Clinical implications of residual shunt after patent foramen ovale closure

Residual shunt (RS) after percutaneous patent foramen ovale (PFO) closure has classically been a question of debate for controversial results about its association with increased risk of recurrent ischemic events. Different underlying processes of neural tissue injury have to be taken into account evaluating clinical impact of residual shunt after PFO closure: clotting mechanisms and non-clotting, vasoactive or oxidative mechanisms. Some biochemical studies demonstrated the importance of effective PFO closure aimed to obtain significant reduction of several molecules involved in PFO related strokes. Blood levels of serotonin and homocysteine seem to significantly decrease after percutaneous procedures. A recent study on a pro-thrombotic phenotype of migraineurs with aura and PFO demonstrated that PFO closure reduce activated platelets and thrombin at the value of healthy subjects, underlining the importance of the correct sealing of the defect. The aim of this review is to examine currently available literature studies. Different and discordant results have been obtained due to heterogeneity of study population, instrumental assessment of RS and follow-up methods and length. In the 2021 American Guidelines for the prevention of stroke, RS was definitely considered a predictor of recurrence of ischemic events. Management of this subset of patients is still an unresolved issue and more studies are encouraged.