a cardiac cycle. The numerical method was validated experimentally and hence was able to predict
important parameters such as regions of recirculation and wall shear stress loading on the valve leaflets.
The broader objective of this study is to provide an improved quantitative and qualitative understanding of the functionality
and potential thrombogenicity of mechanical heart valves beyond that available from earlier studies. The study helps to develop
a computational framework, which would provide new insight into the roles of design features on potential for thrombogenicity.
In the computational study, the flow was governed by Navier–Stokes (NS) equations, which were discretized in space
using a finite volume method. The blood was modeled as an incompressible viscous Newtonian fluid, with density of
ρ = 1025 kg/m3 and kinematic viscosity of ν = 3.81 × 10−6 m2/s. To approximate the NS equations, a finite set of discrete
equations was constructed on unstructured hybrid grids. The study used a cell-centered finite volume approach where the
discretization was based on the integral form of the governing equations over a polyhedral control volume. The domain was
further subdivided into a set of nonoverlapping polyhedral control volume. The finite volume discretization transforms the
surface and volume integrals into a sum of face and control volume integrals and approximates them to second-order accuracy. The second-order Crank Nicholson implicit time discretization with adjustable time-step was used, with the Courant–
Friedrichs–Lewy number = 1. The numerical simulation uses a dynamic moving mesh method to deform and regenerate the
mesh following the moving boundaries in a cardiac cycle of 72 beat per minute. As the purpose of this chapter is to discuss
the findings on the effect of downstream flow due to the different valve designs and implantation angles, detailed numerical
methodology can be found in the earlier work [7,8].
COMPARISON OF THE EFFECTS OF BILEAFLET AND TRILEAFLET MECHANICAL AORTIC
VALVE DESIGN ON DOWNSTREAM FLOW PATTERNS AND BLOOD SHEAR
The flow and wall shear stress observed through the BMHV and TMHV designs have been compared [9]. The BMHV
geometry used in this study was based on the St Jude Medical (SJM) 29 mm BMHV design placed in a downstream curved
aorta at the anatomic position at 0 degrees, which is the preferable orientation of the aortic valve [10]. The 29 mm new
TMHV design was also placed in another downstream curved aorta at similar anatomic position at 0 degrees. The TMHV
design was designed in-house, as shown in Fig. 39.1.
The geometry of the curved aortic arch model was simplified without the three branches on the aortic arch to minimize
the complexity of the flow simulation. The centerline of the aorta model followed the curvature and dimension of the normal diameters for the thoracic aorta of adults obtained by helical computed tomography [11] with a 5D upstream (D = inlet
diameter). The sinus design was based on Pisani et al. [12], which was similar to the native aortic valve. The native valve
consists of three aortic Valsalva sinuses, with approximately 120 degrees rotational symmetry. The orientation of the valve
in relation to the sinus is important in modulating the obstruction of the flow present during the cardiac output. Fig. 39.2
shows the orientation of the SJM BMHV and TMHV as viewed from the inlet position at 0 degrees.
The Spalart Almaras turbulence modeling was used and implemented using the OpenFOAM package. Fig. 39.3 shows
the prescribed velocity and pressure. No-slip boundary condition was assigned at the walls, the leaflets, and all body
FIGURE 39.1 Velocity contour of the trileaflet mechanical heart valve placed in the downstream curved aorta.
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FIGURE 39.2 Orientation of bileaflet mechanical heart valve and trileaflet mechanical heart valve in anatomic position at 0 degrees.
FIGURE 39.3 Velocity and pressure wave profiles with three different time points during the systolic phase (mid-acceleration t = 0.07 s, peak systole
t = 0.115 s, and mid-deceleration t = 0.22 s) at which the results were analyzed.
surfaces. The flow field at peak systole (t = 0.115 s) for each case was investigated. The computational domain for the SJM
29 mm BMHV was subdivided into an unstructured mesh of approximately 3.6 million tetrahedral elements, whereas the
TMHV was subdivided into an unstructured mesh of approximately 3.5 million tetrahedral elements. During the systolic
phase, the BMHV was fully opened at an angle of 85 degrees between the leaflet and the X-Y plane. For the TMHV, the
leaflets were fully opened at 90 degrees.
The centerline of the aorta followed the curvature of the normal diameters for the thoracic aorta of adults obtained by
helical computed tomography [11] without the three aortic branches on the top to minimize the complexity of the flow
simulation. The origin of X and Y-axes is at the center of the flow channel with the Z = 0 plane located at the leading edge of
the leaflets. The streamwise velocity profiles for the BMHV and TMHV were compared at three different locations, Z = 1D,
2D, and 4D along the centerline of the models, as indicated in Fig. 39.4.
The velocity plots at cross-sectional view of Z = 1D, 2D, and 4D for both BMHV and TMHV during mid-acceleration,
peak systole, and mid-deceleration as viewed from the outlet are shown in Fig. 39.5. During mid-acceleration (t = 0.07 s),
the flow through the BMHV showed a triple-jet structure visibly taking shape. Similarly, the central orifice flow of the
TMHV can be seen at position Z = 1D. There was no obstruction in the TMHV in the central region unlike the leaflets of
the BMHV, which gave rise to the triple-jet structures. The shape of the central orifice flow was a hexagon and it followed
the position of the leaflets. At peak systole (t = 0.115 s), the profile of the triple-jet structure of the flow was fully visible
in the BMHV model while central orifice jet flow was visible in the TMHV at position Z = 1D. During mid-deceleration
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