Introduction
A pulmonary arteriovenous fistula is an unusual connection between the pulmonary artery and vein. The blood vessels are dilated and cause a right-to-left shunt between the pulmonary artery and the pulmonary vein. It is a congenital disorder. It is more common in females than males. It is a condition that does not depend on the underlying disease.
What Is Pulmonary Arteriovenous Fistula?
An arteriovenous fistula is an unusual connection between an artery and a vein. It can be congenital or acquired. A pulmonary arteriovenous fistula is an abnormal connection between the pulmonary artery and the pulmonary vein, resulting in a right-to-left shunt between the pulmonary artery and vein. As a result, the blood entering the lungs does not receive enough oxygen.
What Is the Significance of the Pulmonary Artery and Pulmonary Vein?
The pulmonary artery carries oxygen-poor blood from the right side of the heart to the lungs for oxygenation. The pulmonary veins carry the oxygen-rich blood from the lungs to the heart. This forms pulmonary circulation.
What Are the Causes of Pulmonary Arteriovenous Fistula?
A pulmonary arteriovenous fistula is a congenital condition. It can occur as a complication of liver disease. It is common in individuals with Rendu-Osler-Weber disease, also called hereditary hemorrhagic telangiectasia. A pulmonary arteriovenous fistula is common in this disease because abnormal blood vessels exist in many body parts. It can also occur due to the rupture of an arterial aneurysm into an adjacent vein, penetrating injuries, or inflammatory necrosis of adjacent vessels.
What Are the Effects of Pulmonary Arteriovenous Fistula?
An arteriovenous fistula decreases peripheral resistance, which causes the heart to increase cardiac output to regularize the blood flow to all the tissues. It is manifested by normal systolic blood pressure and decreased diastolic blood pressure, which results in wider pulse pressure. An arteriovenous fistula can increase the preload.
Arteriovenous shunts decrease the afterload of the heart. This is due to the blood bypassing the arterioles, which decreases total peripheral resistance. Arteriovenous shunts increase the rate and volume of the blood that returns to the heart. In hereditary hemorrhagic telangiectasia, there is a direct connection between the arterioles and venules at the mucocutaneous region and internal bodily organs without intervening capillary beds. It usually does not cause symptoms, but it may result in difficulty breathing. If the pulmonary arteriovenous fistula is left untreated, it may result in a paradoxical embolism in which the blood clot travels from the lungs to the arms, legs, or brain.
What Are the Types of Pulmonary Arteriovenous Fistula?
A pulmonary arteriovenous fistula is classified into simple and complex fistulas.
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Simple Pulmonary Arteriovenous Fistula - Simple pulmonary arteriovenous fistulas are the common type. It presents as a well-defined peripheral nodule and can be rounded or multilobulated. It appears as a single aneurysmal sac in the histological section. It contains a single segmental artery as the feeding artery.
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Complex Pulmonary Arteriovenous Fistula- It consists of multiple abnormal vessels and one or more lobulated venous sacs of variable size. It is supplied by more than one feeding artery that often arises from the adjacent segmental pulmonary artery branches. A complex fistula involves the lung segment or an entire lobe.
What Are the Symptoms Associated With Pulmonary Arteriovenous Fistula?
Individuals with pulmonary arteriovenous fistula usually do not develop any symptoms.
The following are the symptoms if it develops:
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Difficulty in breathing.
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Difficulty in exercising.
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Sputum with blood.
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Nose bleeding.
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Chest pain.
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Cyanosis (bluish discoloration of the skin).
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Clubbing of fingers.
What Are the Complications of Pulmonary Arteriovenous Fistula?
The complications of pulmonary arteriovenous fistula include:
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Bleeding in the lungs.
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Paradoxical venous embolism results in stroke due to blood clots traveling from the arms and legs.
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Infection in the brain or heart valve in individuals with hereditary hemorrhagic telangiectasia
How Is Pulmonary Arteriovenous Fistula Diagnosed?
The diagnosis is based on examinations and tests. It includes the following clinical findings and tests:
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Abscesses or infections in the heart valves.
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Presence of abnormal vessels on the skin or mucus membranes.
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The presence of abnormal sounds is called murmur when the stethoscope is placed over the abnormal blood vessel.
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Increase in red blood cell count.
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Low oxygen levels.
The tests done to diagnose the pulmonary arteriovenous fistula are:
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Arterial blood gas test.
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Complete blood count.
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A chest X-ray is done to locate the fistula.
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CT (computed tomography) scan of the chest is performed to examine the structure and condition of the fistula.
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Echocardiogram with bubbles to assess the heart's function and identify the presence of a shunt.
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Lung function tests.
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Liver function tests.
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Perfusion radionuclide lung scan to assess the breathing and circulation in all areas of the lungs.
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A pulmonary arteriogram uses a contrast dye to examine the lungs' arteries and the fistula.
How Is Pulmonary Arteriovenous Fistula Treated?
Treatment is not required for individuals who do not develop any symptoms. The main treatment option for a fistula is to block the fistula during an arteriogram. The procedure is called embolization. Embolization is a minimally invasive procedure performed to stop bleeding or block the blood flow to an abnormal area of tissue. Particles like tiny gelatin sponges or beads block the blood vessels. However, the fistula can recur if the embolization fails. Surgery may be required to remove the abnormal blood vessels and adjacent lung tissues. A liver transplant is performed if the pulmonary arteriovenous fistula is caused by liver disease.
What to Expect With Pulmonary Arteriovenous Fistula?
A pulmonary arteriovenous fistula is a genetic condition that cannot be prevented. The prognosis is not good in pulmonary arteriovenous fistula for patients with hereditary hemorrhagic telangiectasia as those without it. Surgical removal of abnormal vessels in patients with hereditary hemorrhagic telangiectasia has a good prognosis.
Conclusion
A pulmonary arteriovenous fistula is a rare condition with an abnormal connection between the pulmonary artery and vein. It is a congenital respiratory disorder. It can be treated but cannot be prevented. Individuals with pulmonary arteriovenous fistula usually do not present any symptoms. Diagnosis and timely intervention help in the prevention of complications.
