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May 19, 2023
An Overview of Arteriovenous Fistula and Graft Failure: Causes,
Interventions, and Risks
Peter Stibbs
Medical Affairs, Argon Medical Devices
Abstract
Arteriovenous fistulas (AVFs) and grafts are crucial components in hemodialysis for patients
suffering from end-stage renal disease. However, their high failure rate remains a consider-
able challenge in medical practice, often resulting in substantial morbidity and compromised
quality of life. This comprehensive review provides an in-depth examination of the potential
causes behind AVF and graft failure. This includes, but is not limited to, neointimal hy-
perplasia, venous hypertension, compromised flow dynamics, and infection. It additionally
outlines the crucial role of patient demographics and comorbidities.
Recognizing the need for efficient and effective intervention in cases of failure, this paper
also reviews and compares the techniques and outcomes of balloon angioplasty and mechan-
ical thrombectomy. These procedures are often necessitated by thrombosis and stenosis,
significant complications leading to AVF and graft failure. Balloon angioplasty, a standard
first-line therapy, is considered for its technical simplicity and relatively low invasiveness. In
contrast, mechanical thrombectomy devices, which physically remove thrombi, are typically
reserved for balloon angioplasty failure or larger, complex thrombi.
Our review then delves into the associated risks and potential complications of these in-
terventions. Notably, rethrombosis and embolization are among the significant risks, which,
if not handled promptly and effectively, could lead to more severe complications and poorer
patient outcomes. We present the latest statistics and analyze the risk factors contributing to
rethrombosis and embolization following balloon angioplasty and mechanical thrombectomy.
This review will be beneficial to medical professionals dealing with AVF and graft man-
agement, offering a concise, evidence-based examination of failure etiology, therapeutic in-
terventions, and their associated risks. We aim to provide a nuanced understanding of these
procedures, facilitating informed decision-making in clinical practice and opening avenues
for future research to improve patient outcomes and longevity of AVF and grafts.
1.
Introduction
Introduction
May 19, 2023
Arteriovenous fistulas (AVFs) and grafts are essential conduits facilitating effective
hemodialysis in patients with end-stage renal disease (ESRD). These vascular access points
allow for efficient blood flow during the hemodialysis process, serving as a lifeline for indi-
viduals with compromised kidney function [1].
Despite their critical role in managing ESRD, AVF and grafts are not without compli-
cations, with failure representing a significant hurdle in optimal patient care. Often, these
failures stem from the development of thrombosis - the formation of blood clots within the
blood vessels. Thrombosis can obstruct the necessary high-volume blood flow, rendering the
AVF or graft unusable for hemodialysis and requiring immediate medical intervention [2].
The implications of AVF and graft failure extend beyond just the affected individuals. It
is a matter of public health concern given its high incidence rates, the emergency nature of
required interventions, and its role as a leading cause of hospitalization among dialysis
patients. Moreover, it also adds substantial economic burden on the healthcare system, with
costs associated with the diagnosis, management, and follow-up of these complications
escalating rapidly [3].
Addressing these challenges necessitates a comprehensive understanding of the mecha-
nisms and risk factors underlying AVF and graft failure, alongside exploring effective pre-
ventative strategies and efficient therapeutic interventions. With this insight, healthcare
professionals can better manage ESRD patients’ dialysis needs, improving patient outcomes
and optimizing the use of healthcare resources.
2.
Creation of AVF and Grafts
The creation of Arteriovenous (AV) fistulas is a crucial procedure for patients requiring
regular hemodialysis. The surgical technique involves the anastomosis, or direct connection,
of an artery and a vein. This process diverts some of the higher-pressure arterial blood into
the vein. The increased blood flow and pressure result in structural changes in the vein,
including dilation and thickening, a process known as maturation.
Maturation of the vein is critical for it to function as a durable and reliable access point
for hemodialysis. Typically, the vein needs several weeks to months to mature after the
surgery before it can be used for dialysis. During this period, it’s crucial to monitor the
fistula to ensure adequate blood flow and to detect any complications such as clotting or
stenosis early on.
The choice of vessels for creating the fistula depends on various factors such as the
patient’s anatomy, health conditions, and previous vascular access procedures. In most
cases, surgeons start with vessels in the non-dominant arm and move up the arm (forearm
to upper arm) or to the other arm in subsequent procedures if needed. The radial artery and
cephalic vein in the forearm are often used for the first AV fistula, as they are easily
accessible and the procedure in this location has a good success rate.
Throughout the procedure, surgeons also need to consider other factors, such as mini-
mizing trauma to the vessels to reduce the risk of complications and planning for potential
future vascular access needs. The patient’s comfort and personal preferences should also be
taken into account.
May 19, 2023
Radiocephalic fistulas
The radiocephalic fistula, commonly referred to as a Brescia-Cimino fistula, is the pri-
mary choice for initial arteriovenous (AV) fistula creation in patients requiring hemodialysis.
This preference is primarily due to its lower complication rate and greater longevity com-
pared to other types of AV fistulas.
In the creation of a radiocephalic fistula, the procedure typically takes place in the
forearm, usually at the wrist, although higher locations may be used if necessary. The
surgeon first exposes the radial artery and the cephalic vein, two vessels conveniently located
in close proximity. To ensure a smooth and efficient blood flow, it is critical to dissect and
fully expose both vessels, verifying their suitability before creating the anastomosis.
The anastomosis in a radiocephalic fistula is typically performed in a side-to-end manner.
In this technique, an incision is made on the side of the artery and the end of the vein is then
connected to this opening. This configuration promotes arterial blood flow directly into the
vein, which leads to its dilation and maturation over time.
When securing the anastomosis with sutures, the surgeon needs to ensure the vein does
not twist or kink. Any misalignment can compromise the blood flow, potentially leading to
early fistula failure or thrombosis. Furthermore, a meticulous suture technique is necessary
to prevent leakage and to encourage optimal blood flow through the newly created fistula.
Following the procedure, the surgical site is thoroughly inspected to ensure there are no
complications such as bleeding or hematoma. Postoperatively, the maturation process is
closely monitored over weeks to months, with regular assessment of the fistula’s patency,
the patient’s symptoms, and potential complications.
Brachiocephalic fistulas
Brachiocephalic fistulas represent another valuable arteriovenous (AV) fistula option for
patients requiring hemodialysis access. Created by anastomosing the brachial artery and
cephalic vein at the elbow, these fistulas are typically considered when the creation of a
radiocephalic fistula isn’t possible due to factors such as inadequate vein or artery size, or
previous unsuccessful fistula placements in the forearm.
The brachiocephalic fistula creation procedure begins with a detailed vascular mapping
to ensure the chosen vessels—the brachial artery and cephalic vein—are of appropriate size,
patency, and condition. This is essential because the health of these vessels significantly
impacts the success rate of the fistula.
In the surgical process, the brachial artery and cephalic vein, located in the antecubital
fossa (the bend of the elbow), are dissected and exposed. Similar to the radiocephalic fistula
creation, a side-to-end anastomosis is usually performed. The end of the cephalic vein is
connected to a lateral incision in the brachial artery. This arrangement allows arterial blood
to flow directly into the cephalic vein, prompting the vein to dilate and thicken, a process
known as maturation.
Brachiobasilic fistulas
Brachiobasilic fistulas provide yet another option for vascular access in hemodialysis pa-
tients when other fistula types aren’t feasible. These fistulas involve connecting the brachial
artery to the basilic vein at the elbow, usually through a two-stage procedure due to the
anatomical position of the basilic vein.
May 19, 2023
The first stage of creating a brachiobasilic fistula involves a careful vascular assessment
to verify the suitability of the brachial artery and basilic vein. These vessels, located at the
antecubital fossa, are then dissected and exposed. A side-to-end anastomosis is typically
performed, connecting the end of the basilic vein to a lateral incision in the brachial artery.
This allows arterial blood to flow directly into the basilic vein, promoting its dilation and
thickening for maturation.
A critical point of difference in the brachiobasilic fistula creation process is that the
basilic vein is typically situated deeply under the skin and muscles, making it less accessible
for regular hemodialysis needle access. Therefore, it usually necessitates a second stage,
known as vein transposition.
In vein transposition, performed after allowing the fistula to mature for several weeks or
months, the basilic vein is surgically relocated to a more superficial position under the skin.
This makes it easier to access for regular dialysis. In the procedure, the vein is dissected
along its length, preserving its branches and tributaries, and then tunneled subcutaneously
to the new position.
Postoperatively, the brachiobasilic fistula is monitored closely to ensure successful mat-
uration and to detect any potential complications such as thrombosis, infection, or stenosis.
Regular patency checks and patient education on fistula care play crucial roles in ensuring
the longevity and functionality of the fistula.
3.
Physiology and Mechanics of Fistulas
The creation of an arteriovenous (AV) fistula instigates a series of physiological and
mechanical changes in the vasculature that allows the fistula to serve as a robust access
point for hemodialysis. The arterialization process, which is initiated once the anastomosis
between the artery and vein is made, sets off a complex series of events leading to maturation
of the fistula.
Arterial blood flow into the vein causes an immediate increase in pressure and blood
flow within the vein. This hemodynamic alteration triggers endothelial cells to release nitric
oxide, a potent vasodilator, which promotes the dilation and thickening of the venous wall,
leading to the maturation of the fistula. The matured fistula is capable of withstanding
the routine punctures required for hemodialysis, and the high flow rate prevents stasis and
consequent clot formation within the fistula.
Simultaneously, these changes induce structural remodeling in the vein known as neoin-
timal hyperplasia. The increased pressure and shear stress incite smooth muscle cells in
the venous wall to proliferate and migrate inward, leading to thickening of the wall and
potential narrowing of the lumen. Though this phenomenon supports the resilience of the
fistula, excessive neointimal hyperplasia can contribute to stenosis and compromise fistula
patency, underscoring the importance of regular monitoring.
While a functioning AV fistula significantly enhances hemodialysis efficiency, long-term
changes in systemic hemodynamics warrant close attention. The increased blood flow can
put additional strain on the heart, causing it to work harder to maintain the expanded
circulatory volume. Over time, this can result in high-output cardiac failure in susceptible
May 19, 2023
patients. Further, a phenomenon known as ’steal syndrome’ can occur, where the high flow
through the fistula "steals" blood flow from the distal extremity, causing ischemia and
related symptoms.
Understanding the multifaceted physiological and mechanical aspects of AV fistulas is
integral to their successful implementation and maintenance. Surgeons need to adopt pre-
cise techniques during fistula creation to optimize the maturation process. Additionally,
rigorous postoperative care and monitoring can preemptively identify and address poten-
tial complications, ensuring the longevity of the fistula and thereby improving the quality
of life for patients with end-stage renal disease. This comprehensive approach, alongside
ongoing research to mitigate the adverse systemic implications, will continue to refine the
effectiveness of AV fistulas as vital lifelines for hemodialysis patients.
4.
Causes of AVF and Graft Failure
Arteriovenous fistula (AVF) and graft failure can result from a multitude of factors,
broadly categorized as mechanical, patient-related, or disease-related. Understanding these
factors is crucial as it can help identify at-risk patients and guide clinical decisions regarding
fistula or graft placement.
Mechanical factors often account for a significant proportion of AVF and graft failure.
Primarily, venous stenosis, often resulting from neointimal hyperplasia, is a leading cause of
failure. The turbulent flow and shear stress at the anastomosis, as well as vascular injury
during the fistula or graft creation, can trigger this process, causing the smooth muscle cells
in the vessel wall to proliferate and thicken, which in turn can narrow the lumen and impede
blood flow.
Another mechanical factor involves inadequate vein or artery size, which can impede
blood flow, affect fistula maturation, and increase the risk of thrombosis. Poor surgical
technique can also contribute to complications such as pseudoaneurysms, where a false
aneurysm forms due to a leak in the arterial wall, or hematomas, which can compress the
fistula or graft and hinder blood flow.
Patient-related factors also play a significant role in AVF and graft failure. Diabetes is
a well-recognized risk factor, given its association with microvascular and macrovascular
complications. Peripheral vascular disease can also compromise the vascular access due to
its impact on the vessels’ integrity. Hypercoagulable states, whether inherited or acquired,
increase the risk of thrombosis in the fistula or graft.
Certain demographic factors have also been associated with higher failure rates. Aging
may affect vessel health and the healing process post-surgery, while female gender has been
associated with higher rates of failure, potentially due to smaller vessel size and other gender-
specific vascular changes.
Lastly, disease-related factors, particularly the pro-inflammatory state associated with
uremia in end-stage renal disease, can affect the vessel wall and promote neointimal hyper-
plasia, contributing to stenosis. Other systemic diseases like hypertension and atherosclerosis
can also impact the fistula’s or graft’s function and longevity.
May 19, 2023
5.
Thrombectomy Procedures
Thrombectomy procedures are integral in the management of arteriovenous fistula (AVF)
and graft thrombosis, aiming to restore the patency of the vascular access. Depending on the
specifics of the case, either surgical or endovascular techniques may be employed. Among
endovascular interventions, balloon angioplasty and mechanical thrombectomy devices are
two common methods.
Balloon Angioplasty: Balloon angioplasty is an endovascular technique widely used for
restoring patency to occluded or stenotic fistulas and grafts. The procedure involves the use
of a balloon catheter to dilate the occluded or narrowed segment of the fistula or graft.
The procedure is performed under local anesthesia, usually with the aid of ultrasound or
fluoroscopic guidance. A puncture is made in the vein, and a guide wire is introduced and
navigated through the occlusion. Over this guide wire, a balloon catheter is then advanced.
Once the balloon is positioned across the stenosis or thrombus, it’s inflated to compress the
blockage against the vessel wall, thereby reestablishing blood flow.
Balloons used for angioplasty come in different sizes, typically ranging from 2mm to
10mm in diameter, and lengths up to 80mm. The choice of balloon size depends on the size
of the vessel being treated. It’s crucial to choose a balloon that’s a similar size to the vessel
to achieve optimal dilation while minimizing the risk of vessel rupture.
However, balloon angioplasty is associated with several risks. Balloon overinflation can
lead to vessel rupture, while underinflation might result in suboptimal dilation. There’s also
a risk of rethrombosis or restenosis due to vessel injury during the procedure, which can
induce neointimal hyperplasia. Additionally, there is a risk of distal embolization where
fragments of the thrombus dislodge and travel downstream, potentially causing occlusions
in smaller vessels.
Mechanical Thrombectomy: Mechanical thrombectomy provides an alternative to bal-
loon angioplasty. Devices like the Cleaner rotational system have been developed to me-
chanically remove thrombus from the occluded fistula or graft.
The Cleaner device utilizes a rotating, flexible, sinusoidal wire to macerate the thrombus
at 4000 rpm, facilitating its removal. The procedure begins similarly to balloon angioplasty,
with the device being introduced through a vascular sheath. Once in place, the device’s wire
is activated to rotate at high speed, breaking down the thrombus. The debris can then be
aspirated or may pass harmlessly into the systemic circulation due to its small size.
Mechanical thrombectomy has the potential advantage of causing less vessel injury com-
pared to balloon angioplasty, potentially reducing the risk of restenosis. However, the proce-
dure still carries risks such as vessel perforation, distal embolization, and incomplete removal
of the thrombus.
Both balloon angioplasty and mechanical thrombectomy have their respective advantages
and risks, and the choice of procedure often depends on the specifics of the case, including
the location and size of the thrombus, the vessel’s anatomy, and the patient’s overall health
status.
Balloon Angioplasty:
One of the most common complications of balloon angioplasty is the risk of recurrence.
May 19, 2023
This is often due to the formation of intimal hyperplasia, where there is proliferation of
smooth muscle cells within the vessel wall. This can occur as a reaction to the vascular
injury caused by the angioplasty, leading to restenosis or reocclusion.
In order to mitigate the risk of restenosis, drug-eluting balloons, which release a med-
ication to inhibit cell proliferation, have been introduced. These have been found to be
particularly effective in reducing the incidence of restenosis and prolonging the patency of
the fistula or graft.
Another approach to decrease the risk of restenosis is stent placement, which can be
particularly beneficial for recalcitrant stenosis or dissection. However, stent placement in
a fistula or graft has its own challenges, including potential mechanical problems due to
repetitive needle puncture for dialysis and the possibility of stent migration.
Mechanical Thrombectomy:
In comparison to balloon angioplasty, mechanical thrombectomy may cause less trauma
to the vessel wall and therefore potentially reduce the risk of neointimal hyperplasia and
restenosis. Devices like the Cleaner rotational thrombectomy system also offer the advantage
of reducing procedure time, as the thrombus maceration and removal can be more efficient
than balloon angioplasty.
However, a potential downside to mechanical thrombectomy is the risk of distal em-
bolization of thrombotic debris, despite the fragmented pieces usually being small enough to
pass through the circulation without causing issues. Thrombectomy devices do not address
vascular stenosis which still requires dilation of the vessel.
6.
Risk of Rethrombosis and Embolization
The risks of rethrombosis and embolization following a thrombectomy procedure are
considerable and can have significant implications on patient outcomes.
Rethrombosis: Rethrombosis refers to the recurrence of a blood clot at the same location
following successful thrombectomy. It is a common issue following these procedures, with
studies showing that up to 60% of patients can experience rethrombosis within one year fol-
lowing an intervention, though the exact rates can vary depending on patient characteristics
and surgical techniques used [7].
Several risk factors contribute to the likelihood of rethrombosis. Persistent stenosis, or
narrowing of the vessel, following the procedure can impede blood flow, increasing the chance
of clot formation. Similarly, inadequate blood flow during dialysis, which might be due to
factors such as suboptimal pump settings or vascular access issues, can also increase the risk
of rethrombosis.
Hypercoagulability, a state in which the blood has an increased tendency to clot, is an-
other significant risk factor. This can be due to inherited conditions, such as Factor V Leiden,
or acquired conditions like antiphospholipid syndrome, cancer, or nephrotic syndrome. In
the setting of end-stage renal disease, the balance of coagulation and anticoagulation factors
can be further disrupted, contributing to a hypercoagulable state.
Embolization: Embolization refers to the migration of a part or the whole clot to a differ-
ent location in the vascular system. While it is less common than rethrombosis, embolization
May 19, 2023
can lead to severe complications.
If a part of the clot travels to the lungs, it can cause a pulmonary embolism, a potentially
life-threatening condition. It is estimated that symptomatic pulmonary embolism occurs in
less than 1% of thrombectomy procedures. However, the rate of asymptomatic pulmonary
embolism, detected incidentally on imaging, may be higher.
Distal arterial embolization, where the clot travels to the arteries supplying the limbs or
organs, is another serious complication. It can cause acute ischemia, necessitating urgent
intervention. The risk of distal embolization varies depending on the specifics of the case
but is generally considered to be low.
It is important to note that these risks can be mitigated by careful procedural technique,
appropriate patient selection, and meticulous post-procedure care and follow-up. The use
of anticoagulants or antiplatelet agents following the procedure may also reduce the risk of
rethrombosis and embolization, though this must be balanced against the risk of bleeding.
Ultimately, the goal is to maintain the patency of the AV fistula or graft while minimizing
complications, to ensure the patient has reliable access for dialysis.
Arteriovenous fistula (AVF) and graft thrombosis are significant complications in patients
undergoing hemodialysis. Detecting these conditions early is crucial for maintaining vascular
access patency and preventing more serious complications. Here are the key signs and
symptoms that may indicate thrombosis:
1.
Decreased or absent thrill or pulse: A properly functioning AVF or graft should have
a palpable thrill (vibration) and a strong, pulsatile flow. The absence or decrease in
thrill or pulse could indicate a clot.
2.
Prolonged bleeding after dialysis: If the access site continues to bleed for a long time
after dialysis, this could suggest a clot blocking the normal flow of blood.
3.
Swelling and pain: Swelling, redness, or pain over the AVF or graft site might indicate
a clot or infection.
4.
Poor dialysis efficiency: Inadequate clearance of waste during dialysis sessions could
be a sign of diminished blood flow due to a clot.
5.
Changes in venous pressure: During dialysis, an increase in venous line pressure or a
need to decrease the blood pump speed to maintain acceptable pressures could suggest
an obstruction in the AVF or graft.
6.
Coldness, numbness, or weakness in the hand or arm: These symptoms might indicate
a more severe situation where blood flow to the extremities is compromised due to a
clot, known as "steal syndrome."
7.
Changes in appearance: Visible changes, such as bulging or distention of veins in the
chest, neck, or face, or a new kink in the graft or fistula, could indicate a blockage.
8. Difficulty placing needles for dialysis: If the needles cannot be easily inserted or if
there is poor blood flow once the needle is inserted, this might suggest a problem with
the AVF or graft.
9.
Pale or blue-tinged skin (cyanosis): This could be a sign of severe ischemia due to a
clot and requires urgent attention.
May 19, 2023
10.
Altered sensation: Unusual sensations such as pins and needles or tingling might
suggest impaired blood flow.
11. Slowing of blood flow: Observed during dialysis, a slowing blood flow could suggest a
developing clot.
12.
Bruits: While a soft, low-pitched bruit is normal over a functioning AVF or graft,
changes in the pitch or loudness of the bruit could indicate a problem.
Remember, it’s critical for patients with an AVF or graft to be aware of these signs and
symptoms and to seek medical attention promptly if they suspect a problem with their
access. Regular check-ups and vigilant follow-ups can prevent more serious complications.
7.
Conclusion
In conclusion, arteriovenous fistula (AVF) and graft failure, chiefly driven by thrombosis,
represent substantial obstacles in the care of patients necessitating hemodialysis. The dura-
bility and performance of AVFs and grafts are critical, as they directly impact the quality
of dialysis, patient outcomes, and healthcare costs.
Balloon angioplasty and mechanical thrombectomy are two key techniques employed to
restore patency when thrombosis does occur. Balloon angioplasty, with its minimal inva-
siveness and high success rates, has been a long-standing option. Innovations such as drug-
eluting balloons have emerged to address challenges like restenosis following angioplasty.
However, balloon angioplasty isn’t without its disadvantages, including the possibility of
vessel trauma leading to neointimal hyperplasia and restenosis.
On the other hand, mechanical thrombectomy offers another avenue for managing throm-
botic occlusions. Devices such as the Cleaner rotational system offer promising results with
potentially less vessel wall trauma and more efficient thrombus removal. Yet, considera-
tions such as the risk of distal embolization of thrombotic debris and device availability can
influence the choice of this procedure.
Regardless of the intervention used, risks of rethrombosis and embolization remain sig-
nificant. Patient-related factors, such as hypercoagulable states and comorbid conditions,
alongside procedure-related factors like persistent stenosis, influence these risks. Education
of patients to recognize early signs of AVF and graft thrombosis, such as changes in thrill
or prolonged bleeding post-dialysis, is vital for early detection and intervention.
Moving forward, more comprehensive and comparative research is needed to fully under-
stand the relative merits and drawbacks of balloon angioplasty and mechanical thrombec-
tomy. Innovations in both techniques continue to emerge, and determining the best appli-
cation of each based on individual patient and procedural factors is a critical area of future
study.
Moreover, research efforts should also focus on risk mitigation strategies for rethrombosis
and embolization, and on better understanding the pathophysiology of AVF and graft failure
to develop preventive strategies. Achieving these goals can significantly improve the quality
of life for patients with end-stage renal disease, providing them with a reliable, long-lasting
vascular access for life-sustaining hemodialysis.
May 19, 2023
8.
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