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The foramen ovale (from Latin 'oval hole') forms in the late fourth week of gestation, as a small passageway between the septum secundum and the ostium secundum. Initially the atria are separated from one another by the septum primum except for a small opening below the septum, the ostium primum .
Atrial septal defect (ASD) is a congenital heart defect in which blood flows between the atria (upper chambers) of the heart.Some flow is a normal condition both pre-birth and immediately post-birth via the foramen ovale; however, when this does not naturally close after birth it is referred to as a patent (open) foramen ovale (PFO).
The fetal heart contains two upper atria and two lower ventricles. It also contains two additional structures, the foramen ovale and the ductus arteriosus, that function as shunts for oxygenated blood. [2] The function of these shunts is to bypass the lungs and maintain proper circulation to important fetal tissue.
The foramen ovale stays open because of the flow of blood from the right atrium to the left atrium. As the lungs expand, blood flows easily through the lungs and the membranous portion of the foramen ovale (the septum primum) flops over the muscular portion (the septum secundum). If the closure is incomplete, the result is a patent foramen ...
Classic for a patent foramen ovale (PFO) or atrial septal defect (ASD). A PFO is lack of closure of the foramen ovale. At first, this produces a left-to-right heart shunt. This does not produce cyanosis, but causes pulmonary hypertension. Longstanding uncorrected atrial septal defects can also result in Eisenmenger syndrome.
These routes include moving through a patent foramen ovale (a congenital hole connecting the right and left atria of the heart), a ventricular septal defect (a congenital hole connecting the ventricles), or a pulmonary arteriovenous fistula, where arteries in the lungs connect directly to veins without capillaries in between.
Although colour Doppler can be used to detect abnormal flows between the chambers of the heart (e.g., persistent (patent) foramen ovale), it has a limited sensitivity. When specifically looking for a defect such as this, small air bubbles can be used as a contrast medium and injected intravenously, where they travel to the right side of the heart.
When the pressure in the left atrium exceeds the pressure in the right atrium, the foramen ovale begins to close and limits the blood flow between the left and right atrium. While the eustachian valve persists in adult life, it essentially does not have a specific function after the gestational period.