ISCHEMIC STROKE / CLASSIFICATION AND PATHOGENESIS

David Goldemund M.D.
Updated on 03/03/2024, published on 31/10/2021

• pulmonary arteriovenous malformation (PAVM) comprises abnormal connections between pulmonary arteries and veins
  • synonyms:  pulmonary AVM, pulmonary arteriovenous fistula, pulmonary arteriovenous aneurysm
• PAVMs are rare in the general population
  • it is estimated that 70-80% of PVAMs are related to HHT (hereditary hemorrhagic telangiectasia – Osler-Weber-Rendu), mainly HHT1 (10 times more than HHT2) → more about HHT see here
  • ≥ 15% of patients do not fulfill the criteria for a diagnosis of HHT and have no other systemic disease
• neurological complications occur in ~ 50% of patients
  • paradoxical embolism can cause  TIA/stroke, ICH, or a cerebral abscess
  • concurrent cerebral AVM (CAVM) can cause ICH or epilepsy

• direct arterio-venous shunts without embedded capillaries
• PAVM, together with PFO, patent ductus arteriosus, and other congenital heart defects, is categorized as a condition at risk of paradoxical embolism
  • contrary to PFO, where the shunt is frequently seen only post-Valsalva maneuver, the shunt in PAVM is continuous
  • concurrent occurrence of PAVM and PFO is possible (consider the possibility of PAVM before PFO closure)
    
    • disproportionately massive and early shunt on the TCCD bubble test in the case of a small/moderate PFO on TEE should raise suspicion of another shunt
• additional pathogenetic mechanisms besides paradoxical embolism include:
  • polycythemia with hyperviscosity syndrome
    
  • hypoxia
  • air embolism originating from a defect in the PAVM wall
• PAVMs may be located in any lung segment, with a predilection for the lower lobes

Classification

• according to the feeding artery
  • simple (2/3) – single feeding artery with a single draining pulmonary vein
  • complex (1/3) – multiple feeding arteries or draining veins
  • diffuse type (~5%) – dozens to hundreds of malformations
• by other symptoms
  • isolated PAVM
  • PAVM in HHT (together with telangiectasias)

• generally slow progression, with potential acceleration during pregnancy and adolescence
• the clinical course differs between isolated PAVM and PAVM associated with HHT
• symptoms most commonly occur between the 3rd and 6th decades of life
• an asymptomatic course is observed in up to 50% of patients (mostly in PAVM < 2cm)
• mortality and morbidity are mostly associated with stroke and brain abscess, less commonly with hypoxemic respiratory failure, hemoptysis, or hemothorax

• therapy targets:
  • prevent neurological complications
  • prevent pulmonary hemorrhage
  • improve hypoxemia, which can lead to fatigue, weakness, and other health problems
• indications for invasive management:
  • progressive PAVM growth (which indicates an increasing risk of complications)
  • paradoxical embolization (when blood clots or other debris travel through the PAVMs to the brain, causing strokes)
  • symptomatic hypoxemia
  • feeding vessels ≥3 mm
• no specific medical treatment

• lifetime antibiotic prophylaxis is recommended for surgical and dental procedures
• extreme caution is necessary during intravenous administrations to prevent air embolism
• in patients with known untreated PAVM, a follow-up CT scan every 2-3 years and annual oximetry are advised
• exclude cerebral AVM (CAVM) in patients with PAVM; evaluation of hepatic AVM is not routinely performed
• annual follow-ups are performed after endovascular treatment
• screening in offspring of parents with HHT includes:
  • pulse oximetry every 1-2 years
  • O₂ saturation < 97% warrants a TTE
    
  • in the presence of TTE abnormalities, a chest CT is indicated