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Endovascular Repair
Endovascular Treatment of Thoracoabdominal Aor tic Aneur ysms
a report by
Timothy A M Chuter
Division of Vascular Surgery, University of California San Francisco
Thoracoabdominal aorta occupy an inaccessible
location high in the retroperitoneum, and their
branches are the sole source of blood to all the
abdominal organs. Both features complicate
conventional surgical repair, which requires wide
aortic exposure and prolonged interruption of aortic
flow. Since thoracoabdominal aortic aneurysm
(TAAA) is a disease of elderly male smokers, many
patients have serious cardiac and pulmonary comorbidities. In addition, many have already
undergone open abdominal aortic aneurysm repair.
These patients tolerate the stresses of conventional
open repair poorly.1–4 The reported morbidity and
mortality rates of conventional surgical repair of TAA
vary widely, depending on the type of disease
(dissection versus aneurysm), the extent of disease,3,4
and the expertise of surgeons, anaesthesiologists and
cardiologists.2 US national and statewide audits
provide the most representative picture of current
results. In California, for example, the 30 day and one
year mortality rates are 19% and 31%, respectively.
Paraplegia rates are similarly alarming.1
In theory, an endovascular approach to TAAA
repair has two main advantages. First, the stent-graft
is inserted through a trans-luminal route; there is no
need to expose the aneurysm. Second, the grafts are
inserted without clamping the aorta; there is no
need to interrupt flow to the abdominal organs.
More than a decade has passed since endovascular
repair of abdominal aortic aneurysm (AAA) and
thoracic aortic aneurysm (TAA) first started to
displace open surgery as first-line therapy, yet
endovascular repair of TAAA is still confined to a
handful of centres worldwide.
The fundamental problem is how to maintain flow to
the visceral branches of a TAAA while excluding the
aneurysm itself from the circulation. The two main
alternatives are: a combination of visceral artery
bypass and endovascular exclusion, and branched
stent-graft insertion.
The first option is a combination of conventional
visceral bypass and endovascular aneurysm exclusion.
The surgical bypass grafts to the visceral arteries
originate outside the field of endovascular exclusion,
usually from the distal aorta or common iliac
aneurysm. Once the aneurysm has been ‘debranched’,
endovascular exclusion can proceed in the usual way.
The second option, multi-branched stent-graft
implantation, eliminates the need for trans-cavitary
incisions and interruption of visceral arterial flow.
However, the procedure is far from simple, because
each branch of the stent-graft represents a separate
line of insertion. All these lines of insertion intersect
in the aorta where the branches join the trunk. The
nature of that junction determines the type of
branched stent-graft. Unibody multi-branched stentgrafts have permanent sutured connections, whereas
modular fenestrated multi-branched stent-grafts have
only a ring of contact between each balloon
expanded covered stent and the corresponding hole
(fenestration) in the wall of the primary stent-graft.
Modular cuffed multi-branched stent-grafts occupy
an intermediate position between these two
extremes. The primary stent-graft of a cuffed multibranched stent-graft has branches sewn into its
surface, but these are not long enough to reach the
orifices of the visceral arteries. Instead, they serve
only to enhance the connection between the primary
stent-graft and self expanding covered stents.
Relative Merits of Different
Approaches
Visceral artery bypass alone would be a big
operation for the typical high-risk patient with
TAAA. Subsequent stent-graft implantation may
not add much in the way of dissection, but the
constrast load is nephrotoxic, the sheath valves leak
blood with every catheter exchange, and the
additional operative time means additional
anaesthesia. The combination of visceral bypass and
1. Rigberg DA, McGory ML, Zingmond DS et al., J Vasc Surg (2006);43: pp. 217–223.
2. Cowan JA Jr, Dimick JB, Henke PK et al., J Vasc Surg (2003);37: pp. 1169–1174.
3. Gloviczki P, Cardiovascular Surg (2002);10: pp. 434–441.
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Endovascular Treatment of Thoracoabdominal Aor tic Aneur ysms
endovascular aneurysm exclusion could hardly be
described as a minimally invasive procedure.
Nevertheless, recent series have reported low
mortality and morbidity rates in high-risk patients
with extensive aneurysms.5,6 The low rate of
paraplegia is particularly noteworthy, because none
of these cases included intercostal artery reimplantation, and most required near total
exclusion of all the native aorta, from the subclavian
origin to the bifurcation. It appears that
haemodynamic stability is more important than
intercostal preservation in preventing paraplegia.7
Figure 1: Post-operative Computed Tomography
Showing Four Downgoing Branches of a Stent-graft
that Extends from the Subclavian Orifice to the
Aortic Bifurcation
In theory, the entirely endovascular operation of multibranched stent-graft implantation should be even less
invasive than the bypass/exclusion. In practice, the
technical challenges inherent in multi-branched stentgraft implantation introduce a wide range of potential
complications. In this regard, simpler is better. The
irreducible complexity of the unibody multi-branched
stent-graft increases exponentially with every
additional branch.8,9 The stent-graft and all the
branches are delivered as a single unit. If any part fails,
the whole device fails. The modular approach, on the
other hand, breaks the procedure down into a series of
bite-sized parts. Not only are modular stent-grafts
simpler, they are more versatile. Variations in
component selection and intercomponent overlap can
accommodate intra-operative findings.
The sole disadvantage of the modular approach is
the potential for component separation, especially
when the inter-component junction is represented
by a single ring of contact between the margin of a
fenestration and balloon expanded covered
stent.10,11 Fenestrated modular stent-grafts are not
stable enough for use in TAAA where the covered
stent has to bridge a wide gap between the primary
stent-graft and the wall of the aneurysm. The 15–20
mm overlap provided by a cuff is far superior in this
regard. Cuffed stent-grafts are also easier to plan,
easier to make and easier to implant,12 because they
do not require the same high degree of precision as
fenestrated stent-grafts. Nevertheless, all devices of
this type are still individually made in Australia. The
delay from sizing to implantation is currently four
to eight weeks.
Cuffed Multi-branched Stent-grafts
Stent-graft Design
All modular fenestrated and multi-branched stentgrafts employ the basic Zenith design, with stainless
steel Z-stents sutured to surgical woven polyester.
The proximal stent has many barbs to enhance
attachment. Three trigger wires control deployment.
A constraining wire keeps the unsheathed stent-graft
in a partially expanded state. Two other wires secure
the proximal and distal ends of the stent-graft to the
shaft of the delivery system. Sheath sizes range from
20 to 24 French. Extensive aneurysms often require
4. Coselli JS, LeMaire SA, Miller CC 3rd et al., Ann Thorac Surg (2000);69:pp. 409–414.
5. Black SA, Wolfe JHN, Clark M et al., J Vasc Surg (2006);43: pp. 1081–1089.
6. Zhou W, Reardon M, Peden EK, Lin PH, Lumsden AB, “Hybrid approach to complex thoraci aortic aneurysms in highrisk patients: surgical challenges and clinical outcomes”.
7. Chiesa R, Melissan G, Marrocco-Trischitta MM, Civilini E, Setacci F, “Spinal cord ischemia after elective stent-graft repair
of the thoracic aorta”.
8. Inoue K, Iwase T, Sato M et al.,, J Thorac Cardiovasc Surg (1997);114–161.
9. Saito N, Kimura T, Toma M et al., Ann Vasc Surg (2006), e-pub ahead of print.
10. Anderson JL, Adam DJ, Berce M, Hartley DE, , J Vasc Surg (2005);42: pp. 600–607.
11. Greenberg RK, West K, Pfaff K et al., J Vasc Surg (2006);43: pp. 879–886.
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Endovascular Repair
additional aortic stent-grafts above or below the
cuffed component at the visceral artery level. This is
typically wider at the ends than in the middle. The
narrow central segment carries the cuffs. The cuffs are
little barrels of woven polyester, 15–18 mm in length
and 6–8 mm in diameter, supported by Nitinol wire
loops. They are sutured into the wall of the primary
stent-graft with one end opening to the inside and
one end open to the outside. Most cuffs, like most
visceral arteries, are downgoing, with the proximal
end opening to the inside of the main stent-graft and
the distal end opening to the outside. Depending on
specific anatomic requirements, they can also be
upgoing, externally mounted, or even helical.
Stent-graft Implantation
The author places a spinal catheter for cerebrospinal
fluid (CSF) pressure monitoring and drainage. In
most cases, the spinal catheter also serves as a means
of regional anaesthesia. Some patients with large
stent-grafts and small arteries require surgically created
conduits to the common iliac artery, but most are
amenable to trans-femoral insertion. A brite-tip
selective catheter in a visceral artery provides a
reference point to guide stent-graft position with the
usual downgoing cuffs 10–25 mm above the
corresponding arterial orifices.
The author inserts the self-expanding covered stents
through a brachial artery, usually the left. The route
from there to the visceral aorta can be very tortuous.
Insertion of catheters and delivery systems through a
conduit of co-axial, kink resistent sheaths (Flexor,
Cook, Bloomington, IN) minimises the potential for
redundant loop formation (in the arch). The outer 12
French sheath provides support, and protects the
aorta. The inner 10 French sheath is large enough to
allow contrast injections around a Fluency covered
stent delivery system.
All covered stent insertions follow the same
sequence: cuff catheterisation, sheath advancement
into the aneurysm, angiographic localisation of the
target artery, catheterisation of the target artery,
selective angiography, stiff guidewire (Rosen, Cook,
Bloomington, IN) insertion, stent-graft insertion,
and Wallstent insertion. Most covered stents measure
60 mm in length, and 7–9 mm in diameter. The
Wallstent prevents kinking and helps stabilise
covered stent position.
Post-operative Management
Multi-branched cases stay in the intensive care unit at
least two days after the operation, for CSF and blood
pressure monitoring. In the absence of lower
extremity neurological symptoms, the CSF drain,
arterial line and Foley catheter are all removed on the
second post-operative day. All patients resume
normal diet, and receive loading doses of Plavix on
the first post-operative day .
Outcome
In the past year the author has inserted 16 cuffed
multi-banched stent-grafts bearing a total of 60
branches, only one of which has occluded. All the
other branches remain patent. Eight of these stentgrafts covered the aorta, from subclavian orifice to
bifurcation (see Figure 1). The only case of
paraplegia occurred in the setting of hypotension
and renal failure caused by a wire-induced
perforation of a branch of the sole renal artery. This
patient refused dialysis and died. There have been
no other deaths, and no other cases of paraplegia,
although one patient was transiently (less than five
minutes) paraparetic during an episode of relative
hypotension (110 mmHg systolic) on the first postoperative night.
Current and Future Roles of Different
Endovascular Stent-grafts in the
Management of Aortic Aneurysm
At UCSF modular cuffed multi-branched stent-grafts
are used for elective endovascular repair of TAAA in
high-risk patients, and reserve combined visceral
bypass/endovascular repair for more urgent repair of
very large or symptomatic aneurysms and healthier
patients. Simple fenestrations are used for juxtarenal
aneurysms, and branched fenestrations for pararenal
aneurysms. The author has also tried to use a
combination of fenestrations and cuffs in the same
stent-graft, in cases where not all of the visceral segment
was dilated to the same degree. However, this was
found difficult to do, because cuffs and fenestrations
cannot be used in close proximity. The cuffed approach
requires space between the stent-graft and the aorta,
whereas the fenestrated approach requires direct
contact between the stent-graft and the aorta.
Despite regulatory hurdles that block access to the
necessary devices and impede dissemination of the
necessary skills, the author expects that modular
cuffed multi-branched stent-grafts will probably
become the mainstay of treatment in most cases of
pararenal and thoracoabdominal aortic aneurysm.
The author also anticipates that covered stents will
largely replace the uncovered stents currently used to
keep simple fenestrations in place, because the
potential for leakage is less. ■
12. Chuter TA, Gordon L, Reilly LM, Pak LK, Messina LM, J Vasc Interv Radiol (2001);12: pp. 391–392.
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