Embolization Therapy: Principles and Clinical Applications, 1 Ed.

Pulmonary Arteriovenous Fistulas

Mary E. Meek • James C. Meek

Apulmonary arteriovenous fistula (PAVF) is a direct connection between a pulmonary artery and pulmonary vein. These high-flow, low pressure, thin-walled fistulae are commonly called pulmonary arteriovenous malformations(PAVMs). Complications of untreated PAVFs are related to the right-to-left shunt. Patients may present with hypoxia, exercise intolerance (59%), stroke/transient ischemic attack (TIA) (30%), brain abscess (9%), or hemoptysis (3%).1 Massive hemoptysis and/or hemothorax occurs in fewer than 8% of patients.2 Enlargement and rupture of the PAVF occurs more commonly in times of increased cardiac output and hormonal surges such as pregnancy.3,4Migraines are present in up to 46% of patients with PAVFs.1

Acquired PAVFs occur in hepatopulmonary syndrome and in patients with Glenn or Fontan shunts, malignancy, trauma, amyloidosis, and erosion from Rasmussen aneurysms. Most (>90%) congenital PAVFs are associated with hereditary hemorrhagic telangiectasia (HHT) or an HHT-like disorder.1 PAVFs are commonly seen in HHT, previously known as Rendu-Osler-Weber syndrome. HHT is an autosomal dominant disorder characterized by epistaxis, telangiectasias (commonly on the lips, nose, and fingers), and AVMs (PAVFs, brain, gastrointestinal [GI] tract). A diagnosis of HHT is made based on the Curacao criteria (Table 19.1) or by genetic testing.5

Genetic defects associated with HHT and HHT-like syndromes are related to the transforming growth factor beta (TGF-β) pathway. Three mutations have been identified: endoglin (ENG), activin A receptor type II like 1 (ACVRL1 or ALK1), and SMAD4. The ENG mutation is associated with a higher incidence of PAVF and cerebral AVM than the ALK1 mutation.6 A new genetic mutation in BMP9 has recently been identified in patients with an HHT-like syndrome.7

Workup for PAVF is required in all patients with HHT, hypoxia of unknown origin, or evidence of a right-to-left shunt such as a young patient with a brain abscess. Patients may experience orthodeoxia, which is a decrease in oxygen saturation when standing. The workup starts with an Echo–bubble study. Delayed appearance of bubbles in the left heart indicates an extracardiac shunt. If the Echo–bubble study is positive, we proceed with a noncontrast chest computed tomography (CT). Contrast is not necessary for the chest CT. It increases the radiation dose and serves as a risk for intravenous air embolus. The 1-mm axial images should be carefully reviewed to identify any abnormal connection between a pulmonary artery and pulmonary vein. Coronal and sagittal reconstructions can also be helpful.

Due to the need for continuous long-term follow-up, not only of PAVFs but also of the other vascular malformations associated with HHT, we and many other experienced interventionalists believe that these patients should be treated at an HHT Center of Excellence. However, patients will present outside of HHT Centers of Excellence with emergent indications for embolization of their PAVF such as hemoptysis, hemothorax, or brain abscess. It is beyond the scope of this text to discuss the entire workup and management of an HHT patient.8 Our goal is to provide a basic guide to performing PAVF embolization with the current embolic technology available.

DEVICE/MATERIAL DESCRIPTION

TECHNIQUE

Embolization for PAVF was first described by Porstmann9 in 1977 and Taylor et al.10 in 1978. Dr. White and colleagues11 further refined the techniques, which led to the development of the White LuMax catheter system (Cook Medical, Inc., Bloomington, Indiana). Early on, coils and detachable balloons were used to close PAVFs. Detachable balloons are no longer available in the United States due to deflation and systemic embolization concerns. The techniques used today are not much different than those described by Dr. White, with the exception of improved embolic devices.1,11,12 Our goal with adult patients is to embolize as many PAVFs in one outpatient setting as possible within the constraints of contrast load and radiation exposure.13 In children, we embolize the PAVFs greater than 3 mm in size with the concern that embolization of smaller vessels in the developing lung will result in a “blocked path” to a PAVF that has recruited smaller feeders, making subsequent embolization more difficult.

Right heart and pulmonary artery pressures should be measured to evaluate cardiac physiology. Large right-to-left shunts can cause increased cardiac output and may lead to heart failure. Rarely, pulmonary hypertension (even with PAVFs) may be present. This is felt to be related to the TGF-β family of receptors.14 If pulmonary hypertension is present, evaluation for a left-to-right shunt, such as in the liver, should be performed.

PAVFs represent a right-to-left shunt; therefore, careful attention to technique is critical. Setup should be similar to neuroangiography cases with in-line air filters, continuous flush lines, a closed system for contrast, and double flush technique (Fig. 19.8).

We use a standard right femoral vein approach using a 7-Fr introducer sheath. A diagnostic pulmonary arteriogram is performed with a 7-Fr MONT-1 catheter (Cook Medical, Inc., Bloomington, Indiana). Alternatively, a pigtail catheter over the back end of a shaped Bentson wire (Allwin Medical Devices, Anaheim, California) or a tip-deflecting wire (Cook Medical, Inc., Bloomington, Indiana) may be used. Pulmonary artery pressure measurements are obtained. Diagnostic angiography is performed in full inspiration in the anteroposterior view and the ipsilateral oblique (40 to 60 degrees; we generally use 40 degrees). This projection may seem counterintuitive as it projects the heart over the lung, but this view is best for spreading out the basilar segments where most PAVFs occur. Contrast injection rates range from 20 to 50 mL at 10 to 25 mL per second depending on the size of the pulmonary arteries, size of PAVFs, and presence of pulmonary hypertension. A frame rate of at least six frames per second should be used. It is important to include deep into the lung bases in the field of view as most PAVFs occur in the bases. Each segmental artery should be carefully followed to evaluate for the fistulous connection. A PAVF looks like a long continuation of the pulmonary artery into the pulmonary vein (Fig. 19.9). Frequently, there is an aneurysmal component at the site of the fistula (Fig. 19.10). The feeding vessel is measured. The standard teaching is that anything larger than 3 mm should be embolized. However, typically, the HHT Centers of Excellence use the technique that embolizes as many PAVFs in one setting as possible in the adult patient even sizes smaller than 3 mm as there are reports of embolic events in PAVFs measuring below the 3-mm “standard.”1315 Over a 260 cm 0.035-in stiff Amplatzer wire, the diagnostic catheter is exchanged for a White LuMax set, which comes in two sizes: 7-Fr or 8-Fr guide catheter with a coaxial angled tip inner catheter. At this point, the patient should receive a bolus of intravenous heparin (~40 IU/kg). The pulmonary artery lower segments are generally easily accessed by “flopping” the Bentson wire down into the basilar segment. A hydrophilic angle tip wire such as a Glidewire (Terumo Medical Corporation, Somerset, New Jersey) may facilitate selection of the feeding vessel but should be used with care as dissection can occur. The middle and upper segments are more challenging to cannulate and may require a more sharply angled catheter such as a Judkins right coronary catheter (Cordis) or a left internal mammary catheter.

Detachable Amplatzer Vascular Plugs (AVPs) (St. Jude Medical, Inc., St. Paul, Minnesota) and pushable Nester 0.035-in coils (Cook Medical, Inc., Bloomington, Indiana) are our embolic devices of choice (Figs. 19.5 and 19.6, respectively). Coils and AVPs should be oversized by 20%. The coils should be densely packed and placed as close the fistulous sac as possible, ideally within 1 cm.16 There are some who believe that packing the aneurysmal fistulous sac has a lower recanalization rate.17 This has yet to be well established in the literature. Occasionally, microcatheters may be needed to deliver 0.018-in coils in a precise location.18 Many different microcoils are available—both pushable and detachable forms. The anchor technique is used when there is concern about a coil passing through the PAVF and ending up in the systemic circulation. This involves “anchoring” the first loop of the coil into a small side branch of the pulmonary artery that is feeding the PAVF.1 Alternatively, a large detachable coil may be used as a scaffold to provide stability for placement of more economical pushable coils.

A noncontrast chest CT should be performed 6 months following embolization to evaluate for any residual PAVF patency. The draining vein and aneurysmal sac should disappear or be reduced by 70%. Any reappearance of the draining vein or aneurysmal sac on future follow-up studies performed every 3 to 5 years indicates recanalization. Reperfusion of a previously embolized PAVF is reported about 7% of the time (Fig. 19.11). Causes include not packing the coils densely enough, an accessory vessel that was not embolized, reperfusion from a collateral pulmonary artery vessel, and reperfusion of a collateral bronchial artery vessel. The significance of these recanalized PAVFs is unknown. Some believe that the risk of embolus from these previously treated lesions is less because the coil pack may act as a “filter” and the flow through these lesions is slower. At our institution, we err on the side of caution and reembolize the recanalized PAVFs.

Follow-up chest CT may also reveal the presence of “new” PAVFs, which may or may not be symptomatic. These lesions were likely present on previous studies or were microscopic and have enlarged over time. All accessible lesions greater than 3 mm in diameter should be treated.11,12

PAVFs are classified as simple or complex.19 Most (85%) AVFs are classified as simple, meaning that the malformation arises from one or more arteries within a single pulmonary segment. Up to 10% of lesions are considered complex with arterial vessels arising from more than one pulmonary segment, whereas 5% or fewer have involvement of multiple lobes. These are considered diffuse and outcomes in these patients are worse. Pulmonary flow redistribution has been used with some success. This involves the lobar occlusion of pulmonary artery feeding the diffusely involved lobe.20,21 Lung transplantation, with or without cardiac transplantation depending on presence of high-output heart failure, has been reported for diffuse PAVFs.22

POTENTIAL COMPLICATIONS

Patients should be evaluated with a preoperative electrocardiogram (ECG) to look for left bundle branch block (LBBB). Passing the catheters through the heart can induce a right bundle branch block. In a patient with a preexisting LBBB, total heart block can ensue.

Air embolism occurs less than 5% of the time but should always be a concern. Due to its anterior origin, the right coronary artery may be unintentionally embolized with air bubbles or clot causing angina or ECG changes, which can be treated with sublingual nitroglycerin and atropine for bradycardia. Rarely, TIAs may occur. The reported complication rate including angina and TIA is less than 2%. Pleurisy is a common postprocedural complaint (12%). This is treated with anti-inflammatory medication. Rarely, severe, delayed pleurisy occurs.

Coil migration into the systemic arteries has been reported along with successful snare retrieval.19,23 If this happens, immediately bolus the patient with intravenous heparin for a target activated clotting time near 250 seconds. Proceed with arterial access and retrieval of the embolized coil.

CONCLUSION

Embolization of a PAVF can be technically challenging. Careful attention to preprocedure imaging, high-quality angiography, meticulous technique, and a good knowledge of embolic agents are keys to success.

TIPS AND TRICKS

Angiography

• Use a 2-s injection of 10–25 mL of iodine contrast.

• Use the ipsilateral oblique (40–60 degrees) to spread the basilar pulmonary artery segments.

• The flush catheter typically enters the left pulmonary artery. Curve the back end of a Bentson wire to facilitate steering the MONT-1 catheter to the right side.

• Carefully review your pulmonary angiogram on the workstation. Avoid “search satisfaction” by following each segmental artery out the entire length. Many patients will have multiple PAVFs.

• Invert the contrast image (so it appears white) to better see the PAVFs when reviewing your angiography (Fig. 19.11).

• Do not oversedate the patient as snoring/deep inspiration causes significant motion and may dislodge your carefully placed catheter.

Accessing the Lesion

• Commonly used wires: 0.035-in Rosen (Cook Medical, Inc., Bloomington, Indiana) or 0.035-in stiff Amplatzer for exchanging the MONT-1 for the White LuMax set, Bentson for flopping into basilar segments, semicurved 0.035-in hydrophilic Glidewire (Terumo Medical Corporation, Somerset, New Jersey) for selecting more difficult branches in the upper and middle lobes.

• Use a Judkins right coronary catheter or a left internal mammary catheter to select upper and middle lobe branches.

• If you need to place an AVP II more distally than your Lumax guide will go, you can place a 6-Fr 100-cm Envoy guide catheter (Codman & Shurtleff, Inc., Raynham, Massachusetts), which will allow you to place up to a 12-mm AVP II plug.

• Prowler Plus (Codman & Shurtleff, Inc., Raynham, Massachusetts) is our microcatheter of choice because it has a 0.021-in inner diameter, which allows for placement of pushable 0.018-in Nesters as well as many detachable coils. The Ruby Coils (Penumbra, Inc., Alameda, California) require a larger diameter microcatheter.

Embolization

• Densely pack the coils as close to the fistula as possible (<1 cm).

• We most commonly use AVP II, AVP 4, and Nester coils.

• We do not use the first-generation AVP device due to recanalization concerns.

• A single detachable coil or AVP can be used as a scaffold for the placement of pushable coils to obtain tight packing with reduced cost.

• Anchor technique: place the first portion of a pushable coil into a distal side branch to prevent distal migration of the coil.

• Wait 5 min after placement of device to assess thrombosis.

• Oversize coils and AVPs by at least 20%. Some interventionalists consider using longer coils (with 20%–30% oversize) and oversize the AVP between 30% and 50% in larger and high-flow PAVF.

• Do not use particles or liquids due to the high-flow right-to-left shunt.

REFERENCES

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 7. Wooderchak-Donahue WL, McDonald J, O’Fallon B, et al. BMP9 mutations cause a vascular-anomaly syndrome with phenotypic overlap with hereditary hemorrhagic telangiectasia. Am J Hum Genet. 2013;93:530–537.

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22. Fukushima H, Mitsuhashi T, Oto T, et al. Successful lung transplantation in a case with diffuse pulmonary arteriovenous malformations and hereditary hemorrhagic telangiectasia. Am J Transplant. 2013;13:3278–3281.

23. Gupta P, Mordin C, Curtis J, et al. Pulmonary arteriovenous malformations: effect of embolization on right-to-left shunt, hypoxemia, and exercise tolerance in 66 patients. AJR Am J Roentgenol