Pulmonary Arteriovenous Malformation

Pulmonary arteriovenous malformation (PAVM) is an abnormal direct connection between pulmonary artery and vein, creating a right to left shunt bypassing the capillary filter.

About 80 to 90% are associated with hereditary haemorrhagic telangiectasia (HHT, ENG, ACVRL1, SMAD4 mutations); 30 to 50% of HHT patients have PAVMs. Others: congenital, post hepatic (hepatopulmonary syndrome), trauma, infection, mitral stenosis, Fontan circulation.

Prevalence about 1 in 2600 overall (HHT 1 in 5000).

Complications from shunt: paradoxical embolism (stroke 10 to 30%, TIA), cerebral abscess (5 to 10%), hypoxaemia, polycythaemia, haemoptysis, haemothorax (life threatening, worse in pregnancy), migraine.

• Dyspnoea, cyanosis, clubbing, platypnoea orthodeoxia (hypoxaemia upright), epistaxis and telangiectasia (HHT), haemoptysis.
• Bruit over lung fields, increased with inspiration.
• Neurological events (stroke, abscess) as presentation.
• Pregnancy may cause haemorrhage and deterioration.

• Contrast (bubble) echocardiography: delayed (after 3 to 8 cardiac cycles) appearance of bubbles in left atrium (grading 1 to 3).
• Pulse oximetry and blood gas (hypoxaemia, 100% oxygen shunt test).
• Thoracic CT (non contrast thin slice) shows feeding artery, nidus and draining vein; CT pulmonary angiography; digital subtraction angiography at embolisation.
• HHT screening: Curaçao criteria (epistaxis, telangiectasia, visceral lesions, family history); genetic testing; brain MRI and liver imaging in HHT.
• Haemoglobin, iron studies.

• Transcatheter embolisation (coils or vascular plugs) for all PAVMs with feeding artery diameter 2 to 3 mm or more, regardless of symptoms: success over 95% closure, improves oxygenation and reduces stroke and abscess risk. Follow up CT at 6 to 12 months, then every 3 to 5 years for persistence or reperfusion.
• Antibiotic prophylaxis before dental and other bacteraemic procedures (amoxicillin 2 g one hour before; clindamycin 600 mg if allergic).
• Air filters on all intravenous lines; meticulous removal of air bubbles; avoid scuba diving.
• Treat iron deficiency (iron 100 to 200 mg elemental, IV iron) and anaemia from epistaxis/gastrointestinal bleeding in HHT (tranexamic acid 1 g three times daily, bevacizumab 5 mg/kg IV every 2 weeks, pomalidomide 4 mg daily).
• Pregnancy: screen and treat PAVMs before conception; second trimester embolisation if needed; obstetric planning at a specialist centre.
• Screen family members.
• Surgical resection or lobectomy only if embolisation fails; avoid anticoagulation if possible in HHT bleeding.
• Brain MRI baseline in HHT for cerebral AVM.