| disease | Arteriovenous Fistula |
An abnormal channel exists between the stirred pulse and the vein, known as an arteriovenous fistula. Since the blood from the stirred pulse flows into the accompanying vein through the normal pathway, it can cause local vascular lesions in the fistula, as well as hemodynamic changes in the fistula area, surrounding circulation, and the entire systemic circulation.
bubble_chart Etiology
Disease Cause
(I) Penetrating Injury The majority of acquired arteriovenous fistulas are caused by penetrating injuries, such as various puncture wounds, especially high-speed bullets, iron fragments, and glass shard injuries. At the time of injury, the artery and vein within the same sheath are damaged together. Closed fractures may also cause arteriovenous fistulas when sharp fracture ends or bone fragments pierce adjacent blood vessels. Percutaneous arterial puncture angiography and surgical trauma are the most common causes. The fourth and fifth lumbar intervertebral discs are close to the iliac vessels, and during disc removal surgery, injury to the iliac vessels can lead to iliac arteriovenous fistulas. Generally, the external opening of a penetrating injury is small, and nearby muscles and soft tissues prevent massive bleeding, forming a hematoma in the local soft tissue. After the hematoma organizes, it forms the wall of the arteriovenous fistula.
(II) Crush Injury Simultaneous crushing of parallel arteries and veins can result in arteriovenous fistulas. Iatrogenic injuries, such as splenectomy and nephrectomy with mass ligation of the splenic or renal pedicle; ligation of the femoral artery and vein during amputation; or mass ligation of the superior polar vessels during thyroidectomy, can all lead to arteriovenous fistulas. External blunt force acting on soft tissues, compressing them against bones (e.g., shoulder or buttock contusions), can cause local arteriovenous fistulas. Skull fractures may also result in arteriovenous fistulas in meningeal vessels.
Pathological Changes
The communication between arteries and veins can be direct or indirect. When adjacent arteries and veins are injured simultaneously, the wound edges may align directly, forming a direct arteriovenous fistula within days. If the arterial and venous wounds do not align directly, a hematoma may form between them. Later, as the hematoma organizes, a sac or duct connecting the artery and vein forms, known as an indirect fistula.
The proximal artery progressively dilates and elongates. In the early stages, the arterial wall thickens slightly, but in later stages, degenerative changes occur: smooth muscle fibers atrophy, elastic fibers decrease, the wall thins, and atherosclerotic plaques form. If the fistula is large, the main artery near the fistula may dilate and form an aneurysm. The distal artery shrinks due to reduced blood flow.
The vein gradually dilates, extending distally to the last valve and proximally to the vena cava. If the fistula is large, venous pressure rises sharply, and within weeks, a pulsatile mass may form due to venous dilation, resembling a pseudoaneurysm. For smaller fistulas, the vein gradually dilates at the fistula site, with thickening of the intima and fibrous tissue proliferation. Over time, the venous wall thickens, forming an "artery-like wall." Thus, about six months after injury, it becomes difficult to distinguish between artery and vein by appearance. The venous wall also undergoes degeneration, with fragmentation and loss of the internal elastic layer. Distal veins dilate and elongate, and venous valve incompetence worsens venous insufficiency. Arteriovenous fistulas promote extensive collateral circulation, with venous collaterals often exceeding arterial collaterals, leading to widespread superficial varicose veins.
bubble_chart Clinical Manifestations
Acute arteriovenous fistula may appear immediately after injury or after the dissolution of blood clots blocking the arteriovenous communication. A hematoma is present at the injury site, and most cases exhibit tremor and murmurs. In most patients, the distal limb of the arteriovenous fistula can still palpate a stirred pulse, though weaker than the unaffected side. In cases of superficial femoral stirred pulse injury accompanied by deep femoral stirred pulse injury, the dorsal pedis stirred pulse cannot be palpated, and symptoms of limb ischemia may occur.
Chronic arteriovenous fistula patients experience limb swelling, numbness, pain, and lack of strength. A buzzing sound is audible near the pulsatile mass. Heart failure may present with chest tightness, palpitation, and shortness of breath. Common signs include: (1) Murmur and tremor in the fistula area: Regardless of the fistula’s size, a typical, rough, and continuous rumbling sound—referred to as a "machinery-like" murmur—can be heard at the fistula site. The murmur intensifies during cardiac systole and propagates along the proximal and distal segments of the main vessels. This murmur must be differentiated from the faint diastolic murmur caused by pseudo stirred pulse aneurysm and the systolic murmur caused by stirred pulse stenosis. (2) Increased pulse rate: This results from the Bainbridge reflex triggered by increased venous return of heart blood or from elevated cardiac workload due to decreased mean stirred pulse pressure (Marey’s law). (3) Cardiac enlargement and heart failure: Due to the rapid flow of large volumes of blood through the fistula into the veins, venous pressure rises, increasing cardiac return blood volume and leading to cardiac enlargement. Progressive cardiac enlargement may result in heart failure. The severity of cardiac enlargement and heart failure is closely related to the fistula’s size, location, and duration. Fistulas closer to the heart—such as those involving direct branches of the aortic arch (carotid stirred pulse, innominate stirred pulse, subclavian stirred pulse) and accompanying veins—tend to cause earlier and more severe heart failure. Pate reported that arteriovenous fistulas in direct aortic branches could lead to heart failure as early as six weeks post-injury. Among limb arteriovenous fistulas, nine cases exhibited local pain, ascites, and abdominal pain shortly after surgery. (4) Local temperature elevation: The skin temperature at the fistula site is elevated, while areas farther from the fistula may be normal or lower than normal. (5) Venous insufficiency: Direct arteriovenous communication increases venous pressure. In most patients, superficial veins near or distal to the fistula become dilated and tortuous. Skin pigmentation, accompanied by cellulitis in the lower leg, often leads to ulcers in the toes or fingers, resembling post-deep vein thrombosis symptoms.
﹝Auxiliary Examinations﹞
(1) Stirred pulse angiography: This can determine the fistula’s location, size, proximal vascular dilation, and collateral circulation. For small fistulas, the stirred pulse is visualized, and nearby veins may also appear, but distal veins are rarely seen. For large fistulas, rapid imaging is required to visualize the stirred pulse, while dilated veins near the fistula are prominently displayed. The most dilated area often indicates the fistula site, and distal veins may appear increased in number and tortuous.
(2) Fistula compression test (Branham’s sign): Compressing the fistula to block blood shunting allows measurement and comparison of heart rate and blood pressure before and after occlusion. After blocking the shunt, the heart rate significantly slows. This occurs because fistula closure forces blood flow through normal capillary networks, increasing peripheral resistance. Additionally, the sudden blockade redirects previously shunted blood into the systemic stirred pulse system, raising blood pressure due to increased peripheral resistance and sudden volume expansion. This stimulates the aortic depressor nerve and carotid sinus nerve endings, activating vasomotor inhibition and slowing the pulse rate.
(3) Measurement of mean stirred pulse pressure at the distal end of arteriovenous fistula When the fistula is large and collateral circulation is scarce, the mean stirred pulse pressure drops significantly; when the fistula is small and collateral circulation is abundant, the mean stirred pulse pressure at the distal end of the fistula changes little. Generally, stirred pulse pressure measurement requires direct puncture of the stirred pulse, but Doppler ultrasound and limb plethysmography can also be used to measure the stirred pulse pressure at the distal end of the fistula.
(4) Cardiac Output Measurement Echocardiography and indicator dilution methods can be used to measure cardiac output and assess cardiac function.
(5) Venous Blood Oxygen Measurement Blood is drawn from the venous side of the arteriovenous fistula or from a vein proximal to the fistula, and compared with venous blood from the same site on the contralateral limb. The venous blood on the affected side is redder than that of the normal limb, and the oxygen partial pressure is significantly higher.
(6) Venous Pressure Measurement Venous pressure is elevated in the affected limb. The increase in venous pressure is more pronounced near the fistula.
The diagnosis of arteriovenous fistula is generally not difficult. With a history of penetrating trauma, the patient may notice a pulsatile mass accompanied by a local buzzing sound. The diagnosis of arteriovenous fistula should be considered when there is unilateral limb swelling, varicose veins, venous valve insufficiency, local skin temperature higher than the contralateral side, scars at the injury site, murmurs, and tremor. Patients with acute arteriovenous fistulas often have severe multiple trauma or penetrating injuries in the limbs. During examination, due to the focus on severe bone and soft tissue injuries, the diagnosis and management of arteriovenous fistulas are often delayed.
bubble_chart Treatment Measures
In recent years, due to rapid advancements in vascular surgery, the techniques of vascular suturing and grafting have continuously improved. Once an arteriovenous fistula is definitively diagnosed, early surgical intervention is generally recommended. This approach helps avoid severe hemodynamic changes and complications during the waiting period.
(I) Surgical Treatment of Acute Arteriovenous Fistula Once the diagnosis is confirmed and the patient's general condition permits, early surgery is performed. The wound is thoroughly debrided, and the proximal and distal ends of the injured artery and vein are freed and controlled with plastic bands. Depending on the injury, procedures such as fistula repair, resection of the fistula followed by end-to-end anastomosis of the artery, or autologous great saphenous vein grafting may be performed. During emergency surgery, ligation of a major artery can lead to limb ischemia and necrosis. Lonbean reported that emergency ligation of the common femoral artery proximal to the deep femoral artery resulted in an amputation rate of 80%, while ligation of the superficial femoral artery distal to the deep femoral artery had an amputation rate of 50%. Veins also need to be repaired to restore blood flow, which can reduce limb edema. Early surgery offers many advantages, as there is no fibrous adhesion or collateral circulation around the arteriovenous fistula, making the procedure easier. Additionally, there is no significant difference in the caliber of the proximal and distal vessels, facilitating vascular reconstruction.
(II) Surgical Treatment of Chronic Arteriovenous Fistula
1. Ligation and Closure of Arteriovenous Fistula Closure surgery is an ancient method. For non-major vessels, closure surgery is a safe and effective approach. However, for major vessels (brachial artery, femoral artery, popliteal artery), closure surgery can lead to distal limb ischemia, especially in the lower extremities, resulting in chronic circulatory insufficiency and nutritional disturbances, manifesting as intermittent claudication, ischemic pain, numbness, cold intolerance, edema, ulcers, and muscle atrophy. Therefore, this method is not recommended.
(1) Proximal Artery Ligation (Hunter's Operation): Theoretically, when the resistance of the collateral arteries is not greater than that of the main artery supplying the fistula, proximal artery ligation can reduce peripheral circulation blood flow and pressure while also decreasing arterial perfusion to surrounding tissues. In practice, however, the efficacy of this procedure is unsatisfactory, and it is rarely used today. If the patient's general condition is poor, especially in cases complicated by heart failure where other surgeries are not feasible—such as high-position internal carotid arteriovenous fistulas or deep pelvic arteriovenous fistulas—and the anatomical location makes vascular clamping and suturing difficult, proximal artery ligation may be considered to reduce cardiac return and improve local symptoms.
(2) Quadruple Ligation: Bramann first proposed in 1886 the ligation of all communicating vessels and resection of the arteriovenous fistula. This method was still commonly used before and during World War II. To ensure sufficient collateral circulation, this surgery should be performed at least 3 months after the injury. Various methods have been used to test the adequacy of collateral circulation. The Moscheonitz Congestion Test involves applying a pneumatic tourniquet above the limb with the arteriovenous fistula for 5 minutes, then suddenly releasing it. If the limb's blood flow is immediately restored, with proximal redness spreading distally and reaching the extremity within 2 minutes, collateral circulation is deemed sufficient. Another method is the Henle-Coenen phenomenon: if the distal artery continues to pulsate after complete proximal artery occlusion, collateral circulation is considered adequate. The author suggests that for non-major vessels, such as arteriovenous fistulas in the hands, forearms, feet, or lower legs, with a prolonged course and well-developed collateral circulation, quadruple ligation may be employed. The ligation should be performed as close to the fistula as possible to reduce the risk of recurrence. Postoperatively, distal arterial blood supply can gradually recover through collateral circulation. Arteriovenous fistulas often have accompanying collateral vessels, making simple ligation prone to recurrence. When collateral circulation is abundant, the fistula should be excised after ligation to minimize recurrence.
(3) Obliteration endoaneurysmorrhaphy: In 1888, Matas first applied the technique of obliterative endoaneurysmorrhaphy to treat stirred pulse aneurysms. Later, this method was also successfully used to treat arteriovenous fistulas. Before incising the arteriovenous fistula, a tourniquet should be applied. If a tourniquet cannot be used, the proximal arteries and veins of the arteriovenous fistula must be separately dissected and controlled with plastic bands to manage bleeding. The fistula sac is then incised, and all vascular openings within the sac are sutured.
Hughes and Janhke reported 202 cases with traumatic arteriovenous fistulas and 215 stirred pulse aneurysms. The long-term results of closed surgery were poor in 50% of cases, with postoperative limb pain, cold intolerance, and claudication.
2. Resection of arteriovenous fistula and vascular reconstruction Although Rudolf Matas proposed vascular reconstruction for arteriovenous fistulas as early as 1922, it was not widely applied until after World War II. Surgeons gradually demonstrated that vascular reconstruction was superior to quadruple ligation. During the Korean War, vascular reconstruction became routine. With improvements in angiography and the diagnostic accuracy of vascular diseases, vascular surgical techniques and instruments have advanced significantly. In recent years, acquired arteriovenous fistulas have primarily been treated with fistula resection and arteriovenous reconstruction.
(1) Fistula repair via venotomy: Based on the principles of the Matas procedure, Bickham first used venotomy to repair the fistula opening, maintaining the patency of the stirred pulse lumen. The Matas-Bickham procedure has the advantage of minimal damage to collateral circulation and a simple surgical approach. However, its drawback is that when the stirred pulse wall is severely degenerated, damaged, or structurally unsound, suturing the fistula opening may easily lead to stenosis of the stirred pulse lumen.
(2) Fistula resection with side-to-side suture repair of the stirred pulse and venous openings.
(3) Fistula resection with end-to-end anastomosis of the stirred pulse: If the stirred pulse defect is short and suturing can be performed without tension, an end-to-end anastomosis of the stirred pulse can be performed, with side suturing of the vein.
(4) Fistula resection with vascular graft: If the stirred pulse defect is extensive, autologous vein or synthetic vascular grafts can be used.
3. Fistula exclusion with stirred pulse synthetic vascular graft In some cases where the lesion is located in an anatomically difficult-to-expose area or is tightly adherent to adjacent proximal bleeding vessels or nerves, complete resection of the arteriovenous fistula may not be possible. Instead, the proximal and distal stirred pulse of the fistula can be ligated and divided, while vascular grafts are placed proximal and distal to the lesion to maintain distal limb blood supply. The authors treated three cases of femoral arteriovenous fistula with fistula exclusion. Two cases had good postoperative follow-up, but one case, caused by a gunshot wound, had undergone three prior surgeries at other hospitals, with wound infections requiring skin grafting. Angiography at Shanghai Zhongshan Hospital confirmed a femoral arteriovenous fistula with a systolic murmur audible at the mid-thigh. Due to severe scar tissue around the fistula, incisions were made proximal and distal to the fistula to expose the stirred pulse, followed by fistula exclusion and stirred pulse synthetic vascular grafting. The calf ulcer healed three weeks postoperatively, but recurred after six months. Further investigation suggested that the recurrence might be due to the proximal and distal stirred pulse ligations being too far from the fistula, allowing collateral stirred pulse flow into the fistula circulation, leading to symptom recurrence.
(III) Key Surgical Considerations
1. Methods for hemorrhage control Due to extensive adhesions, arteriovenous fistula surgery can result in significant bleeding. Adequate surgical exposure, strict hemorrhage control, and meticulous, precise, and skillful sharp dissection are crucial. Three common methods for hemorrhage control are:
(1) Use of a tourniquet: For lesions in the distal extremities, such as the hands or feet, a tourniquet can be applied proximally. If the lesion is in the proximal extremity and a tourniquet cannot be applied, the following methods are used:
(2) Proximal stirred pulse occlusion: A segment of the proximal stirred pulse (e.g., subclavian or external iliac stirred pulse) is isolated, and a stirred pulse clamp is temporarily applied to reduce bleeding.
(3) Balloon catheter occlusion: If dense scar tissue around the fistula prevents dissection, an incision can be made in the distal stirred pulse, and a balloon catheter inserted to the proximal stirred pulse of the fistula. Inflating the balloon compresses the proximal stirred pulse to achieve hemorrhage control.
2. How to locate the fistula intraoperatively Generally, it is not difficult. Preoperatively, it is necessary to auscultate the area where the murmur is most pronounced, and compression of this area may cause a slowing of the heartbeat, which is easily detectable. Once the fistula is identified, mark the location locally. If preoperative localization is challenging, a sterilized stethoscope or Doppler probe can be prepared for intraoperative exploration. If necessary, intraoperative stirred pulse contrast examination can be performed.
(4) Postoperative complications. Postoperative complications include wound bleeding, infection, insufficient blood supply to the affected limb, swelling of the affected limb, and superficial varicose veins. With adequate preoperative preparation and meticulous surgical techniques, these complications can be avoided.
