Special causes of lower limb ulcers-arteriovenous fistula

This is the 5237th article of Da Yi Xiao Hu

There is an old patient with lower limb ulcer in the outpatient clinic. He came to our wound clinic many years ago and his wound healed through dressing change. Subsequent evaluation considered it to be a venous ulcer. After checking ABI, the patient was advised to wear elastic stockings. Recently, the patient was admitted to the interventional department because of repeated lower limb ulcers. After hospitalization, the CTA results of the lower limb arteries showed atherosclerosis of both lower limb arteries, mild premature veins of both lower limbs, and local varicose veins. It turned out that the patient had a lower limb ulcer caused by arteriovenous fistula.

So what is an arteriovenous fistula? We know that the blood vessels of the human body are divided into arteries, veins and capillaries. Arterial blood rich in oxygen and various nutrients is transported from the heart along the arteries to various organs and tissues throughout the body; while venous blood carrying carbon dioxide and metabolites is transported back to the heart by the veins. Capillaries connect arteries and veins. Capillaries can connect venules and arterioles. The main function of capillaries is to supply nutrients and excrete metabolites. There is no channel between arteries and veins. When there is an abnormal channel between arteries and veins, it is called an arteriovenous fistula.

Arteriovenous fistulas are divided into congenital and acquired. They can occur in any part of the body, but are most common in the limbs. Congenital arteriovenous fistulas often involve countless small arteries and venous branches, so the fistulas are multiple. Acquired arterial fistulas can occur in large, medium, and small arteries and veins. Fistulas are generally single. Due to the abnormal channels between arteries and veins, the blood in the arteries is shunted, which can produce varying degrees of systemic and local hemodynamic changes.

What are the clinical manifestations of arteriovenous fistula?

Continuous vascular murmurs occur locally: When blood flows through the fistula, murmurs may be produced, which are usually loudest at or near the fistula, such as "machine rolling murmurs" or systolic murmurs. Fistulas with murmurs may be palpable near them, and this feature is often the basis for diagnosis. Arteriovenous fistula diseases often have pressure changes. The venous pressure at the proximal end of the fistula may be very low, which is due to low outflow resistance and good adaptability of the venous wall to its blood flow. At the distal end of the fistula, due to the impact of arterial pressure, the venous lumen expands, the venous wall thickens, and the venous pressure also increases greatly. Due to the influence of blood flow and pressure, the arteries and veins around the fistula expand and twist, and the vascular wall becomes thinner. In the late stage, degenerative changes in the vascular wall and aneurysmal expansion may occur. The closer the fistula is to the heart, the more obvious the changes in its vascular wall. The lumen of the artery and vein can expand by more than 2-3 times. Due to the influence of blood flow and blood pressure, the venous pressure near the fistula increases significantly, and venous pulsation may occur.

Congenital arteriovenous fistulas can occur in any part of the body, but are common in the limbs, with the lower limbs being the most common, especially the ankles. Venous valve insufficiency: high-pressure blood flow in the arteries flows through the fistulas to the veins, increasing the intravenous pressure, dilating the venous cavity, damaging the venous valves, and causing venous blood to flow backwards, resulting in superficial venous tortuosity, stasis, pigmentation, eczema, infection, and stagnant ulcers. Insufficient arterial blood supply: arterial blood in the affected limb is diverted to the veins, and the distal artery blood flow at the fistula is low. Due to insufficient blood supply to the tissues, muscle atrophy and cold finger (toe) tips occur, and the distal skin temperature is low. Insufficient blood supply to the finger (toe) tips leads to ulcers or gangrene.

So what tests can we use to diagnose arteriovenous fistula?

1. Peripheral venous pressure measurement and blood oxygen analysis

When arteriovenous fistula occurs, venous pressure increases and the oxygen content in the veins increases.

2. Color Doppler Ultrasound Examination

It can reveal arterial blood shunting and whether there is a systolic or diastolic murmur.

3. Arteriography

Rapid continuous filming can be used to show the location of the fistula and the extent of the lesion. In the case of arteriovenous fistula, the proximal artery may be dilated and twisted. The corresponding vein may be developed early. There may also be hemangioma-like dilation and the arteriovenous branches may be developed in a massed manner.

So once the diagnosis is clear, how should it be treated?

For localized congenital arteriovenous fistulas that affect the function of the limbs, surgical resection can be considered, which has a good effect. However, most congenital arteriovenous fistulas are complicated and difficult to treat because the communicating branches between the arteries and veins are numerous and small, and the lesions are extensive, sometimes involving the entire limb. If the resection is not thorough, not only can the lesions recur, but it may also stimulate the further development of the lesions. Whether to use surgical treatment requires careful consideration.

Indications for surgery

Rapidly growing arteriovenous fistulas accompanied by obvious clinical symptoms should require early surgery; lesions involving surrounding tissues, such as nerve compression pain, bleeding, ulcers or concurrent infections, and even affecting the heart and causing heart failure; visceral arteriovenous fistulas, hepatic and gastrointestinal arteriovenous fistulas causing bleeding, or intrapulmonary arteriovenous fistulas causing cyanosis and shortness of breath, should all require early surgery.

Surgical method

Depending on the type of lesion, different options can be selected, such as embolization therapy, arteriovenous fistula resection, ligation of the main arteriovenous branches of the arteriovenous fistula, and amputation.

During the operation, our interventional doctors used ultrasound positioning, directly injected sclerosant and radiofrequency ablation, and blocked the fistula from the venous end after sclerosing. Since the venous blockage was effective, no embolization was performed from the arterial end. Because long-term high venous pressure leads to the destruction of venous valve function, elastic stockings are still necessary to prevent ulcers from recurring after surgery.

Author: Ostomy Wound Clinic, Shanghai Eighth People's Hospital

Liu Lifang, deputy chief nurse