An arteriovenous fistula is an abnormal connection or passageway between an

artery An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

and a

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...

. It may be congenital, surgically created for

hemodialysis Hemodialysis, also spelled haemodialysis, or simply dialysis, is a process of purifying the blood of a person whose kidneys are not working normally. This type of dialysis achieves the extracorporeal removal of waste products such as creatinin ...

treatments, or acquired due to

pathologic ''Pathologic'' ( rus, Мор. Утопия, Mor. Utopiya, ˈmor ʊˈtopʲɪjə, , More. Utopia – a pun on Thomas More's ''Utopia'' and the Russian word for "plague") is a 2005 role-playing and survival game developed by Russian studio Ice-Pic ...

process, such as

trauma Trauma most often refers to: * Major trauma, in physical medicine, severe physical injury caused by an external source * Psychological trauma, a type of damage to the psyche that occurs as a result of a severely distressing event *Traumatic i ...

or erosion of an arterial

aneurysm An aneurysm is an outward bulging, likened to a bubble or balloon, caused by a localized, abnormal, weak spot on a blood vessel wall. Aneurysms may be a result of a hereditary condition or an acquired disease. Aneurysms can also be a nidus ( ...

Clinical features

Pathological

Hereditary hemorrhagic telangiectasia Hereditary hemorrhagic telangiectasia (HHT), also known as Osler–Weber–Rendu disease and Osler–Weber–Rendu syndrome, is a rare autosomal dominant genetic disorder that leads to abnormal blood vessel formation in the skin, mucous membranes, ...

is a condition where there is direct connection between arterioles and venules without intervening capillary beds, at the mucocutaneous region and internal bodily organs. Those who are affected by this conditions usually do not experience any symptoms. Difficulty in breathing is the most common symptom for those who experience symptoms. Just like berry aneurysm, a

cerebral arteriovenous malformation A cerebral arteriovenous malformation (cerebral AVM, CAVM, cAVM) is an abnormal connection between the arteries and veins in the brain—specifically, an arteriovenous malformation in the cerebrum. Signs and symptoms The most frequently observed ...

can rupture causing subarachnoid hemorrhage.

Causes

The cause of this condition include * Congenital (developmental defect) * Rupture of arterial

into an adjacent vein * Penetrating injuries * Inflammatory necrosis of adjacent vessels * Complication of

catheter In medicine, a catheter (/ˈkæθətər/) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgi ...

insertion rarely causes arteriovenous fistula. It is usually caused by brachial artery puncture because brachial artery is located between two

brachial veins In human anatomy, the brachial veins are venae comitantes of the brachial artery in the arm proper. Because they are deep to muscle, they are considered deep veins. Their course is that of the brachial artery (in reverse): they begin where r ...

. Surgically created Cimino fistula is used as a vascular access for hemodialysis. Blood must be aspirated from the body of the patient, and since arteries are not easy to reach compared to the veins, blood may be aspirated from veins. The problem is that the walls of the veins are thin compared to those of the arteries. The AV fistula is the solution for this problem because, after 4–6 weeks, the walls of the veins become thicker due to the high arterial pressure. Thus, this vein can now tolerate needles during hemodialysis sessions.

Mechanism

When an arteriovenous fistula is formed involving a major artery like the abdominal aorta, it can lead to a large decrease in

peripheral resistance Vascular resistance is the resistance that must be overcome to push blood through the circulatory system and create flow. The resistance offered by the systemic circulation is known as the systemic vascular resistance (SVR) or may sometimes be cal ...

. This lowered peripheral resistance causes the heart to increase cardiac output to maintain proper blood flow to all tissues. The physical manifestations of this typically consist of a relatively normal systolic blood pressure accompanied by decreased diastolic blood pressure, resulting in a wider

pulse pressure Pulse pressure is the difference between systolic and diastolic blood pressure. It is measured in millimeters of mercury (mmHg). It represents the force that the heart generates each time it contracts. Resting blood pressure is normally appro ...

. Normal blood flow in the brachial artery is 85 to 110 milliliters per minute (mL/min). After the creation of a fistula, the blood flow increases to 400–500 mL/min immediately, and 700–1,000 mL/min within 1 month. A brachiocephalic fistula above the elbow has a greater flow rate than a radiocephalic fistula at the wrist. Both the artery and the vein dilate and elongate in response to the greater blood flow and shear stress, but the vein dilates more and becomes "arterialized". In one study, the

cephalic vein In human anatomy, the cephalic vein is a superficial vein in the arm. It originates from the radial end of the dorsal venous network of hand, and ascends along the radial (lateral) side of the arm before emptying into the axillary vein. At the e ...

increased from 2.3 mm to 6.3 mm diameter after 2 months. When the vein is large enough to allow

cannulation A cannula (; Latin meaning 'little reed'; plural or ) is a tube that can be inserted into the body, often for the delivery or removal of fluid or for the gathering of samples. In simple terms, a cannula can surround the inner or outer surfaces ...

, the fistula is defined as "mature".Vascular, Vol. 14, Supl. 1, Nov. 2006, p. S1 An arteriovenous fistula can increase preload. AV shunts also decrease the afterload of the heart. This is because the blood bypasses the arterioles which results in a decrease in the total peripheral resistance (TPR). AV shunts increase both the rate and volume of blood returning to the heart.

Diagnosis

The diagnosis of this condition can be done via ultrasound

References

External links

{{Vascular diseases Diseases of arteries, arterioles and capillaries Cutaneous congenital anomalies Fistulas Nephrology procedures