Version May 2024
INTRODUCTION — Arteriovenous fistulas (AVFs) are anomalous connections between the arterial and venous system that divert blood from the normal anatomic capillary beds. Fistulas may occur anywhere in the body, be single or multiple, and be congenital or acquired (eg, trauma) (table 1). Acquired AVF of the lower extremity is by far the most common AVF secondary to the use of the groin (femoral vessels historically and preferentially) as a site for percutaneous arterial and venous access.
The evaluation and treatment of acquired lower extremity arteriovenous fistula will be reviewed here. AVFs affecting other sites, such as the brain and lungs, and patent ductus arteriosus are discussed separately. (See "Vascular malformations of the central nervous system" and "Pulmonary arteriovenous malformations: Epidemiology, etiology, and pathology in adults" and "Clinical manifestations and diagnosis of patent ductus arteriosus (PDA) in term infants, children, and adults".)
ANATOMY AND PATHOPHYSIOLOGY — Throughout the body, arteries and veins are within close proximity to one another. Generally, arteries have laterally paired veins, although not in the groin, which is the most common location for lower extremity AVF. More distally in the extremity, the paired veins have intervenous communications (ie, venae comitantes) that pass anterior or posterior to the artery. The larger arteries may have one closely associated vein, or the second vein may be diminutive in size. Venous tributaries also often pass anterior to the artery before emptying into a larger vein.
Any instrument that traverses an artery and vein may result in an AVF. The direction of puncture may be from artery to vein or vein to artery. During percutaneous access, lateral or medial needle deviation or needle placement through vena comitantes or venous tributary can lead to shared artery and vein puncture. In many cases, the errant needle placement is noticed (eg, dark blood during arterial puncture, pulsatile blood during venous puncture) and the needle is withdrawn. Usually, the communication between the artery and vein will spontaneously seal. However, in the face of certain risk factors, the communication between the artery and vein may not seal and AVF will result.
Large common femoral AVFs can result in hemodynamic shifts due to the diversion of blood from the high-resistance arterial circulation to the low-resistance venous circuit. The shunt increases venous volume and pressure with a resultant decrease in peripheral vascular resistance. The ensuing increase in stroke volume and heart rate may lead to a dramatic rise in cardiac output. Another consequence of high-flow AVF is reduced blood flow to the lower extremity, which, in the face of preexisting peripheral artery disease (PAD), can lead to the onset or worsening of lower extremity ischemic symptoms [1]. (See 'Clinical features and diagnosis' below.)
RISK FACTORS — Risk factors for iatrogenic arteriovenous fistula include female sex, hypertension, anticoagulation or antifibrinolytic therapy, left femoral punctures, punctures below the common femoral arteries/veins or multiple punctures, increased body mass index, and advanced patient age [2-7].
Operator-dependent factors that can be modified include the following:
●Low groin puncture – Low groin puncture is more likely to access the deep femoral artery just distal to the common femoral artery bifurcation. The profunda femoris vein passes between the femoral artery and the profunda femoris artery to drain into the common femoral vein. Punctures to the proximal femoral artery are particularly vulnerable to producing an AVF because the needle tip frequently punctures the underlying profunda vein. This risk can be theoretically be reduced by using ultrasound-guided rather than landmark-based access. Ultrasound-guided access allows direct visualization of the needle tip as it enters the desired vessel and increases the success with a single puncture. (See "Central venous access in adults: General principles", section on 'Use of ultrasound' and "Placement of femoral venous catheters".)
●Sheath placement – Dilation of the tract between an artery and vein reduces the likelihood that the communication will close. The larger the sheath size, the greater the risk that the AVF will not spontaneously seal and close.
ETIOLOGY AND INCIDENCE — In the lower extremity, AVF is most commonly iatrogenic, primarily due to arterial access in the groin for percutaneous cardiovascular procedures. Although less common, iatrogenic AVF can result from endoluminal manipulation. Devices that have led to AVF include endovenous laser for saphenous ablation [8], percutaneous directional atherectomy [9], and devices used for re-entry during subintimal angioplasty [10]. Penetrating trauma can cause AVF anywhere in the extremity depending upon the trajectory of the projectile. AVF may be due to central venous access procedures, but this is less common than with arterial intended punctures.
Percutaneous groin access — The incidence of AVF following percutaneous groin access varies from 0.006 to 0.88 percent [2,3,11-13]. The incidence, similar to iatrogenic femoral pseudoaneurysms, is affected by the intensity of imaging to look for asymptomatic findings. Puncture below the common femoral artery is the main culprit of post-catheterization AVFs [2,14]. The incidence is higher in therapeutic compared with diagnostic catheterization (0.87 versus 0.15 percent in one report) [5,7]. The presence of one or more risk factors increases the potential that combined artery and venous puncture will result in a clinically important AVF. (See 'Risk factors' above.)
Following any cardiovascular intervention, the puncture site should be carefully evaluated, and a complete lower extremity vascular examination should assess for adequacy of the pulses; ideally, the pulses are compared with the pre-interventional vascular examination. Any findings suggestive of a vascular complication warrant further investigation. (See 'Clinical features and diagnosis' below.)
Although the use of arterial closure devices may reduce the rates for femoral pseudoaneurysm, rates for AVF have not changed [15]. Hemorrhagic complications of cardiovascular intervention are discussed elsewhere [2-4,16]. (See "Complications of diagnostic cardiac catheterization".)
Trauma — AVFs may also result from penetrating injury to the lower extremity, including stab wounds, gunshot, and shotgun injuries, and surgical trauma [17-25]. Although there are no large epidemiologic studies on the prevalence of traumatic AVFs, the incidence may be rising due to the increasing number of firearm injuries over the last 30 years. (See "Severe lower extremity injury in the adult patient".)
CLINICAL FEATURES AND DIAGNOSIS
History and physical — Following combined artery and vein puncture, almost all AVFs are initially clinically silent. When symptoms occur, the time of onset ranges from two days to several months [26]. Symptoms suggestive of AVF include abnormal sensation (eg, vibration) in the groin, fatigue, and new-onset or worsened lower extremity ischemia symptoms. Long-standing AVFs can cause limb edema, aneurysmal degeneration of the artery, or high-output cardiac failure [11,26-29].
Clinical conditions that are related to lower extremity AVF include deep venous thrombosis, symptoms of nerve compression, and new-onset or worsened varicose veins [5,11,30]. The diagnosis of these conditions is discussed in separate topic reviews. (See "Clinical presentation and diagnosis of the nonpregnant adult with suspected deep vein thrombosis of the lower extremity" and "Clinical manifestations of lower extremity chronic venous disease", section on 'Varicose veins (C2)'.)
The most significant condition related to AVF is high-output heart failure, which has been estimated to occur after 0.01 to 0.02 percent of cardiac catheterizations [26]. The clinical diagnosis of high-output heart failure is discussed elsewhere. (See "Causes and pathophysiology of high-output heart failure".)
On physical examination, the presence of an AVF is further supported by palpation and auscultation of the affected vessel that demonstrates a bruit, hematoma, or pulsatile mass. The patient may exhibit lower extremity edema [31].
Diagnosis — An AVF may be strongly suspected based upon clinical examination; however, it requires vascular imaging for confirmation, typically using duplex ultrasound.
Patients with known peripheral artery disease (PAD), or those with new-onset symptoms of PAD, should also be evaluated with physiologic vascular studies to evaluate the hemodynamic impact of the AVF on the distal lower extremity circulation.
Duplex ultrasound — Duplex ultrasound is the diagnostic test of choice for evaluating patients with suspected AVFs.
Doppler waveform analysis high-frequency, low-resistance flow with continuous flow and elevated diastolic velocities through the pulse cycle is typical of AVFs. A mosaic color pattern on duplex is also typical (image 1). Often the specific artery and vein involved can be identified. Duplex ultrasonography also provides a potential means of treatment. (See 'Ultrasound-guided compression' below.)
Other vascular imaging — Although not considered a first-line diagnostic modality, computed tomographic (CT) or magnetic resonance (MR) angiography may demonstrate an AVF [32]. These studies may have been performed following trauma or to evaluate lower extremity symptoms for an unrelated reason [33].
Conventional catheter-based arteriography provides a diagnostic modality with potential for catheter-based treatment in select symptomatic patients. On arteriography, the AVF appears as a blush with rapid opacification of the adjacent deep vein. (See 'Endovascular repair' below.)
MANAGEMENT
Observation — The majority of small asymptomatic AVFs will spontaneously close with observation alone. In a study of 81 lower extremity AVFs, 57 patients who did not require immediate surgical repair were followed conservatively. Of these, 46 (81 percent) had spontaneous resolution of the AVF at a mean of 23 days. The remaining 11 elected for surgical closure at a mean of four months [30]. Treatment is indicated for the reasons listed below [12,30]. (See 'Indications for intervention' below.)
For patients who are being observed for iatrogenic AVF, a follow-up ultrasound study is obtained after approximately one month to evaluate for spontaneous closure. (See 'Duplex ultrasound' above.)
Indications for intervention — Repair of AVF is indicated for patients with:
●Clinical symptoms related to the AVF including:
•Arterial steal from significant diversion of blood into the venous system manifested by claudication or distal limb ischemia
•Significant edema or venous insufficiency due to venous hypertension
•Heart failure in instances of high-flow fistula
●Progressive enlargement under ultrasound surveillance
●Large AVF following stab, gunshot, or other projectile injury
●Iatrogenic AVFs that do not seal spontaneously (generally accepted duration is AVF that persists for greater than one year)
Interventions — Surgical repair of AVF is the traditional approach, but ultrasound-guided compression (UGC) and percutaneous techniques are alternative treatments, if anatomically feasible. Image-guided compressive treatment and percutaneous-based interventions are clearly best suited for patients who may not tolerate even minor bleeding, have a hostile groin (eg, prior surgery), or have a prohibitive risk for anesthesia.
Ultrasound-guided compression — UGC involves image-guided compression with an ultrasound probe by placing the probe directly over the AVF and applying sufficient force to obliterate flow through the fistula without unduly reducing distal perfusion. Some protocols include conscious sedation secondary to the tenderness of groin examination and manipulation. The duration of compression is usually approximately 10 minutes.
Failure of UGC is frequent and is because the fistula track is too short or the AV fistula is too large to be compressed effectively by the transducer. In the post-catheterization period, the groin is also often too tender to allow sufficient compression, and if the procedure becomes too painful, it should be abandoned. In observational studies of UGC, up to one third of patients with AVFs may avoid the need for other forms of treatment [27,31,34,35]. UGC is most successful within the first several weeks from the initial inciting percutaneous catheterization that resulted in AVF. Chronic AVFs (>2 to 3 weeks) rarely respond to compression. Ongoing anticoagulation also decreases success rates of UGC therapy [28,36].
Concomitant pseudoaneurysm (PSA) can occur, and the presence of the AVF has typically been considered a contraindication to duplex-guided thrombin injection to obliterate the PSA in such instances. However, limited experience has been reported and contradicts this classical thinking. In a series that included 40 combined AVF/PSA, the rate of successful combined closure was 70 percent [37]. Low end diastolic velocity (<25 cm/sec) was suggested as a predictor of safe closure by thrombin injection. (See "Femoral artery pseudoaneurysm following percutaneous intervention", section on 'Ultrasound-guided techniques'.)
Surgery — Surgery for AVF that is not associated with hematoma or pseudoaneurysm is relatively straightforward. The procedure can be performed under general or neuraxial anesthesia or peripheral nerve block depending upon patient and surgeon preference and underlying anesthetic risk. Just prior to the procedure, duplex ultrasound should be performed to confirm that the AVF is still patent and to mark its position on the skin. In some cases, the AVF may be difficult to identify [7,38]. Under this circumstance, intraoperative duplex ultrasound may help identify the fistula and its origin.
In general, an incision is made overlying the site of the fistula as identified by duplex ultrasound or other imaging modality. It is important to note that the superficial veins of the skin and subcutaneous tissues are pressurized, and care must be taken to avoid uncontrolled transection. The superficial veins should be taken by two clamps and carefully divided and ligated to minimize the potential for blood loss. The artery and vein proximal to the site are dissected free of the surrounding tissue and vascular control obtained with hemostatic loops. The artery is dissected from proximal to distal until the fistula is identified. The presence of localized inflammation usually identifies the site of the fistula. For acute AVFs, inflammation is typically minimal. During dissection of the fistula, care must be taken to avoid stripping the adventitia from the artery, which weakens the arterial wall and complicates the repair. Before the AVF is closed, the involved vein is under excess pressure and is easily damaged.
Once the arteriovenous connection is divided, direct pressure is usually all that is needed to control bleeding from the venous wall defect. The arterial wall defect can be controlled with pressure, or arterial hemostatic loops or clamps. Each defect is sutured closed with nonabsorbable, vascular suture (eg, Prolene). Generally, a single stitch in each is needed. Once the repair is completed, control on the artery is released and the pulse distal to the repair site evaluated with a Doppler.
Complications of surgical AVF repair include intraoperative blood loss owing to venous hypertension and groin infection.
Endovascular repair — Percutaneous interventions, including covered stent placement or embolization techniques, may be effective as an alternative to surgical repair. Endovascular repair can be used in those patients deemed high risk or who may not tolerate the consequences of bleeding that may occur with surgical control of the AVF, and for those with a hostile groin (eg, prior surgery) due to excessive scar tissue. However, these endovascular repairs also require arterial puncture, which could lead to a similar complication in the contralateral groin.
The ability to use a covered stent depends upon the location of the fistula, the presence of underlying peripheral artery disease, and the overall medical status of the patient. The common femoral artery is a less suitable location for a stent due to the potential for stent deformation and fracture from hip flexion and rotation. Placement of short covered femoral artery stents appears to have adequate mid-term patency. However, stent placement at this location may preclude the use of the site for future femoral access. In addition, if the stent is placed into either the deep femoral or femoral artery, arterial compromise may result. Iatrogenic AVF that originates from the proximal femoral just distal to the bifurcation of the common femoral artery or deep femoral artery (profunda femoris) may be more amenable to covered stent placement because these sites are less likely to be mechanically distorted; however, because the deep femoral vessels are smaller in caliber, it may be at risk for thrombosis. Reported patency rates for covered stent placement of AVF range between 88 and 100 percent at follow-up (eight months to one year) [34,38-40].
Although long-term follow-up is limited, percutaneous coil or N-butyl-cyanoacrylate embolization are alternative endovascular treatment approaches, provided the connecting channel of the AVF can be appropriately imaged and is of sufficient length, which in some series has been very uncommon [34,41].
OUTCOMES — The prognosis for AVF following repair is excellent. Physiologic derangements reverse immediately after the fistula is closed. In one report, the mean cardiac output decreased from 12.2 L/min to 5.4 L/min after surgical repair [42]. For patients with underlying peripheral artery disease, arterial flow to the lower extremity following fistula repair can be expected to increase, returning the patient to their baseline functional status.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Percutaneous coronary intervention".)
SUMMARY AND RECOMMENDATIONS
●Arteriovenous fistula – Arteriovenous fistulas (AVFs) are abnormal connections between the arterial and venous system. They may be congenital or acquired, may be single or multiple, and can affect any organ in the body but are commonly found in the extremities. (See 'Anatomy and pathophysiology' above.)
●Etiology – The most common etiology of lower extremity AVF is iatrogenic, primarily the result of percutaneous cardiovascular diagnostic procedures or interventions. AVFs may also result from surgical intervention or penetrating lower extremity traumatic injury, the prevalence of which may be rising due to the increasing number of firearm injuries. (See 'Risk factors' above and 'Etiology and incidence' above.)
●Clinical features – Symptoms suggestive of AVF include fatigue, new-onset or worsened lower extremity ischemia, or abnormal sensation (eg, vibration, thrill) in the groin. Clinical signs include a machinery-like murmur or bruit in the groin, hematoma, pulsatile mass, lower extremity edema, deep vein thrombosis, or new-onset high-output cardiac failure. (See 'History and physical' above.)
●Diagnosis – Duplex ultrasonography is indicated in any patient with signs and symptoms suspicious for AVF. High-frequency, low-resistance flow and a mosaic color pattern are typical duplex findings of AVFs. Often, the specific artery and vein involved can be identified. On arteriography, the AVF demonstrates rapid filling of the adjacent deep vein. For patients with symptoms of lower extremity ischemia, physiologic studies (eg, ankle-brachial index) should be obtained. (See 'Diagnosis' above.)
●Management – For patients with asymptomatic iatrogenic AVF, we suggest initial observation with interval duplex ultrasound (Grade 2C). (See 'Observation' above.)
•For AVF that becomes symptomatic or persists beyond three weeks, image-guided therapy (ie, ultrasound-guided compression) can be tried, but treatment should be abandoned if pain during the procedure cannot be controlled with moderate sedation techniques. An ultrasound probe is placed over the AVF to provide compression with a sufficient force to abolish flow through the fistula without unduly reducing distal perfusion. With ultrasound-guided compression, up to one third of patients may avoid the need for other forms of treatment. (See 'Ultrasound-guided compression' above.)
•For symptomatic patients with AVFs that do not respond to ultrasound-guided compression, we recommend surgical repair (Grade 1B). Endovascular repair with a covered stent or coil embolization are alternative treatments for patients who may not tolerate trivial bleeding, have a hostile groin (eg, prior surgery), or have a prohibitive risk for general anesthesia. (See 'Surgery' above and 'Endovascular repair' above.)
ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Emile R Mohler, III, MD, now deceased, who contributed to an earlier version of this topic review. UpToDate also acknowledges Dr. Mohler's work as our Section Editor for Vascular Medicine.
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