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Chapter 23 Mesenteric Ischemia Following Abdominal Aortic Aneurysm Repair 335
11 . Sakakibara Y , Jikuya T , Saito EM , et al : Does laser Doppler flowmetry aid the
prevention of ischemic colitis in abdominal aortic aneurysm surgery ? Thorac
Cardiovasc Surg 45 : 32 – 34 , 1997 .
12 . Bergman RT , Gloviczki P , Welch TJ , et al : The role of intravenous fluorescein
in the detection of colon ischemia during aortic reconstruction . Ann Vasc Surg
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13 . Gharagozloo F , Bulkley GB , Zuidema GD , O’Mara CS , Alderson PO . The use of
intraperitoneal xenon for early diagnosis of acute mesenteric ischemia . Surgery.
1984 Apr ; 95 (4) : 404 – 11 .
14 . Fiddian-Green RG , Amelin PM , Hermann JB , et al : Prediction of the development
of sigmoid ischemia on the day of aortic operations: Indirect measurements of
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15 . Champagne BJ , Darling RC , 3rd , Daneshmand M , Kreienberg PB , Lee EC , Mehta
M , Roddy SP , Chang BB , Paty PSK , Ozsvath KJ , Shah DM : Outcome of aggres-
sive surveillance colonoscopy in ruptured abdominal aortic aneurysm . J Vasc Surg
39 : 792 – 96 , 2004 .
16 . Bjorck M , Bergqvist D , Troeng T : Incidence and clinical presentation of bowel
ischaemia after aortoiliac surgery--2930 operations from a population-based regis-
try in Sweden . Eur J Vasc Endovasc Surg 12 : 139 – 44 , 1996 .
17 . Brewster DC , Franklin DP , Cambria RP , Darling RC , Moncure AC , Lamuraglia
GM , Stone WM , Abbott WM : Intestinal ischemia complicating abdominal aortic
surgery . Surg 109 : 447 – 54 , 1991 .
18 . Senekowitsch C , Assadian A , Assadian O , Hartleb H , Ptakovsky , H , Hagmuller
GW : Replanting the inferior mesentery artery during infrarenal aortic aneurysm
repair: Influence on postoperative colon ischemia . J Vasc Surg 43 : 689 – 94 , 2006 .
19 . Ernst CB , Hagihara PF , Daugherty ME , Griffen Jr. WO : Inferior mesenteric artery
stump pressure: A reliable index for safe IMA ligation during abdominal aortic
aneurysmectomy . Ann Surg 187 : 641 – 46 , 1978 .
20 . Mehta M , Veith FJ , Ohki T , Cynamon J , Goldstein K , Suggs WD , Wain RA , Chang
DW , Griedman SG , Scher LA , Lipsitz EC : Unilateral and bilateral hypogastric
artery interruption during aortoiliac aneurysm repair in 154 patients: A relatively
innocuous procedure . J Vasc Surg 33 : S27 – 32 , 2001 .
21 . Mehta M , Veith FJ , Darling RC , 3rd , Roddy ST , Ohki T , Lipsitz EC , Paty PS ,
Kreienberg PB , Ozsvath KJ , Chang BB , Shah DM : Effects of bilateral hypogastric
artery interruption during endovascular and open aortoiliac aneurysm repair . J Vasc
Surg 40 : 698 – 702 , 2004 .
22. Mulholland MW, et al; Greenfield’s Surgery: Scientific Principles & Practice. 4th
ed. Philadelphia, PA: Lippincott Williams & Wilkins, 2006. http://thegreenfieldso-
lution.com
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Abstract Aortic aneurysms are the 13th leading cause of mortality in the Unit-
ed States. Thoracoabdominal aortic aneurysms (TAAAs), defined as strad-
dling the diaphragm and extending anywhere between the left subclavian
artery down to the aortic bifurcation, remain a less common entity compared
to the more frequently presenting aneurysms involving the ascending or infrar-
enal aorta. In 1986, E. Stanley Crawford popularized a classification scheme for
TAAA based on their extent, a surrogate for the risk of postoperative neurologi-
cal deficit. This system essentially classifies the extent of aneurysm as primarily
involving the thoracic aorta with varying degrees of extension into the abdomi-
nal aorta (types I and II), and contrasts them to those primarily involving the
abdominal aorta with varying degrees of extension into the thoracic aorta (types
III and IV). The natural history of aortic aneurysms remains that of inexorable
expansion and rupture. Classic early studies on the natural history of untreated
TAAA demonstrated a 2-year mortality of 76%, predominantly from aortic
rupture. The strongest determinant of the risk for rupture is greatest for those
aneurysms with diameters larger than 5 cm. However, other determinants of rup-
ture include advanced age, a history of hypertension, tobacco use, or chronic
obstructive pulmonary disease. Aneurysms presenting with preexisting dissec-
tion, or those that are larger, typically have higher growth rates and represent a
higher risk for rupture. This chapter will discuss the indications for intervention,
as well as operative approaches, both open and hybrid.
Keywords
Thoracoabdominal aorta , Open operative TAAA repair , Hybrid
TAAA repair
Preoperative Evaluation for Patients with
Thoracoabdominal Aortic Aneurysm
Despite advances in perioperative care, thoracoabdominal aortic aneurysm
(TAAA) repair remains among the most formidable of operative procedures
with reported rates of mortality varying from 4%to 20%.
1–
4
In addition, the
Chapter 24
Operative Therapy for the Descending
and Thoracoabdominal Aorta
Himanshu J. Patel, Gilbert R. Upchurch, Jr., and G. Michael Deeb
G. Upchurch and E. Criado (eds.) Aortic Aneurysms, Contemporary Cardiology
DOI: 10.1007/978-1-60327-204-9_24, © Humana Press, a part of
Springer Science + Business Media, LLC 2009
337
https://t.me/med1917
338 Himanshu J. Patel et al.
frequent presence of comorbid conditions including coronary artery disease,
chronic obstructive pulmonary disease, renal failure, and peripheral vascular
disease increases risk for major postoperative morbidity. The typical age of pres-
entation also reaches the sixth decade of life, and can often result in a delayed
functional recovery. It is in this setting that the aortic surgeon must conduct the
preoperative evaluation to be certain that the outcome is optimal.
The aneurysm extent is typically evaluated with computed tomography (CT)
angiography. The images are in thin 1–2 mm slices, and are obtained during
peak opacification of the aorta to give the best visualization of the offending
pathology, the location of critical intercostal vessels, and to determine whether
branch vessel obstruction is present (Table 1 ). Although previously universally
utilized as part of the preoperative evaluation, conventional aortography is rarely
used and does not give the same detailed information obtained by CT scanning.
Although other modalities may be used, including magnetic resonance imaging
and echocardiography, these do not give the same detail as CT scanning.
Assessment of comorbid conditions is paramount in deciding whether the
patient is able to withstand the physiological insult imposed by this operative
procedure. We evaluate cardiac status in everyone for elective open repair
with coronary angiography and transesophageal echocardiography. If obstruc-
tive coronary lesions are present, they are all treated with either percutaneous
intervention or coronary artery bypass grafting, and TAAA repair is then per-
formed at a later stage (usually 4–6 weeks later). If major valvular pathology
is identified, this is also addressed at that time. Those patients with severely
impaired ejection fraction (i.e., <35%) are often not considered for open repair.
Pulmonary function is assessed by standard evaluation and those patients with
FEV1 or DLCO < 60% all referred for preoperative evaluation and optimiza-
tion. If patients are actively smoking, we will not operate in the elective setting
until they have been free from tobacco use for at least 6 weeks. Normal renal
function is important not only for risk stratification but also for potential opti-
mization to minimize perioperative complications. Assessment of coexisting
peripheral arterial disease is assisted by obtaining carotid duplex scanning and
baseline ankle brachial indices. Finally, hepatic function is assessed; cirrhosis
remains a relative contraindication for open operation.
In the event that open TAAA repair is contraindicated secondary to
comorbid conditions, an evaluation for a hybrid endovascular approach is
entertained. In this option, a thoracotomy is avoided. If the aneurysm extends
into the visceral or pararenal aortic segments, a debranching procedure is indi-
cated whereby the respective involved vessel is bypassed and then the TAAA
excluded with a stent graft to include coverage of the bypassed vessel(s). By
avoiding the thoracotomy, and limiting the incision to an abdominal approach
only, the morbidity is theoretically decreased. Although long-term results of
Table 1
Thoracoabdominal aortic aneurysm classification.
Type Extent of pathology
I Distal to left subclavian artery to above renal arteries
II Distal to left subclavian artery to aortic bifurcation
III From sixth intercostal space to infrarenal aorta
IV From aortic diaphragm to infrarenal aorta (total abdominal aorta)
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Chapter 24 Operative Therapy for the Descending and Thoracoabdominal Aorta 339
this approach are not well characterized, early data are encouraging. Note that
the debranching procedure itself is not altogether benign and has been associ-
ated with significant morbidity in some series.
5,
6
The preoperative workup for hybrid TAAA repairs is similar to that seen
for open TAAA repair. We typically obtain adenosine nuclear medicine stress
tests and selectively catheterize only those with abnormal results. Although
the remaining preoperative testing is similar, it is primarily performed to
risk stratify the patient and present him/her with an estimate of procedural
morbidity. If the procedure is totally endovascular (i.e., no debranching pro-
cedure needed, or thoracic endovascular aneurysm repair (TEVAR )), we and
others have performed this procedure in patients considered a prohibitive
risk for open repair with good early and late results.
7,
8
In contrast to medical
therapy, previous work suggests that this approach may reduce the risk for
early mortality even in this frequently elderly and debilitated group.
9
For
those patients needing a debranching procedure, a more selective approach
is taken since this additional operation requires laparotomy with its attendant
morbidity.
6
Operative Techniques for Repair of TAAA
Open Operative TAAA Repair
Open TAAA repair is approached via a left thoracoabdominal incision. If the
aneurysm is confined to the descending thoracic aorta, an abdominal extension
is not made. We typically extend our abdominal incision in the left paramedian
line and stay in the retroperitoneal plane. All type I, II, and III TAAA repairs
are done with spinal drains to minimize the risk for spinal cord ischemia. In
addition, the use of extracorporeal perfusion is standard in all TAAAs. We
will often use full cardiopulmonary bypass with deep hypothermic circulatory
arrest for all TAAA repairs done for acute type B dissections or for those with
isolated type I TAAA (as a spinal protective adjunct). Otherwise, left heart
bypass with an oxygenator is used for all others.
The sequence of the operative repair for a type II TAAA is described
as follows and the final result is illustrated in Fig. 1 . Briefly, the proximal
anastomosis is constructed first. We use a sequential clamping technique to
maximize perfusion times to all viscera and the spinal cord. We attempt to
reimplant lower (T8–T11) intercostal vessels in all patients unless they are
thrombosed, or the adjacent aorta is heavily calcified. The diaphragm is left
intact to minimize postoperative pulmonary complications. The visceral and
renal vessels are then sequentially bypassed using the prefabricated side
branches on the main Dacron aortic graft. In this manner, flow is maintained to
the viscera throughout construction of the anastomosis. In addition, the avoid-
ance of reimplanting the visceral vessels as a patch eliminates all aneurysmal
aortic tissue and the risk of formation of visceral patch aneurysms. When
renal arterial bypasses are constructed, 10 mg of furosemide is administered
prior to renal artery clamping and administer a cold (4°C) renal preservation
solution containing heparin and mannitol directly into the ostium. Finally, the
distal aortic anastomosis is constructed, and the patient then weaned from
extracorporeal support.
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340 Himanshu J. Patel et al.
Hybrid TAAA Repair
For those patients undergoing a purely endovascular procedure (i.e., typically
pathology confined to the descending aorta), the access vessel is made ready
for isolation. The delivery of the endograft is typically via a transfemoral
approach, but iliac exposure is needed in approximately 15–20% (predomi-
nantly women, smaller men, or those with significant external iliac atheroscle-
rosis). We use lumbar drains for spinal cord protection for all those patients
requiring long segment (>20 cm) coverage or those who have prior infrarenal
AAA repairs. The endograft is then delivered to the intended aortic segment
via the isolated access vessel, and the vessel is then repaired following com-
pletion aortography.
If a debranching procedure is needed for coverage into the visceral and
pararenal segments, this is performed first, and endografting is then
subsequently performed after allowing for 4–6 weeks of recovery. Abdominal
debranching is often performed by basing the inflow of the branch vessels
on the iliac artery or occasionally the terminal infrarenal aorta. Bypasses are
constructed with 7- or 8-mm Dacron or Goretex grafts and are typically an
end-to-end bypass graft to the branch vessel. Endografting is then performed
as described above.
Fig. 1 A completed repair of a type II thoracoabdominal aortic aneurysm. Note the
reimplantation of the lower sets of intercostal vessels, as well as individual bypasses to
the visceral and renal vessels
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Chapter 24 Operative Therapy for the Descending and Thoracoabdominal Aorta 341
In lieu of abdominal debranching, a totally endovascular approach may be
undertaken at select centers who have access to custom fabricated fenestrated
and branched endografts.
10
These endografts are designed specifically for the
patient’s individual anatomy and allow for cannulation and endografting into
the branch vessels via the main aortic endograft to perform a totally endovas-
cular TAAA. Early results are encouraging.
Postoperative Management
Recovery from repair of a TAAA requires a stay of 2–4 days in the intensive
care unit for open procedures, and 1–2 days following TEVAR. During this
time, permissive hypertension is maintained to improve spinal cord perfusion,
and the spinal fluid is drained to maintain intrathecal pressures < 10 mmHg.
Following this period, attention is paid to ambulation, resumption of enteral
nutrition when bowel function returns, and aggressive pulmonary toilet. There
is a phenomenon of delayed paraplegia that can occur at any time after an
operation, but usually occurs within the first week. It has often been associ-
ated with hemodynamic instability, and thus we attempt to maintain permis-
sive hypertension (systolic blood pressure 120–140 mmHg) throughout the
hospitalization.
11
Outcomes following open TAAA repair have been analyzed in multiple
series. Essentially, the risk for mortality varies from 4% to 18%.
1–
3
A recent
analysis of the Nationwide Inpatient Sample administrative database, however,
suggested a nationwide mortality estimate exceeding 20%.
4
At the University
of Michigan, we have reported a mortality rate of 3% in the elective setting.
12
Other risks include those of renal failure (temporary or permanent) of 10%
and a risk for spinal cord ischemia of 5–12%. In contrast, the risks of purely
endovascular TAAA repair are lower, with reported rates of mortality of 1–5%
and of paraplegia of 1–5%.
5–
10
Conclusion
In summary, repair of TAAAs remains a daunting task. Over the last 40 years,
changes in operative and perioperative care as well as newer minimally inva-
sive options are improving outcomes to ameliorate the risks of dissection or
rupture and aneurysm-related mortality.
References
1 . Crawford ES , Crawford JL , Safi HJ , et al . Thoracoabdominal aortic aneurysms:
preoperative and intraoperative factors determining immediate and long term results
of operations in 605 patients . J. Vasc. Surg. 1986 ; 3 : 389 – 404 .
2 . Svensson LG , Hess KR , Coselli JS , et al . Influence of segmental arteries, extent
and atriofemoral bypass on postoperative paraplegia after thoracoabdominal aortic
operations . J. Vasc. Surg. 1994 ; 20 : 255 – 62 .
3 . Coselli JS , LeMaire SA , Conklin ND , et al . Morbidity and mortality after extent II
thoracoabdominal aortic aneurysm repair . Ann. Thorac. Surg. 2002 ; 73 : 1107 – 15 .
4 . Cowan JA , Jr. , Dimick JB , Henke PK et al . Surgical treatment of intact thoracoab-
dominal aortic aneurysms in the United States: hospital and surgeon volume-related
outcomes . J. Vasc. Surg. 2003 ; 37 : 1169 – 74 .
https://t.me/med1917
342 Himanshu J. Patel et al.
5 . Fulton JJ , Farber MA , Marston WA , et al . Endovascular stent graft repair of para-
renal and type IV thoracoabdominal aortic aneurysms with adjunctive visceral
reconstruction . J. Vasc. Surg. 2005 ; 41 : 191 – 8 .
6 . Chiesa R , Tshomba Y , Melissano G , et al . Hybrid approach to thoracoabdominal
aortic aneurysms in patients with prior aortic surgery . J. Vasc. Surg. 2007 ; 45 :
1128 – 35 .
7 . Patel HJ , Williams DM , Upchurch GR , Shillingford MS , Dasika NL , Proctor MC ,
Deeb GM . Long term results from a 12 year experience with endovascular therapy
for thoracic aortic disease . Ann. Thorac. Surg. 2006 ; 82 : 2147 – 53 .
8 . Greenberg RK , O’Neill S , Walker E , et al . Endovascular repair of thoracic aortic
lesions with the Zenith TX1 and TX2 thoracic endografts: intermediate-term
results . J. Vasc. Surg. 2005 ; 41 : 589 – 96 .
9 . Patel HJ , Shillingford MS , Williams DM , et al . Survival benefit of endovascular
descending thoracic aortic repair for the high risk patient . Ann. Thorac. Surg. 2007 ;
83 : 1628 – 34 .
10 . Roselli EE , Greenberg RK , Pfaff K , Francis C , Svensson LG , Lytle B W .
Endovascular treatment of thoracoabdominal aortic aneurysms. J. Thorac.
Cardiovasc . Surg. 2007 ; 133 : 1474 – 82 .
11 . Wong DR , Coselli JS , Amerman K , et al . Delayed spinal deficits after thoracoab-
dominal aortic aneurysm repair . Ann. Thorac. Surg. 2007 ; 83 : 1345 – 55 .
12 . Upchurch GR , Jr. , Patel HJ , Rectenwald JE , et al . Open repair of thoracoabdominal
aortic aneurysms: when and how . In Pearce WH , Matsumura JS , Yao JST (eds.),
Vascular Surgery in the Endovascular Era . Greenwood Academic . Evanston IL .
2008 : pp. 146 – 155 .
https://t.me/med1917
Abstract Endovascular repair is particularly appealing in cases of thoracic
aortic aneurysm because the surgical alternative requires thoracotomy and
aortic cross-clamp, resulting in pulmonary dysfunction, cardiac strain, down-
stream ischemia, and reperfusion injury. Moreover, localized aneurysms of the
thoracic aorta are relatively easy to treat by endovascular means, using simple
aortoaortic stent-grafts; hence, the endovascular thoracic aortic aneurysm repair
was rapidly adopted in the early 1990s.
1
Yet this area of endovascular tech-
nology remains something of a work in progress. Thoracic aortic stent-grafts
still fail to meet many of the requirements of long-term success because the
affected segment is long, wide, curved, far from the femoral arteries, and close
to the origins of visceral or cerebral branches. There remain many obstacles to
be overcome before endovascular repair can be considered safe, durable, and
effective for the majority of thoracic aortic aneurysms. Some problems affect
repair in any part of the thoracic aorta, while some are segment-specifi c; some
problems are amenable to refi nements of operative technique, while others
must wait for fundamental advances in stent-graft technology.
Keywords Endovascular , Thoracic aortic aneurysm, Stent-graft
Arterial Access
Even in its healthy state, the descending thoracic aorta is wider and longer
than the infrarenal abdominal aorta, and thoracic aortic stent-grafts have to be
wider and longer than abdominal aortic stent-grafts. The additional width is a
particular problem in women and patients with common femoral or external
iliac stenosis, because wider stent-grafts need wider delivery systems. If the
delivery system is too large to traverse the external iliac artery, one needs
an alternative route of access, to the common iliac artery, or even the aorta.
Although direct puncture has been described, most surgeons prefer to create a
conduit to the central arterial circulation, which may be surgical or endovas-
cular, simultaneous or staged.
Chapter 25
Endovascular Repair of Thoracic
Aortic Aneurysms
Timothy A. M. Chuter
G. Upchurch and E. Criado (eds.) Aortic Aneurysms, Contemporary Cardiology
DOI: 10.1007/978-1-60327-204-9_25, © Humana Press, a part of
Springer Science + Business Media, LLC 2009
343
https://t.me/med1917
344 A.M. Chuter
An endovascular conduit consists of a covered stent, or stents, within the
external or common iliac artery, which permits aggressive balloon-induced
dilatation to the point of arterial rupture. This technique works well when the
arterial narrowing spares the proximal external iliac artery. Otherwise, there is
a risk that the covered stent will either occlude the internal iliac artery or fail
to prevent bleeding from rupture of the proximal external iliac artery.
The simplest form of conduit is a conventional surgical graft with one end
sutured to the margins of a common iliac arteriotomy.
2
An encircling loop
of cloth tape compresses the conduit around the delivery system or sheath,
providing hemostasis. Better still, the wall of the conduit is punctured and the
sheath is inserted over a wire, as though the conduit were a native artery. A
tight fit between the margins of the hole and the wall of the sheath is usually
sufficient hemostasis. On occasion, a small incision at the puncture site may be
needed to permit large bore sheath insertion. In theory, a blind-ended conduit
can be left in an accessible location under the skin as the first part of a staged
procedure. The second stage then starts with thrombectomy of the graft. A
more satisfactory alternative involves attaching the proximal end of the graft
to the transected end of the common iliac artery and the distal end to the side
of the external iliac artery, creating a bypass with antegrade flow through the
femoral artery to the limb and retrograde flow up the native external iliac
artery to the internal iliac territory.
3
This graft need not be exposed during the
second stage of the operation. Instead, access to the conduit can be obtained
through the femoral artery.
Aortic Tortuosity
An aneurysm of the descending thoracic aorta often lengthens as it dilates,
raising the distal aortic arch and creating a transverse segment of redundant
aorta just above the diaphragm. The resultant angles impede stent-graft inser-
tion and compromise both stent-graft sealing and attachment.
The aortic arch and diaphragmatic hiatus tend to fix the aorta in position,
preventing the straightening that would otherwise accompany the insertion
of a smoothly tapered delivery system over a stiff guidewire. Under these
circumstances, the delivery system has to flex without kinking. The simplest
way to make a sheath kink resistant is to thicken its wall, but this remedy is
limited by the size of the access arteries. The incorporation of a spiral wire, or
ribbon, into the wall of the sheath has the same effect without the added bulk,
and most sheath-based delivery systems incorporate this approach. This design
appears to achieve the two primary goals: atraumatic insertion and unrestricted
sheath withdrawal. Indeed, the TX2 Superflex delivery system (Cook Medical,
Bloomington, IN) (Fig. 1 ) will deploy even when tied in a knot. The TAG
stent-graft (WL Gore, Flagstaff, AZ) employs a different approach. The sheath
is too short to reach the level of the diaphragm. Instead of a sheath, the stent-
graft has a corset of PTFE fabric with a lacing of a PTFE thread. The corset
opens when the thread is removed. In rare cases, the tip of the corset may fail
to open. Under these circumstances, a high pressure balloon has been used to
rupture the thread.
A very stiff guidewire, such as the Lunderquist (Cook Medical, Bloomington,
IN), helps the delivery system follow an atraumatic path through the aorta to
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Chapter 25 Endovascular Repair of Thoracic Aortic Aneurysms 345
its implantation site. When “ultrastiff” is not stiff enough, additional support
can be provided by applying traction to the ends of a through and through
brachiofemoral wire. In such cases, a catheter or sheath helps cover the bra-
chiocephalic portion of the wire and minimize the risk of arterial injury.
A short, angulated proximal implantation site is the single most common
cause of primary technical failure. Unless the end of the stent-graft and the
wall of the nondilated segment of aorta share the same longitudinal axis, blood
leaks between them into the aneurysm (type I endoleak). The proximal end of
the stent-graft has to assume the orientation of the implantation site (neck),
while the rest of the stent-graft assumes the orientation of the aneurysm.
The greater the angle, the more the stent-graft has to bend. A long neck will
usually generate the necessary torque. A short neck, on the other hand, is less
able to impose coaxial orientation on the stent-graft. At the very least, the
lower lip of the stent-graft tends to lift from the inner curvature of an angu-
lated distal aortic arch. There are two possible remedies: increase the effective
length of the neck or uncouple the mechanical linkage between the proximal
end of the stent-graft and the body of the stent-graft.
The most direct way to lengthen the neck is to cover the arteries that origi-
nate from the distal aortic arch. This used to be standard practice for several
reasons: the subclavian artery is richly supplied with collaterals, asymptomatic
subclavian artery occlusion is a common incidental finding, and subclavian
coverage at the time of endovascular aneursysm repair rarely produces serious
complications.
4
However, recent studies have shown subclavian occlusion to
be associated with neurological complications, such as stroke and paraple-
gia.
5,
6
The current consensus favors subclavian artery preservation, even in
the absence of left vertebral artery dominance or left internal mammary artery
(LIMA) coronary bypass.
7
For one thing, the subclavian artery is a source of
collateral flow to the spine, and subclavian preservation lowers the risk of
paraplegia. When the proximal end of a thoracic aortic aneurysm approaches
the level of the subclavian orifice, the alternatives for subclavian preservation
include: carotid-subclavian bypass (mandatory in the presence of a LIMA
grafts), subclavian-carotid transposition, subclavian stenting, stent-graft fenes-
tration, or stent-graft branching (see The Aortic Arch section below).
Mechanical uncoupling of the proximal stent-graft from the rest (flexibility)
depends on the potential for a change in the relative lengths of the inner and
outer aspects of the bend. The problem is that the stents are designed to change
their diameter, not their length. Changes in length occur between stents (Fig. 2 ).
Long stents, small gaps between stents, and wide stents all reduce the flexibility
Fig. 1 Photograph of the Superflex delivery system (TX2, Cook Medical, Inc.,
Bloomington, IN), showing its characteristic flexibility (See Color Plates)
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