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Understand the anatomy and embryology of the interatrial septum and patent foramen ovale (PFO).
Develop an overview of the many clinical associations of a PFO.
Appraise the clinical evidence for and against closure of PFO.
Patent foramen ovale (PFO) is a common finding, occurring in up to 25% of people.1 ,2 An association between PFO and stroke has consistently been seen in up to 50% of patients without an identifiable cause, that is, the so-called cryptogenic stroke (CS) and only in 20% with an identified cause.3 ,4 Many studies have been published testing the hypothesis that paradoxical emboli through a PFO may be implicated, however the available evidence is mixed and conflicting,5 ,6 perhaps in part due to the low recurrence rate and long-term nature of these events. PFOs are associated with numerous other conditions including migraine with aura, decompression sickness, other venoarterial embolic phenomena and platypnoea orthodeoxia.
In this review we will describe the embryological development of the interatrial septum, discuss the diagnosis and clinical associations of PFO, as well as evaluate the available data for and against closure.
Anatomy and embryology
The embryological development of the interatrial septum and foramen ovale is complex, starting at 4–5 weeks post conception with fusion of ventral and dorsal endocardial cushions. Closure of the atrioventricular canal creates two cavities that develop into atria and ventricles and divide into left and right sides. Initially the septum primum grows from the roof of the atria towards the fused endocardial cushion (figure 1A), while the gap, the ostium primum, allows interatrial flow. Before complete atrial separation, a new communication, the ostium secundum, develops by fenestration of the superior region (figure 1B), allowing continuous right-to-left shunting of oxygenated blood from the umbilical arteries bypassing the fetal pulmonary circulation (figure 1 …
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