Foramen Ovale: Definition, Development, Function, Clinical Significance, Medical Care and Complications

In the fetal heart, it is the opening in the interatrial septum in the heart that allows blood to enter the left atrium from the right atrium.

The foramen ovale (or ovalis), is also known as the foramen Botalli, the ostium secundum of Born or falx septi,

This allows blood to bypass the baby’s lungs since, while in the womb, the baby receives oxygen from the mother’s placenta.

It is one of the two fetal heart shunts , the other is the ductus arteriosus, it allows blood (which still escapes to the right ventricle) bypassing the pulmonary circulation and the non-ventilated lungs, from the right atrium to the left atrium.

Specifically, it represents the opening between the upper and lower parts of the secundum septum. Another similar adaptation in the fetus is the ductus venosus. In most people, the foramen ovale closes at birth. Later it forms the oval fossa.

Development

The foramen ovale (from Latin, meaning “foramen ovale”) forms at the end of the fourth week of gestation, as a small passageway between the septum secundum and the ostium secundum.

Initially, the atria are separated from each other by the septum primum, except for a small opening under the septum, the ostium primum. As the septum primum grows, the ostium primum narrows and eventually closes.

Before it does, the blood flow from the inferior vena cava wears away a part of the primary septum, forming the ostium secundum. Some embryologists postulate that ostium secundum can form through programmed cell death.

The ostium secundum provides communication between the atria after the ostium primum closes completely. Subsequently, a second wall of tissue, the septum secundum, grows over the ostium secundum in the right atrium.

So the blood only passes from the right atrium to the left through a small passage in the septum secundum and then through the ostium secundum. This passage is called the foramen ovale.

Closing

The foramen ovale normally closes in the immediate postnatal period, specifically at birth. At birth, when the lungs become functional, the foramen closes under the influence of changing pressures in the cardiac chambers when:

Placental flow ceases, raising right atrial pressure, and the lungs aerate and ventilation occurs, increasing venous return from the lungs, increasing left atrial pressure.

This forces the septum primum against the septum secundum, functionally closing the foramen ovale. Over time after closure, the septa eventually fuse, a small oval depression persists in the interatrial wall, leaving a remnant of the foramen ovale, the fossa ovale.

Function

A fetus receives oxygen not from its lungs, but from the mother’s oxygen-rich blood through the placenta. Oxygenated blood from the placenta travels through the umbilical cord to the right atrium of the fetal heart.

Since the fetal lungs are not functional at this time, it is more efficient for the blood to avoid them. This is accomplished through 2 cardiac leads. The first is the foramen ovale that derives blood from the right atrium to the left atrium.

The second is the ductus arteriosus, which diverts blood from the pulmonary artery (which, after birth, carries blood from the right side of the heart to the lungs) to the descending aorta.

Clinical significance

In about 25% of adults, the foramen ovale does not close completely and a small amount of blood can continue to cross from the right side to the left side of the heart without passing through the lungs.

This is called a patent foramen ovale (PFO). In most of these people, a patent foramen ovale does not cause problems and remains undetected throughout life.

Patent foramen ovale has long been studied because of its role in paradoxical embolism (an embolism that travels from the venous side to the arterial side). This can lead to a stroke or transient ischemic attack.

Transesophageal echocardiography is considered the most accurate investigation to demonstrate a patent foramen ovale. A patent foramen ovale can also be an incidental finding.

Patent foramen ovale has been found to be more common in patients experiencing migraine with aura.

However, many patients with a patent foramen ovale do not have migraines, and many patients with migraine do not have a patent foramen ovale. Furthermore, there is no conclusive evidence that fixation of a patent foramen ovale benefits migraines.

Medical care

Most patients with a patent foramen ovale as an isolated finding do not receive any special treatment. There is no consensus on the treatment of patent foramen ovale in patients with transient ischemic attack (TIA) or stroke.

When patent foramen ovale is associated with an otherwise unexplained neurological event, the traditional treatment has been antiplatelet therapy (i.e., aspirin) alone in low-risk patients or combined with warfarin in high-risk individuals to prevent stroke cryptogenic.

With the administration of warfarin, the international normalized ratio (INR) remains at 2-3. Consultation with a neurologist is mandatory to direct this treatment.

The recurrence rate of stroke or transient ischemic attack has been reported to be as high as 3.4-3.9% per year.

In patients with atrial septal aneurysm and patent foramen ovale, the risk of first recurrent stroke in 2 years has been reported to be up to 9%, while the rate of subsequent stroke or transient ischemic recurrence in 2 years increases to 22% .

In a study that evaluated the antiplatelet effects of clopidogrel and acetylsalicylic acid in 140 patients who underwent patent interveinal closure or atrial septal defect (ASD).

Polzin et al. reported a 71% incidence of high on-treatment platelet reactivity (HTPR) to clopidogrel but only 4% of on-treatment high platelet reactivity for aspirin.

Of the 12 complications observed, 9 were bleeding events (including 3 major bleeding events) and the remaining 3 were transient ischemic attacks.

The investigators noted that despite the high incidence of high platelet reactivity to clopidogrel treatment in this patient population, there were no reports of stroke or thrombus formation in the occluder.

Complications

Complications of patent foramen ovale catheter closure, such as device embolism, device entrapment within the Chiari network, frame fracture, vascular damage, or perforation of the atrial wall, may require additional surgery.

Other possible complications include air embolism during device delivery, thrombus formation around the device, and infective endocarditis.