Centers of Excellence in Interventional Cardiology and Radiology

Pediatric Angiology

Pulmonary Arteriovenous Communications

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Generalities

Pulmonary arteriovenous malformations (PAVMs) consist of abnormal communications between the pulmonary arteries and the pulmonary veins. These are also referred to as pulmonary arteriovenous fistulae.

Most patients with pulmonary arteriovenous malformations have the autosomal dominant disease hereditary hemorrhagic telangiectasia (HHT).

Pulmonary arteriovenous malformations may also be an acquired condition found in patients with liver disease, mainly liver cirrhosis, patients with congenital heart disease.

Pulmonary arteriovenous malformations may also be acquired rarely secondary to chronic infections (such as schistosomiasis, actinomycosis, tuberculosis) and metastatic thyroid cancer, mitral stenosis, bronchiectasis.

Hereditary hemorrhagic telangiectasia (HHT) is an autosomal dominant disorder. The clinical manifestations are secondary to growth of vascular malformations in various organs, most commonly the skin, nasopharynx, GI tract, lungs, and brain. HHT is generally recognized as a triad of cutaneous telangiectasia, recurrent epistaxis, and a family history of this disorder.

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Approximately 70% of pulmonary arteriovenous malformation cases are associated with HHT. Conversely, approximately 15-35% of persons with HHT have pulmonary arteriovenous malformations.

Approximately 53-70% of pulmonary arteriovenous malformations are found in the lower lobes.

Approximately 70% of patients have unilateral disease, 36% have multiple lesions, and 50% of those with multiple lesions have bilateral disease. Pulmonary arteriovenous malformations may be microscopic (ie, telangiectasis), but they are typically 1-5 cm. Occasionally, pulmonary arteriovenous malformations as large as 10 cm are encountered. Approximately 10% of patients may have diffuse microvascular pulmonary arteriovenous malformations in combination with larger, radiographically visible pulmonary arteriovenous malformations.

Most pulmonary arteriovenous malformations drain into the left atrium, but anomalous drainage to the inferior vena cava or innominate veins has been reported. The malformations may appear as one of the following: a large single sac, a plexiform mass of dilated vascular channels, or a dilated tortuous direct communication between artery and vein.

Pulmonary arteriovenous malformations can be classified as simple or complex types on the basis of their architecture. Simple pulmonary arteriovenous malformations have a single feeding segmental artery leading to single draining pulmonary vein. Approximately 21% of pulmonary arteriovenous malformations are complex, having 2 or more feeding arteries or draining veins. They often occur in the lingula and right middle lobe distributions.

The natural history of pulmonary arteriovenous malformations has not been studied carefully. In one study of 16 patients, serial chest radiographs obtained over a median observation period of 18.9 years demonstrated enlargement in 4 patients and near total regression in 1 patient. The growth rate tended to be slow, with an increase of approximately 5-10 mm every 5-15 years.

How Common are PAVMs?

As we pointed above, approximately 70% of the cases of pulmonary arteriovenous malformations are associated with HHT. Conversely, approximately 15-35% of persons with HHT have pulmonary arteriovenous malformations.

HHT is an autosomal dominant disorder; however, 20% of cases involve no family history of telangiectasia or recurrent bleeding. Penetrance is age related and nearly complete by age 40 years. Although the arteriovenous malformations in HHT are inherited and should be present at birth, they commonly manifest clinically during adult life, after the vessels have been subjected to pressure for several decades.

Mortality caused by pulmonary arteriovenous malformations is due to rupture, brain abscess, and stroke due to paradoxical embolization. In addition, therapeutic interventions for pulmonary arteriovenous malformations carry a low risk of mortality.

The risk of mortality appears to be significantly higher in patients with bilateral, diffuse pulmonary arteriovenous malformations.

Pulmonary arteriovenous malformations occur twice as often in women than in men, but a male predominance is observed among newborns.

Approximately 10% of the cases of pulmonary arteriovenous malformations are identified in infancy or childhood; however, the incidence gradually increases through the fifth and sixth decades of life.

Signs and Symptoms associated with PAVMs

Symptoms caused by pulmonary arteriovenous malformations (AVMs) are often insidious, as the arteriovenous malformations slowly enlarge.

Dyspnea, especially with exercise, may develop over many years. In severe cases, dyspnea in the upright position (platypnea) may be present. Visible cyanosis may be present if a significant degree of desaturation is present.

Hemoptysis and rarely massive hemoptysis may occur.

Less common complaints include chest pain, cough, migraine headaches, tinnitus, dizziness, dysarthria, syncope, vertigo, and diplopia. The cause of these symptoms is not entirely clear, but it may be related to hypoxemia, polycythemia, or paradoxical embolization through the pulmonary arteriovenous malformations.

Because most patients with pulmonary arteriovenous malformations also have HHT, the characteristic mucocutaneous telangiectasias are frequently observed in patients with pulmonary arteriovenous malformations. The lesions are present on the face, mouth, chest, and upper extremities.

Associated noncardiac conditions

1. The most frequently reported associated noncardiac conditions are central nervous system (CNS) complications, which occur in 30% of patients:

Strokes occur in 18% of patients with CNS complications

transient ischemic attacks occur in 37%

brain abscesses occur in 9%

migraine headaches occur in 43%

seizures occur in 8%.

Paradoxic embolism across pulmonary arteriovenous malformations is the most likely mechanism for major noninfectious strokes. Embolism of infected material accounts for solitary or recurrent brain abscesses. These complications most commonly occur when the feeding arteries are larger than 3 mm in diameter.

2. Hemoptysis and hemothorax are other potentially life-threatening complications. Hemoptysis occurs from ruptured pulmonary arteriovenous malformations or endobronchial telangiectasia.

Idiopathic congenital pulmonary arteriovenous malformations

Idiopathic congenital pulmonary arteriovenous malformations are likely to be single. They are less likely to become enlarged, and they are associated with fewer physical findings than other pulmonary arteriovenous malformations. Idiopathic pulmonary arteriovenous malformations are diagnosed by using the same criteria as for other pulmonary arteriovenous malformations. Idiopathic congenital pulmonary arteriovenous malformations are successfully treated with embolotherapy.

Acquired arteriovenous malformations after surgery for congenital cyanotic heart disease

Pulmonary arteriovenous malformations may develop after some procedures for congenital cyanotic heart disease. Contrast echocardiography and radionuclide shunt studies have been used to diagnose pulmonary arteriovenous malformations, and embolotherapy has been used successfully to occlude the pulmonary arteriovenous malformations in these cases.

Complications

Seizure

Migraine headaches

Transient ischemic attack

Cerebral vascular accident

Brain abscess

Hypoxemia, orthodeoxia

Hemothorax

Life-threatening hemoptysis

Pulmonary hypertension

Congestive heart failure

Polycythemia

Anemia

Infectious endocarditis

Diagnosis of PAVMs

Consider the diagnosis of pulmonary arteriovenous malformations (PAVM) in individuals with any of the following presentations:

1. one or more pulmonary nodules associated with typical chest radiographic findings of pulmonary arteriovenous malformations;

2. mucocutaneous telangiectases;

3. unexpected findings such as dyspnea, hemoptysis, hypoxemia, polycythemia, clubbing, cyanosis, cerebral embolism, or brain abscess.

Laboratory studies:

With chronic hypoxemia, the hemoglobin and hematocrit rise. The rise is roughly proportional to the degree of cyanosis.

However, because may patients with pulmonary arteriovenous malformations (AVMs) also have hereditary hemorrhagic telangiectasia (HHT), bleeding from epistaxis and GI telangiectasias may lead to anemia

Pulse oximetry

Pulse oximetry is a useful tool in initial screening for pulmonary arteriovenous malformations. Pulse oximetry should be performed in the supine and upright position. Oxygen saturations less than 95% are suggestive of either right-to-left shunting, or pulmonary disease. With significant pulmonary arteriovenous malformations, the oxygen saturation typically decreases in the upright position.

Imaging studies:

Chest radiography

Electrocardiography (ECG)

Echocardiogram is a useful tool for excluding other sources of intracardiac right-to-left shunt.

Echocardiogram with bubble contrast

Pulmonary angiography: despite advances in noninvasive diagnostic techniques, contrast-enhanced pulmonary angiography remains the criterion standard in the diagnosis of pulmonary arteriovenous malformations. This test is usually necessary if embolotherapy is being considered. Perform pulmonary angiography in all lobes of the lungs to look for unsuspected pulmonary arteriovenous malformations.

Right heart catheterization

Radionuclide perfusion lung scanning

Contrast-enhanced CT scanning

MRI

Other Tests

Pulmonary function tests

Oxygenation is commonly affected in individuals with PAVM. Most patients have saturation levels of less than 90% at rest. Patients with this finding have normal spirometric findings and a mildly reduced diffusing capacity.

Exercise testing

Patients with pulmonary arteriovenous malformations have reduced exercise tolerance. In most patients, incremental exercise testing results in decreased saturation.

Indications

Drug therapy is not currently a component of the standard of care for pulmonary arteriovenous malformations (PAVMs).

Patients with pulmonary arteriovenous malformations should be given antibiotic prophylaxis before dental and surgical procedures to prevent seeding of the pulmonary arteriovenous malformation and the subsequent development of a cerebral abscess.

Not all PAVM require immediate intervention. A decision to intervene must weigh the risk of complications from the PAVM (eg, stroke, cerebral abscess) with complications of the procedure (usually percutaneous transcatheter embolization). Indications for the treatment of PAVM have not been clearly defined due to a lack of high quality studies evaluating the efficacy in different populations. However, the following guidelines are supported by consensus opinion and small uncontrolled studies:

●Patients who have one or more PAVMs with a feeding artery diameter (FAD) >2 to 3 mm on chest CT, regardless of symptoms, should undergo pulmonary angiography. At the time of pulmonary angiography, PAVMs with FAD ≥3 mm are targeted for embolization and smaller PAVMs are embolized if technically possible due to their propensity to enlarge or become symptomatic over time.

●Symptomatic PAVMs should be targeted for embolization, regardless of the FAD. Symptoms can include hypoxemia, paradoxic embolization (eg, stroke or brain abscess), and hemoptysis.

●Asymptomatic PAVMs with FAD <2 mm should be followed with non-contrasted CT, usually every three to five years. Embolization should be considered for PAVMs with progressive enlargement or those that become symptomatic over follow-up.

Definite therapy for pulmonary arteriovenous malformations (PAVM) involves therapeutic embolization or surgical resection.

Procedure

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1. Transcatheter embolization – minimally invasive

2. Surgical intervention : Surgery is almost never the procedure of choice, but may rarely be the preferred option in patients with untreatable allergy to contrast material or PAVM that are not technically amenable to embolotherapy (very rare). Surgical techniques used to treat PAVM include vascular ligation, local excision, lobectomy, and pneumonectomy. Surgical therapy is not always curative long-term. Recurrence or enlargement of PAVM has been reported in up to 12 percent of patients. In addition, enlargement of previously unrecognized PAVM and stroke have been reported.

Procedure – Transcatheter embolization

Embolization therapy (ie, embolotherapy) is a form of treatment based on occluding the feeding arteries to a pulmonary arteriovenous malformation. Embolic materials include: steel coils, polyvinyl alcohol, cotton wool coils, and stainless coils.

The procedure begins with diagnostic conventional pulmonary angiography to fully characterize the PAVM, followed by catheter-directed placement of embolic material into the feeding artery of the PAVM until blood flow ceases. Diagnostic angiography is usually performed in the same session as embolization therapy to identify additional PAVMs amenable to embolization. Multiple PAVM may be embolized during a single session, and additional sessions may be performed after a hiatus of one to two weeks if additional PAVM remain perfused.

Diffuse PAVM are a unique management challenge. Discrete PAVMs with feeding arteries greater than 2 to 3 mm should be embolized. This often has little effect on the severe hypoxemia that accompanies PAVM because shunting through the other PAVM persists; however, the goal is to reduce the severe complications associated with PAVM, such as stroke or cerebral abscess. Embolizing the pertinent segmental arteries from the periphery toward the center may improve symptoms in highly symptomatic patients.

Metallic coils (steel, titanium, or platinum) or detachable balloons are the usual embolic materials. When coils are used, optimal results are obtained when at least two coils are placed as close as possible to the AVM sac. Generally speaking, coils should be 2 mm wider than the feeding artery. An advantage of using detachable balloons rather than steel coils is that the balloons can be deflated and repositioned if necessary.

Alternative embolic materials include polyvinyl alcohol, wool coils, and Amplatzer vascular plugs. Amplatzer plugs are relatively new. Potential benefits of the Amplatzer plugs over conventional coils include more rapid occlusion of PAVM, a reduced procedure time, the ability to occlude more PAVM in a single session, occlusion of feeding vessels with shorter necks, theoretical reduction of paradoxical thrombus embolization during the procedure, and a potentially lower incidence of later reperfusion.

The procedure is performed in catheterism lab. As we pointed above, the technique of coil embolotherapy involves localization of the PAVM by angiography followed by selective catheterization of the feeding artery. Usually, it is done under general anesthesia. Thus, after local asepsy, a small inguinal incision is made. Through this incision, the physician will introduce a small narrow tube into the femoral vein, then through this tube a catheter will be introduced which will reach the right ventricle, under fluoroscopic control (X ray control). The catheter tip is advanced past the point of any proximal vessels that supply normal lung parenchyma and positioned as close to the neck of the PAVM as possible. A steel coil is advanced through the catheter and released at this point, angiography is repeated, and additional coils are positioned if needed until blood flow to the PAVM has ceased. Up to 10 coils have been used on a single PAVM. Pulmonary arteriovenous malformations with short feeding arteries may be embolized by placement of large coils in the venous sac. Depending on patient tolerance and the amount of contrast material used, multiple PAVM may be embolized during a single session. Additional sessions may be performed after a hiatus of 1 to 2 wk if additional PAVM remain open.

The second major embolotherapy technique makes use of detachable balloons. Following localization of the PAVM by angiography, a balloon catheter is exchanged over a guidewire and positioned at the neck of the PAVM. The balloon is inflated with radiopaque contrast material, angiography is repeated to ensure vessel occlusion, and the balloon is detached. An advantage of the balloon technique is that the balloon can be deflated and repositioned if necessary. For PAVM with feeding vessels greater than 7 to 10 mm in diameter, a combination of coils and balloons is commonly used to achieve total occlusion. Autodeflation of balloons, with or without recanalization, and recurrence of symptoms in the recanalized cases have been reported. Balloon deflation may be minimized by use of iohexol 140, which is isotonic to blood, to fill the balloons.

Is it painful?

No, usually, the intervention is performed under general anesthesia.

How long does it take?

The duration of the procedure is about 1-2 hours and takes place in the cardiac catheterization laboratory.

Risks

The complications are rare; the complications are reduced by the proper preparation and the continuous surveillance of the patient. Potential complications:

allergic reactions to administered substances, including renal disfunction

reactions to anesthetic compounds

arteriovenous fistulas at the vascular puncture site

minor bleeding at the vascular puncture site

fever

headache, migraine

infection

gaseous embolism

cardiac arrythmias

extremely rare – cardiac perforation and cardiac tamponade (perforation of the cardiac wall and bleeding in the pericardial sac, which compresses the heart)

hemorrhage, vascular disruption after balloon dilation

pain, nausea and vomiting

arterial or venous obstruction from thrombosis or spasm

pleuritic chest pain is the most common complication and is observed in 12% of patients. This pain usually responds well to analgesics (usually responds to a short course of non-steroidal inflammatory agents, but occasionally a course of prednisone is necessary for more protracted pain)

pulmonary infarction

device migration

a new or increased pulmonary hypertension after embolization has been reported in several patients. Incidence of complication appears to be higher when the feeding vessels of more than 8 mm were occluded

symptomatic recanalization was observed with 0.5% of procedures

stroke (<0.5 percent of patients), transient ischemic attaches (1 percent)

Before procedure

The preoperative assessment will establish if the closure of the defect can be done percutaneously or there is an indication of surgical closure of the defect.

Prior to the intervention, the interventional cardiologist must be prevented about any history of allergic reactions. Blood tests are taken including hemoglobin level, coagulation, renal function, and other specific tests.

The patient is admitted the day before the intervention, and he/she should not eat before the procedure.

After procedure

You will be connected to monitors that will constantly display your electrocardiogram (ECG or EKG) tracing, blood pressure, other pressure readings, breathing rate, and your oxygen level. You will be given pain medication for incisional pain or you may have had an epidural during surgery which will help with postoperative pain.

Since the procedure is minimally invasive, the postprocedural recovery is usually very fast. The majority of patients can leave the hospital the following day. Indications about recovery and postprocedural treatment will be clearly specified to all patients.

Following embolization, patients should be monitored closely because of the propensity of some PAVM to enlarge and the risk of recanalization or reperfusion. One reasonable approach is to perform spiral chest computed tomography (CT) with thin slice formatting three to six months after embolization and then three years later.

Patients with PAVM are at risk for air embolism. Meticulous care should be taken to avoid the introduction of air bubbles when medications are given intravenously.

Patients with PAVM should also avoid SCUBA diving. Interestingly, despite the occurrence of hypoxemia in association with PAVM, in-flight complications are uncommon.

Patients with PAVM are also at risk for cerebral abscess. Therefore, patients with discrete or diffuse PAVM should be given lifelong antibiotic prophylaxis prior to dental and other procedures to avoid bacteremia and the subsequent development of cerebral abscess.

If steel coils are used, MRI of the brain (in order to screen for brain AVM in HHT patients) should be deferred for at least 6 weeks to allow the coils to fibrose into position, thereby minimizing their chance of movement during the MRI.

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Embolotherapy appears to be the treatment of choice because major surgery, general anesthesia, and loss of pulmonary parenchyma may be avoided. Embolotherapy is a clear choice in patients with multiple or bilateral pulmonary arteriovenous malformations or in patients who are poor surgical candidates.

DOCTORS
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Sună Mesaj