Introduction
Proper vascular access function is required for efficient dialysis. With an unchanged
incidence of patients undergoing renal replacement therapy and an increasing life
expectancy, an increase in the insufficiency of dialysis accesses has accordingly
been seen [1]. By maintaining long-term function, the use of dialysis catheters associated with
a higher mortality rate can be avoided [2].
The most common complications in dysfunctional AV fistulas are stenosis of the vascular
access vessels (14 – 42 %), thrombosis (17 – 25 %), and steal syndrome (2 – 8 %) [3]. In the case of AV fistulas, stenoses often occur in the region of the anastomosis
[4] and in the course of the vascular access vein [5]. Moreover, dialysis patients develop central venous stenoses often as a reaction
to wall trauma associated with the dialysis catheter and as a result of the arterialized
flow conditions in the venous circulation [6] vascular access thromboses typically arise as a result of these stenoses and can
occur as a segmental thrombosis or extensive thrombotic occlusion [3].
Vascular access insufficiency is ideally diagnosed and treated in the framework of
continuous interdisciplinary cooperation between nephrologists, vascular surgeons,
and interventional radiologists [7]
[8]
[9].
Duplex sonography is the method of choice for imaging insufficient dialysis vascular
access. Central vessels that cannot always be viewed sonographically can be visualized
via angiography. In addition, diagnosis and treatment can be performed in one session.
Sectional imaging techniques are used as secondary methods. Computed tomography (CT)
is suitable for visualizing central veins and the complete vascular tree in the case
of an inconsistent sonographic finding. Gadolinium-enhanced MRI is not recommended
for visualizing vascular access vessels due to the potential risk of nephrogenic systemic
fibrosis (NSF) in dialysis patients.
In the case of an insufficient dialysis vascular access, prompt treatment is decisive
for being able to avoid a possible loss of the vascular access and the use of a temporary
dialysis catheter. A number of angiographic techniques are available for this purpose.
Elastic or rigid stenoses can be treated by conventional PTA and stent implantation
as well as by cutting balloon, for example [10]
[11]. To prevent recurrent stenoses, the use of drug-coated balloons is increasingly
being reported [12]
[13]. There are currently no randomized studies or even larger case series showing a
superior long-term patency rate for endovascular brachytherapy [14]
[15] and cryoplasty [16].
In addition to thrombolysis via medication, thrombosed AV fistulas and vascular access
grafts can be treated in a combined pharmacomechanical manner or purely mechanically
with thrombectomy catheters [17] or hydrodynamic systems [18].
The present article is based on the currently available published guidelines including
the European Best Practice Guidelines (EBPG) and KDOQI Guidelines of the National
Kidney Foundation [19]
[20]
[21]
[22]
[23], the upcoming guidelines of the European Society for Vascular Surgery and a search
of the literature in the database info system (DBIS) Science Citation Index Expanded
(SCI Expanded/ Web of Science), and in the PubMed literature database.
Diagnosis
Ultrasound
Due to its wide availability and lack of invasiveness, duplex sonography is the most
widely used vessel visualization method. As a cost-effective method, it allows evaluation
of vascular access maturity and diagnosis of complications in experienced hands [24]
[25]
[26]
[27]. As a result of sonographic stenosis detection, flow measurement and the diagnosis
of thrombotic occlusions, the cause of a vascular access insufficiency can usually
be reliably identified on ultrasound [28]
[29]. In addition to stenosis detection, sonographic follow-up after treatment is readily
possible ([Fig. 1]). Therefore, ultrasound has become established as the primary imaging method in
the case of suspicion of vascular access insufficiency [8]
[21]
[26].
Fig. 1 Sonographic visualization of a venous stenosis with significantly accelerated blood
flow (A) control after percutaneous therapy (B).
Malik et al. reported that long-term follow-up via three-month duplex sonography can
significantly extend the patency rate of dialysis vascular access [30]. The authors state that this was achieved by earlier detection of stenosis with
correspondingly faster treatment.
Amin et al. stated that a flow rate of less than 600 ml/min within implanted PTE grafts
is a predictor of significant stenoses [31]. However, there is no relationship between the blood flow within the vascular access
graft and the length, location, and number of possible definable stenoses.
Although infections of vascular accesses and vascular access systems are typically
diagnosed clinically, the extent of paravascular infections and possible consecutive
thromboses can be diagnosed via ultrasound [32].
A disadvantage of the method is the dependence of the diagnostic quality on the experience
of the examiner [33]
[34]. Moreover, ultrasound examinations cannot be used to create a direct anatomical
representation of the entire vascular tree [35].
However, experienced examiners can use the sonographic findings to create drawings
for exact documentation of the vascular access, thus allowing intervention and operation
planning [36].
However, evaluation of the central veins is still only possible on a limited basis
[8]. Methods such as digital subtraction angiography are used for this purpose. This
method allows better visualization of the central veins and the exclusion of central
obstructions [21].
Angiography
Contrast angiography is the gold standard for the visualization of stenoses, occlusions,
and aneurysms of dialysis vascular access and offers the advantage of complete vessel
visualization. Digital subtraction angiography (DSA) requires radiation and contrast
agent containing iodine or CO2. Purely diagnostic DSA without a therapeutic measure is not recommended for reasons
of radiation hygiene [8]. DSA is used for preoperative mapping of vascular systems only in select cases.
In particular, if central venous stenosis is suspected, DSA is clearly superior to
ultrasound [8]. A further advantage is the possibility of parallel detection and treatment of stenoses.
DSA allows periinterventional as well as postoperative evaluation of stenoses of the
afferent and efferent legs of a dialysis vascular access and the detection of central
thrombi. Any remaining stenoses [37] and central vein stenoses can also be detected in this manner [6]. Complete angiographic visualization, which can also be conducted in an ambulant
setting [38], is performed via retrograde arterial fine-needle puncture of the brachial artery
near the elbow or antegrade puncture of the efferent vascular access vein.
In the latter case of venous puncture, arteriovenous anastomosis via compression of
the vascular access vein (preferably via blood pressure cuff) can be visualized via
the retrograde contrast medium flow. Alternatively to arterial puncture, stenoses
of the arterial branch in a more proximal position can be visualized via retrograde
introduction of the catheter through the anastomosis into the native portion of the
arterial vessel. Duijm and colleagues were able to achieve successful visualization
with this technique in 21 of 22 patients with known arterial stenoses. Retrograde
visualization was not possible in one patient since the anastomosis was impassable
due to additional subtotal stenoses. Of the remaining patients, 18 could be successfully
endovascularly treated [38].
The use of contrast agents containing iodine can result in a further limitation of
kidney function in patients with terminal renal insufficiency. However, DSA can be
performed by an experienced examiner with a very low contrast agent volume. Diluted
iodine-containing contrast agent (e. g. 1:2 or 1:3 diluted in a physiological NaCl
solution) with a contrast agent volume of 10 ml to a maximum of 20 ml is usually sufficient
for diagnostic visualization.
Asif et al. showed that after application of 10 – 20 ml of a low-osmolar contrast
agent, 1 of 25 patients with severely limited renal function was able to undergo dialysis
after 4 weeks [39].
To date, there is no conclusive evidence of the influence of contrast agent osmolarity
on the development of contrast-induced nephropathy [40]. No significantly reduced nephrotoxicity was seen in a comparison of low-osmolar
and iso-osmolar contrast agents in 324 patients with renal insufficiency undergoing
percutaneous coronary intervention [41].
CO2 angiography represents an alternative to conventional DSA. Compared to DSA, CO2
angiography had a sensitivity of 97 % and a specificity of 85 % regarding the detection
rate of central venous pathologies [42]. In addition, this method was successfully used for the diagnosis and intervention
of dysfunctional dialysis vascular access [43]. In the selection of an arterial access, the potential risk of cerebral CO2 embolization
must be taken into consideration. In principle, gadolinium-enhanced DSA is a further
effective method for angiographic vessel visualization. However, this is not recommended
due to the risk of nephrogenic systemic fibrosis in dialysis patients [44].
For treating dialysis vascular access, alternatives such as CT and MRI-guided interventions
are currently neither more user-friendly nor more technically successful than angiography.
Computed tomography
CT angiography (CTA) should only be used to clarify vascular access insufficiency
if a comparable method cannot be performed or other methods yielded inconclusive findings.
In the case of suspicion of external vascular compression, paravascular soft tissues
can be visualized, thus making it possible to diagnose malignant stenoses, for example.
Examination should be performed in two consecutive contrast-enhanced series in the
arterial and venous phase. Approximately 40 – 60 ml of contrast agent are sufficient
for modern CT protocols [45].
In particular, central venous thromboses can be effectively detected with CT ([Fig. 2]). CTA can provide important information for the further course of treatment also
for recommended operative and interventional procedures. Some authors therefore refer
to CTA as superior to purely diagnostic DSA for economic reasons [46]. CTA allows diagnosis of dysfunctional vascular access [47]
[48] as well as simultaneous visualization of the entire vascular tree [49]
[50]. Moreover, CTA is capable of diagnosing hemodynamically relevant stenoses or occlusions
of dialysis vascular access [50]
[51]. Moreover, flow-limiting stenoses can be detected also in the case of forearm fistulas
with moderate sensitivity and high specificity [52]. The detection rate of central venous stenoses depends on the type of examination
protocol and CT scanner used. Karadeli et al. postulate that this method should only
be taken into consideration if ultrasound examination or DSA does not provide a clear
and conclusive result [47]. Current studies show that combined examinations via modern ultrasound and CT devices
have comparable diagnostic reliability to that of DSA [53]. In regard to the required contrast agent quantity and radiation exposure, angiography
is superior to CT in the case of compliance with the above conditions.
Fig. 2 Indirect CT venography after contralateral injection of 90 ml Iomeprol and a delay
of 100 seconds demonstrates central venous thrombosis (arrow in A–C), compared to normal blood flow in the axillary and subclavian vein (arrow in D–F).
Magnetic resonance imaging (MRI)
Gadolinium-enhanced MRI can trigger nephrogenic systemic fibrosis (NSF) in patients
with severe or terminally limited renal function [54]. Limited renal function is specified as the most important patient factor for the
development of NSF in the guidelines of the European Society for Urogenital Radiology
[55]. However, in the case of only moderate limitation of renal function, the use of
contrast agent containing gadolinium with a low or moderate NSF risk can be considered
[44]. Adaptation of the contrast agent dose and protocol results in a reduced incidence
of new NSF cases even in dialysis patients [56].
In a French study regarding the evaluation of the incidence of NSF in 571 dialysis
patients, half of whom had received macrocyclic gadolinium-based contrast agent, no
new disease was seen in the observation period of four months [57]. After gadolinium-enhanced MRI, Becker and colleagues found histologically verified
NSF in 2 of 49 dialysis patients [58]. However, both patients had received linear gadolinium complexes with a high NSF
risk. Therefore, gadolinium-enhanced MRI examination should still not be used in dialysis
patients in particular if methods equivalent or superior to sonography and angiography
are available for clarifying a vascular access insufficiency [44]. If MRI examination is clinically indicated for another issue, only highly stable
macrocyclic gadolinium complexes with a low NSF risk should be used at the lowest
possible dose in dialysis patients [59]. Long-term data with large patient collectives regarding the specific NSF risk in
dialysis patients is currently not available.
To prevent NSF risk in dialysis patients, there are some studies with unenhanced MRI
examinations without gadolinium. These were able to show that preoperative vessel
mapping via unenhanced MRI is technically possible [60]. However, these methods with complex sequences are still far from being able to
be used in the clinical routine. To the authors' knowledge, there is currently no
valid data for the evaluation of insufficient dialysis vascular access via unenhanced
MRI.
Interventional treatment
In dialysis patients, a reduction of vascular diameter of more than 50 % with a significant
flow reduction of the ipsilateral fistula during dialysis and vascular access thrombosis
are indications for treatment.
The selection of the adequate percutaneous access and the treatment method depends
not only on the location, morphology, and extent of the pathology to be treated but
also on the availability of an interventional radiologist with corresponding experience.
Contrast agent injection via the brachial artery after retrograde fine-needle puncture
in the Seldinger technique should be used to visualize the total vascular access anatomy
including the venous outflow. Given a known location and stenosis morphology or thrombus
extent, the intervention catheter is inserted via an introducer directly so that it
allows optimum access to the region to be treated antegrade or retrograde to the flow
direction. Slight overdilation (by approximately 10 – 20 %) is recommended for treatment
via percutaneous angioplasty (PTA). In the case of minimal dilation, there are increased
recurrent stenoses with correspondingly lower long-term patency [61]. There are possible indications for additional stent implantation in the case of
an insufficient PTA result and central venous stenoses and in the case of complications
such as dissections or vascular perforations [62]
[63]. In total, endovascular treatment complications in the case of dialysis vascular
access are rare [64]. [Table 1] shows a list of possible complications.
Table 1
Possible complications of endovascular therapy with rate of occurrence modified from
Haage & Vorwerk 2010 [64].
|
possible complication
|
frequency
|
|
venous rupture (usually able to be treated endovascularly)
|
~ 8 %
|
|
vessel rupture with loss of vascular access and with need for surgical intervention
|
0.3 – 2 %
|
|
pseudoaneurysm in region of the puncture with need for surgical intervention
|
< 0.5 %
|
|
pronounced hematoma with need for surgical intervention
|
< 0.2 %
|
|
arterial embolism
|
very rare but in 2 – 6 % of thrombosed brachiocephalic AV fistulas in the upper arm
|
|
symptomatic pulmonary artery embolism
|
< 1 %
|
|
mesenteric ischemia, cutaneous contrast agent reaction, metabolic acidosis, pulmonary
edema
|
< 0.1 % in each case
|
|
Infection or bacteremia
|
< 0.5 %
|
Insufficient AV fistula
Stenosis of the anastomosis
There is a treatment indication in the case of a stenosis diameter of greater than
50 % with a consecutive flow reduction, reduced dialysis rate, or previous thrombosis
[21]. Stenoses of AV fistulas between the radial artery and cephalic vein (Brescia-Cimino
vascular access) are primarily located in the region of the anastomosis and in the
further course of the vascular access vein [4]
[5]. In the case of AV fistulas in the distal forearm, anastomosis stenoses can be treated
via surgical proximalization [21]. PTA shows slightly worse long-term results and is used as an alternative method
([Fig. 3]). However, primary endovascular treatment via PTA is indicated for the proximal
forearm. Stenosis of the arterial inflow – more than 2 cm from the anastomosis – is
rare but can decrease the flow rate within the AV fistula and thus result in insufficiency
of the dialysis vascular access. Stenoses of the arterial inflow should also be treated
via primary PTA [21].
Fig. 3 Stenotic anastomosis (arrow) in a patient with radiocephalic AV fistula A. Uncomplicated PTA B with good postinterventional result C.
For stenoses near the anastomosis in the case of radiocephalic AV fistulas, residual
stenosis after initial PTA represents a relevant prognosis factor. In a retrospective
analysis of 73 patients, Mortamais et al. compared residual stenoses with a diameter
reduction of more or less than 50 %. In the case of residual stenosis of less than
50 %, the assisted primary patency rate after 12 and 24 months was 84.6 % and 76.1 %,
respectively. For patients with residual stenosis of at least 50 %, the corresponding
values of 62.3 % and 46.8 % [65] were significantly lower.
Promising patency rates were described in the use of drug-coated balloons. In the
case of use in stenoses near the anastomosis, Patane et al. observed primary patency
rates of 96.1 % after 6 months, 81.8 % after 12 months, and 57.8 % after 24 months.
The secondary patency rate was 95.4 % after 12 months and 94.7 % after 24 months [13].
Stenosis of the vascular access vein
Stenoses of the efferent arm vein in forearm fistulas are treated via primary PTA
[66]
[67]. Upper arm fistulas are typically stenosed in the region of the confluence of the
superficial vein (typically the cephalic vein or the basilic vein) with the deep vein
system [67] and should also be treated via primary PTA. In principle, vascular access vein stenoses
in the forearm are accessible for interventional treatment ([Fig. 4]).
Fig. 4 Depiction of venous stenosis (arrow) in the forearm of a patient with radiocephalic
AV fistula A after injection into the brachial artery. Uncomplicated PTA B with good result of angioplasty via an additional antegrade venous access.
Supplementary stent implantation is to be considered in the case of an insufficient
PTA result and recurrent stenoses. However, stent implantation in the puncture segment
should be avoided since there is no verified data regarding repeat and permanent puncture
of the endoprosthesis. Overlapping of the stent into the basilic vein can prevent
placement of a future brachiobasilic fistula. Interdisciplinary planning is therefore
decisive for ensuring that the placement of proximal replacement vascular access is
not prevented.
In a randomized study including 40 patients with stenoses in the venous branch, a
higher primary patency rate (70 %) compared to conventional PTA (25 %) was observed
6 months after use of a drug-coated balloon [12]. However, there is currently no long-term data for this study.
In particular, in extremely rigid vascular access vein stenoses, the use of a cutting
balloon ([Fig. 5]) showed higher success rates compared to conventional PTA [10]. Due to the cut surfaces, overdilation results in an increased risk of perforation.
Therefore, the ratio of cutting balloon to reference vessel should not be greater
than 1.1 to 1 [11]. However, compared to conventional PTA, cutting balloons require a greater introducer
diameter and are comparatively expensive.
Fig. 5 Extremely rigid stenosis of the vein near the anastomosis A was successfully dilated C by a Cutting balloon B.
When using cryoplasty catheters, reduced postinterventional neointima formation is
expected due to the supplementary application of cold. As a result, lower dissection
rates with similar long-term patency compared to conventional PTA in the case of arterial
stenoses of the femoropopliteal circulation were described [68]. In a case series of only five patients with dialysis grafts, the superiority of
cryoplasty compared to conventional PTA could be shown in the case of pronounced recurrent
stenoses of the venous anastomosis [16]. However, the use of cryoplasty catheters has not yet become established. Moreover,
there are no randomized studies that could confirm their superiority.
Endovascular brachytherapy and external radiation are additional interventional methods
that have not yet been able to be proven to be superior and are thus not used in the
clinical routine [69]. With the goal of preventing neointimal hyperplasia, brachytherapy was examined
in a pilot study including 25 patients [15].
For ultrasound-guided PTA, there is currently only an insufficient number of studies
of insufficient dialysis vascular access [70]
[71].
Thrombosed AV fistula
In the case of thrombosis of the AV fistula, the age, position, and extent of the
thrombosis determine the primary treatment success and the long-term patency. Treatment
should ideally be initiated within 48 hours. As a result of early revascularization,
placement of an alternative vascular access, such as a temporary dialysis catheter,
can be prevented. Primarily urokinase and rt-PA are used as fibrinolytic agents. Accompanying
mechanical thrombus manipulation via external vascular access massage or endovascular
fragmentation can increase treatment success.
A short, segmental thrombosis can be sufficiently treated via PTA alone. Extensive
thromboses must typically be treated via pharmacomechanical thrombolysis and consecutive
balloon angioplasty [21]. Using this combination with additional thrombus aspiration, Poulain et al. achieved
a one-year patency of 90 % in 14 thrombosed AV fistulas [72]. Zaleski et al. treated 17 patients with thrombosed Brescia-Cimino fistulas via
PTA and urokinase infusion. After a year, 71 % of the AV fistulas were still patent
[73]. Turmel-Rodrigues et al. describe an initial success rate of 81 % in 16 patients
as a result of the combined use of thrombus aspiration and PTA [74]. To conduct thrombolysis, the catheter tip (e. g. 5F catheter) should be placed
within the thrombosis. After administration of a bolus of 100 000 to 200 000 IU urokinase,
100 000 to 200 000 IU urokinase/h should be infused over a period of 6 to 20 hours
with a maximum amount of approx. 2000 000 IU urokinase. In addition, approx. 5000 IU
heparin should be administered during the intervention.
As a result of thrombus fragmentation via conventional PTA, Liang and colleagues achieved
a direct success rate of 93 % with a patency rate of 70 % after one year [75]. Residual thromboses were additionally treated via urokinase.
To date, there are no randomized studies proving the superiority of mechanical thrombectomy
instruments over conventional mechanically supported pharmacological thrombolysis.
The percutaneous thrombolytic device (PTD), a wire-guided instrument for mechanical
thrombolysis, is mentioned as an example. The catheter is comprised of two components,
the outer protective cover and an inner self-expanding fragmentation basket that is
operated via the battery motor. After placement in the thrombosed vessel, the fragmentation
basket is expanded. Quick rotation thereof results in mechanical thrombolysis [17].
In addition to mechanical thrombus fragmentation, hydrodynamic thrombectomy represents
a further percutaneous method. In a prospective study of the angio-jet system including
187 patients with 261 dialysis grafts and 24 AV fistulas, an assisted primary patency
rate after 1, 6, 12, and 18 months of 72.4 %, 45.1 %, 30.3 %, and 22.4 %, respectively,
was described [18].
In a retrospective comparison between PTD and angio-jet in 275 thrombosed AV fistulas,
Yang et al. observed slightly more time-efficient thrombectomy via PTD. The primary
patency rates after 6 months were 45 % with the use of the angio-jet and 43 % after
PTD. The secondary patency rates after a year were 74 % and 87 %, respectively [76].
In total, the treatment of the underlying stenosis determines the long-term success
of thrombectomy or thrombolysis. However, this is often first visible after thrombosis
treatment and should then be treated directly at the same time.
Insufficient dialysis graft
Lumen reduction of more than 50 % with significant flow reduction is a recommended
indication for treatment even in dialysis grafts [21]. The most common cause of an insufficient dialysis graft is stenosis of the venous
anastomosis [77]. Dialysis grafts are used in patients with "worn out" peripheral veins. Therefore,
vessel-preserving endovascular methods should be primarily used in the case of graft
insufficiency. Stenosis of the arterial inflow can also be effectively treated via
PTA [21]. Several workgroups even observed success rates of 98 % [78]. PTA can be performed without complication if only the afferent artery proximal
to the vascular access or the anastomosis is affected but the artery distal to the
anastomosis is not stenosed. If the efferent artery also has a distal stenosis, simultaneous
dilation is recommended. PTA of the stenosed anastomosis would otherwise increase
the risk of peripheral ischemia due to the steal effect as a result of the increased
vascular access volume. Stenoses within the graft occur mainly in the puncture region.
They are the result of connective tissue growing into the puncture tracts and can
be successfully treated via PTA [21].
Supplementary stent implantation should be taken into consideration in recurrent stenoses
[62]. In the case of repeat stent occlusion, it is necessary to surgically place the
graft again.
A number of current studies describe improved patency rates compared to PTA alone
for stenoses of the dialysis graft in the region of the venous anastomosis and the
venous outflow when using covered stent grafts [79]
[80]. The study by Haskal et al. is a prospective randomized multicenter study with only
a six-month follow-up [80]. A significantly lower re-stenosis rate of 28 % compared to PTA with 78 % after
stent graft is described.
Karnabatidis et al. compare the patency rates in 35 patients after previous PTA or
bare metal stent implantation with the results after a revision procedure with a covered
stent graft [79]. Significantly improved primary patency rates of 61.4 % compared to 8.6 % after
conventional PTA were observed a year after the use of a stent graft.
In the not yet published REVISE study (e. g.: http://www.accessdata.fda.gov/cdrh_docs/pdf13 / P130 006b.pdf),
the treatment of stenoses of the venous anastomosis via covered stent graft and PTA
alone was compared. The results showed at least no significant superiority of covered
stent prostheses. Primary patency rates of 43.4 % after 6 months, 21.4 % after 12
months, and 9.6 % after 24 months were observed for the use of stent grafts. After
the use of PTA alone, the corresponding primary patency rates were 29.4 %, 15.2 %,
and 6.8 %, respectively.
The secondary patency rates were 91.2 % after 6 months, 82.7 % after 12 months, and
68.9 % after 24 months in patients with stent grafts and 86.5 %, 78.8 %, and 66.6 %,
respectively, after PTA alone.
Graft thromboses should be treated before the next dialysis if possible [81]. Kakisis et al. examined the use of nitinol stents in the region of venous anastomosis
in patients with thrombosed brachio-axillary vascular access grafts after surgical
thrombectomy. They observed significantly improved assisted primary and secondary
patency rates compared to conventional PTA [82].
Older thromboses of the vascular wall (more than 5 days old) are often located behind
the venous anastomosis and are difficult to access via surgical resection. Similar
to thrombosed AV fistulas, thromboses of PTFE grafts can also be treated with a number
of different percutaneous techniques. Thrombus aspiration, thrombolysis via fibrinolytic
agents (see above) or mechanical thrombectomy can be used in combination. The treatment
results of thromboses and associated stenoses of synthetic dialysis grafts were summarized
by Aruny and colleagues [83]. The primary success rates of thrombolysis and mechanical thrombectomy were between
75 % and 94 %. After 6 months, the patency was still 18 – 39 %. The patency rates
6 and 12 months after thrombolysis were 62 – 80 % and 57 – 69 %, respectively. Trerotola
and colleagues demonstrated a 95 % primary success rate with a patency rate after
3 months of 39 % as a result of the use of PTD [84]. Compared to different mechanical thrombolysis instruments, Smits et al. concluded
that the treatment of the underlying stenosis was the only relevant factor for the
treatment success of a thrombosed dialysis graft [85]. Therefore, the method should be selected as a function of the experience of the
particular interventional radiology center.
Central venous stenoses and occlusions
In addition to the superior vena cava, the brachiocephalic vein, and the subclavian
vein, the opening region of the cephalic vein is also included as a central venous
vessel ([Fig. 6]). Due to the accelerated flow rates in the venous branch, dialysis patients develop
rigid central venous stenoses in 11 – 50 % of cases [6]. Previous trauma to the venous wall caused by central venous dialysis catheters
or flow obstructions caused by port catheters or pacemaker electrodes represent additional
risk factors [6]
[86]. Therapy is indicated in the case of symptomatic central venous stenosis with painful
swelling of the arms, restricted movement, or insufficient hemodialysis. Antegrade
puncture of the vascular access vein is performed for interventional therapy. The
balloon diameters to be used for PTA are selected in relation to the non-stenosed
vessel segment. Careful dilation of the vasoconstriction to the caliber of the healthy
vessel segment is recommended [6]. In the case of dialysis patients, central stenoses in the opening region of the
cephalic vein and the brachiocephalic vein are described [87]
[88]. Both regions are accessible for percutaneous intervention via the antegrade venous
access. Alternatively, femoral-venous access is possible in the case of impassable
brachial stenoses or occlusions. If a treatable central venous stenosis or occlusion
is identified as the cause of the central flow disturbance, treatment with PTA is
recommended. In the case of untreatable malignant compression or pacemaker electrodes,
there is an indication for primary stent implantation [21]. A stent in the region of a venous confluence should be avoided if possible since
a consecutive stenosis can occur in the case of overlapping into the non-stenosed
vessel. Therefore, for example, a stent in the confluence of the cephalic vein and
the subclavian vein can induce stenosis and prevent venous drainage of the arm which
would then prevent subsequent placement of a brachial AV fistula. A subclavian stent
with overlapping into the opening of the jugular vein can complicate the cervical
placement of a temporary dialysis catheter. In-stent recurrent stenoses ([Fig. 7]) can be treated via repetitive PTA.
Fig. 6 Cephalic arch stenosis A with uncomplicated balloon dilation B and good PTA result.
Fig. 7 Right-sided cephalic arch stenosis A with uncomplicated stent implantation due to insufficient PTA B. In-stent stenosis was diagnosed three years after stent implantation C and was successfully treated by PTA D.
Both PTA and stent implantation are effective and reliable methods for central venous
stenoses. Ozyer and colleagues observed a comparable complication rate after stent
implantation and PTA alone in a single-center analysis of 126 patients with central
venous stenoses. However, a significantly higher re-intervention rate was seen after
stent implantation and significantly higher primary patency rates after PTA alone
[89]. Due to the necessity for repeat treatment of relapses, avoidance of central venous
dialysis catheters as a prophylaxis for central venous obstructions continues to be
recommended [21]. In patients with central recurrent stenoses of the cephalic vein, superiority of
covered stent grafts compared to normal bare stents in relation to the patency rate
was able to be shown [90]. However, these results are a subject of controversy since the placement of a covered
stent could induce central stenoses and occlusions that would prevent future placement
of an ipsilateral vascular access [91].
In the case of a central venous occlusion ([Fig. 8]), there is a significant increase in the volume of the ipsilateral arm [92]. Moreover, prominence of the superficial arm veins due to the collateral flow, paresthesia,
and pain are observed. The treatment of central venous occlusions and of in-stent
thromboses ([Fig. 9]) can also be performed via PTA or primary stent implantation [21]. However, dialysis can remain possible in the case of a sufficient collateral system
with a corresponding flow volume despite central venous occlusion.
Fig. 8 Unrecanalizable central venous occlusion by brachial approach A with delayed outflow via collateral vessels (arrows in B). Additional visualization of the occlusion via femoral access C. Simultaneous injection displayed the complete length of the occlusion D, but the occlusion was still not recanalizable via the femoral approach.
Fig. 9 Angiographic diagnosis of a stent occlusion 6 months after implantation in the left
brachiocephalic vein A. Uncomplicated recanalization by PTA B. Post-interventional angiography showed a significant reduction of collateral vessels
C.
After treatment, frequent clinical monitoring should be performed. The occurrence
of pain or swelling as well as a flow reduction during dialysis are an indication
for performing clarification again.
Complications such as pulmonary artery embolism, vascular wall damage, and perforation
are extremely rare ([Table 1]). However, vascular wall rupture of a central vein can be associated with life-threatening
pericardial tamponade or a large pleural effusion. In the case of the slightest indication
of a tear in the wall of a central vein, the PTA balloon should be left near the lesion
to be able to inflate it again quickly as needed to cover the site of the perforation.
Implantation of a bare metal stent can treat smaller damage to the vascular wall.
However, implantation of a covered stent is recommended in the case of a perforation.
Periinterventional medication
The use of anticoagulants in the treatment of central venous lesions pre-, peri-,
and postinterventionally is not confirmed by large studies. The following data are
thus to be viewed as recommendations.
After placement of the introducer, a bolus of 3000 to 5000 IU unfractionated heparin
is administered intravenously before intraluminal treatment [86]
[93]. After stent implantation, PTT-relevant intravenous administration of up to 1000 IU
heparin per hour for 24 hours can be considered. With respect to the administration
of low-molecular heparin (e. g. enoxaparin), the manufacturer specifications for dose
adaptation and monitoring should be taken into consideration particularly in patients
with limited renal function to avoid bleeding complications.
The effectiveness of thrombocyte function inhibition via medication in venous intraluminal
treatments is not proven in contrast to the arterial vascular system. However, it
is conceivable that there is an advantage based on the arterialized flow. Oral application
of acetylsalicylic acid has been propagated for over a decade. The administration
of clopidogrel at 75 mg per day for 4 to 6 weeks after stent implantation currently
seems advisable.
Discussion
At present, the number of patients with chronic renal insufficiency continues to increase
as a result of continuously improving treatment methods and a decreasing mortality
rate. The dysfunction of arteriovenous fistulas is a main cause for the high morbidity
and hospitalization rate (20 – 30 %) of hemodialysis patients. Despite all improvements
in the care of this patient collective, only approximately 15 % of ateriovenous fistulas
remain functional over the long term. As a result, the diagnosis and treatment of
vascular access dysfunction in hemodialysis patients are extremely important and are
a central point in treatment.
Unfortunately, the recommendations in all guidelines of the various associations and
organizations regarding the improvement of the treatment of ESRD (end-stage renal
disease) must relate to publications with evidence levels 2 and 3, far removed from
level 1 randomized studies. Nonetheless, internationally accepted and recognized diagnostic
and therapeutic procedures can be derived from these available guidelines and from
evidence collected by many workgroups over decades and these are described in this
article.
This includes a collaboration of interventional radiologists, vascular surgeons, and
nephrologists which is the starting point for sufficient diagnostics and indication
determination in the treatment of insufficient dialysis vascular access ([Table 2]). Diagnosis is made via a combination of clinical symptoms, duplex sonography, and
supplementary angiography in the case of expected intervention.
Table 2
List of possible pathological findings in vascular access insufficiency with corresponding
treatment indications and different treatment options.
|
pathology
|
treatment indication
|
treatment modality
|
|
AV fistula
|
anastomosis stenosis
|
> 50 % stenosis with flow reduction, insufficient dialysis, or thrombosis
|
|
|
venous stenosis near anastomosis
|
> 50 % stenosis with flow reduction, insufficient dialysis, or thrombosis
|
|
|
venous stenosis of the efferent vein
|
> 50 % stenosis with flow reduction, insufficient dialysis, or thrombosis
|
-
primary endovascular treatment with PTA
-
stent implantation in case of an insufficient result, complications, or early relapse
(< 3 months)
|
|
thrombosis of the AV fistula
|
insufficient dialysis
|
dependent on age, location, and extent of thrombosis
|
|
Dialysis graft
|
stenosis
|
> 50 % stenosis with flow reduction,
insufficient dialysis, or thrombosis
|
-
primary endovascular treatment with PTA
-
stent implantation in case of an insufficient result, complications, or early relapse
(< 3 months)
|
|
stenosis of venous anastomosis
|
> 50 % stenosis with flow reduction, insufficient dialysis, or thrombosis
|
|
|
thrombosis
|
insufficient dialysis
|
dependent on age, location, and extent
|
|
Central venous obstruction
|
stenosis/occlusion
|
painful arm swelling with loss of function
> 50 % stenosis with flow reduction, insufficient dialysis, or thrombosis
|
-
primary endovascular treatment with PTA via brachial access
-
femoral access in case of impassable stenosis
-
stent implantation in case of an insufficient result, complications, or early relapse
(< 3 months)
|
Compared to ultrasound, DSA allows better evaluation of the central veins. Moreover,
it is superior to CT with respect to the required contrast agent quantity. In the
diagnosis of a vascular access insufficiency, CT is currently still a secondary method.
However, in the case of suspected mediastinal vascular compression, diagnosis via
sectional imaging is essential.
Brachial stenoses of the efferent vascular access veins and central venous stenoses
should be primarily treated via PTA or in combination with stent implantation after
careful consideration in the case of complication or an insufficient PTA result. To
date, no stent type has proven to be superior among uncoated bare metal stents [89]. The use of cutting balloons can be considered in the case of extremely rigid or
elastic stenoses. With respect to the re-stenosis rate, drug-coated balloons show
promising results. However, studies with larger patient collectives and long-term
data are currently not available. Long-term results for stent grafts in the region
of venous anastomosis of vascular access grafts are also not yet available. To date,
endovascular brachytherapy and external radiation have not been able to show superior
results and currently do not play a major role in the treatment of vascular access
insufficiency.
In the treatment of vascular access thromboses, surgical and interventional thrombectomy
has comparable results. Among interventional methods, purely mechanical and pharmacomechanical
approaches yield comparable patency rates. Segmental thromboses should therefore be
treated interventionally and extensive occlusions should be treated surgically. Regardless
of the method used, subsequent PTA of the etiological stenosis is the most important
prognostic factor after thrombosis treatment [85].
Central venous occlusion should be treated primarily percutaneously via PTA. Stent
implantation should be discussed in the case of PTA failure due to recoil, incomplete
PTA, or quick re-obstruction within three to six months. Open surgical treatment should
only be considered in the case of occlusion that cannot be treated via intervention
due the higher level of invasiveness. Large vascular access aneurysms should preferably
be treated surgically. Endovascular treatment can be performed as an ambulant intervention.
The vascular access can subsequently be used directly for dialysis.
In summary, the indication for treatment should always be made in interdisciplinary
consensus and the treatment modality should be selected as a function of the local
expertise.
