What is Arteriovenous Fistula (AV Fistula)?
An arteriovenous fistula (AVF) is an abnormal link between an artery and a vein. They can be called arteriovenous malformations in some cases. An AVF can develop anywhere in the body, depending on the source. They are of two types: naturally occurring or acquired. The acquired ones are additionally divided into those created surgically for purposes like dialysis, or those originating from an injury or medical procedure.
The location of the fistula in the body will dictate its structure. When created for dialysis purposes, AVFs are most commonly formed in the limbs, preferably the upper limbs. For their surgical creation, the cephalic and basilic veins are often used. The radial artery in the wrist or the brachial artery in the elbow/upper arm are typical locations for fistula creation. The preferred first choice for dialysis access would be a fistula between the radial artery and cephalic vein.
There are two types of surgical AVFs in the lower limb for dialysis described in medical resources. In one, a vein in the thigh or behind the knee is joined with an artery in the thigh. In the other, the saphenous vein could form a loop on the front thigh and join with the main artery in the groin.
While congenital AV fistulas are not common, they have been reported in the lungs, lower spine, the coverings of the brain, areas around the neck, heart, and liver. Some children are even born with these abnormal connections between the arteries and veins in the neck.
Some AVFs result from injuries during surgeries, placement of invasive lines, or needle biopsy. Reports show several instances of such injuries surfacing years after the surgical procedures. Traumatic AVFs can appear wherever an injury has happened and these too can show up quite late. More than half of them occur in the lower limbs, with about 33% found in the thigh vessels, and 15% in the vessels behind the knee.
What Causes Arteriovenous Fistula (AV Fistula)?
Arteriovenous fistulas, which are abnormal connections between arteries and veins, can happen in several ways. They can be done on purpose in surgery for things like dialysis, occur naturally due to a genetic condition, or caused by injury or medical treatment. Healing from certain types of injuries can sometimes cause arteries and veins to heal together, bypassing the smaller blood vessels downstream.
Because of medical procedures, the most commonly seen arteriovenous fistulas are those that happen due to heart catheterization when needles access both the femoral vein and artery. However, they can also occur in the neck areas due to the placement of central lines. Another common type of fistula due to medical procedures is kidney fistulas. They usually happen because of biopsy procedures but luckily, most are temporary and very few require extra treatment.
Fistulas caused by injury are usually associated with direct damage to an artery and with serious bone fractures near arteries and veins. Ninety percent of the time, these fistulas are due to penetrating injuries like gunshot wounds. Minor neck fistulas can happen due to neck overstretching injury or spine surgery. Fistulas that connect the carotid artery and the cavernous sinus, usually due to trauma, can be life-threatening and are often linked with skull base fractures, penetrating trauma to that area, and burst aneurysms. Two-thirds of these types of arteriovenous fistulas are found within one week of the damage occurring, although some can appear weeks or even years later.
Congenital fistulas, those that people are born with, aren’t fully understood yet. Congenital arteriovenous fistulas in the brain can be found in the outer layers (dura) or where the carotid artery and cavernous sinus connect. Neck fistulas are mainly due to injury. However, fibromuscular dysplasia, neurofibromatosis, and other collagen disorders are linked to them. Pulmonary vascular malformations are usually simple and are more similar to arteriovenous fistulas than to malformations. Other types of arteriovenous fistulas are very uncommon.
Risk Factors and Frequency for Arteriovenous Fistula (AV Fistula)
The concept of arteriovenous fistulas (AVFs), abnormal connections between arteries and veins, has been known since 1757. Much of what we know about AVFs comes from cases resulting from injuries during the Second World War, the Korean War, and the Vietnam War. For instance, there were 215 cases reported from the Korean War alone.
In non-military populations, AVFs caused by trauma to the abdomen or limbs are quite evenly balanced. However, within the military, most AVFs happen to the limbs. This is likely because of the protective body armor soldiers wear. It’s important to remember that AVFs caused by injuries are more common than ones present at birth, which are usually rare and discussed in small, specific studies.
- Understanding of AVFs largely comes from war injuries.
- 215 cases of AVFs were reported as a result of the Korean War.
- In the general population, traumatic AVFs in the abdomen and limbs occur equally.
- In the military, traumatic AVFs typically happen in the limbs due to the use of body armor.
- AVFs caused by injuries are more common than congenital (present from birth) AVFs.
According to 2013 figures from the National Institute of Diabetes and Digestive and Kidney Diseases, over 468,000 patients were receiving hemodialysis – a treatment for impaired kidney function. Twenty percent of these patients were receiving their treatment via a surgically created AVF. This study found that the use of AVFs was less common among females, black people, those who are obese or elderly, and those with peripheral arterial disease. The rate of creating AVFs also differs regionally, being most frequent in the Northeast United States, and least frequent in the Southwest.
- By 2013, over 468,000 patients were on hemodialysis, with 20% of them using a surgically created AVF.
- AVF use was least common among females, black individuals, obese or elderly people, and those with peripheral arterial disease.
- The rate of surgically creating AVFs differs regionally in the United States, being highest in the Northeast and lowest in the Southwest.
Signs and Symptoms of Arteriovenous Fistula (AV Fistula)
An arteriovenous fistula, or AVF, occurs when an artery and a vein are directly connected, disrupting normal blood flow. The symptoms of an AVF can be different based on where it is and what caused it. Many AVFs are created intentionally for patients requiring hemodialysis (a procedure to clean the blood when the kidneys can’t). These patients have a surgical incision on the wrist, forearm, or upper arm. A functioning AVF can be recognized as a palpable thrill or continuous sound, called a bruit. Sometimes, if the blood flow out of the AVF is blocked, the patient may have a pulsing fistula or bleeding from a hemodialysis puncture site.
Regardless of where they are or how they happened, AVFs in the arms or legs can cause signs of venous hypertension, which means the veins are under too much pressure. This can cause varicose veins, pain, and swelling. If an AVF has been there for a long time, one limb might be noticeably bigger than the other. If a patient has had a trauma or injury, especially with fractures or ongoing neurologic deficits, an AVF could be suspected even if their exam seems normal.
Some people are born with AVFs but don’t show symptoms until later in life. The location of these kinds of congenital fistulas will affect their symptoms. Some may start as low-flow and turn into high-flow lesions in adulthood. People with AVFs in the brain can have headaches, neurologic problems, seizures, or a mix. There can also be a risk of bleeding or lack of blood to the brain tissue around the AVF.
Severe or long-term fistulas can result in high output cardiac failure. This means their heart can’t pump enough blood to meet the body’s needs. Oxygenated blood gets shunted back to the right side of the heart instead of going to the body. This forces the heart to pump more blood, leading to heart failure. A specific sign of this condition is the Nicoladoni-Israel-Branham sign – a slowing heart rate when the fistula is compressed.
AVFs on the skin can show up as a pink stain, a mass, bulging veins, unequal limb size, or skin ulceration. They may cause a heavy feeling in the limb, that gets worse with hanging down and better with raising it. The painful sensation could be because of a lack of blood supply to tissues or compression on surrounding nerves.
Physical exam could reveal a larger limb size, swelling, discoloration, or prominent vessels with a murmur or palpable thrill. The fistula may also show as a pulsatile lesion. Additionally, the skin over the lesion could be excessively sweaty, warm, or hairy. It could also make a noise when listened to with a stethoscope. If the mass effect impairs the function of limbs and joints, or if a lesion causes tissue death from prolonged lack of blood supply, it can show up as an impaired function of limbs and joints.
Internal fistulas can cause blood in vomit, urine, or stool. Sometimes, these patients may present with symptoms of heart failure, especially when the fistula is between a major artery and vein.
Testing for Arteriovenous Fistula (AV Fistula)
Duplex ultrasound (US) is a cheap and non-invasive way to confirm the diagnosis of Arteriovenous Fistula (AVF), especially when it is close to the skin surface. This type of ultrasound can illustrate how the blood is flowing through the artery and veins, showing low resistance in the feeding artery and high-velocity, turbulent flow at the point of anastomosis, or where the artery and vein are joined. It can also display any possible anomalies like a pseudoaneurysm, a venous aneurysm, or a dilated feeding artery.
In addition to the ultrasound, Computed Tomography Angiography (CTA) and Magnetic Resonance Angiography (MRA) can also provide useful information. They do this by showcasing early contrast filling during the arterial phase in the involved vein. CTA is often more preferred due to its accessibility and reliability, even if it is non-invasive. It is also a common choice for initial diagnostic tests. The downsides of CTA include interference from metal objects, motion artifacts, and reliance on contrast timing.
Selective angiography is also a diagnostic method but is more invasive. It is the gold standard – meaning, it is the most reliable test – as it can precisely indicate where the artery and vein communication is, the surrounding vascular anatomy, and how blood flow is moving. However, it is a costly method and requires a specialized team to perform it.
Lastly, the placement of an AVF requires evaluation, especially with end-stage renal disease patients who need vascular access. The preference is usually for the upper extremity, and more so for non-dominant hands and forearms. Again, a duplex ultrasound scan is the go-to evaluation method. Blood gas analysis can also add to the assessment by showing oxygen content in the venous side of the blood and platelet count. Large AVFs, however, might show decreased platelet count due to consistent turbulence and platelet trapping.
In conclusion, whether it is identifying anomalies, diagnosis, or placement of AVF, a duplex ultrasound scan is the primary non-invasive, economic method supported by other imaging techniques, or in some cases, blood analysis.
Treatment Options for Arteriovenous Fistula (AV Fistula)
In the past, arteriovenous fistulas were often managed conservatively during wartimes and then achieved surgical treatment if necessary. Now, early intervention is preferred. Here, the goal is to treat the fistula, a channel between an artery and a vein, in such a way that essential blood flow is maintained. Various methods can be employed to achieve this goal, including direct repair, bypass or grafting, or a less invasive procedure known as endovascular repair.
The decision to move forward with treatment can depend on a number of factors:
– In cases where a fistula leads to unstable blood circulation or where other methods of treatment have not been successful, the surgical team may opt for an open surgery.
– Fistulas resulting from trauma usually warrant repair if they don’t naturally disappear in a couple of weeks.
– Congenital fistulas, those present from birth, are usually corrected when they start causing problems in later life.
– Fistulas created for dialysis that have stopped working, are no longer necessary, or have failed to develop properly may need to be closed off.
– Symptoms such as bleeding, pain, heart trouble due to fistulas, limb size differences, non-healing ulcers, and functional impairment all might indicate the need for surgical remedy.
Endovascular management, a less invasive procedure that involves inserting a stent to treat the fistula, is often the preferred method of management. This method appeals to both patients and doctors because of its several advantages – less pain and disability after-operations, as well as speedy recovery. Different materials can be used to close off the fistula, and stents can be used to isolate the fistula while maintaining vital blood vessels. However, complications can arise, including damage to arteries, misplacement of devices, or clot formation leading to blockage of blood vessels.
When the endovascular approach is not suitable, open surgery remains a valuable option. It’s usually considered when less invasive methods have failed. The drawbacks of this method include the potential risks of more bleeding, various post-surgery complications such as clot formation in veins, and difficulty of controlling blood flow in the operated leg. The surgery might involve grafting and the use of natural or synthetic materials, but its success depends on various factors, and it may not work in every case.
If no symptoms or complications arise or the fistula is likely to resolve on its own, doctors may opt for conservative management, which involves monitoring the condition without immediate surgical intervention.
What else can Arteriovenous Fistula (AV Fistula) be?
When trying to identify the cause of conditions leading to an increased blood flow in the body, like rapid heartbeat, high heart performance, and lowered resistance in the blood vessels, certain diseases could be considered.
- Arteriovenous malformation: This is a birth defect which comes from the abnormal development of blood vessels in a fetus. When these malformations are complex or have increased blood flow, they might display more resistance, almost like small blood vessels, and hence, could show no symptoms. Tests like computed tomography angiography (CTA) or magnetic resonance angiography (MRA) can discern between arteriovenous malformations and arteriovenous fistulas.
- Hemangioma: These are blood vessel tumors and could show symptoms similar to arteriovenous fistulas; however, they usually manifest with clear signs of bleeding. Hemangiomas can grow quite rapidly. Like arteriovenous malformations, CTA or MRA can rule these out.
- Pseudoaneurysm: These usually appear as a throbbing lump, often linked with a procedure involving vascular access. They, along with true aneurysms, may create noticeable thrills because of significant turbulence in the area. Doppler ultrasound can distinguish these from a fistula.
- Malignancy: Cancerous lumps can need a lot of blood flow and could be noticed as a pulsing lump if they’re near a bigger blood vessel. Doppler ultrasound and various scanning techniques can help pinpoint these.
- Cyst/Abscess/Hematoma: These are generally identified as simple, low-density lesions on the duplex ultrasound and typically don’t show blood flow.
What to expect with Arteriovenous Fistula (AV Fistula)
While some inborn abnormalities of blood vessels (known as congenital arteriovenous fistulas) can result in a person not surviving, usually, the overall outlook is favorable. Peripheral arteriovenous fistula, a type of this condition, generally doesn’t cause wider problems to the body’s blood flow, and this is true for about 15% of all such cases.
The Schobinger Classification is a system used to predict the success of treatment. Stage 1 involves little noticeable change other than blush and warmth on the skin where the fistula is. The second stage, referred to as expansion, may exhibit darkened skin, a throbbing spot with a whooshing sound or vibration on examination. In stage 3 or the destruction phase, skin changes, ulcers, and reduced blood flow to the ends of the body are observed. This essentially siphons off blood flow from rightful places. The final stage, Stage 4, is indicated by severe heart failure due to the excessive effort to pump blood. However, the intensity of the heart failure can be fully reversed by closing the high-flow fistula, implying better prognosis for patients who are diagnosed and treated earlier.
Quick diagnosis is key for a good outcome. In regards to spinal dural AVFs, a specific variant of arteriovenous fistulas, Brinjikji and colleagues found that these tend to be frequently overlooked or misdiagnosed in imaging studies. They noticed that a delay in properly diagnosing these cases can lead to additional permanent disability, which often can’t be corrected through surgery or other treatments.
Possible Complications When Diagnosed with Arteriovenous Fistula (AV Fistula)
Chronic venous insufficiency, also known as venous hypertension, can show up as swelling of the affected limb that tends to get worse over time and may limit movement. This issue happens when the arterial pressure becomes too much for the thin venous walls to handle, and the one-way valves in the veins stop working. Symptoms of this problem can include changes in skin color, varicose veins, and ulcers.
There’s also something called high cardiac output failure. This was found in about 23% of 120 heart failure patients in a study, most of whom had some sort of AV shunt, including congenital, traumatic, and hemodialysis fistulas. The increased stroke volume seen in all patients with high-output heart failure was due to reduced vascular resistance, an issue commonly seen in people with AVFs, especially high-flow ones.
Another potential issue is arterial insufficiency. Here, there is a risk of developing ‘steal syndrome,’ which affects up to 6% of patients with an AVF or arteriovenous graft for hemodialysis. This problem happens when a high-flow fistula causes shortness of blood supply or ‘ischemia. Patients with this condition may experience severe pain, swelling, or indicators of ischemia like cool skin, discolored fingers or toes, diminished pulses, hair loss, or atrophy. It’s a result of blood moving towards the lower resistance fistula instead of supplying blood to the distant tissues. This situation can worsen when the arterial supply has a blockage called ‘stenosis.’
Hemorrhage, or bleeding, is another potential complication but is less common than the ones listed above. This can happen when the high flow through the blood vessels causes them to extend or ‘dilate’ throughout the venous drainage system. These blood vessels can become thin-walled and be at risk for bursting. It can be particularly problematic with hemodialysis fistulas, where the vein and overlying skin can get ulcers. The high flow through the fistula can make it difficult to stop bleeding after dialysis.
Common Issues with AVFs:
- Chronic venous insufficiency or venous hypertension
- High cardiac output failure
- Arterial insufficiency or ‘steal syndrome’
- Hemorrhage or bleeding
Preventing Arteriovenous Fistula (AV Fistula)
For people with severe kidney disease, the creation of an arteriovenous fistula (AVF) may be necessary. However, if you want to prevent the formation of AVFs, the best way is to avoid unnecessary injuries or procedures that could lead to their development. The origin of congenital AVFs, which you are born with, isn’t well understood, so there’s not much we can do in terms of prevention.
If you’re diagnosed with an AVF, or suspect you might have one, you should first visit your primary doctor. After an in-depth assessment, you might be recommended to a specialist for possible AVF treatment. It is crucial to note any symptoms, changes in the body part in question, or significant history, like injuries or procedures in the same area, before any appointment. Even an old injury can cause an AVF later on in your life.
Your doctor may require more lab tests or images, like an ultrasound, a CT scan, or an MRI. During the initial evaluation, your doctor will observe, listen to, and physically check the affected area. Besides answering your questions and discussing your symptoms, your doctor will probably ask additional questions to accurately diagnose the issue.
