Standard of Practice for the Endovascular Treatment of Thoracic Aortic Aneurysms and Type B Dissections
Michael D. Dake
M. D. Dake Department of Cardiothoracic Surgery Radiology, Stanford University School of Medicine, Falk Cardiovascular Research Center
, 300 Pasteur Drive,
Stanford, CA 94305-5407, USA
F. Fanelli (&) Department of Radiological Sciences, Vascular and Interventional Radiology Unit
'' University of Rome
, 324 Viale Regina Elena,
00161 Rome, Italy
Thoracic endovascular aortic repair (TEVAR) represents a minimally invasive technique alternative to conventional open surgical reconstruction for the treatment of thoracic aortic pathologies. Rapid advances in endovascular technology and procedural breakthroughs have contributed to a dramatic transformation of the entire field of thoracic aortic surgery. TEVAR procedures can be challenging and, at times, extraordinarily difficult. They require seasoned endovascular experience and refined skills. Of all endovascular procedures, meticulous assessment of anatomy and preoperative procedure planning are absolutely paramount to produce optimal outcomes. These guidelines are intended for use in quality-improvement programs that assess the standard of care expected from all physicians who perform TEVAR procedures.
Thoracic endovascular aortic repair (TEVAR) represents a
minimally invasive alternative to conventional open
surgical reconstruction for the treatment of thoracic aortic
pathologies. It is a valid therapeutic option for the
treatment of thoracic aortic aneurysms and thoracic aortic
dissections by virtue of its lower mortality, morbidity, and
paraplegia rates compared to open thoracic repair. Rapid
advances in endovascular technology and procedural
breakthroughs have contributed to a dramatic
transformation of the entire field of thoracic aortic surgery \15 years
after the first report of stent-graft repair of thoracic aortic
aneurysms . TEVAR procedures can be challenging and,
at times, extraordinarily difficult. They require seasoned
endovascular experience and refined skills similar to all
endovascular procedures. In addition, meticulous
assessment of anatomy and preoperative procedure planning are
absolutely paramount to produce optimal outcomes.
These guidelines are intended for use in
qualityimprovement programs that assess the standard of care
expected of all physicians who perform TEVAR
procedures. The issues addressed in this article include:
Definition, Diagnosis, and Symptoms
The permanent and irreversible dilation of an artery is
called aneurysm. Conventionally, according to the
definition of the Ad Hoc Committee on Reporting Standards of
the Society for Vascular Surgery and the North American
Chapter of the International Society for Cardiovascular
Surgery, a transverse diameter exceeding at least 150% of
the diameter of the remaining part of the artery can be
judged aneurysmatic .
According to conventions proposed by these societies,
thoracic aortic aneurysms can be divided into:
aneurysms that exist at the level of the ascending aorta,
arch, or descending aorta, or involving all three of these
thoracoabdominal aneurysms, with involvement of both
the descending aorta and the abdominal aorta.
Based on the extent of disease and in compliance with
the Crawford and coworkers classification, these can be
categorized further .
Type 1: involving the proximal half of the descending
aorta with extension as far as the renal arteries.
Type 2: stretching from the proximal half of the
descending thoracic aorta to the intrarenal aorta.
Type 3: extending from the distal half of the descending
thoracic aorta to the abdominal aorta.
Type 4: affecting most of the abdominal aorta, with
proximal involvement above the renal arteries.
According to their shape, thoracic aneurysms can be
divided into two types:
Fusiform: These aneurysms typically involve all three
layers of the aortic wall and, thus, are usually true
aneurysms. The abnormal dilation is often along an
extended section of the aorta and involves the entire
circumference of the aorta. Generally, the weakened
portion appears as a symmetrical bulge.
Saccular: These look like a small blister or bleb on the
side of the aorta and are asymmetrical. Typically they
are pseudoaneurysms caused either by trauma such as a
car accident or as the result of a penetrating aortic ulcer.
Thoracic aorta aneurysms have a mean growth rate of
0.42 cm/year at the level of the descending aorta and of
0.56 cm/year at the level of the aortic arch [6, 7].
The larger the diameter of a thoracic aortic aneurysm,
the higher the annual rupture risk [8, 9]:
[4 cm, 0.3%;
[5 cm, 1.7%;
[6 cm, 3.6%.
A surgical or endovascular treatment is recommended
when the diameter at the level of the ascending aorta
exceeds 49 mm and when the caliber at the level of the
arch and of the descending aorta the diameter is [45 mm
[10, 11]. Cambria et al.  reported a 52% survival rate
2 years postdiagnosis and a 17% survival rate at 5 years in
untreated patients. In patients diagnosed with Marfan
syndrome, treatment is recommended if the aortic diameter
is [43 mm .
Idiopathic cystic medial degeneration, atherosclerosis,
connective tissue disorders (Marfan syndrome,
EhlersDanlos syndrome), trauma, infection of the aortic wall, and
Takayasus arteritis are the principal aortic pathologies
associated with thoracic aneurysm .
Aortic dissection is caused by the formation of a false
channel within the aortic wall consequent to a disruption of
the intimal lining. A dissection plane that separates the
intima from the surrounding adventitia is created within the
media over a variable length of the aorta. This produces a
false lumen or a double-barreled aorta that can reduce
blood flow to the major arteries arising from the aorta .
If the dissection involves the pericardial space, cardiac
tamponade may result.
The most common site for the initiation of dissection
when the ascending aorta is involved is within its first few
centimeters. In fact, the entry tear for the process occurs
within 10 cm of the aortic valve in 90% of cases. The
second most frequent site for the initiating tear is just distal
to the left subclavian artery (LSA) . The dissection can
proceed for a variable distance, usually in an antegrade
direction but sometimes retrograde from the site of the
intimal tear. However, in the majority of cases, the
dissection affects the descending aorta, with the primary entry
tear located at the level of the origin of the left subclavian
artery in 40% [16, 17]. Between 5% and 10% of dissections
do not have an obvious intimal tear and are often attributed
to rupture of the aortic vasa vasorum as first described by
Krukenberg in 1920 [16, 17].
According to the site of aortic involvement, aortic
dissections can be divided into two groups (Stanford
Type A: The dissection involves the ascending aorta
and may extend distally to include the aortic arch and
the descending aorta. The primary entry tear is typically
located at the level of the ascending aorta or in the arch,
substernal pain that may radiate to the upper back can
also be present.
Aortic arch aneurysms: These may be associated with
upper chest or interscapular back pain. When aortic
arch aneurysms are large, both the esophagus and the
airway can be compressed. Difficulty swallowing and/
or hoarseness are the initial symptoms.
Descending thoracic aneurysms: These are mostly
asymptomatic. They can occasionally cause back pain.
but may be in the descending aortic segment and
associated with retrograde propagation to affect the
Type B: The primary entry tear is typically after the
origin of the left subclavian artery and the descending
aorta and/or aortic arch are affected exclusively,
without involvement of the ascending aorta.
Uncommonly, the entry tear may be located in the arch, with or
without extension to the descending segment, but not
into the ascending aorta.
On the basis of the time from the onset of the initial
symptoms, a dissection can be categorized as either acute
(\14 days) or chronic ([14 days) .
Moreover, Crawford et al. divided chronic type B
dissections into different categories .
Type 1: The dissection involves the descending aorta
up to the origin of the renal arteries
Type 2: The descending aorta is dissected over its entire
length and the abdominal aorta up to the iliac arteries is
Type 3: The dissection starts at the level of the midthird
of the descending aorta and involves the entire
Type 4: The whole abdominal aorta, below the
diaphragm, is involved.
The main causes of dissection are cystic medial necrosis,
atherosclerosis (occlusion of the vasa vasorum), connective
tissue disorders (Marfan syndrome, Ehlers-Danlos
syndrome), hypertension, metabolic disorders, pregnancy, crack
cocaine use, and iatrogenic (arterial catheterization) .
Dissection can also be divided into uncomplicated and
complicated disease. Complicated dissection consists of
one or more of the following manifestations: rupture,
imminent rupture, branch vessel involvement with
malperfusion syndrome or persistent or worsening thoracic
pain, drug-resistant hypertension, and false lumen
When carotid or coronary pathology does not coexist,
thoracic aorta aneurysms are generally silent and diagnosed by
sheer chance. But if the maximum diameter of the aneurysm
exceeds 70 mm, symptoms that correlate with the
compression of adjacent organs may be reported [7, 8, 22, 23].
Ascending aortic aneurysms: These often provoke
aortic root dilation and leakage of the aortic valve,
with consequent shortness of breath and even heart
failure when the incompetence is severe. A dull
When the initial tear and dissection occur, the symptoms
are severe, with an abrupt onset of pain . The sudden
pain is generally located at the midsternum for dissection
of the ascending aorta and in the interscapular region for
descending thoracic aortic dissection. Migratory pain
should be regarded suspiciously as a sign of dissection
extension in an antegrade or retrograde direction .
Painless dissection has been described and usually occurs
in the presence of an existing aneurysm, where the pain of
a new dissection may not be differentiated from chronic
aneurysm pain .
Depending on the evolution of the dissection process,
symptoms can be complicated by hypotension, bradycardia,
abdominal pain, and intestinal or inferior limb ischemia
. However, a differential diagnosis for chest pain should
be considered, with myocardial ischemia, aortic aneurysm,
acute aortic regurgitation, pericarditis, musculoskeletal
pain, and pulmonary embolus entertained [27, 28].
Both thoracic aortic aneurysm and dissection are diagnosed
by the same spectrum of imaging evaluations: plain chest
radiography, CT angiography (CTA), magnetic resonance
angiography (MRA), conventional digital subtraction
angiography (DSA), and transesophageal
echocardiography (TEE) .
On X-ray, abnormal findings are evident in 88% of cases
and include the following.
Widened mediastinum (25% of cases): differential
diagnosis is tumor, adenophaty, lymphoma, and
Abnormal aortic knob contour (66% of cases).
Tracheal or esophageal deviation.
Ring sign (dissection), with displacement of the aortic
margin [5 cm beyond the calcified aortic intima.
CTA: CTA is the best noninvasive alternative to DSA
and is considered the gold standard and primary diagnostic
modality today. With a single breath-hold acquisition, after
contrast medium injection, it can evaluate the thoracic and
abdominal aorta, supraaortic vessels, abdominal branches,
and iliac-femoral axis. Images can be studied in the
standard axial format, and after postprocessing multiplanar
reconstructions using different algorithms (volume
rendering [VR], maximum intensity projection [MIP],
multiplanar reformation [MPR], shaded surface display [SSD],
etc.) provide three-dimensional characterizations.
CTA evaluations can provide the following:
diameter and morphology of the aorta;
diameter and length of the proximal and distal necks;
intimal flap anatomy, extent of the dissection, and true
and false lumen morphologies;
site of the primary entry tear;
presence of thrombus or calcifications;
patency of the abdominal branches;
size, tortuosity, and disease status of iliac and femoral
Recently a new imaging modality, electrocardiogram
(ECG)-gated CTA, has been introduced. The 3D
volumetric data sets allow rotation of the aorta while viewing it
in different phases of the cardiac cycle. This may improve
diagnostic accuracy, as motion artifacts, often the cause of
false-positive findings of a thoracic dissection, are minimal
MRA: MRA allows limiting the exposure to ionizing
radiation and forgoing the use of noniodinated contrast
media, which are preferable in those cases where multiple
follow-up examinations are required and in patients with
iodinated contrast allergies. MRA was once considered
ideal for patients with renal failure, but after the discovery
of nephrogenic systemic fibrosis in patients with renal
dysfunction receiving intravenous gadolinium, the initial
enthusiasm drastically decreased. MRA gives the same
information that can be achieved using CTA. The
introduction of axial images, acquired with black-blood
sequences, allows a better evaluation of the aortic wall and
of any dissection, ulcer, or thrombus accumulation. This
sequence takes advantage of the lack of signal from blood
flowing perpendicular to the imaging plane.
MRA does have some limits; it gives no information
about the presence of calcium in the aorta or conduit
arteries and cannot be performed in patients with old
cardiac valve prostheses or pacemakers [31, 34].
DSA: DSA is still considered the definitive diagnostic
test for thoracic pathology, but it clearly displays limitations
compared to the more modern CTA and MRA. Principally,
this is because of the complications associated with an
invasive procedure not encountered with noninvasive
imaging tests and its inability to evaluate the thrombus
quantity, when present, along the aortic wall. DSA is
usually performed before any interventional procedure and
when CTA and MRA cannot answer all diagnostic doubts.
DSA is mandatory when patients exhibit ischemic
problems with mesenteric, renal, or lower extremity
malperfusion, because it provides the final diagnostic data that
contribute to the determination of whether a therapeutic
intervention is required and feasible. It also provides vital
morphological and hemodynamic data to guide any
TEE: TEE can be quickly performed at the patients
bedside, in no more than 20 min. It has a diagnostic
sensitivity ranging from 98% to 100% for dissection and a
technical suitability for patient application, ranging from
90% to 100% . Moreover, it can be performed more
than once, its cost is limited, and it is useful during the
follow-up of patients who have undergone surgery and
patients treated with medical therapy.
The limitations of TEE include that it can be performed
only at selected medical centers, it requires a specialized
operator, and it cannot provide information about false
lumen extension at the level of the abdominal aorta or
about the involvement of abdominal aortic branch vessels
The natural history of a thoracic aneurysm is expansion,
rupture, and death, with the greatest risk of rupture in larger
aneurysms . Factors affecting aneurysm expansion are
increasing age, smoking, chronic obstructive pulmonary
disease, and hypertension. The larger the aortic diameter,
the higher the rate of aneurysm expansion, and in fact, an
aneurysm[50 mm expands faster than a smaller one. Also,
the location of an aneurysm is crucial. Aneurysms located
in the proximal descending aorta expand more rapidly than
those located in the distal descending aorta [3, 4].
Thoracic aortic type B dissection presents a severe
prognosis in the acute phase; without any treatment it has a
mortality rate of 33% at 24 h, 50% at 48 h, and 75% at
2 weeks . After the acute phase, uncomplicated type B
dissection, which does not require interventional treatment,
has a survival rate of 91% at 1 month and 89% at 1 year
. After 40 to 50 months, a thoracic aortic aneurysm
develops in 20% to 30% of cases. This requires
interventional management to prevent aortic rupture in 18% .
However, those patients who survive the acute phase have
a good prognosis. Thus, any strategy that recommends
intervention for all chronic stable type B dissections must
ensure that the majority of survivors have an acceptable
long-term outcome .
In patients with a thoracic aneurysm that is B50 mm in
diameter, no treatment is usually recommended, but
regular-interval imaging follow-up must be performed (every
6 months). In these patients, moreover, close clinical
surveillance is necessary, especially in order to monitor and
maintain blood pressure at recommended values (systolic
BAP level, B110 mmHg).
Repair of a thoracic aortic aneurysm should be
considered when patients present with one of the following
symptoms: chest discomfort, symptoms of surrounding
organ compression (dyspnea, dysphagia, SOB, hemoptysis,
etc.), and/or an aortic diameter [55 mm . Treatment is
also indicated when the aneurysm diameter increases by
more than 1 cm per year or when signs of aneurysm
rupture are evident. Surgical therapy of descending aortic
aneurysm with prosthetic graft repair is associated with a
perioperative mortality rate ranging from 5% to 20%,
depending on the clinical conditions of the patient and the
aneurysm diameter .
Aneurysms of the ascending aorta are generally treated
with surgical reconstruction, while aneurysms of the
descending aorta are addressed using either surgery or
endovascular techniques. Endovascular treatment, based on
the insertion of an endograft, represents a valid alternative
to the conventional open repair with lower early morbidity
and mortality rates. It is associated with a 30-day mortality
rate ranging from 0% to 20% and a periprocedural stroke
rate of from 0% to 7% [21, 22].
For type A dissection, surgery is still the treatment of
choice. The surgical procedure should be performed
emergently due to the possibility of serious ensuing
complications related to rupture and/or involvement of the
coronary arteries by the intimal flap.
In the case of type B dissection three treatment options
should be considered:
Selection is based on the specific characteristics of the
dissection and the clinical status of the patient.
Beta-blockers and ACE inhibitors in combination are
considered the current treatment of choice in case of
uncomplicated type B dissection, but in complicated cases
with lower extremity malperfusion, visceral ischemia, and/
or renal failure, an immediate interventional treatment is
necessary. Medical therapy provides good early-term
results in uncomplicated dissection, with 85% of patients
surviving the initial acute phase. The 30-day mortality rate
is 10% for uncomplicated patients, versus 30% for those
with complicated dissection . Long-term results are
poor, however, with a 50% mortality at 5 years and a high
incidence of aneurysm formation (25%) at 4 years .
In cases of complicated type B dissection (renal or
abdominal ischemia) or unstable conditions (shock, severe
uncontrollable hypertension), an invasive treatment should
Open operative repair represents a valid therapeutic option
in cases of acute type B dissection complicated by
retrograde extension into the ascending aorta, Marfan syndrome,
rupture, or involvement of vital organs. However, similar to
the existing operative management considerations for
thoracic aneurysms, surgery in the setting of complicated
dissection is associated with a high incidence of paraplegia,
prolonged hospital stay, and pulmonary complications.
Endograft placement is the new frontier for the treatment of
type B dissection. The first report of endografting for an
acute dissection was by Dake et al. in 1994 . The
rationale for endovascular therapy is to obliterate the false
lumen and restore normal thoracic aortic anatomy.
Stentgraft therapy will promote thrombosis of the false lumen
and, in so doing, mitigate aneurysm development.
Compared to open surgical repair, reports of this technique
detail lower morbidity and mortality rates, especially for
complications correlated to spinal cord ischemia .
Indications are as follows.
Acute type B dissection in unstable patients when
medical therapy cannot guarantee that blood pressure is
controlled at a recommended low level (systolic BAP,
Complicated acute type B dissection when the
dissection involves an abdominal branch or the peripheral
arteries, with consequent ischemia.
Chronic type B dissection to avoid progressive
dilatation of the aorta, with aneurysm formation and
progressive risk of rupture.
Chronic type A dissection after surgical repair of the
ascending aorta when the descending aortic false lumen
is still patent and a progressive increase in its size/
volume is observed during follow-up.
Endovascular treatment is also recommended to solve
ischemic branch complications correlated with the dissection.
A 30-day mortality rate of 10% is reported for
uncomplicated type B dissection, while in cases of complicated
dissection, mortality rates are higher: 20% at 2 days and
25% at 30 days . Early results from different clinical
series of stent-graft management in patients with acute and
chronic type B dissection are encouraging [39, 42].
Obliteration of flow across the entry tear into the false lumen is
achieved in [90% of cases, with complete thrombosis of
the proximal thoracic aortic false lumen over the length of
the device in 80% to 95% .
Endovascular treatment of the thoracic aorta should be
performed either in an operating room or in an angiosuite,
in a sterile configuration, and with all the equipment
necessary in case a surgical conversion is necessary. As the
procedure requires angiograms to be performed in severe
and/or compound oblique views in order to optionally
evaluate the landing zones, it is crucial to use a
state-ofthe-art fluoroscopy machine or dedicated new-generation
C-arm. Procedures can be performed with patients under
local, epidural or general anaesthesia depending upon the
patients clinical conditions. General anesthesia should be
selected, especially in unstable patients, to maintain
appropriately low blood pressure levels.
The large diameter of the stent-graft device (2225 Fr)
requires a surgical cutdown to expose the common femoral
artery, but recently TEVAR can also be performed with a
completely percutaneous access with the use of
percutaneous access closure devices. Avoidance of surgical
femoral exposure may also result in shorter procedure times,
consequent fewer local and systemic complications, and
increased patient comfort. The technique is well tolerated
by patients, with almost none of the postoperative
discomfort typical of groin incision and with a rapid return to
normal activities .
A graduated-marker pigtail catheter (45 Fr, 110 cm
long) is introduced via the controlateral femoral site
through a small introducer (45 Fr, 11 cm long). The
stentgraft device is then advanced over a stiff guidewire in order
to have enough support throughout the femoral and iliac
systems. Through the pigtail catheter, several automated
injections of contrast media are performed to correctly
evaluate the morphology of the aorta. Then the device is
advanced up to the desired position using fluoroscopy. If
the stent-graft is deployed at the level of the aortic arch, the
final aortogram should be performed with the device in its
final position because the presence of a large and stiff
device can modify a shift the arch morphology.
During the entire procedure, it is important to insure that
the blood pressure never exceeds 100 mmHg, to avoid
Thoracic aortic repair by endovascular stent-graft
placement requires suitable proximal and distal landing zones for
stable fixation and complete sealing of the endoprosthesis to
the aortic wall. As the majority of the proximal fixation
targets will be adjacent or within the aortic arch, this can be
considered the Achilles heel of TEVAR. The reasons are
multiple and related mainly to the anatomy. In terms of
endograft conformation to the underlying aortic wall, the
arch is geometrically challenging and it contains critical
branches. The knuckle of the arch refers to the area of the
distal arch where the descending aorta takes its origin. This
point represents a potential problem spot because presently
available devices are unable to conform to such abruptly
angled geometry, especially along the lesser curve, and/or a
lack of fixation in this area can lead to a fatal disaster.
A problem arises when there is a short distance
(\20 mm) between the origin of the LSA and an adjacent
distal arch aneurysm or the primary entry tear of a type B
dissection. Several options have been proposed to
overcome this problem, such as prophylactic transposition of
the LSA to the left common carotid artery (LCCA) or
creation of a bypass graft between the left LCCA and LSA
in order to provide sufficient blood flow to the arm .
Intentional occlusion of the LSA by thoracic stent-graft
represents a valid alternative to the surgical procedures,
especially in those patients with critical or emergent
clinical conditions. In this case if symptoms, ischemic or
neurological, develop, subsequent surgical
revascularization of the LSA can be easily performed . Total arch
debranching is also possible, but it requires a sternotomy,
with ascending aorta-based bypass grafts to all of the arch
branches, followed by retrograde or antegrade endograft
placement across the entire arch .
Alternatively, there are no easy management strategies to
deal with a short distal neck above the celiac trunk.
Intentional coverage of the celiac is not an innocuous procedure
even in cases a coexisting normal superior mesenteric artery
(SMA) capable of supporting an apparently normal network
of collateral flow. Some authors report that pretreatment
embolization of the celiac trunk is a reasonably safe
alternative to create a longer landing zone at the level of the
SMA. However, an accurate pretreatment evaluation is
mandatory to evaluate the collateral flow at the level of the
gastro-duodenal artery. In these cases, to guarantee patency
of the SMA, a 4- to 5-Fr angiographic catheter is frequently
placed within the SMA to serve as a reference marker
during the thoracic device deployment.
Patients undergoing TEVAR often have concomitant
peripheral vascular disease involving the femoral and iliac
arteries. Because the currently available devices employ
relatively large delivery systems, their insertion can be
challenging. Several techniques have been described to
facilitate safe introduction of these device . If a focal
iliac lesion exists, a simple method to increase arterial
caliber is to perform a PTA of the stenotic segment.
However, dilation should be done very carefully, especially
when the artery is calcified.
In cases where the femoral arteries are too small or
where disease exists at the level of the external iliac
arteries, the stent-graft device can be inserted through a
common iliac artery exposed via a right or left
lowerquadrant oblique incision. The device can be inserted either
after direct arteriotomy or, alternatively, after
anastomosing a vascular graft to the common iliac artery and
creating a temporary conduit.
Alternatively, a right brachial approach can be used to
insert the device if no other peripheral access is available,
but this approach may be associated with neurological
complications related to crossing the origin of the
innominate trunk. A rare, but possible access that may be required
in very unusual conditions is the common carotid artery.
Generally speaking, the right side provides a better angle
for the insertion and delivery of the stent-graft device. It is
advisable, however, to perform an accurate evaluation of
the intracranial circulation to confirm the presence of
adequate collateral flow via the anterior or posterior
communicating arteries to avoid cerebral ischemia. Alternatively,
the most direct approach for device introduction is to insert
the delivery system via the abdominal aorta.
In cases of aortic aneurysm, gentle dilation of the
stentgraft is performed at the level of the proximal and distal
attachment sites to secure optimal wall apposition of the
stent-graft. Dilation should be performed in a particular
way with a rapid deflation of the balloon because balloon
expansion is similar to aortic clamping and provokes a
marked increase in blood pressure. Stent-graft dilation
should be avoided in cases of dissection. A stent-grafts
radial force is generally sufficient to obtain good aortic
wall apposition and expansion of the true lumen. In fact, in
these cases dilation may be associated with a progression
of the dissection or rupture of the intimal flap. When more
than one stent-graft device is implanted, dilation of the
overlap zone between pieces is mandatory to ensure
circumferential sealing between the different elements.
Selection of the stent-graft (type, diameter, and length) is
performed before the procedure, after accurate analysis of
the diagnostic images. Selection of the correct diameter of
the stent-graft can be difficult in dissection cases because
the true lumen is only a fraction of the overall transaortic
diameter and is rarely cylindrical in shape. Thus, several
measurements should be performed along the dissected
aorta, with special attention to the diameter of the
nondissected aorta immediately proximal to the entry tear.
Stent-graft selection is based on evaluation of the diameter
of the healthy aorta just before the dissection .
Treatment of acute aortic dissections should be performed with
minimal (\2 mm) or no oversizing using the nondissected
midaortic arch as the target segment for measurement.
In cases of an aortic aneurysm, the stent-graft diameter
is calculated on the basis of the proximal and distal neck
diameters. In aneurysm cases, a device oversize factor,
ranging between 20% to 30%, is applied to select the most
correct diameter of the endoprosthesis and to ensure a
secure anchoring and a tight circumferential seal .
In cases of aortic dissection, another critical factor to
decide is the length of the aorta to cover, in order to
completely exclude the false lumen. Devices that are longer than
the entry tear are often used, with resultant rapid formation
of thrombi within the false lumen over the length of the
device. The total length of the implant, however, must be
weighed against the risk of spinal cord ischemia, which is
increased with more extensive aortic coverage.
The complete exclusion of the aneurysm sac is based on
the implantation of an endoprosthesis, at least 2 cm above
and below the lesion. If more than one endoprosthesis is
implanted, the overlap between two elements should be
[5 cm to avoid separation of the elements during the
follow-up, especially in cases with very tortuous anatomy .
In the presence of a mismatch between the proximal and
the distal landing zone diameters that exceeds 4 mm, the
procedure should be completed either using a tapered
stentgraft or using two endoprosthesis of different diameters.
The small endoprosthesis should be deployed first, and the
larger device should be inserted into the smaller to
facilitate good sealing.
Selection of the ideal endograft for a particular case
should be made on the basis of the morphological
characteristics of the aorta in order to promote easy and
accurate deployment, permanent fixation, and long durability.
Endograft parameters that should be considered when
making the choice are stent configuration, graft material,
fixation mechanism, sizes, delivery system, tapered design,
and radial force. Currently, different stent-grafts are
commercially available on the European market:
Gore TAG (W. L. Gore & Associates, Flagstaff, AZ,
Valiant (Medtronic, Minneapolis, MN, USA)
Zenith TX 2 (Cook Inc, Bloomington, IN, USA)
Relay (Bolton Medical, Sunrise, FL, USA)
EndoFit (LeMaitre Vascular, Burlington, MA, USA)
E-vita (Jotec, Hechingen, Germany)
TAG (W. L. Gore & Associates)
The TAG is formed from a nitinol stent skeleton lined with
ePTFE (expanded-polytetrafluoroethylene) reinforced with
a layer of ePTFE/fluorinated ethylene propylene (FEP).
Both the proximal and the distal ends of the stent-graft
have scalloped flares to facilitate conformity of the
endograft to tortuous anatomy. A gold radiopaque marker at
each end is located at the base of the flares. The TAG
stentgraft is released from its middle portion toward each end
simultaneously to reduce the deployment time. This is very
important to avoid stent-graft misplacement, which can
occur as a consequence of strong aortic flow forces that
may distort and displace a partially deployed endograft.
The stent-graft is inserted via an introducer sheath that
ranges from 20 to 24 Fr, in accordance with the stent-graft
diameter. The TAG device is available in diameters
ranging from 26 to 45 mm and in lengths of 10, 15, and 20 cm.
The Valiant represents the latest evolution of the Talent
stent-graft. It is made of a nitinol stent covered with
polyester fabric. To improve deployment accuracy and
technical ease, the long connecting bar of the Talent device
has been removed, while columnar support has been
optimized through stent spacing and the skeleton design. The
proximal portion of the stent-graft is bare (free flow), while
the distal end is covered. The metallic structure is
supported by different rings of nitinol Z-stents connected to
the grafts material with multiple polypropylene sutures.
Stent-graft diameters range from 22 to 46 mm, with
different lengths10, 15, and 22 cmand with a delivery
system of 22-25 Fr. The Valiant is available in both straight
and tapered designs. The use of a special releasing system,
Xcelerant technology, allows a deployment that is more
precise, more stable, and easier than that of the old Talent,
even in cases of severe angulation of the aortic arch.
Zenith TX2 (Cook Inc.)
The Zenith TX2 is designed as a two-piece modular
system, with one proximal and one distal component, although
the implantation of a single piece may be sufficient for
focal lesions. It is composed of stainless-steel Gianturco
modified Z-stents covered with polyester (Dacron). At the
ends of the endograft the stents are sewn inside the fabric,
however, in the midportion they lie outside it. This design
promotes fabric apposition to the aortic wall and
fabric-tofabric interstent junctions. The proximal element presents a
proximal bare end with protruding barbs with distal
angulation to secure a better fixation to the aortic wall. The
distal end of the proximal component is fully covered. The
distal component presents a covered proximal portion and a
distal bare stent with barbs.
Zenith endograft diameters range between 22 and
42 mm for the proximal component and from 28 to 42 mm
for the distal element. Lengths range from 108 to 206 mm
for the proximal element and from 127 to 207 mm for the
distal one. The delivery system (2022 Fr) is covered with
a hydrophilic coating and is very flexible.
Recently, a new component was introduced on the
market: the Zenith Dissection Endovascular Stent (TXD).
It is a completely bare stent that is used to treat aortic
dissection in conjunction with the TX2 proximal element in
order to increase the true lumen diameter and reduce the
risk of spinal cord ischemia.
Relay (Bolton Medical)
The Relay is composed of a polyester vascular graft fabric
supported by a Nitinol stent and a spiral Nitinol wire that
provides longitudinal stability. The stent-graft provides
different levels of radial force over its length in order to
create optimal wall apposition: the higher radial force is
applied at both ends, while in the middle portion the radial
force is less. A bare stent (free flow) is present at the
proximal end of the endoprosthesis to better orient the
angle of the proximal graft margin. The stent-graft is
constrained within a flexible secondary sheath that is
further constrained within an outer primary sheath. Once the
device is advanced into the abdominal aorta, the secondary
sheath is pushed out of the primary sheath. The flexibility
of the secondary sheath allows easier navigation into the
aortic arch and reduces friction during stent-graft
The delivery system ranges from 22 to 26 Fr according
to the diameter. The Relay is available in both straight and
tapered designs, with diameters ranging from 22 to 46 mm
and lengths up to 25 cm.
EndoFit (LeMaitre Vascular)
The EndoFit is composed of an encapsulated body with two
layers of laminated expanded polytetrafluoroethylene graft
with nitinol Z-stent rings in between. Two different
proximal end designs are available, with and without a bare stent.
The deployment system is based on a traditional
pullback mechanism consisting of a 22- to 24-Fr device.
Endofit graft diameters range from 34 to 42 mm, with lengths
up to 20 cm.
The E-vita is basically a nitinol stent covered with a
polyester graft. An innovative release system for the graft
provides full control and deployment accuracy even in
cases with tortuous anatomy. Different proximal and distal
configurations are available.
The Straight Open design allows precise and safe
positioning in the aortic arch.
The Twin stent design features maximum radial force
and an optimal sealing surface.
The Straight Cut design features a circular distal
terminus designed especially for type B dissections,
whereas the Free Wire design allows a safe and secure
anchoring mechanism while ensuring blood flow into
the existing branch vessels.
Diameters range from 24 to 44 mm, with varying
lengths, up to 23 cm. The size of the delivery system
ranges from 20 to 24 Fr.
As the procedure is still considered relatively new, the
adoption of a general protocol for accurate follow-up is
necessary in order to critically evaluate any post stent-graft
evolution of aortic morphology and the structure of the
device. CTA is the current imaging method of choice
because it provides all the critical information required to
evaluate the aorta, its branches, the aneurysm sac
morphology, and the presence of any endoleak. DSA is
performed only in equivocal cases with ambiguous CT
findings or when a complication occurs and conventional
DSA is employed immediately prior to an endovascular
A CTA follow-up exam is usually performed before the
patients discharge (3 to 5 days after the procedure), after 6
to 12 months, and yearly thereafter. Overall, aortic size,
flow in the true and false lumens, diameter of the two
lumens, endoleak, and characteristics of the stent-grafts are
evaluated in each patient.
A postimplantation syndrome consisting of fever, mild
leukocytosis, and elevated C-reactive protein was reported
by Won et al. in 23 patients within 20 days of stent-graft
placement for thoracic aortic dissections or aneurysms .
The initiation of false lumen thrombosis by sealing the
primary entry tear induces both consolidation of the false
lumen and remodeling of the aortic wall. Aortic stability
results from both thrombosis of the false lumen and the
endoprosthesis itself. Aortic remodeling consists of an
active component (expansion of the true lumen) and a
passive component (thrombus retraction in the false lumen)
and mimics a natural healing process because a thrombosed
false lumen is associated with a lower risk for future
adverse events and better survival than a partially
thrombosed or patent false channel.
Left Subclavian Artery
Typically, the use of commercially available stent-grafts
requires a proximal neck length of at least 20 mm in the
proximal descending aorta to achieve secure fixation and a
tight seal between the graft and the aortic wall. If
intentional occlusion of the LSA is planned to create a
sufficiently long landing zone, accurate prestenting evaluation
of both vertebral arteries with duplex ultrasound, DSA,
CTA, or MRA is necessary to analyze their anatomy,
patency, and continuity with the basilar artery.
In addition, the potential for ischemia of the left arm after
the procedure may be predicted before stent-graft
deployment by performing a 20-min test balloon occlusion of the
proximal LSA. During the period of balloon occlusion,
clinical monitoring of left arm symptoms is performed to
assess the status of the collateral circulation. However, if
there is documented normal flow in both vertebral arteries
and intact anatomical connections to the basilar artery, a
preinterventional balloon occlusion test may be avoided.
Several papers document the safety of intentional
occlusion of the LSA by an aortic stent-graft without
prophylactic surgical transposition [44, 49]. Alternatively,
it is possible to limit any ischemic complication associated
with LSA exclusion by adjunctive operative strategies of
surgical transposition of the LSA to the left common
carotid artery or of the left common carotid artery to the LSA
surgical bypass. These interventions must be performed
prior to stent-graft coverage of the LSA in those patients
with a documented incomplete circle of Willis that
compromises collateral flow, critical stenosis of the vertebral
arteries, anatomical variant of the right subclavian artery
(lusorian subclavian artery), or compromised collateral
circulation to the left arm from variant anatomy such as an
independent left vertebral artery origin from the arch or a
previous aortocoronary bypass performed with the left
internal mammary artery.
Recently, a new strategy to manage the LSA has been
introduced with the development of a branched stent-graft
designed to maintain the normal antegrade flow into the
LSA [51, 52].
abdominal aortic procedure or in whom a long stent-graft
must be implanted.
Cheung et al. reported that no single intercostal arterial
pair at any vertebral level is absolutely necessary for spinal
cord integrity. Moreover, they noted that the risk of
paraplegia increases if more than 10 intercostal pairs are
Endovascular treatment of the thoracic aortic pathologies
has been firmly established as a valid alternative to surgery.
As this treatment becomes more and more widespread,
procedural-related complications are more widely
recognized, although the majority of these treatment-related
problems can be managed with catheter-based
interventions. Only critical conditions, such as stent-graft infection
and migration, may ultimately require endograft removal
followed by conventional open surgery repair.
Spinal Cord Ischemia
One major problem related to type B dissection repair is
spinal cord ischemia, especially after surgery . The
effect of endoluminal repair on the spinal cord is still
uncertain but the absence of aortic clamping, which may
cause left-sided heart failure and spinal cord ischemia, may
reduce the incidence of paraplegia (in many series it is
\3%) relative to open surgery [17, 37].
TEVAR is generally associated with a 3% to 6%
frequency of spinal cord ischemia secondary to the
interruption of multiple-branch vessels that provide spinal cord
perfusion. Sacrificing critical intercostals can lead to
immediate paraplegia but the multiple collateral pathways
between the aorta and the spinal cord allow the
maintenance of good perfusion in many cases, even if some
intercostals are sacrificed. Factors that influence the
development of spinal cord ischemia include prior
abdominal aortic repair, length of thoracic aortic coverage,
hypogastric artery interruption, subclavian artery coverage,
emergency repair, and hypotension.
To reduce the risk of spinal cord ischemia during
surgical procedures, several interventions have been
suggested, such as cerebrospinal fluid (CSF) drainage,
intercostal artery reimplantation, maintenance of
normotension, and hypothermia. CSF drainage via a lumbar drain
can be easily performed and is used to maintain the
pressure of the cerebrospinal fluid at B15 mmHg, in concert
with keeping the mean arterial blood pressure at
C90 mmHg. Initial results suggest that this policy is
applicable to patients treated with endovascular therapy,
particularly for patients who have undergone a previous
Endoleak represents the most common complication
following the endovascular treatment of aortic pathologies,
with a rate ranging from 4% to 24% . Leakage is
classified according to the site of its origin at the proximal,
distal, or mid graft. Proximal or distal endoleak is due to
incomplete fixation of the stent-graft to the aortic wall
neck(s) (type I), while a leak at the midgraft level is
consequent to retrograde blood flow via an aortic branch (type
II) or graft defects (type IV). Endoleaks can also originate
from an incompetent overlap seal between stent-grafts
(type III) when multiple devices are implanted [40, 41].
The prognosis for type I endoleak is generally poor and
aggressive treatment is mandatory. Endovascular or
surgical intervention is recommended when a type I endoleak
is documented more than 24 weeks after stent-graft
implantation. Type I endoleak at the level of the proximal
neck represents a very dangerous event, with continuous
direct arterial pressurization of the false lumen. In these
cases an immediate intervention is mandatory, with the
deployment of one or more endograft cuffs.
Type II endoleak is associated with residual blood flow
into the aneurysmatic sac or the false lumen from patent
intercostals arteries, bronchial arteries, or patent LSA. In
cases of TAA, if no documented enlargement of the sac is
observed, regular-interval follow-up imaging surveillance
is the most prudent course of action. In the case of sac
enlargement or persistent patency of the false lumen,
percutaneous treatment with selective catheter embolization is
suggested and easily performed.
Type III endoleak, secondary to the disconnection of
different stent-graft elements, requires immediate treatment
to avoid severe complications due to continuous flow
within the aneurysm or the false lumen. In these cases,
endovascular therapy can be performed with the insertion
of a new endoprosthesis inside the previous ones. In more
complex cases, surgical explantation is the best solution.
Type IV endoleak is related to the porosity or damage of
the graft material.
Retrograde Aortic Dissection
Retrograde aortic dissection represents a catastrophic
sequela more evident during treatment of type B dissection.
This complication is associated with the use of an
especially stiff device, especially in cases where there is a
severe angle of the aortic arch. In fact, if insufficient
support is provided by the guidewire during advancement, the
device can be pushed against the greater curvature of the
aortic arch, increasing the risk of wall damage. Retrograde
aortic dissection, involving the aortic arch and the
ascending aorta, can also be caused by an endograft with
excessive radial force that may cause an intimal tear within
the proximal landing zone. Sometimes, the aggressive or
inappropriate manipulation of catheters and wires can be
responsible for a new intimal tear that facilitates a
retrograde dissection. Several studies have reported retrograde
dissection involving the aortic arch and ascending aorta
after stent-graft deployment . In these cases, the new
intimal tear can be managed either with deployment of an
additional stent-graft over it or with surgery.
The etiology of intracranial injuries associated with
endograft placement is multifactorial. Different authors indicate
neurological complications secondary to LSA exclusion, as
well as stent-graft and wire manipulations at the level of
the arch . This condition seems to be more frequent in
patients with atherosclerotic aneurysms. Moreover, Feezor
et al. reported that 56% of individuals with stroke during
TEVAR had documented intraoperative hypotension with a
systolic blood pressure \80 mmHg .
Endovascular treatment of a variety of aortic pathologies is
considered a valid alternative to open surgery, with reduced
rates of morbidity and mortality relative to conventional
operative repair. This less invasive method for treating
these potentially catastrophic aortic lesions has created
great enthusiasm, however, careful and sound
considerations regarding an individual patients anatomic
suitability, clinical appropriateness, and institutional experience
should always be carefully judged. An important debate
regarding the long-term effectiveness of thoracic aortic
stent-grafting is ongoing among researchers interested in
defining the legitimate role of this therapy in the
management of thoracic aortic pathologies.
As technology and available devices improve day by
day, the number of patients undergoing endovascular repair
will certainly increase. At the same time, it is anticipated
that the limitations associated with this technology will
decrease as delivery systems become smaller in size, and
interventionists gain more experience determining optimal
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