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_5760_Библиотеки_им_академика_М_И_Перельмана.pdf
2.1 · Pelvic andLeg Arteries
a
b
103
2
. Fig. 2.36 Restenosis after stenting. a Patient with in-stent restenosis of the external iliac artery. Hemodynamic grading based on the peak systolic
velocity (PSV) ratio indicates 50–60% stenosis (PSV ratio>2, calculated from intrastenotic PSV of 341cm/s and prestenotic PSV of 148cm/s). The waveform was obtained by moving the transducer over the skin, while maintaining a constant Doppler angle, from the prestenotic segment to the site of
stenosis (indicated by “> <”). b Stent in supercial femoral artery with excessive neointimal proliferation causing circumferential narrowing of a long
portion of the stented arterial segment with high- grade stenosis at the distal stent end (arrow; PSV ratio of approx. 5, calculated from intrastenotic PSV
of 249cm/s and prestenotic PSV of 55cm/s). The angiogram obtained before repeat PTA conrms narrowing of the stent lumen with stenosis at the
distal stent end (arrow). The example illustrates the problem of stenosis grading. The intrastenotic PSV of 249cm/s is low for the degree of stenosis.
Good collateralization (ow divider, see angiogram) results in reduced ow and ow velocity in the femoral artery, as reected by the low prestenotic
PSV of 55cm (see . Figs.2.16b and 1.46b, c and . Table 1.10). The PSV ratio of 5, however, is consistent with high-grade stenosis and better reects
the hemodynamic situation here. Conversely, use of absolute intrastenotic PSV alone (cutos determined by ROC analysis; see . Figs.2.18 and 2.19)
underestimates the severity of stenosis in this case, illustrating the superiority of the PSV ratio over absolute PSV for stenosis grading
A stent is identied by its serrated or mesh-like appearance. A focal increase in ow velocity is the most important
sign of residual or recurrent stenosis aer PTA, stenting
(where special attention must be paid to the stent ends), and
bypass graing (primarily at the anastomotic sites)
(. Fig.2.36).
In most cases, ow evaluation within a stent requires a
higher color gain. Eddy currents and turbulent ow at the
proximal and distal ends suggest that the stent does not t
snugly to the wall, which can promote restenosis.
e accurate diagnosis of complications such as arteriovenous (AV) stula, pseudoaneurysm, and hematoma and the
timely identication of residual or recurrent stenosis are crucial for post-PTA patency. A hemodynamically signicant
residual or recurrent stenosis
is suggested by focal doubling
of the ow velocity within the treated segment. e detection
of a hemodynamically signicant stenosis by duplex ultrasound is a predictor of patency. e above- quoted study of
Mewissen etal. (1992) reported a 1-year patency rate of 83%
in the absence of stenosis as opposed to only 15% when a
functional stenosis was diagnosed (Mewissen etal. 1992).
Several studies have shown duplex imaging to be more
sensitive than angiography in detecting residual stenosis
or residual ow disturbance following PTA.In one study,
20% of residual stenoses >50% based on duplex ultrasound
were classied as causing <30% diameter reduction at
angiography. e sonographic stenosis criteria were PSV
>180cm/s (. Fig.2.37) and an intrastenotic-to-prestenotic
PSV ratio>2.5 (Kinney etal. 1991; Mewissen etal. 1992).
e presence of residual stenosis classied as causing >50%
diameter reduction by duplex scanning was found to predict late failure (15% success rate) while late patency was
observed for <50% diameter reduction (84% success rate).
Based on these results, it is recommended to perform a
follow-up duplex scan within 1 month of PTA to iden-
tify patients with residual/recurrent stenosis who should
undergo reintervention.
Earlier studies in other vascular territories (carotid artery,
renal artery) identied 10–20% higher PSV cutos (ROC
curve analysis) for in-stent restenosis (due to greater wall
rigidity and smaller lumen of the stented segment) compared
with native arteries. In contrast, more recent studies in
stented peripheral arteries suggest that PSV cutos should
rather be lower than for untreated arteries. ese studies
report sensitivities and specicities as well as negative predictive values (NPV) and positive predictive values (PPV) on
the order of 95% for the following absolute PSV and PSV
ratio cutos (Baril etal. 2008; Shrikhande etal. 2011):
104
Chapter 2 · Extremity Arteries
2
a b
. Fig. 2.37 a Patient after PTA and stenting of high-grade common iliac artery stenosis. In the gray-scale image (left), the stent is identied by
its serrated appearance. The color duplex image shows aliasing at the proximal stent end and backward and forward ow components within the
stent (red and blue) (A = aorta, A.I.C = common iliac artery, V = common iliac vein, VA = vibration artifact, SA = mirror artifact). The Doppler waveform from the site of aliasing demonstrates very turbulent ow with a PSV of 422cm/s, consistent with high-grade stenosis. b Angiogram fails to
adequately show the stenosis or its cause. The patient underwent repeat PTA on the basis of the duplex ultrasound ndings. Following repeat PTA,
the patient’s clinical symptoms resolved (patient’s walking distance before reintervention was limited to 180m), color duplex conrmed elimination of the stenosis, and the ABI normalized from 0.8 to 1.1
5 >50% stenosis: PSV >190cm/s and PSV ratio>1.5
5 >70% stenosis: PSV >223cm/s and PSV ratio>2.5
5 >80% stenosis: PSV >275cm/s and PSV ratio>3.5
e PSV ratio is a very reliable parameter for identication
of in-stent restenosis. However, according to the continuity
equation, one would expect the cuto ratio to be 2 for 50%
stenosis and 4 for 75% stenosis. ese theoretically predicted PSV ratios are based on the assumption that stenosis
is caused by concentric plaque. Hence, the lower actual
ratios suggest that in-stent restenosis tends to be caused by
eccentric luminal narrowing. Remember that an eccentric
stenosis results in a smaller cross-sectional area reduction
than a concentric stenosis with the same diameter reduction. erefore, the hemodynamic eect of an eccentric
stenosis is less pronounced and the sonographically measured intrastenotic increase in PSV is smaller (. Fig.2.17d).
2.1.7.3 Bypass Graft Surveillance
e sonographic appearance of a bypass depends on the
material used.
e thin wall of an autologous venous bypass graft is
very dicult to delineate when occlusion has occurred. Such a
bypass is easier to identify, in particular in older occlusion, if
the examiner has information on its course (anatomic, extraanatomic). In patients with a venous bypass gra, the entire
length must be scanned because the former valves are common
sites of stenosis, especially in an in situ bypass with residual
valve cusps. An AV stula developing from a perforating vein
that has not been ligated can be identied by the presence of
perivascular tissue vibration artifacts in the color duplex mode.
In contrast, the walls of a synthetic bypass graft are always
clearly seen. A PTFE (polytetrauoroethylene) prosthesis has a
characteristic double-line appearance and a Dacron bypass a
sawtooth-like appearance.
In the postoperative evaluation and surveillance of a synthetic gra, special attention must be paid to possible anastomotic stenoses. Narrowing within the bypass is due to
neointimal hyperplasia and occurs later. About 20–30% of
venous bypass gras develop strictures on the basis of neointimal hyperplasia within the rst year of surgery.
Dierent factors can cause occlusion of a bypass at different times aer surgery:
5 Immediate postoperative occlusion within the rst days
aer surgery may be due to an inadequate surgical
technique, resulting in anastomotic stenosis, or poor
distal runo. erefore, the examination should include
hemodynamic evaluation of the recipient artery.
5 Early occlusion, within the rst year, chiey results from
neointimal hyperplasia, predominantly causing stenosis
at the proximal or distal anastomosis, or from deteriora-
tion of the outow situation due to progression of
atherosclerosis distal to the bypass. If the occlusion is
due to an impaired inow secondary to atherosclerotic
lesions of the proximal artery with loss of the triphasic
waveform, the examiner must carefully evaluate the
native artery upstream of the bypass to identify the site
of obstruction.
5 Late occlusion is predominantly caused by progression
of atherosclerosis, especially in the segments close to the
bypass ends.
Abnormal uid around a bypass gra should be punctured
under ultrasound guidance for microbiologic testing, in particular in patients with clinical signs of infection. Before
puncture, a suture aneurysm should be ruled out by color
duplex imaging (see
. Fig.2.72 (Atlas)). Hematoma, seroma,
and suture aneurysm appear as pulsatile masses at the site of
anastomosis, each having a characteristic color duplex
appearance, which allows it to be dierentiated at a glance.
2.1 · Pelvic andLeg Arteries
105
2
2.1.7.3.1 Methodological Considerations
andStenosis Criteria
Duplex ultrasound is a valid imaging modality for identifying bypass gra complications (stenosis, occlusion).
Published data suggest good agreement with CTA and DSA
(Willmann etal. 2004) as well as good interobserver agreement with 85% sensitivity, 93% specicity, and 91% diagnostic accuracy compared with DSA (Ihlberg etal. 1998).
e criteria for grading stenosis severity in a bypass gra
are based on those for the native peripheral arteries. However,
the hemodynamic changes in a bypass gra may occasionally
lead to a monophasic waveform that does not suggest abnormal ow. Eddy currents at the anastomoses cause spectral
broadening, which is likewise normal (. Figs. 2.41, 2.74
(Atlas), 2.75 (Atlas), and 2.76 (Atlas)).
Normal peak systolic velocity (PSV) is a function of the
relative cross sections of the bypass and the proximal and
distal native arteries. e complex relationships make it difcult to give a reliable general threshold velocity. Still, one
can rule out a hemodynamically signicant stenosis with
some condence if PSV at the site of anastomosis is below
2m/s on condition that there is no size mismatch between
the gra and the native artery (. Table2.15).
Flow within a gra is inuenced by several factors, which
should be borne in mind when interpreting spectral Doppler
recordings from within the gra to predict bypass patency.
is is especially important in patients with severe atherosclerosis and in assessing bypass gras onto a calf artery
(. Fig.2.43). Pulsatility is physiologically dependent on the
demand-oriented widening of the arterioles (monophasic
ow). In a bypass, pulsatility is additionally aected by dierences in elasticity (depending on the material used for the
gra) and an increase in outow resistance if there is stenosis
distal to the bypass (more pulsatile ow). ese opposing
eects on the ow prole preclude simple monocausal inter-
. Table 2.15 Duplex ultrasound criteria in bypass graft
surveillance. Identication of complications: suture aneurysm,
abscess, imminent occlusion (failing bypass), stenosis
(. Figs.2.38, 2.41, and 2.42)
Method (indirect/direct
criteria)
Single PSV measure-
ment in the bypass graft
(indirect sign of ow
obstruction/stenosis in
the graft)
Analysis of representa-
tive spectral waveform
(indirect criterion)
Mapping of bypass graft
and anastomoses:
increased PSV indicates
stenosis (direct criterion)
Interpretation of criteria
Reduced PSV in the bypass graft:
PSV <45 cm/s suggests failing
bypass (exceptions)
Distal to stenosis: damped
waveform, delayed systolic rise
Triphasic: good graft function
Monophasic: ow obstruction,
peripheral vasodilation
PSV ratio >2: moderate stenosis
PSV ratio >4: high-grade stenosis
PSV >2–2.5 m/s: moderate stenosis
PSV >3–3.5 m/s: high- grade stenosis
pretation of the waveform obtained from a bypass gra.
Hence, slow ow should prompt an evaluation of both the
distal anastomosis and the recipient artery for the presence of
stenosis even if the waveform is triphasic (see
. Fig. 2.73
(Atlas)).
While a synthetic gra should primarily be searched for
stenosis at the proximal and distal ends (the preferred sites of
stenosis in this type of gra), the entire length of an
autologous venous gra must be examined for stenosis at
valve sites (see . Fig.2.76 (Atlas)). As with native arteries,
the examiner can save time by comparing Doppler waveforms from representative sites to narrow down possible sites
of stenosis. When scanning an autologous in situ venous
bypass immediately aer surgery, the examiner must also
look for any patent perforating veins, which could give rise to
an AV stula and would thus need to be ligated aer having
been localized sonographically.
PSV cutos ranging from 2m/s (Passman etal. 1995) to
3m/s (Westerband etal. 1997) have been proposed to identify stenosis that should prompt gra revision. It should be
clear, though, that there is no single PSV cuto that applies
throughout a gra. For example, a PSV of up to 2.5m/s may
be considered normal at the distal anastomosis, especially
when there is a transition from a wide bypass lumen to a narrow recipient vessel as is the case with a crural bypass. A PSV
of 2.5m/s is abnormal, however, when it occurs at the proximal anastomosis or within the gra.
Other investigators use the ratio of intrastenotic PSV to
PSV in the normal proximal segment to identify hemodynamically relevant bypass gra stenosis. However, the
ratio
(also known as peak velocity ratio/PVR) above which
PSV
>70% stenosis requiring gra revision is assumed ranges
from 3 (Calligaro etal. 1996; Dougherty etal. 1998) to 4 (Idu
etal. 1999). Overall, cutos proposed for moderate stenosis
(50–70%) in a bypass gra range from 2–4 for PSV ratios
(Wixon etal. 2000; Mills etal. 2001) and from 2–3.5m/s for
absolute PSV (. Table2.16).
When grading the severity of anastomotic stenoses in
synthetic gras, the PSV ratio must be used with caution due
. Table 2.16 Stenosis grading in the sonographic surveillance
of bypass grafts and therapeutic consequences (Modied from
Mills etal. 2001 and Wixon etal. 2000)
Stenosis criteria in bypass
graft
Normal PSV<200cm/s
PSV ratio<2
Moder-
ate
stenosis
High-
grade
stenosis
PSV of
200–300cm/s
PSV ratio of 2–4
PSV>300cm/s
PSV ratio>4
Suggested management
Low risk → follow-up
Moderate risk → close
follow-up, revision in case of
progression
High risk (PSV in graft >45cm/s)
→elective intervention
Highest risk (PSV in graft
<45cm/s) →urgent intervention
106
Chapter 2 · Extremity Arteries
to mismatches in size and elasticity between the bypass gra
and the proximal native artery. With these limitations in
mind, it may be assumed that a PSV ratio >2.5 indicates
2
>60% stenosis. Size mismatches between the gra and the
recipient artery oen result in a ow acceleration downstream of the distal anastomosis, in particular when the anastomosis is located below the knee. Here, an even higher PSV
ratio (>3) should be used as a cuto in order to minimize
false-positive results (Polak 1992).
Mapping of an entire bypass gra including the proximal
and distal anastomes is very time-consuming. erefore,
protocols have been proposed to make sonographic gra
surveillance more ecient. Such protocols rely on the comparison of Doppler waveforms from a few representative sites
using the same indirect criteria as in native peripheral arteries (. Figs.2.14, 2.37, 2.38, 2.39, 2.40, 2.41, and 2.43). e ow
prole and PSV are evaluated. If there is triphasic ow with a
PSV of 55cm/s or greater in the gra, then higher- grade stenosis within the gra or at the anastomoses is unlikely –
especially if the bypass was established for critical ischemia
of the leg. In this situation, a stenosis would lead to a monophasic waveform (resulting from reduced peripheral resistance due to demand-adjusted widening of arterioles). If the
waveform is not triphasic and ow velocity is slow, the entire
bypass must be mapped for the presence of stenosis, with
special attention being paid to the anastomoses. However, a
monophasic waveform may also be obtained if no stenosis is
present in the gra, especially if the bypass was established to
improve inow in patients with multilevel obstruction and
there is persistent poor perfusion in the periphery due to
additional stenoses more distally. In contrast, an initially triphasic ow prole in a bypass gra that becomes monophasic at later follow-up indicates peripheral vasodilation in
response to an
impairment of peripheral perfusion. is
again warrants sonographic evaluation of the entire bypass
and the anastomoses. Another possible cause of impaired
peripheral perfusion is progressive atherosclerosis with stenotic narrowing of the segments proximal and distal to the
bypass gra.
Based on these considerations, a
graft surveillance strategy
is proposed (. Figs.2.38, 2.41,
time-efficient bypass
and 2.42), which relies on duplex imaging and spectral
Doppler interrogation at the following sites (. Figs. 2.39
and 2.43):
5 Femoral artery bifurcation
5 Proximal gra anastomosis with spectral Doppler
interrogation
5 Distal gra anastomosis with spectral Doppler interro-
gation including the receiving artery just distal to the
anastomosis and the gra just upstream of the anasto-
mosis
nation (e.g., the feeding artery). Waveforms are obtained by
moving the transducer across the proximal and distal anastomoses, and interpretation of the waveforms from these representative sites using the indirect stenosis criteria provides
information on inow and outow. Comparison of the spectral tracings from the proximal and distal ends of the bypass
allows the examiner to suspect or rule out stenosis within the
gra (see, however, . Fig.2.43).
Long-term bypass graft patency depends on the devel-
opment of stenosis within the gra (predominantly involving
the anastomoses) and ow in the recipient artery. Poor runo
aects the blood ow velocity in the gra and, in conjunction
with systemic factors such as a hypercoagulable state, can
lead to occlusion. Several investigators use PSV as the most
important parameter in the surveillance of bypass gras
(Bandyk etal. 1985, 1989; Buth et al. 1991; Calligaro etal.
1996; Grigg et al. 1988; Lundell et al. 1995; Passman et al.
1995). Postoperative mean or median PSVs reported in the
literature range from 0.68 to 1.12 m/s (Belkin et al. 1994;
Nielsen etal. 1995; WölfIe etal. 1994) and decrease thereaer
if the gra remains patent (from 1.125 to 1m/s aer 1year
according to Wöle etal. and by 30% within the rst 6months
according to Nielsen etal. 1993).
A markedly reduced overall PSV in a bypass graft has
been proposed as a supplementary indicator of a poor
prognosis (Calligaro etal. 1996; Hoballah etal. 1997). Slow
ow in a bypass can point to an outow obstruction caused
by stenosis of the distal anastomosis or poor runo (stenosis of recipient artery, obstructed collateral outow).
Hence, various velocity thresholds have been suggested as
predictors of imminent bypass occlusion. Most authors
assume that a bypass is likely to fail if blood ow velocity
drops below 45cm/s (Calligaro etal. 1996; Hoballah etal.
1997; Mohan etal. 1995), while others propose thresholds
of 40cm/s (Green etal. 1990) or 55 cm/s (Nielsen et al.
1995). Other data suggest that assuming a single velocity
threshold for all types of bypass gras and recipient vessels
is not sensitive and specic enough to identify a failing
bypass (Chang etal. 1990; Hoballah etal. 1997; Idu etal.
1999; Mohan etal. 1995; Treiman etal. 1999). Since ow
velocity in a bypass is determined by its diameter and by
the diameter and outow of the recipient vessel, crural
bypass gras with far distal anastomoses have slower ow
velocities even under normal conditions. Still, slow ow in
a bypass is a risk factor for occlusion, especially in patients
with other predisposing conditions such as a hypercoagulable state, increased blood viscosity, or low systemic blood
pressure. Some authors therefore investigated the predictive power of a prognostic factor combining an increased
focal PSV and a low global PSV in the gra (Calligaro etal.
1996). In a study of 85 PTFE gras, this combined crite-
rion had 81% sensitivity, 93% specicity, a PPV of 63%,
Spectral Doppler interrogation of these sites will directly
identify most gra complications/stenoses, guiding the
examiner to abnormal segments that warrant closer exami-
and an NPV of 93% (similar results were reported by Green
et al. 1990). Other investigators (Hoballah et al. 1997;
Mohan etal. 1995) did not conrm these results. In the
2.1 · Pelvic andLeg Arteries
107
2
a
c
. Fig. 2.38a–c Bypass graft surveillance. Duplex examination of a venous femoropopliteal bypass graft (P3 segment). There is no agreement
about the need for sonographic venous bypass graft surveillance or the extent of the examination. An ecient procedure is to obtain Doppler
waveforms from representative sites to identify those patients who should undergo comprehensive mapping. At a minimum, a Doppler waveform
is obtained from an arbitrary site in the main body of the graft (a) and interpreted with regard to bypass prognosis and signs of stenosis. A more
comprehensive evaluation comprises examination of the proximal and distal anastomoses (where most stenoses occur) and a site within the graft
slightly distal to the anastomosis (duplex and spectral Doppler). Signs of abnormal ow should prompt mapping of the entire graft, which may
also include evaluation of the inow artery. a The color ow image and waveform from a site within the graft show normal ndings. The waveform
is triphasic with a PSV of 129cm/s– there is no sign of bypass graft stenosis and no risk of imminent bypass failure. No further evaluation would
be required in this patient. b For illustration, the examination proceeds with evaluation of the proximal anastomosis (to rule out anastomotic
stenosis or neointimal hyperplasia with relevant luminal narrowing). This is done by placing the sample volume at the origin of the venous bypass
graft (V.BP) from the common femoral artery; triphasic Doppler waveform indicates adequate inow. The profunda femoris artery and supercial
femoral artery (A.F.S) arise distally (to the right of the anastomosis). c Examination of the distal anastomosis: Doppler waveform from the bypass
target artery distal to the anastomosis shows high PSV (70cm/s), steep systolic upstroke, and pulsatile ow as evidence of good outow, ruling
out relevant proximal stenosis. Overall, there is no evidence of imminent bypass failure in this case
b
study of Hoballah et al., 24 of 27 patients with bypass
occlusion showed no abnormalities in the preceding
duplex examination (low ow manifested by PSV<45cm/s
or threefold focal increase in PSV compared with adjacent
segment).
A noteworthy nding is that low-ow bypass gras identied by duplex ultrasound (drop in blood ow velocity below
45cm/s) appear to benet from
lation treatment
(warfarin). While continuation of antico-
maintenance of anticoagu-
agulation was found to result in a markedly higher patency
rate in low-ow gras (decrease in occlusion rate from 24% to
4%, p<0.0001), no benet was observed for high-ow gras
(Brumberg etal. 2008). Surprisingly, gra PSV in this study of
130 bypass gras was <45cm/s in 47% of cases.
2.1.7.3.2 Controversy About theBenet ofDuplex
Bypass Graft Surveillance Programs
Although studies present conicting evidence (Wixon etal.
2000; Golledge etal. 1996; Davies etal. 2005), many authors
advocate duplex ultrasound surveillance aer bypass graing, at least for vein gras and during the rst postoperative
. Table2.15) when the risk of occlusion is highest and
year (
the prognosis of bypass revision is good (Harris etal. 1988;
Passman etal. 1995; Taylor etal. 1990).
108
A
P
artery
Common femoral artery
Chapter 2 · Extremity Arteries
2
. Fig. 2.39 Common sites of bypass graft stenosis and corresponding
spectral Doppler changes (A, B) illustrated for femoropopliteal bypass
graft bridging occluded supercial femoral artery. I Stenosis of proximal
bypass anastomosis (A) with poststenotic waveform (B). II Stenosis within
vein graft (at former valve site) with focal doubling of ow velocity (A)
compared with prestenotic waveform (C) and postocclusive ow prole
distal to the stenosis (B). III Stenosis of distal bypass anastomosis (A) with
poststenotic ow prole in the popliteal outow tract (B). IV Stenosis of
the native artery proximal to the bypass anastomosis, which is due to
progressive atherosclerosis: stenotic waveform (A) in the arterial segment proximal to the stenosis and poststenotic ow prole in the artery
distal to the stenosis and in the bypass graft (B). V Stenosis of the artery
distal to the lower bypass anastomosis: stenotic waveform (A) at the
site of stenosis with poststenotic ow prole distally (B) and prestenotic
waveform (C) in the proximal arterial segment and in the bypass graft
. Fig. 2.40 A venous bypass graft is susceptible to a number of spe-
cic complications (I–VI), which must be taken into account in bypass
surveillance in addition to the preferred sites of stenosis illustrated in
. Fig.2.39. I A reversed vein graft is prone to stenosis just distal to the
proximal stenosis, the narrowest portion of the graft. II Scar formation
with narrowing at valve sites. III Dilatation with elongation and kinking of
the graft. IV In situ vein graft with a narrow distal end can result in luminal
narrowing just proximal to the distal anastomosis. V Failure to ligate all
perforating veins communicating with an in situ vein can give rise to an
AV stula (between the bypass graft and the venous system). VI Residual
valve in an in situ vein graft giving rise to graft stenosis or occlusion
Common
femoral
artery
opliteal
IV
A
C
II
A
C
Vein
Popliteal
artery
B
I
A
B
III
AA
V
VI
Notwithstanding the ongoing controversy, it seems
important to document the baseline ow characteristics dur-
B
ing the rst 3months aer surgery. If there is a decrease in
PSV or triphasic ow becomes monophasic over time, this
A
should prompt a search of the gra, the anastomoses, and the
inow and outow segments for stenosis using the criteria
described above.
In a cost-eectiveness analysis, infrainguinal venous
B
bypass gra surveillance with revision for duplex-detected
stenoses resulted in a 1-year patency rate of 93% versus 57%
for gras revised aer thrombosis (Wixon etal. 2000). e
C
B
amputation rate was also lower (2% vs. 33%). Especially
patients with critical leg ischemia at the time of bypass graing appear to benet from sonographic surveillance and gra
revision (Visser et al. 2001). In this study, patients in the
V
duplex surveillance group had a major amputation rate of
1.7% compared with 7.7% in patients undergoing surveillance with clinical examination and ABI only. e cost of
diagnosis and treatment was only half as high in the duplex
group. e subgroup of patients with intermittent claudication at the time of bypass surgery beneted less from sonographic surveillance.
Overall, these ndings show a benet of routine duplex
surveillance for patients with autologous vein gras, while a
benet is less apparent for patients with synthetic gras.
Many studies are limited by the fact that they investigated
mixed populations of patients with venous and synthetic
bypass gras. e poorer predictive value of routine surveillance in patients with synthetic gras seems to be attributable to the complexity of factors that can cause occlusion of
these gras. Oen, a stenotic lesion is not detectable and the
mechanism of occlusion remains unclear. It is obvious, then,
that duplex surveillance can contribute little to the identication of failing synthetic gras.
A large meta-analysis (Golledge etal. 1996) comparing
I
2680 duplex surveillance and 3369 nonsurveillance vein
gras showed that routine duplex surveillance improved
bypass patency rates but not the (long-term) limb salvage
rate.
II
e Vein Gra Surveillance Randomised Trial (VGST)
had great impact regarding the role of routine duplex sur-
III
veillance in patients with venous gras (Davies etal. 2005).
In this prospective, randomized multicenter trial of 594
patients, no dierence was found between clinical and
duplex surveillance in terms of primary patency, primary
IV
assisted patency, secondary patency, and amputation rates.
A limitation of the VGST is that no subgroup analysis was
done.
us, while there is no added benet of routine duplex
monitoring of leg bypass gras (as shown by Kaplan–Meier
analysis), a duplex ultrasound evaluation is warranted whenever serial clinical examination, pulse status, or the ABI
shows deterioration. Moreover, patients with venous bypass
gras who have a poorer prognosis from the start also benet from being enrolled in a duplex surveillance program.
Several gra-related and patient-related factors contribute to
a poorer prognosis (. Table2.17):
ab
e
2.1 · Pelvic andLeg Arteries
109
2
c d
f
. Fig. 2.41 Bypass graft surveillance. a Long stenosis in a femorocrural reversed vein bypass graft just distal to the proximal anastomosis (due
to use of a small-caliber vein segment for grafting). Spectral Doppler interrogation of the stenotic segment (indicated by aliasing in the color
image) demonstrates monophasic ow with a peak systolic velocity (PSV) of 4.1m/s and an end- diastolic velocity (EDV) of 1m/s. b The Doppler waveform from within the graft downstream of the anastomotic stenosis shows a monophasic, poststenotic pattern with slow ow (PSV
of 25cm/s). c If no ow obstruction is present above, within, or below a bypass graft, an altered ow velocity within the graft may be due to a
size mismatch between the graft (synthetic or venous) and the recipient artery (e.g., a calf artery). Very slow ow in the absence of upstream or
downstream stenosis can occur when a synthetic graft with too large a diameter has been used or a vein graft has become dilated over time (as
in the example, where PSV is 21cm/s). A triphasic waveform obtained in a bypass graft indicates good graft function with adequate peripheral
perfusion. In the example, the vein graft anastomosed onto the tibiobular trunk is dilated to 1.3cm, and the bular artery is the only patent
calf artery. d An in situ vein graft must be scrutinized for the presence of an AV stula (arising from a nonligated branch or perforating vein),
especially if peripheral pulses are poorer than would be expected after a bypass procedure. There is monophasic ow with a large diastolic component in the graft segment proximal to and within the AV stula due to direct outow into the venous system (BP=bypass). The site of the AV
stula is marked for ligation. e High-grade stenosis at the proximal bypass anastomosis (AN) due to neointimal hyperplasia (hypoechoic). f Iliacofemoral bypass graft (BP) with high-grade proximal stenosis in the common iliac artery (A.I.C.) giving rise to a monophasic Doppler waveform
with a PSV of 550m/s. A poststenotic waveform is obtained in the bypass graft (as in b). A.I.I. = internal iliac artery; A.I.E. = occluded external
iliac artery
110
Chapter 2 · Extremity Arteries
loss. e 65% of patients without stenosis had a cumulative
patency rate of 82% (Modi etal. 2009). Tinder etal. (2008)
found a similar association between early detection of steno-
2
sis and bypass patency in a study of 353 venous bypasses. In
this study, patients with normal duplex ndings had a cumulative bypass patency rate of 84% at 54months compared
with 62% in patients with stenosis (including mild and moderate stenotic lesions). Investigators reporting angiographic
ndings for comparison found a surprisingly high percentage of early postoperative stenoses (25–37%) within the rst
a
3months (neointimal proliferation) despite normal intraoperative completion angiograms. Over time, the rate of de
novo stenosis decreased, and patients with early duplexidentied stenosis had a signicantly higher occlusion rate
(Ihnat etal. 1999; Mercer etal. 1999).
decision for bypass revision is based on the severity
e
of stenosis and poststenotic ow rates; clinical symptoms
alone may be misleading as they vary with the patient’s disease stage at the time of the bypass procedure (
. Fig.2.43).
erefore, demonstration of a higher-grade stenosis by
duplex ultrasound should prompt an intervention (typically
PTA) to maintain gra patency, even in asymptomatic
patients. In estimating the degree of gra stenosis, the proposed threshold velocities must be applied exibly, taking
into account the diameters of the gra and recipient artery.
b
Future studies should establish rened threshold velocities
for dierent types of gras (autologous vein versus pros-
. Fig. 2.42 a High-grade venous bypass graft stenosis. Stenosis in
a vein graft is typically due to scar formatiom at retained valve cusps
and is graded most reliably using the peak systolic velocity (PSV)
ratio. In the example, the waveform shows the prestenotic situation
on the left (PSV<50cm/s) and the intrastenotic situation on the right
(PSV>3.5m/s). b Neointima (hypoechoic area around patent lumen) in
a synthetic femoropopliteal bypass graft (7mm in diameter), reducing
the patent lumen to 2.6mm (calipers). Unlike a focal stenosis, a very
long segment of luminal narrowing is associated with ow reduction
(due to friction) instead of a circumscribed increase in PSV.However,
downstream of the narrowed graft, a postenotic ow prole is obtained
thetic gras, bypass diameter), level of bypass (target vessel
above or below the knee), and other factors (status of runo
vessels).
2.1.7.4 Ultrasound Vein Mapping Prior
toPeripheral Bypass Surgery
Autologous vein gras are superior to other materials in
peripheral bypass surgery in terms of short-term and longterm patency rates. However, vein preparation may be timeconsuming in patients with anatomic variants, such as an
5 Low-ow bypass and small-caliber vein gra
5 Non-great-saphenous vein gras and composite gras
5 Abnormal intra−/postoperative ndings
5 Bypass graing in chronic critical limb ischemia (no
alternative options for restoring blood ow)
5 Distal-origin bypass in patients with severe inow
atherosclerosis.
aberrant course or duplication, and in obese patients. When
the great or small saphenous vein is considered, the supercial course can be identied with a high-resolution transducer (6.5–10MHz) and marked on the skin before surgery.
Moreover, duplicated veins can be localized and the most
suitable branch selected for graing. When an in situ bypass
is planned, perforating veins can also be marked for intraoperative ligation to prevent development of an AV stula. e
Other investigators explored the benet of a single duplex
follow-up examination
3–6months aer surgery to estimate
bypass prognosis and identify patients requiring revision or
continuing duplex surveillance (Modi etal. 2007; Tinder
etal. 2008). In a study of 365 patients, a single postoperative
duplex examination performed 6 months aer vein gra
bypass surgery to identify gras at risk (PSV ratio,
PSV<45cm/s) demonstrated that critical stenosis was associated with much poorer gra patency and that most intermediate lesions identied by early duplex surveillance
showed progression (>75%), resulting in gra dysfunction or
vein diameter is measured in transverse orientation with the
great saphenous vein normally having a diameter of 3–4mm
below the knee; very thin veins (<2mm) are unsuitable for
graing. If two branches are present, the one with the larger
caliber is selected. Finally, preoperative ultrasound avoids
unnecessary dissection by identifying unsuitable varicose or
postthrombophlebitic veins with thickened walls and sclerosis. Overall,
selection of a suitable graft
preoperative sonographic vein mapping for
shortens the length of surgery
and can prevent unnecessary incisions and extensive exposure (. Figs. 3.81 and 2.67 (Atlas)).
bc
2.1 · Pelvic andLeg Arteries
a
111
2
. Fig. 2.43 a In a crural bypass, a stenosis just below the distal anastomosis has the same signicance as an anastomotic stenosis. The color duplex
examination reveals high-grade stenosis of the anterior tibial artery (ATA), resulting in slow ow in the bypass (<30cm/s). These ndings suggest a failing
bypass and are an indication for graft revision to maintain patency, even in an asymptomatic patient (rightmost image: angiogram obtained during PTA).
b, c Femorocrural bypass (BP) onto the anterior tibial artery (A.TIB.ANT) with high-grade stenosis (b) just distal to the anastomosis (PSV of 440cm/s). In
this case, a single measurement within the graft would have failed as an indirect stenosis criterion because the PSV of 71cm/s measured in the graft (c)
in this patient is above the cuto of 45cm/s. While the waveform shows adequate, pulsatile ow in the graft and runo through the proximal anterior
tibial artery, this case also underlines that reliance on a single midgraft PSV measurement is an inadequate criterion. PSV in a bypass crucially depends
on graft conguration and outow hemodynamics rather than bypass complications alone
. Table 2.17 Dierentiated approach to the use of duplex ultrasound in the surveillance of patients with lower extemity bypass grafts.
The strategy recommended here has been derived from the conicting scientic evidencea and is based on a single postoperative duplex
follow-up examination (after 3–6months) in all patients, with further ultrasound examinations necessary depending on the type of bypass
graft and clinical ndings (regular clinical follow-up with ABI at 6-month intervals, duplex ultrasound only in case of bypass deterioration)
Expected benet of routine duplex
surveillance at 6-month intervals
No benet, except for a single
examination 3– 6 months after
surgery
Probably no benet, except for a
single examination 3– 6 months
after surgery
Benet likely Venous bypass graft:
Bypass graft material and perioperative ndings
Infrainguinal synthetic bypass graft
Exception: clinical deterioration (decrease in ABI)
→ Search for underlying cause using duplex ultrasound
Venous bypass graft (in situ, reversed) in patients who meet the following conditions:
– Large-caliber bypass graft vein (>5 mm), normal graft vein
– Normal intra-/postoperative completion study
– Bypass grafting performed in patients with stage II PAOD (intermittent claudication)
– Good patient compliance
– Thin bypass vein
– Non-great-saphenous-vein grafts and composite grafts
– Abnormal intra-/postoperative ndings (increased outow resistance, low ow, poor runo vessel)
– Bypass grafting performed in patients with chronic critical limb ischemia (stage III or IV PAOD)
– Poor patient compliance
– All distal-origin bypasses with upstream atherosclerosis
a
Study of Davies etal. (2005) not taken into account because it does not present a subgroup analysis for a dierentiated approach
112
Chapter 2 · Extremity Arteries
2.1.8 Role of(Color) Duplex Ultrasound
Compared withOther Modalities:
Problems andPitfalls
2
In the stepwise diagnostic workup of peripheral arterial
occlusive disease (PAOD), the patient’s history, clinical
examination with evaluation of pulses, and determination of
the ankle-brachial index (ABI) should be followed by noninvasive duplex imaging before invasive angiography is contemplated (. Fig. 2.7). e clinical stage of PAOD and the
sonographic ndings are the basis for further patient management, either initiation of treatment or additional diagnostic tests (. Tables 2.18 and 2.19).
For example, patients with sonographically diagnosed
iliac or femoropopliteal stenosis can undergo diagnostic
angiography with PTA standby. In contrast, patients with
longer occlusions of the pelvic or thigh arteries and sonographically adequate peripheral runo with patency of the
popliteal artery can be scheduled for bypass surgery without
prior angiography if indicated on clinical grounds.
Ultrasound alone is also sucient in patients with a popliteal
artery aneurysm.
Patients in whom ultrasound reveals external compression (popliteal entrapment syndrome, adventitial cystic
disease) can also be operated on without prior angiography, which provides no additional information and merely
serves to document the vascular status. Depicting only the
vessel lumen, angiography is inferior to ultrasound in
evaluating perivascular structures. A further drawback of
angiography is the reduction of the three-dimensional vessel lumen to the two-dimensional plane of the lm (see
. Fig. 5.27).
With this limitation, the diameter reduction randomly
depicted in the imaging plane does not necessarily represent the true cross-sectional area reduction, as the wall
. Table 2.18 Advantages and disadvantages of duplex
imaging
Advantages Disadvantages
changes may vary along the length of the stenosis (concentric– eccentric; regular– irregular). Angiographic stenosis
severity may thus dier from the degree determined by
spectral Doppler, which reects the hemodynamic eects of
Noninvasiveness
Evaluation in dierent planes
Evaluation of
– Wall morphology
– Surrounding structures
– Intraluminal structures
– Plaque
Stenosis grading based on
– Morphology
– Hemodynamics
Low cost
Documentation of ndings
Evaluation of collateral
pathways
Long training period
Poor visualization of terminal
vascular bed
Specic methodological
limitations (calcication, air,
obesity, edema)
the stenosis. Even dierent ultrasound modes may yield discrepant results regarding the degree of luminal narrowing
caused by atherosclerotic plaque because they process different types of information: conventional B-mode imaging
relies on the morphologic gray-scale appearance of the arterial lumen in the longitudinal plane, color duplex on the
absence of ow signals in the lumen, and spectral Doppler
on the hemodynamic eects of the stenotic lesion in terms
of ow acceleration. For accurate and reproducible morphologic quantication by both B-mode ultrasound and
angiography, it is thus necessary to always evaluate a stenosis in dierent planes (
. Table 2.17). is is especially
important when assessing the pelvic arteries and femoral
. Table 2.19 Advantages and disadvantages of angiography
trifurcation, where eccentric plaques of the posterior wall
are common. e mere morphologic assessment of an
Advantages Disadvantages
Documentation of
ndings
Visualization and
evaluation of collateral
pathways
Adequate evaluation
of terminal vascular
bed
Fairly short training
period
Invasiveness and complications
(pseudoaneurysm, embolism,
bleeding, local thrombosis, AV stula)
Visualization of patent lumen only
Projection-related problems:
– Stenosis grading
– Evaluation of bifurcations
Some vascular territorities cannot be
consistently evaluated in 2 (or 3)
planes (iliac artery, femoral bifurcation)
No information on hemodynamic
relevance of dierent plaque
congurations
Nonvisualization:
– Vessel wall
– Surrounding structures
High cost
Radiation exposure and contrast
medium administration
eccentric plaque aorded by angiography may overestimate
the resulting stenosis compared with its hemodynamic
eects, even when evaluated in dierent planes. Moreover,
stenosis caused by eccentric plaque may be overlooked or
underestimated if only an anteroposterior angiogram is
available.
An aspect that tends to be overlooked in the scientic discussion is that
plaque conguration (concentric versus
eccentric) determines the hemodynamic severity of the
resulting stenosis in terms of peripheral perfusion impairment and the patient’s clinical symptoms. e hemodynamic
severity in turn depends on the cross-sectional area reduction, which is the basis for calculating the sonographic degree
of stenosis from intrastenotic ow acceleration (see . Fig.
5.27
). Recall that a concentric stenosis that reduces the vessel
diameter by 50% reduces the cross-sectional area by 75% as
opposed to 50% or less when an eccentric stenosis with the
same diameter reduction is present. Sonographically, the former is classied as higher-grade stenosis (PSV ratio of 4