Pulmonary arteriovenous malformations

Abstract

Within the past decade, pulmonary arteriovenous malformations (PAVMs) have evolved from rare curiosities to not uncommon clinical states, with the latest estimates suggesting a prevalence of ~1 in 2,600. PAVMs provide anatomic right-to-left shunts, allowing systemic venous blood to bypass gas exchange and pulmonary capillary bed processing. Hypoxemia and enhanced ventilatory demands result, although both are usually asymptomatic. Paradoxical emboli lead to strokes and cerebral abscesses, and these commonly occur in individuals with previously undiagnosed PAVMs. PAVM hemorrhage is rare but is the main cause of maternal death in pregnancy. PAVM occlusion by embolization is the standard of care to reduce these risks. However, recent data demonstrate that currently recommended management protocols can result in levels of radiation exposure that would be classified as harmful. Recent publications also provide a better appreciation of the hematologic and cardiovascular demands required to maintain arterial oxygen content and oxygen consumption in hypoxemic patients, identify patient subgroups at higher risk of complications, and emphasize the proportion of radiologically visible PAVMs too small to treat by embolization. This review, therefore, outlines medical states that exacerbate the consequences of PAVMs. Chief among these is iron deficiency, which is commonly present due to concurrent hereditary hemorrhagic telangiectasia: iron deficiency impairs hypoxemia compensations by restricting erythropoiesis and increases the risk of ischemic strokes. Management of periodontal disease, dental interventions, pulmonary hypertension, and pregnancy also requires specific consideration in the setting of PAVMs. The review concludes by discussing to what extent previously recommended protocols may benefit from modification or revision.

Keywords: HHT; embolization; hypoxemia/hypoxia; iron deficiency; radiation.

Figure 1.

(A) Chest X-ray indicating a pulmonary arteriovenous malformation (PAVM) (thick arrow) and the subtle appearance of associated artery and vein (thin arrows) in a patient with resting Sa_O2 of 94%. (B) Thoracic computerized tomography scan images. (C) Angiographic appearances before (left) and after (right) embolization. Images, courtesy of Dr. James Jackson, were taken minutes apart. Preferential blood flow through the PAVM led to reduced perfusion of non-PAVM–associated arteries and to dilatation/early filling of the draining vein. After embolization with two Amplatzer plugs (arrows), arterial blood flow to normal pulmonary arteries was restored. (D) Chest radiographs of the same region 8 months after embolization, when the Sa_O2 was 97%. PAVM sac, feeding artery, and draining vein have regressed. The tips and bodies of the Amplatzer plugs are visible.

Figure 2.

Drawing indicating the major functions of the pulmonary capillary bed that are bypassed in the setting of pulmonary arteriovenous malformations (red arrow). Adapted with permission from Reference .

Figure 3.

Typical 2013 flow chart. *At rest; ^†on exercise in Reference 8. Medical management to include use of supplemental oxygen when needed, prophylactic antibiotics (including for group with possible microscopic pulmonary arteriovenous malformations), and avoidance of SCUBA diving (8). Dashed arrow: As indicated in international guidelines (see Reference . HHT = hereditary hemorrhagic telangiectasia; PAVM = pulmonary arteriovenous malformation. Adapted from Reference .

Figure 4.

Inverse relationship between right-to-left shunt fraction and oxygen saturation. Shown are 309 paired same-day values of right-to-left (R-L) shunt (quantified by nuclear medicine perfusion scans using Tc-labeled albumin macroaggregates) and the mean Sa_O2 after 7, 8, 9, and 10 minutes of standing. Data are from 198 individuals. Regression coefficient, −1.22 (95% confidence interval, −1.31 to −1.14; P < 0.0001). All subjects would be predicted to have grade 3 shunts by contrast echocardiography. Adapted with permission from Reference .

Figure 5.

2014 proposed management flowchart. Irrespective of why pulmonary arteriovenous malformations (PAVMs) are identified, all should be considered for embolization if technically feasible and suitable expertise is available. *Caution required if preexisting severe pulmonary hypertension is present when risk benefit considerations change (increased risk of procedural related mortality; reduced benefit form prevention of paradoxical embolic strokes [90]). ^$Advise of risks of brain abscess and hemorrhagic strokes that may modify stroke management (early MRI scan, caution with thrombolysis). CT = computerized tomography; HHT = hereditary hemorrhagic telangiectasia.