Definition - What is the foramen ovale?

The heart consists of two atria and two chambers, which are usually separated from each other. The foramen ovale, however, represents an opening, which causes the fetus to pass blood from the right atrium into the left atrium. Normally, the blood would pass from the right atrium into the right ventricle and through the pulmonary circulation into the left atrium. In the fetal circulation, the pulmonary circulation is largely drained from the bloodstream, which is functionally facilitated by the shorting of the foramen ovale. Reason for the redirection of the blood is that the lungs in the fetus can not take on any respiratory function and therefore initially only has to be supplied with low blood. Due to the birth process and the function of the lungs, the foramen ovale closes.

Anatomy of the heart

The heart is composed of a right and a left atrium and a right and a left ventricle. Between the two atria is the atrial septum, which divides the heart into a right and a left half. The atrial septum is thinner compared to the ventricular septum and has a thinner muscle layer.

The blood enters the right atrium via two large body veins, the inferior vena cava and superior vena cava. From there, the blood is passed into the right ventricle and further into the pulmonary circulation. Via the pulmonary veins, the oxygenated blood from the pulmonary circulation returns to the left atrium. Here it is transmitted via the left ventricle into the aorta and thus enters the large body cycle.

In the fetal circulation, there is an opening between the right and left atria called the foramen ovale. This opening is absolutely normal because the lungs are not ventilated in the fetal circulation.

After birth, when the pulmonary circulation is opened, pressure changes within the heart lead to a change in the blood circulation via the right ventricle and the pulmonary circulation to the left atrium.

The foramen ovale is now no longer needed, so this usually closes quickly. If the foramen ovale does not occlude or only incompletely closes, it can lead to pathological symptoms.

What role does the foramen ovale play in the baby?

After birth and as a result of a baby's first breath, there is a change in pressure within the lungs and heart. The blood is no longer passed through the foramen ovale, but goes through the natural lung and systemic circulation. The foramen ovale is now no longer needed and usually closes by merging the atrial septum layers. This leads to a complete demarcation of the right side of the heart from the left side of the heart.

The closure of the foramen ovale by fusion of the septum usually occurs within the first days or weeks after birth. However, the closure may last longer than a few weeks or even never completely during the course of life. This does not necessarily have to be a malignant disease. Depending on the size of the foramen ovale and possible combined heart defects, a life without necessary treatment is possible or not. However, an examination by a specialist should be made in any case.

What is a forum ovale apertum / persistens?

If the foramen ovale does not close or does not close completely after birth, it results in a foramen ovale apertum, which is also called foramen ovale persistens.

Normally, after the lungs have been ventilated as a result of a baby's first breath, the blood is passed on to the left atrium through the pulmonary circulation. The foramen ovale is therefore no longer necessary and closes with time. In some babies, however, there is no closure of the septum, whereby the disease develops foramen ovale persistens. In most cases, however, the disease is very low and no compulsory treatment is necessary as the heart automatically guides the blood through the pulmonary circulation due to high pressures in the left atrium and correspondingly lower pressures in the right atrium. In a healthy heart, without further heart defects, therefore, only a small proportion of the blood is transmitted via the foramen ovale between the atria. It comes to a kind of valve-like closure. This unlocked foramen ovale occurs in about 25% of humans.

If there is an excessive crossing of the foramen ovale, for example, by changing the pressure conditions, more blood can pass from the right side of the heart to the left side of the heart without passing through the pulmonary circulation. Since a task of the lungs in addition to the enrichment with oxygen is also a filtering, more oxygen-poor and unfiltered blood is transported via the foramen ovale directly into the large body cycle. Depending on the amount of this blood, this may cause symptoms such as shortness of breath, decreased performance or migraine.

Paradoxical Embolism

A paradoxical embolism, also called "crossed embolism", is the passage of a blood clot (embolus) from the venous into the arterial part of the bloodstream. The reason for this is a defect in the area of ​​the heart septum, usually due to an unlocked foramen ovale. When the foramen ovale is closed, the lung takes over the function of filtering possible thrombi.

As a rule, after birth, by opening the pulmonary circulation, even in the case of an open foramen ovale, hardly any blood changes from the right to the left atrium. This is due to a highly regulated pressure gradient within the heart that dictates the flow direction of the bloodstream. If this pressure gradient changes when the foramen ovale is open, excessive passage through the open atrial septum may occur. If necessary, a clot may also pass over and thus enter directly into the arterial circulation system. If this now blocks blood vessels, it can lead to a closure, which manifests itself symptomatically.

The change in pressure can have many different causes such as coughing, sneezing, pressing or a pulmonary embolism.

What is the role of the foramen ovale in hitting?

One of many causes of a stroke may be an unclosed foramen ovale. This form of stroke is called a cryptogenic stroke. Cryptogen, in this regard, only states that none of the classic causes caused the stroke.

In an unlocked foramen ovale, small venous thrombi from the right atrium can enter the left atrium directly. This provides a quick and easy transition into the large body cycle. The pulmonary circulation is simply left out - the thrombus is directed from the right into the left atrium and from there directly into the left ventricle and the aorta, whereby such a thrombus can reach the brain correspondingly quickly.

How can you lock the foramen ovale?

The foramen ovale can be closed in adults by minimally invasive procedures.

A small incision is made on the groin, allowing a tube system (catheter) to be inserted and advanced across the blood vessels to the heart. At the heart, a small implant in the form of a screen on the open foramen ovale can then be inserted. The umbrella consists of two parts, which are made of a soft wire mesh. One of the shares is placed on the opening of the foramen ovale in the right atrium, while the other part is placed on the opening of the foramen ovale in the left atrium. The two parts are connected via a small bridge through the atrial septum opening. Within a few days, the wire mesh fuses into the heart wall, resulting in the final closure of the foramen ovale.

The procedure lasts between one and two hours and is performed in a cardiac catheterization lab. The implant used can remain in the heart for a lifetime if no discomfort occurs.

However, such an intervention is not universally recommended. Depending on the size of the foramen ovale and possible existing symptoms, a drug treatment by blood thinning may be sufficient or even no treatment at all.

Do you need a blood thinning in a foramen ovale?

In case of an open foramen ovale, it is not absolutely necessary to have a medication setting for blood-thinning medications.

Thrombi can pass through the foramen ovale, which is why the foramen ovale indirectly increases the likelihood of a possible stroke in the brain or other emboli within the large circulatory system. Blood thinning can greatly reduce the likelihood of thrombus formation.

However, blood thinning medications can also have negative consequences, as they cause an increased risk of bleeding. The drug setting should therefore be discussed in detail with a doctor.

Function of the foramen ovale

The main function of the foramen ovale is to transport the blood from the right to the left atrium, thereby preventing the blood from passing through the pulmonary circulation.

The lung is not yet ventilated in the fetal circulation. The fetus is supplied with oxygen via the placenta. Because of these facts, it is not necessary to bleed the lungs excessively. Only a small proportion of the blood must reach the lungs to supply the tissue and the training of the pulmonary vessels.

Due to a pressure gradient within the heart and lungs, most of the blood is directed directly into the left atrium via the foramen ovale. This pressure gradient plays a decisive role after birth. At birth, the pressure within the pulmonary circulation is reduced by the development of the lung, while the pressure in the left atrium is increased. Blood always takes the path of the least resistance prevailing by the change in pressure in the lungs. As a result of these pressure changes, there is an altered blood conduction and subsequent closure of the foramen ovale. The blood is therefore no longer passed through the foramen ovale, but now takes the natural bloodstream of a healthy person with blood flow through the lungs.

The ductus arteriosus botalli represents a similar form of bypassing the pulmonary circulation. However, this is not an opening of the septum, but is made possible by a physiological vascular connections between the pulmonary artery (trunk pulmonalis) and the aorta.

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