Arteriovenous fistula

Definition

An arteriovenous fistula is an abnormal channel or passage between an artery and a vein.

Description

An arteriovenous fistula is a disruption of the normal blood flow pattern. Normally, oxygenated blood flows to the tissue through arteries and capillaries. Following the release of oxygen in the tissues, the blood returns in veins to the heart. An arteriovenous fistula is an abnormal connection of an artery and a vein. The blood bypasses the capillaries and tissues and returns to the heart. Arterial blood has a higher blood pressure than blood in veins. Although both the artery and the vein retain their normal connections, the new opening between the two causes some arterial blood to shunt (be diverted) into the vein because of the blood pressure difference. As a result, the vein swells.

Demographics

Congenital arteriovenous fistula is rare. Acquired arteriovenous fistula is also uncommon in children. When it occurs, it is most likely to be found in the arms or legs.

Causes and symptoms

There are two types of arteriovenous fistulas, congenital and acquired. A congenital arteriovenous fistula is a rare birth defect that formed during fetal development. In congenital fistulas, blood vessels of the lower extremity are more frequently involved than other areas of the body. An acquired arteriovenous fistula is one that develops after a person is born. It usually occurs when an artery and vein that are side-by-side are damaged, and the healing process results in the two becoming linked. For example, after catheterizations, arteriovenous fistulas may occur as a complication of the arterial puncture in the leg or arm. Fistulas also form without obvious cause. In the case of patients on hemodialysis, physicians perform surgery to create a fistula. These patients receive many needle sticks to flush their blood through dialysis machines and for routine blood analysis testing. The veins used may scar and become difficult to access. Surgery is used to connect an artery and vein so that arterial blood pressure and flow rate widens the vein and decreases the chance of blood clots forming inside the vein.

The main symptoms of arteriovenous fistulas near the surface of the skin are bulging and discolored veins. In some cases, the bulging veins can be mistaken for varicose veins. Other fistulas can cause more serious problems without obvious symptoms, depending on their location and the blood vessels involved.

When to call the doctor

If you have any of these signs and symptoms, and think you might have an arteriovenous fistula, make an appointment to see your doctor. Early detection of an arteriovenous fistula can make your condition easier to treat and may reduce your risk of developing complications, such as blood clots or, in severe cases, heart failure.

Diagnosis

Using a stethoscope, a physician can detect the sound of a pulse in the affected vein (bruit). The sound is a distinctive to-and-fro sound. Dye injected into the blood vessels can be tracked by x ray to confirm the presence of a fistula.

Treatment

Small arteriovenous fistulas can be corrected by surgery. Fistulas in the brain or eye are very difficult to treat. If surgery is not possible or is very difficult, injection therapy may be used. Injection therapy, also called sclerotherapy, is the injection of an irritating chemical that causes scaring at the site of the injection. In the case of an arteriovenous fistula, this procedure should stop the passage of blood from the artery to the vein. Surgery is the most common method of treating acquired fistulas.

Prognosis

The prognosis for treated acquired arteriovenous fistula is usually very good. Congenital arteriovenous fistula is not usually treated quite as successfully, but it can also be treated in such a way as to minimize further problems.

Prevention

As of 2004, there is no known way to prevent arteriovenous fistula.

Parental concerns

If not treated, arteriovenous fistulas can be very dangerous. Tissues below the fistula may not get enough blood and may die. If too much blood is diverted through the fistula, heart complications may occur.

CASE HISTORY

A 20-year-old man presented at the emergency department with one-week history of haemoptysis that was associated with anterior pleuritic chest. He had a known history of tracheal telangiectasia for which he had had three prior bronchoscopies and ablation therapy. He had no known history of coronary artery disease. He was hypotensive at time of presentation and was quickly stabilized with one litre of intravenous crystalloid solution. His respiratory status was stable at that time and he was admitted for observation. On the second day of admission he developed massive haemoptysis that resulted in respiratory arrest. He was cyanosed and hypotensive. He was intubated with a size 8 single-lumen endotracheal tube. Initially, a large amount of blood was suctioned from the endotracheal tube, but the bleeding slowed down after intubation. His blood pressure was stabilized with transfusion of four units of packed cells and further crystalloid fluid therapy. However, the arterial oxygen saturation remained at 90% despite intermittent positive pressure ventilation with 100% oxygen and use of PEEP + 10 cm H2O. Chest radiography showed bilateral lung infiltrates consistent with massive bleeding. His electrocardiogram (ECG) showed extensive ST elevations (>2 mm) in the inferolateral leads. This was associated with a raised troponin I (>50 µg/l) and creatine kinase levels (816 U/l). The ECG changes resolved within thirty minutes.

The patient was brought to the operating theatre within an hour of presentation for urgent fibreoptic bronchoscopy. Large amounts of fresh blood and clots were suctioned from the major airways. Diffuse telangiectasia within the trachea and bronchi were seen, but these lesions were not bleeding actively. Transoesophageal echocardiography in the operating room did not show any obvious patent foramen ovale or other septal defect. A coronary angiogram was performed to investigate the cause of the ECG changes. The coronary arteries were normal, but there was moderate segmental left ventricular systolic dysfunction with apical hypokinesis extending to the mid segments.

A suspicious small pulmonary arterial lesion was seen in the left lower lobe. Selective bronchial angiography confirmed the presence of a left lower lobe arteriovenous malformation that was treated with a combination of alcohol injection and coil embolization with no complications. Further small vascular abnormalities were present within the lung, but there was no arteriovenous shunting at the time of examination. The presence of multiple abnormalities increases the likelihood of an underlying disorder such as hereditary haemorrhagic telangiectasia (Osler-Weber-Rendu syndrome).

A CT of his head was performed because of right upper limb weakness. The CT scan was unremarkable except for a subtle hyperdensity in the left parietal region, which may also have been a small arteriovenous malformation. However, on further examination by a neurologist, the neurological deficit was attributed to ulnar nerve neuropraxia, probably secondary to nerve compression.

The patient's oxygenation improved on the removal of blood clots and intermittent positive pressure ventilation, and he was extubated on the same day after the successful angiographic embolization. He was discharged from the hospital 14 days later after treatment of left basal pneumonia.

DISCUSSION

Massive haemoptysis is a potentially fatal emergency that requires prompt resuscitation. The first priorities are to maintain the airway, optimize oxygenation and stabilize the haemodynamic status2. After the initial stabilization, identification of the exact location of bleeding is the key aspect of management3. Localization by physical examination may be possible in up to 43% of patients, but can be inaccurate 3% of the time4. Chest radiography and CT scan can localize intra-bronchial haemorrhage with reasonable confidence in only 63% of cases5. In our patient, the chest X-ray was non-specific to the site of bleeding. Bronchoscopy should be performed preferably during active bleeding to lateralize and if possible identify the cause6. Early bronchoscopy gives a higher yield for localizing the site of bleeding7. In cases where bronchoscopy fails to identify the cause, angiography of the bronchial arteries can be diagnostically helpful, since the bronchial arteries are frequently the cause of massive haemoptysis (90%)8,9. Angiographic embolization achieves immediate control of bleeding in 64 to 100% of patients3. In our patient, injection of alcohol and coils obliterated all the feeder arteries to the pulmonary arteriovenous malformation.

Coronary artery air embolism has been previously described during cardiopulmonary bypass10, CT guided lung biopsy11, and even in a case of inhalation of pressurized helium12. It seems likely that our patient suffered from coronary air embolism, based on the temporal sequence of ECG changes and resolution. Positive pressure ventilation after tracheal intubation may possibly have introduced air into the pulmonary venous circulation through the bleeding arteriovenous malformation, by causing an elevation in the intra-alveolar pressures. Air in the pulmonary veins drains into the left atrium and ventricle and eventually enters the systemic circulation. However, there was no way of proving that a coronary air embolism occurred, and the degree of hypoxaemia and hypotension at the time of the ECG changes were not well documented.

Coronary artery air embolism can induce ECG changes typical of ischaemia and infarction, dysrhythmias and even cardiac arrest13. Treatment of air embolism consists of 100% oxygen to promote exchange of oxygen for nitrogen within the air bubble. Maintaining normovolaemia is essential for optimizing the microcirculation. Inotropic support may be necessary if the patient remains hypotensive despite adequate fluid resuscitation.

Pulmonary arteriovenous malformations occur in more than 30% of patients with hereditary haemorrhagic telangiectasia. Hereditary haemorrhagic telangiectasia is an autosomal dominant condition characterized by mucocutaneous and gastrointestinal telangiectasia, and arteriovenous malformations involving cerebral, hepatic and pulmonary circulations. Our patient is a possible case since he fulfilled two of the Curacao criteria: (1) multiple telangiectasia; and (2) pulmonary arteriovenous malformations'4. Pulmonary arteriovenous malformations in hereditary haemorrhagic telangiectasia are usually multiple and commonly occur in the lung bases15. The larger malformations are associated with arterial hypoxaemia, transient ischaemic attacks, and stroke secondary to paradoxical embolism and cerebral abscess. Patients with pulmonary arteriovenous malformations should receive antibiotic prophylaxis prior to dental and surgical interventions to reduce embolie abscesses1. Pulmonary arteriovenous malformations in hereditary haemorrhagic telangiectasia tend to increase in size and rarely regress spontaneously. As such, patients with hereditary haemorrhagic telangiectasia should be screened regularly for pulmonary arteriovenous malformations, especially during puberty or pregnancy when pulmonary arteriovenous malformations may enlarge and rupture.

There is continuing debate regarding which screening method should be used. Cottin and colleagues16 published a retrospective study to address the question of which is the most accurate test to diagnose clinically significant pulmonary arteriovenous malformations while avoiding computed tomography or angiography in most patients. They recommend that patients with hereditary haemorrhagic telangiectasia should be screened with chest X-ray and contrast echocardiography. If either is positive, a chest CT should be performed. If the presence of pulmonary arteriovenous malformation is confirmed on CT, selective angiography should then be performed to assess if the malformations are suitable for coil embolization.

Surgical resection of pulmonary arteriovenous malformations have largely been replaced by embolization techniques because of concerns regarding loss of functioning lung in patients at risk of recurrent disease in non-resected lobes17. Our patient will be followed up with spirometry and shunt measurement to detect further pulmonary arteriovenous malformations or recurrence of the embolized pulmonary arteriovenous malformations, in which case early interventional embolization should be performed to reduce the frequency of cerebral events and risk of massive haemoptysis.

Resources

BOOKS

Steiger, Hans-Jacob, et al. Neurosurgery of Arteriovenous Malformations and Fistulas: A Multimodal Approach. New York: Springer-Verlag, 2002.

PERIODICALS

Hung, Po-Cheng, and Huei-Shyong Wang. "Successful endovascular treatment of cerebral arteriovenus fistula." Pediatric Neurology 27 (October 2002): 300–03.

"'Gigantic' Coronary Arteriovenous Fistula Closed in Neonate." Medical Devices & Surgical Technology Week (February 1, 2004): 85.

Nakayama, Hideki, et al. "Multiple cerebral arteriovenous fistulas and malformations in the neonate." Pediatric Neurology 25 (September 2001): 236–39.

ORGANIZATIONS

American Heart Association. 7272 Greenville Avenue Dallas, TX 75231. Web site: <www.americanheart.org>.

WEB SITES

Morasch, Mark D., and Dipen Maun. "Arteriovenous Fistulas." eMedicine.com, October 23, 2003. Available online at <www.emedicine.com/med/topic169.htm> (accessed November 16, 2004).

Tish Davidson, A.M. John T. Lohr, PhD

REFERENCES

1. Mohler ER, Monahan B, Canty MD et al. Cerebral abscess associated with dental procedure in hereditary haemorrhagic telangiectasia. Lancet 1991; 338:508-509.

2. Cahill BC, Ingbar DH. Massive hemoptysis. Assessment and management. Clin Chest Med 1994; 15:147-167.

3. Dweik RA, Stoller JK. Role of bronchoscopy in massive hemoptysis. Clin Chest Med 1999; 20:89-105.

4. Pursel ST, Lindskog GE: Hemoptysis. Am Rev Resp Dis 1961; 84:329-336.

5. Knott-Craig CJ, Oostuizen JG, Rossouw G, Joubert JR, Barnard PM. Management and prognosis of massive hemoptysis. Recent experience with 120 patients. J Thorac Cardiovasc Surg 1993; 105:394-397.

6. Sternbach G, Varon J. Massive hemoptysis. Intensive Care World 1995; 12:74-78.

7. Saumench J, Escarrabill J, Padro L et al. Value of fibreoptic bronchoscopy and angiography for diagnosis of the bleeding site in hemoptysis. Ann Thorac Surg 1989; 48:272-274.

8. Remy J, Remy-Jardin M, Voisin C. Endovascular management of bronchial bleeding. In: Buttler J, Ed. The Bronchial Circulation. Marcel Dekker, New York, 1992; 667-723.

9. Stoller JK. Diagnosis and management of massive hemoptysis: A review. Respir Care 1992; 37:564-581.

10. Ziser A, Adir Y, Lavon H, Shupak A. Hyperbaric oxygen therapy for massive arterial air embolism during cardiac operations. J Thorac Cardiovasc Surg 1999; 117:818-821.

11. Mokhlesi B. Ansaarie I. Bader M. Tareen M. Boatman J. Coronary air embolism complicating a CT-guided transthoracic needle biopsy of the lung. Chest 2002; 121:993-936.

12. Tretjak M, Gorjup V Mozina H, Horvat M, Noc M. Cerebral and coronary gas embolism from the inhalation of pressurized helium. Crit Care Med 2002; 30:1156-1157.

13. Muth CM, Shank ES. Gas embolism. N Engl J Med 2000; 342:476-482.

14. Shovlin CL, Guttmachcr AE, Buscarini E et al. Diagnostic criteria for hereditary hemorrhagic telangiectasia. (RenduOsler-Weber syndrome). Am J Med Genet 2000: 91:66-67.

15. Morrell NW. Screening for pulmonary arteriovenous malformations. Am J Respir Crit Care Med 2004: 169:978-979.

16. Cottin V Plauchu H, Bayle J-Y, Barthelet M, Revel D, Cordicr J-E Pulmonary arteriovenous malformations in patients with hereditary hemorrhagic telangiectasia. Am J Respir Crit Care Med 2004; 169:994-1000.

17. Shovlin CL, Lctarte M. Hereditary haemorrhagic telangiectasia and pulmonary arteriovenous malformations: issues in clinical management and review of pathogenic mechanisms. Thorax 1999; 54:714-729.

[Author Affiliation]

G. P. Y. LOKE*, D. A. STORY[dagger], F. LISKASER[double dagger], S. SEEVANAYAGAM§

Departments of Anaesthesia and Surgery, Austin Health, Heidelberg, Victoria

[Author Affiliation]

* M.B., B.S., M.Med.Anaes., Provisional Fellow.

[dagger] M.B., B.S.(Hons), B.Med.Sci.(Hons), M.D., F.A.N.Z.C.A., Joint Coordinator of Anaesthesia Research, The University of Melbourne, Department of Surgery.

[double dagger] M.B., B.S., F.A.N.Z.C.A., Staff Anaesthetist.

§ M.B., B.S.(Hons), F.R.A.C.S., Consultant Cardiothoracic Surgeon.

Address for reprints: A./Prof. David A. Story, Department of Anaesthesia, Austin Hospital, Studley Rd, Heidelberg, Victoria 3084.

Accepted for publication on August 8, 2005.