Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3924_Библиотеки_им_академика_М_И_Перельмана
.pdf
224 Stents, covered stents, stent–grafts
2 cm in length and most iliac artery stents are
4cm or longer. ese are the places where balloon-
expandable stents are most useful. ey are com-
monly used to treat arch branch origin lesions; in
addition to the renal arteries, they are also useful
at the origin of the inomminate, carotid, subcla-
vian, and visceral arteries. In the lower extremity,
there is a much higher degree of mobility, which
promotes intimal hyperplasia, and there is also
less surrounding tissue, which exposes the stent
to external crush forces. Since we have no bailout
stents for the tibial vessels, coronary drug-eluting
stents are sometimes used in an o-label manner
to deal with this challenge. e medium Palmaz
™
Stent can be expanded from a diameter of 4.0 mm
to 9.0 mm and the large stent can be expanded
from 8.0 mm to 12.0 mm. An aortic stent is also
available that can be expanded to more than 2 cm
in diameter. is may be used to stent the infrare-
nal aorta for occlusive disease or the aortic neck in
the treatment of a Type I endoleak aer endovas-
cular exclusion of an abdominal aortic aneurysm.
e Wallstent
®
is made of Elgiloy
®
, a stainless
steal alloy, and is a exible, self-expanding, wire
mesh tube that is deployed by retracting a covering
sheath. It is used today mainly for deep vein and
carotid bifurcation stenting. Self-expanding stents
are now more commonly constructed of nitinol,
a nickel-titanium alloy that has thermal mem-
ory and a high degree of contourability. Nitinol
self-expanding stents are used commonly in the
iliac, supercial femoral, and popliteal arteries.
Self-expanding stents are packaged on their own
delivery catheters. ey are intentionally oversized
at the time of deployment in the artery, usually by
1–2 mm, and they maintain continual outward
radial force aer deployment. Self-expanding stents
A
B
C
D
Fig. 19.1 Stent choices. (A) Balloon-expandable
stents are rigid. The stent is crimped onto an
angioplasty balloon and deployed by balloon
inflation. (B) Self-expanding stents made of
nitinol, a nickel-titanium alloy, are flexible and
may be delivered on low-profile catheters. Their
outward force and flexibility are substantially
influenced by the degree to which the sequence
of rings that comprise the stent are con-
nected to each other. (C) Woven nitinol stents
(Supera
®
) have high crush resistance and high
flexibility. (D)The self-expanding, wire mesh
closed cell stents are made of Elgiloy
®
, a metal
alloy (Wallstent
®
).
Table 19.1 Stent characteristics
Balloon-expandable stent Self-expanding stent
Slotted-tube design Wire mesh or slotted tube
High resistive force Chronic outward radial force (oversize for vessel)
Rigid (do not oversize) Flexible
Most functional at short lengths Longer lengths very functional
Premounted, or mount onto balloon of choice Delivery catheter with covering sheath
Some shortening with expansion Variable shortening; some do not shorten
Stainless steel, cobalt, chromium Nitinol or metal alloy
Moderate radiopacity Poor radiopacity (most have markers)
https://t.me/med1917
Covered stents 225
are not as suscept ible to damage from externa l forces
since they are more exible, but they have much
less hoop strength than balloon-expandable stents.
Self-expanding stents cover more distance and
there are some available that could cover most
of a supercial femoral artery (SFA) (20–25 cm).
ey are more dicult to place with great accu-
racy. Self-expanding stents are deployed from the
direction of the tip of the delivery catheter to the
hub of the delivery catheter. erefore, the leading
edge of a self-expanding stent can be placed very
accurately, but the trailing end cannot be placed
with as much accuracy. is requires experience
and some guesswork. e vessel must be prepared
so that the stent can fully open within the lumen.
Aer a self-expanding stent is placed, poststent
placement balloon angioplasty is performed in the
hope of having the stent fully expanded and gain-
ing as much lumen as possible. Self-expanding niti-
nol stents can be open cell or closed cell. Open cell
stents have fewer metal-to-metal connections; this
makes them more exible but also with a little less
outward force. is may be important in stenting
of the carotid bifurcation. In some lesions, greater
exibility may be required to conform to a tortu-
ous artery. In other lesions, higher outward force
and a little more densely packed metal coverage
of a lesion may be desirable, as is found in closed
cell stents. Self-expanding nitinol stents can also be
tapered, which might be useful in a carotid bifur-
cation stent. ere is also a helical stent, which is
intended to create a swirling ow pattern with the
idea of reducing restenosis when treating a lengthy
lesion in the femoropopliteal segment. Woven niti-
nol stents are also available and have very dierent
features from other self-expanding stents. ey
are produced by weaving separate nitinol wires
together. e stent is delivered in rings, and it bears
some similarity to a “slinky”. e operator has a
lot of control on how tightly to pack the rings. is
type of stent has a high degree of crush resistance
and has the ability to stand up to severe calcication
in a manner than standard self-expanding nitinol
stents generally do not. Woven nitinol stents, in
order to achieve nominal deployment, require that
the artery is well prepared. Vessel preparation must
be performed, usually with balloon angioplasty or
angioplasty with modied balloons, such as scoring
balloons, to gain adequate lumen.
Self-expanding and balloon-expandable stents
tend to play complementary roles. Deciding which
type of stent to use may be subjective from one
practice to another, but endovascular specialists
must become facile with the use of each of these
two general stent types. In addition, numer-
ous stents, both balloon- and self-expanding, are
available. ese compete with one another and
have continued to improve with each iteration.
Balloon-expandable stents are for the most part
reliably premounted, have become lower prole
with each generation and easier to deliver, and con-
tinue to have excellent hoop strength, while being
constructed of less metal than once was required.
Self-expanding stents have a variety of designs, as
described above, adding to exibility to the inven-
tory. Self-expanding stents are useful in more ex-
ible arteries. Delivery has improved and tends to be
more accurate than was previously possible.
COVERED STENTS
A variety of covered stents are available that may
be very helpful in the peripheral vasculature and
can be used for occlusive disease, aneurysms, and
trauma. Self-expanding covered stents include
Viabahn
®
and Fluency
®
. Balloon-expandable cov-
ered stents with a polytetrauoroethylene (PTFE)
covering are available from several companies.
Covered stents have tremendous utility in trauma
and in iatrogenic trauma and can be used as a bridge
to denitive therapy, which can be performed
under more elective circumstances. Covered stents
or stent–gras can be used to treat aneurysmal
disease of almost any vascular bed. e treatment
of popliteal aneurysm has evolved in recent years
to include stent–gra treatment with Viabahn
®
in
selected patients. ere is also increasing evidence
for the use of covered stents in occlusive disease,
especially in the aortoiliac system, and to consider
when reconstructing the aortic bifurcation.
In general, the sheath that is required is depen-
dent on the diameter of the covered stent and tends
to be larger than a bare metal noncovered stent.
Self-expanding covered stents may be used in
the same exible locations where noncovered
self-expanding stents are used, such as the SFA.
Self-expanding covered stents are also extremely
helpful for the acute management of trauma, either
as a denitive repair or as a bridge to therapy in
a more elective setting. Iatrogenic injuries to the
carotid, subclavian, axillary, iliac, supercial femo-
ral, popliteal, and other vessels can be treated with
https://t.me/med1917
226 Stents, covered stents, stent–grafts
self-expanding covered stents. One major chal-
lenge with self-expanding covered stents is gra
sizing. Because they are self-expanding, they must
be oversized slightly to ll the lumen and provide
adequate radial outward force. However, if they are
oversized too much, there will be an abundance of
redundant material, which may be associated with
thrombosis. e best methods of sizing the artery
include IVUS, qualitative angiography, and uo-
roscopic evaluation with an expanded balloon of
a known size, and then follow the instructions for
use carefully.
Balloon-expandable covered stents may be
used in arteries that are less exible, such as the
iliac arteries. ey may be used to reconstruct the
aortic bifurcation and are also helpful as parallel
gras for major branch preservation during endo-
gra treatment of pararenal aortic aneurysms or
abdominal aortic aneurysms that present with a
short proximal neck. Parallel gras with covered
stents are performed to improve the landing zone
for the aortic stent gra in this situation.
In addition to sheath size, there are other issues
for consideration. Stent–gras are more expensive.
ey also cover collateral vessels and, occasionally,
branches. In the case of lower extremity occlu-
sive disease, covering collaterals from the SFA or
popliteal artery may have later negative eects,
especially if the covered stent should occlude at a
later time. An advantage of covered stent usage in
occlusive disease is that in-stent restenosis does not
occur due to intimal hyperplastic growth through
the interstices of the stent. Covered stents do tend
to develop stenosis at the ends of the stent; this is
the so-called “candy wrapper” type lesion. is can
be minimized with appropriate sizing of the stent
and this lesion is usually readily detectable with
duplex surveillance and, because it is focal, is read-
ily treatable.
INDICATIONS FOR STENTS:
PRIMARY OR SELECTIVE STENT
PLACEMENT
ere is a key dierence between primary and
selective stent placement: with primary place-
ment the operator intends in the planning of the
procedure that a stent will be placed whereas with
the selective approach the operator must decide
during the procedure whether a stent is required.
When primary stent placement is practiced, the
operator still needs to have enough space in the
lesion to deliver the stent. erefore, predilation or
vessel preparation may still be required. e con-
cept of primary stent placement presupposes that
the patient is better o with a stent, regardless of
the results of treatment of the lesion with balloon
angioplasty or other tool. Primary stent placement
has made endovascular intervention a very reason-
able option in some areas of treatment, for example
for renal artery origin lesions. is approach is also
used for carotid bifurcation and aortoiliac occlu-
sive disease. e idea behind primary stent place-
ment is that the short- and/or long-term results are
generally improved with stent placement to the
point where it justies the upfront increase in cost.
As stents have become more reliable, more sophis-
ticated, and more user friendly, and additional
data are gathered, it has made more sense to con-
sider stent placement in more situations.
Selective stent placement assumes that the
cost and risk of stent placement are not justied
in every case and that not every patient requires
a stent to have acceptable treatment results.
Balloon angioplasty was widely practiced for
more than 15 years before stents became avail-
able. e experience with balloon angioplasty
yielded reasonable long-term results for many
aortoiliac, infrainguinal, and nonorice renal
lesions, and some upper extremity lesions. Aer
balloon angioplasty is performed, the results are
assessed. If the results are not acceptable, stent
placement is performed. Indications for selective
stent placement aer balloon angioplasty include
residual stenosis, a persistent pressure gradient,
and signicant dissection. Other denitive and
potentially stand-alone treatments such as ather-
ectomy, scoring balloon angioplasty, or drug-
coated balloon angioplasty might also be followed
by selective stent placement in certain situations.
e indications for stents have expanded
steadily since they became available. Endovascular
specialists have become more adept at placing
stents, and the development of new stents and
simpler ways of placing them have assisted in this
process. In the management of peripheral arterial
occlusive disease, each stent added to the mix in a
given case also brings the entire process closer to a
point of diminishing returns from a standpoint of
cost and the potential long-term disadvantages of
overall metal burden. e temptation with stents
is to continue to lay them in place until the entire
https://t.me/med1917
Which lesions should be stented? 227
arterial tree appears to be perfect. e “stack of
stents” phenomenon should be avoided.
In most vascular beds, stent placement has
become readily accepted. In general, stents are
placed at the carotid bifurcation, at aortic branch
origin lesions, and in the aortoiliac segment.
Stents are used selectively in the lower extremi-
ties. Stents are avoided in certain highly mobile
locations where they may be crushed, such as the
subclavian–axillary artery near the rst rib and
the arteries of the mid- and distal lower leg and
ankle. e distribution of disease is such that the
lower extremity arteries comprise a signicant
part of vascular practice. e stent versus no stent
debate is more nuanced in the femoral, popliteal,
and tibial vessels than it is in most other locations.
ere are numerous stents available for use in
the SFA and popliteal artery. Self-expanding niti-
nol stents, woven nitinol stents, and drug-eluting
self-expanding nitinol stents are all approved for
the SFA and proximal popliteal artery. Stenting
of longer lesions has worse outcomes than stent-
ing of shorter lesions. In-stent restenosis remains
a problem and tends to be worse in longer lesions.
Stent occlusion in the lower extremity has a higher
than desirable recurrence rate, no matter how it is
treated. Oversizing of stents, strut size, material
used, and length of disease all aect the long-term
outcome. Balloon-expandable stents have not been
helpful for the SFA or popliteal artery. e stents
that are approved in the US are typically approved
for the SFA and very proximal popliteal artery.
Acouple of stents have been approved for the pop-
liteal artery, and the considerations there are usu-
ally dierent due to the high degree of exibility
and the presence of collaterals. ere are no stents
approved in the US for the below-the-knee arter-
ies or tibial arteries. Balloon-expandable coronary
stents can be considered for bailout of inadequate
results of angioplasty below the knee. Additional
challenges in the below the knee arteries include
the length of the artery, the smaller caliber and
lower ow, the lack of a specically designed stent,
and the exposure of these areas anatomically to
external crush forces.
In the short term, stents have better results
than angioplasty in the SFA and popliteal artery.
In the long term, however, results diminish due to
the chronic inammatory response of the artery
to the stent. Drug-coated balloon angioplasty
has better results than plain angioplasty and is
competitive with bare metal nitinol stenting.
Inadequate results of drug-coated balloon angio-
plasty due to dissection may require repair with
some type of scaolding. e goal in this setting
is to minimize the metal footprint and repair the
dissection as focally as possible. Bare metal stents
below the knee have not proven to be more eca-
cious than balloon angioplasty and, therefore, have
been used as a bailout in this situation.
WHICH LESIONS SHOULD BE
STENTED?
Although each specialist must decide the appropri-
ate level of aggressiveness of stent placement, there
are specic situations where stents are useful.
Postangioplasty dissection
Dissection is the method by which balloon angio-
plasty functions. Dissections are locations along
the treatment site where tissue has been torn
away from the arterial wall and encroaches on
the lumen. In the quest for safe lumen gain and
a smooth and stable ow surface, it makes sense
that leaving these behind is a gamble. Which
dissections will lead to acute occlusion? Which
dissections will form a nidus for recurrent steno-
sis? However, under existing paradigms for stent
placement, coverage of every dissection with stents
will lead to a substantial amount of metal burden
that may not be required or may cause down-
stream negative eects with potential for in-stent
restenosis. Because plaque fracture is the mecha-
nism of angioplasty, some degree of dissection is
almost always demonstrable. Dissections can be
assessed angiographically and this assessment pro-
cess is usually enhanced by obtaining more than
one view of the treated vessel. IVUS provides more
detail than angiography and permits the opera-
tor to evaluate and measure the residual lumen
and to assess the post-treatment segment for
mobile tissue aps. Unfortunately, there is no good
method of predicting how a dissection will behave
(Figure 19.2). Dissections are also dynamic and
may appear dierently over time during the proce-
dure and may respond to some extent to repeat but
prolonged balloon ination.
Stent placement should be considered for any
signicant dissection aer angioplasty, even if
there is no gradient. Stents should be placed for
https://t.me/med1917
228 Stents, covered stents, stent–grafts
any false channel or for any intimal aps that
impede ow, worsen during the procedure, or
extend into a previously uninvolved segment of
artery. Understanding which postangioplasty dis-
sections require scaolding is a work in progress.
Nevertheless, the concept of “ow-limiting dis-
section” requires attention. It is oen said that
the operator need only respond to ow-limiting
dissections. is is a term that is frequently used
but never dened. Angiographic assessment is
qualitative. erefore, a ow-limiting dissection
could be one that is visualized on angiography to
slow down the blood ow. is is not quantitative
and is not reliable. e “ow” is dependent on the
volume and pressure of the contrast administra-
tion and the inow and runo. Likewise, pres-
sure measurement may be performed. is has
the advantage of being quantitative; however, no
one knows what level of gradient is clinically sig-
nicant. e gradient will also be dependent on
the quality of the runo and whether the mea-
suring catheter that crosses the lumen is aect-
ing the pressure measurement. Note: if there is no
runo, there will be no gradient, no matter how
signicant the lesion. In addition, the moment
the patient takes their rst post-procedure step,
A B
D E
C
Fig. 19.2 Degrees of dissection after angioplasty. (A) An external iliac artery stenosis is treated with
balloon angioplasty. (B) Angioplasty creates separations between the intima and media that are demon-
strated on completion arteriography as small dissection flaps. (C) A more prominent dissection flap may
not impede flow but does protrude into the lumen. Stent placement should be considered. (D) Dissections
that impede flow, cause tissue to hang into the lumen, lengthen during the procedure, or extend into an
adjacent nondiseased segment of artery should be stented. (E) The worst dissections may cause occlusion
of the artery or severely diminish the flow, and usually involve multiple flaps. The angiographic picture is
usually convoluted in appearance and direct visualization of the flow channel may not be possible.
https://t.me/med1917
Residual stenosis after angioplasty 229
the gradient will change. If more than one lesion
has been treated, the gradient is additionally dif-
cult to interpret. erefore, measuring pressure
is useful in some situations but is not likely to be
the answer to how dissections should be managed.
Angiographic and/or IVUS visualization are most
commonly used at present.
RESIDUAL STENOSIS AFTER
ANGIOPLASTY
Residual stenosis can usually be resolved with stent
placement. e concept of preventing recurrence
by eliminating residual stenosis makes empiric
sense. A 30% postangioplasty stenosis is used as
a general threshold for continued intervention,
although there is limited scientic justication
for using this particular degree of stenosis. When
residual stenosis is due to a severely calcied lesion,
other methods may be required to treat it, such as
scoring angioplasty or atherectomy. If stent place-
ment is required, a woven nitinol stent might also
be considered.
Pressure gradient
A pressure gradient (more than 10 mmHg systolic)
aer angioplasty usually indicates a signicant
residual stenosis or a dissection that is functioning
as a bae. e gradient threshold for treatment is
somewhat arbitrary. It is possible that any pressure
gradient is signicant since pressure is measured
at rest and patients’ lives are lived on the go. Some
aspects of pressure measurement are discussed in
the previous section.
Pressure gradients are measured when it is
unclear whether the reconstruction is hemody-
namically eective. e most common place where
this occurs is in the lower extremity vessels, mainly
because other areas are more routinely treated with
stents. Most of the time, a stent can be brought to
full expansion and satisfy the operator on the basis
of visual inspection indicating that no impediment
to ow exists. If well performed, and angiography
shows a residual stenosis of unclear hemodynamic
signicance, pressure can be measured. Pressure
measurement can be helpful when considering
stent placement.
Systemic pressure can be obtained from an
arterial line if one is already in place. Typically,
the side arm of the sheath can be used to measure
systemic pressure. A pressure wire or low-prole
catheter is placed across the lesion and pressure is
measured at this location, distal to the lesion, until
it becomes stable. If the proximal pressure can be
measured at the exact same time and the curves
are superimposed on the monitor, this is the best
way to understand whether there is a gradient of
10 mmHg systolic or more. One challenge with
measuring pressure through a catheter is that if
there is a very small residual stenosis at the location
of the lesion, the catheter used to measure pressure
could also aect the pressure distal to the lesion.
In this case a pressure wire would be helpful. It is
common for the blood pressure to uctuate during
pressure measurement and care should be taken to
ensure that it is stabilized when assessing the mag-
nitude of gradient.
Recurrent stenosis after angioplasty
Treating recurrence with stent placement aer
previous angioplasty is an empiric approach with
reasonable results.
Occlusion
Balloon angioplasty alone for occlusions has only
fair results and these are improved with stent place-
ment. Stent placement may make the procedure
safer by stabilizing residual thrombus that could
embolize from the lesion site. Stent placement in
the treatment of iliac artery and SFA occlusions
is widely accepted but not in the tibial arteries,
where balloon angioplasty is used as a stand-alone
procedure.
Embolizing lesion
Stent placement at the site of an embolizing lesion
is thought to trap the embologenic plaque and
prevent further embolization. Because emboliz-
ing lesions are oen so, care must be taken dur-
ing guidewire and catheter crossing. A covered
stent or stent–gra of the appropriate size should
also be considered in the treatment of an emboli-
zing lesion, with the idea that the material in the
lesion is trapped behind the material. e lesion
must also be evaluated to assess whether it could
be an aneurysm, especially if it is in the popliteal
artery. e presence of an aneurysm may change
the treatment plan.
https://t.me/med1917
230 Stents, covered stents, stent–grafts
As experience is gained and new technological
iterations are produced with stents, indications for
their placement have been continuously modied
and generally increased (Table 19.2). Other relative
indications include a long lesion or a highly irregu-
lar, calcied plaque.
e location of the intended angioplasty site also
aects the likelihood of stent placement. Since most
atherosclerotic renal artery lesions are aortic plaque
that has spilled over into the artery, stent placement
is usually necessary to resolve these stenoses. Stent
placement appears to be safer than angioplasty alone
at the carotid bifurcation, possibly because these
are primarily embolizing lesions. Eventually, mesh
covered stents may play a role in carotid stenting.
Aortoiliac angioplasty is fairly durable without stents
and stents can be used selectively with reasonable
results, but the preponderance of more recent data,
especially in patients with more severe disease mor-
phology (TASC C and D), has been to support rou-
tine stent placement in this segment. Infrainguinal
angioplasty is not as durable and stent placement
oers some improvement in long-term results, espe-
cially in the femoral and popliteal arteries.
PLACEMENT TECHNIQUE FOR
BALLOON-EXPANDABLE STENTS
Considerations include selection of stent length
and diameter, sheath size, and whether a single
stent or multiple stents will be required. Diameter
selection is an important decision in the placement
of balloon-expandable stents. Stent size is selected
based on the anticipated diameter of the recon-
structed artery. If the selected stent is too small in
diameter, it may not adhere well to the vessel wall
aer deployment and could migrate, even before it
can be more completely expanded. In this case, the
balloon must be rapidly exchanged for a larger one,
which is used to expand the stent further. Placing
the new balloon into the underexpanded stent is
the key maneuver. If the stent is too large, it will
overstretch the artery and may cause rupture or a
dissection in the healthier vessel just beyond the
end of the stent. If selective stent placement is per-
formed, the inated balloon prole from the initial
angioplasty may be used to size the artery. When
primary stent placement is performed, sometimes
it is necessary to predilate the lesion with a plain
Table 19.2 Which lesions should be stented?
Indication
Rationale Reality
Postangioplasty
dissection
Prevents acute
occlusion
Makes angioplasty safer because dissection can be
managed without emergency open surgery. More
complex lesions can be treated with angioplasty. Which
dissections need stents is not known. Most dissections
should be treated if a smooth flow surface is desired
Residual stenosis
after angioplasty
(>30%)
Causes early failures
and late recurrence
Makes empiric sense. Mild residual stenosis may not
cause harm. Moderate residual stenosis (>50%) can
almost always be resolved with stent placement
Occlusion Poor results with
angioplasty alone
Better short- and long-term results with stents. Avoids
open surgery in most patients with iliac occlusion or
femoropopliteal occlusion
Recurrence Limited success of
primary angioplasty
Makes empiric sense since the initial angioplasty failed
Long lesion Poor results with
angioplasty alone
More likely to result in a significant dissection after
angioplasty of a longer length lesion
Embolizing lesion Cages and compacts
the embolic
material
Covered stent or stent–graft should be considered. Be
certain it is not an aneurysm since that may change
the treatment plan. Control outflow during
procedure or use distal filter
All lesions (primary
stent placement)
Extends long-term
results
Looks great. Provides excellent opportunity to practice
stent placement. Unclear if long-term results justify
the up-front cost and complications
https://t.me/med1917
Placement technique for balloon-expandable stents 231
balloon to size the lesion and create enough space
for the stent delivery catheter to be placed across the
lesion. Balloon-expandable stents can be dilated a
few millimeters larger than the intended speci-
cations, but as the diameter increases, the length
decreases. e shortest stent that will cover the
lesion is typically placed. Longer balloon-expand-
able stents are available (up to 8 cm) but there are
disadvantages due to the rigidity of these stents
over longer distances. ey do not conform well
to any tortuosity or any change in vessel diameter
along the length of the stent. Balloon-expandable
stents have limitations in situations where long or
diuse lesions are encountered.
Prior to placing a stent, the lesion length is
assessed as well as the tortuosity and tapering
eect present at the segment intended for stenting.
Balloon-expandable stents are usually premounted
in the factory. Hand crimping is sometimes
required; for example, in the case of the largest
balloon-expandable stent, which is used in the aor-
tic neck aer aortic stent–gra placement. If hand
crimping is to be performed, the balloon chosen
for deployment must be of either the same length
or preferably longer than the stent. If the balloon is
longer than the stent, the stent should be mounted
so that its end is on either the proximal or distal
radiopaque marker on the balloon; the stent’s loca-
tion is thus known when it is time for deployment.
Vigorous crimping with the thumb and foren-
ger secures the stent without bending it. e stent
should not be able to slide on the balloon unless
rm traction is applied. Test the adherence of the
stent to the balloon, but do not slide the stent back
and forth on the balloon because the sharp end of
the stent can pierce the balloon. Mounting of the
stent on the balloon is usually performed prior to
advancing the sheath across the lesion so that the
stent is ready for deployment. When advancing a
catheter that has the stent mounted on it, support
the stent at its trailing end as it is pushed through
the sheath hemostatic valve so that the stent is not
loosened on the balloon sha. All the major endo-
vascular companies make a puncture-resistant bal-
loon that is designed for stent delivery. A medium
Palmaz
™
or Palmaz style stent requires a 6-Fr or
7-Fr sheath. Larger vessel stents, such as those
used for large iliac arteries up to 12 mm, are placed
through an 8-Fr or 9-Fr sheath. e largest, 5-cm
length balloon-expandable stent is available for the
infrarenal aorta and this stent has been used oen
in bailout of Type I endoleaks during stent–gra
repair of aortic aneurysms. It may have other niche
uses in the aorta, such as for coarctation and other
conditions.
For many years, the general approach to
balloon-expandable stent placement has been to
pass the appropriate sheath and dilator combina-
tion through the lesion and proceed to stent place-
ment (Figure 19.3). If the lesion has a residual
lumen of less than the diameter of the sheath (for
a 6-Fr sheath this is approximately 2.0 mm and
for a 7-Fr sheath it is about 2.3 mm), the lesion
should be predilated or the sheath and dilator will
dotter the lesion. e sheath must be of adequate
length to pass from the skin entry site to the lesion.
Aradiopaque tip on the sheath is useful so that it
is clear where the sheath tip is located relative to
the lesion. e dilator is removed and the sheath
ushed. e sheath may stop or impede blood ow,
since it occupies the remaining lumen at the site of
the lesion. If there is any question about the exact
location for stent placement, a repeat arteriogram
should be obtained prior to placement. e bal-
loon catheter, with the stent crimped into place,
is passed over the guidewire and into the sheath.
A cannula may be used to temporarily open the
hemostatic valve on the sheath. However, the stent
may also be passed through the hemostatic valve by
hand. Grab the balloon–stent with a pincer grasp
at the end of the stent that is farthest from the valve
and push the balloon and stent through the valve.
Using uoroscopy, the balloon and stent are passed
into the appropriate location. Check the balloon
while it is still in the sheath using a magnied eld
of view to visualize the stent on the balloon and
ensure it is still located where it was crimped on
the balloon. e sheath is withdrawn, exposing the
balloon and stent. Before deployment, it is impor-
tant to make sure that the stent is still in the correct
place on the balloon and that it is well positioned
to cover the lesion. e balloon is then inated to
expand the stent. e stent should be slightly over-
dilated to embed its metal struts into the plaque.
Another option for access, and one that is more
commonly used at present, is to pass the tip of
the sheath close to the lesion but not through it.
If you are passing the tip close to the lesion, keep
an eye on the unmarked dilator, as it may inadver-
tently encounter the lesion. e sheath tip is used
as a platform for pushing, for easy arteriography,
for stabilizing the back end of the stent aer it is
https://t.me/med1917
232 Stents, covered stents, stent–grafts
A B
D E F
C
Fig. 19.3 Placement technique for balloon-expandable stents. (A) The dilator and sheath are
advanced through the lesion. (B) The dilator is removed, leaving the sheath across the stenosis.
(C)The stent is premounted or is mounted on the balloon and crimped into place between the
radiopaque markers. The balloon and stent are advanced into the sheath. (D) Using fluoroscopy,
the stent is placed at the desired location within the lesion. (E)The sheath is withdrawn to expose
the stent. (F)The balloon is inflated to deploy the stent.
https://t.me/med1917
Placement technique for balloon-expandable stents 233
deployed, and for helping to gather up the balloon
aer it has expanded the stent. Lower-prole, well-
secured, and premounted balloon-expandable
stents have made it far less necessary to pass the
sheath across the lesion in order to deliver the stent.
Balloon-expandable stents expand initially to
an hourglass shape with the proximal and distal
ends of the balloon lling rst and consequently
aring the proximal and distal ends of the stent.
e middle portion of the stent lls out at the com-
pletion of balloon ination. e proximal or distal
end of the stent is sometimes only partially dilated
into an oval shape, which is not always apparent on
completion arteriography. e balloon is deated
aer the stent has been fully deployed. e balloon
may be advanced slightly and reinated so that
the proximal end of the stent is fully dilated. is
maneuver may be repeated on the distal end of the
stent.
If there is a sense that the stent is loose in the
lesion, either because it is underdilated or because
it has migrated during deployment to an area that
is slightly less narrow, take the next steps very
deliberately. is occurrence is not too unusual in
situations where a substantial poststenotic dilation
of the vessel is present. is results in a substantial
vessel diameter change over a short distance. e
lesion may be one in which a balloon-expandable
stent is required (e.g., innominate artery origin)
but in which this type of stent is not well suited to a
vessel taper. Advance the tip of the sheath up to the
expanded end of the stent then catch the edge of
the stent and support it so that it cannot move. is
can usually be done right over the balloon cath-
eter that delivered the stent prior to removing the
balloon catheter. It is when removing the balloon
catheter that the stent might begin to move. is is
a common maneuver in renal stenting, which helps
avoid a problem from getting out of hand. In addi-
tion, oen aer placement of a balloon-expandable
stent the balloon wings will stick a bit, perhaps
becoming caught under the tines of the stent. If this
is the case, and more than a gentle pull does not
solve it, use these steps. Perform aggressive aspira-
tion, implosion level, negative pressure on the bal-
loon. Support the stent by advancing the sheath as
described earlier. Try rotating and/or advancing
the balloon catheter gently for a few millimeters
before withdrawing it. Sometimes, reinating the
balloon will loosen the balloon material; if this
happens, these steps can be repeated.
Precise stent deployment is challenging. e
stent may be dicult to visualize in larger indi-
viduals, especially if it is in a location with a lot
of ventilatory motion, such as the visceral and
renal arteries, where balloon-expandable stents are
used quite oen. A dierence in location of a few
millimeters may be the dierence between a per-
fect placement and a misplaced stent. Road map-
ping is routinely used to help improve the precision
of stent placement. Bony landmarks may be useful,
especially the vertebral bodies or some identiable
vascular calcication. An external marker, such as
a stent guide, might be helpful. is is an adher-
ent, radiopaque measuring tape that can be placed
on the patient parallel to the guidewire. Stent
guides are particularly useful when treating longer
lesions. Be aware that external markers are suscep-
tible to parallax error if the eld of view is modi-
ed. ey are also in error if there is any change
in the angle of view or any signicant ventilatory
motion. When external markers are used, recheck
the lesion before deploying the stent.
One method for precise placement of balloon-
expandable stents is as follows. Position the image
intensier and set the eld of view in a manner
that provides the best view of the lesion. is view
should include the tip of the sheath, the entire lesion
length, and at least a few centimeters of outow.
Ifthe lesion is too long to permit adequate magni-
cation and the stent to be placed is just a portion of
the reconstruction, magnify the location intended
for the stent placement and place one stent at a
time. Typically, there is one edge of the stent to
be placed that will be the deciding factor as to its
accuracy and precision. For example, provided the
selected stent is long enough, when performing a
stent of the renal artery orice, the trailing end of
the stent should protrude into the aorta by about
1 mm to ensure adequate treatment of any aortic
plaque that is spilling over into the renal artery.
is same general scenario repeats itself with other
aortic branch orice lesions with spillover plaque
that is creating a circumferential napkin ring of
atherosclerosis. Balloon-expandable stents work
well in these scenarios and all of these situations
involve deep imaging (in a body cavity) with sig-
nicant ventilator motion. A smaller eld of view,
such as a 6-inch eld, is oen best since it provides
magnication. Choose bony landmarks or place
external markers. Perform arteriography. Once
the image intensier is positioned, do not move
https://t.me/med1917
Соседние файлы в папке Библиотека им академика М.И. Перельмана