TEVAR

Thoracic
Endografts and
Future Goals
Vahe Varzhapetyan
Research Intern
Dr. Khoynezhad Lab
Heart Institute
Cedars Sinai Medical Center

Content
 The Thoracic Aorta
 Endograft Design
 Frontiers

Thoracic Endografts
 TEVAR approved in 2005 for
descending aortic aneurysm repair.
 It is important to understand
endograft design and possible
advancements as strides are being
made for use in aortic dissection, in
supraaortic pathologies and
thoracoabdominal disease.
 Lower perioperative mortality,
neurological injury, hospital stay
compared to open repair
 Midterm and long term outcomes
have yet to be determined

Challenges in the
Thoracic Aorta
 Pulsatile turbulent blood flow
 Respiratory movement
 Curved anatomy
 Diverse pathologies (retrograde and antegrade dissections)
 Larger lumen
 Distance from access point

Challenges in the
Thoracic Aorta

Challenges in the
Thoracic Aorta
 High tension in the thoracic wall aorta.
Tension=(Pressure) x (radius).
 In the disease state the scattered loss of elasticity
throughout the length of the aorta produces a complex
change in the vessel stiffness.
 The Pressure-Strain Modulus, a measure of stiffness
is utilized in studies of computational analysis and fluid
dynamics. These are areas of active research to improve
endograft design.
(Ps-Pd)Dd P=Pressure
(Ds-Dd) D=Diameter
s=systolic
d=diastolic

Endograft
Design
 Ease of Deployment
 Exclude the lesion with a good seal and fix
 Durable
 Conformatible
 Biocompatible

Endograft
Design
Nitinol
stent frame
Bare metal
stent
Polyester fabric
graft

Endograft Design
(Considerations for good seal and fixation)
 Sufficient landing zone with
consideration for thrombus and
calcifications.
 Optimal radial pressure of the
stent frame is essential to provide
good apposition to the aortic wall
with minimal trauma.
 Radial pressure determined by
stent frame geometry, length,
spacing, wire material and
oversizing.

Endograft Design
(Considerations for good seal and fixation)
 Proximal bare metal stent provides good anchorage and
fixation with allowance to branching vessels. (extends the
landing zone)
 Staples, screws, clips, balloon angioplasty, Bowden cable
and fibrin glue may be utilized
 The use of bars in the stent frame design and stiffer fabric in
the graft increases longitudinal stiffness decreasing the risk
of migration

Endograft Design
(Considerations for conformability and
durability)
 Stent frame spacing, wire and graft material are major
determinates of conformability.
 Nitinol is a nickel and titanium alloy. It is super elastic (allows
for crimping) and has shape memory. Shape memory allow
the stent to expand in the artery during deployment when
the sheath is removed and the stent is exposed to the
temperature in the vessel.
 Biocompatible and resistant to fatigue

Endograft Design
(Considerations for conformability and
durability)
 Graft covering composed of either polyester or expanded
polytetrafluoroethylene ePTFE (Gor-tex). They are flexible,
conformable, lightweight, biocompatible with low porosity.
 Manufacturing techniques affect the filament and weave
pattern which in turn determine conformability and
durability.

Endograft Design
(Considerations for deployment)
 High torque adjustable catheters with hydrophilic coverings
improve accessibility.
 Different deployment methods are utilized to maintain
accuracy.
 Gore TAG addresses this issue by starting the deployment in
the middle of the graft followed by inflation of a balloon
that results in apposition to the aortic wall.
 Valiant Captiva system uses a two step process. First the
graft is deployed with the bare metal stents closed. Then
after adjustment the bare metals are deployed to make the
seal

Frontiers
 Hybrid procedures, chimney technique, fenestrated
devices allow the landing zone to extend and to treat the
ascending aorta.
 Developing tapered endografts utilizing the clinically
measured aortic taper ratio will allow better fixation
especially in dissection.
 New materials are under investigation to decrease the
profile of the graft while maintaining the same durability.

Frontiers
 The Cardiatis Multilayer utilizes a bare metal stent composed
of braided cobalt alloy and currently is in clinical trails.
 It reduces flow velocity
and increases laminar flow
in the aneurysm.
 Allows laminar flow in
branched vessels

Frontiers
Computation analysis of flow
velocity in thoracic aorta
Same analysis after
Cardiatis stent
placement

Frontiers
Flow preserved in branched
vessels

References
1.Greenberg RK, Lu Q, Roselli EE et al. Contemporary analysis
ofdescending thoracic and thoracoabdominal aneurysm
repair: a comparison of endovascular and open techniques.
Circula-tion 2008;19;118(8):808 – 817
2. Jenna M. Weidman, Malhar Desai, Arif Iftekhar, Kevin Boyle,
Judith S. Greengard,bLois M. Fisher, Richard L.S. Thomas,
Simona Zannett. Engineering Goals for Future Thoracic
Endografts — How Can
We Make Them More Effective? Progresses in Cardiovascular
Diseases 56 (2013) 92-102
3. Desai ND, Burtch K, Moser W, et al. Long-term comparison of
thoracic endovascular aortic repair (TEVAR) to open surgery
for the treatment of thoracic aortic aneurysms. J Thorac
Cardiovasc Surg. 2012;144(3):604-609.

4. Canaud L, Alric P, Laurent M, et al. Proximal fixation of
thoracic stent-grafts as a function of oversizing and increas-
ing aortic arch angulation in human cadaveric aortas.
J Endovasc Ther.
2008;15(3):326-334.
5. Humphrey JD, Holzapfel GA. Mechanics, mechanobiology,
andmodeling of human abdominal aorta and aneurysms.
J Biomech.
2012;45(5):805-814.
6. Cheng D, Martin J, Shennib H, et al. Endovascular aortic
repair versus open surgical repair for descending thoracic aortic
disease a systematic review and meta-analysis of comparative
studies.

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