The past and present of patent foramen ovale

Author: Zhang Tingting, attending physician at the Fuwai Hospital of the Chinese Academy of Medical Sciences

Reviewer: Wang Hao, Chief Physician, Fuwai Hospital, Chinese Academy of Medical Sciences

As people's health awareness improves, more and more people will undergo cardiac ultrasound examinations during health checkups. Some people are diagnosed with "patent foramen ovale". So, what is patent foramen ovale? Is it necessary to treat a patent foramen ovale found during ultrasound examination? Today, let us learn about the "past and present" of patent foramen ovale.

1. What is patent foramen ovale?

"Patent foramen ovale" literally means that the foramen ovale is not closed, so what is the foramen ovale? We know that the heart is composed of left and right atria and left and right ventricles, that is, the structure of "two rooms and two halls". The foramen ovale is an essential physiological channel connecting the left and right atria during the fetal period, which is equivalent to a functional small hole between the atria.

Figure 1 Copyright image, no permission to reprint

2. What is the function of the foramen ovale? Under what circumstances will the foramen ovale not close?

First, let's take a brief look at the blood circulation during the fetal period. In adults, the right heart system receives venous blood returning from the whole body and discharges it into the lungs for gas exchange, and then the left heart system ejects oxygen-rich blood into the various organs of the body to provide them with the nutrients and oxygen they need; but during the fetal period, because the fetal lungs are not fully developed and do not yet have the function of gas exchange, the fetus obtains oxygen and nutrient blood directly from the mother through the umbilical cord. After this oxygenated blood reaches the right atrium through the veins, it bypasses the lungs and directly passes from the right atrium through the foramen ovale to the left atrium, and then to the left ventricle. Through the ejection of the left ventricle, it reaches various organs throughout the body, thereby maintaining the blood oxygen balance in the fetus.

With the first cry of the fetus after birth, gas enters the alveoli, the alveoli gradually open, the lungs officially begin to perform its breathing mission, the pressure in the lungs and the pressure in the right heart gradually decrease, and the "foramen ovale", which was once a life channel, gradually loses its meaning of existence. Blood enters the pulmonary circulation through the right atrium and the right ventricle, and no longer enters the left atrium through the right atrium. The foramen ovale gradually closes functionally, and most people will achieve anatomical closure about 1 year after birth. If the foramen ovale persists and does not close, we call it a patent foramen ovale. Of course, in a few cases, such as patients with pulmonary hypertension and massive tricuspid regurgitation, the foramen ovale that has been physiologically closed will open again due to increased pressure in the right atrium. At this time, we will also diagnose it as a patent foramen ovale.

3.Is patent foramen ovale a congenital heart disease?

We do not usually classify it as a congenital heart disease because it is not a congenital developmental defect like atrial septal defect, but is caused by physiological failure of the channel to close.

4. How to diagnose patent foramen ovale?

The best means of evaluating cardiac structure and function is cardiac ultrasound, also known as echocardiography. Of course, this is also the main method for diagnosing patent foramen ovale. Transthoracic cardiac ultrasound has a high detection rate for patent foramen ovale in children, and can usually clearly show the structure of the atrial septum and the shunt at the atrial level. For adults and a few children, there may be a poor acoustic window of transthoracic echocardiography. At this time, the diagnostic accuracy of patent foramen ovale is low, and it is easy to misdiagnose or miss the diagnosis. At this time, transesophageal echocardiography can be selected. For patients suspected of having patent foramen ovale and related clinical symptoms, in order to further clarify whether there are surgical indications, transcranial Doppler ultrasound acoustic contrast examination may be required, which is what we usually call TCD bubble test. The principle is that during transcranial Doppler ultrasound examination, normal saline is injected through the peripheral vein. If there is a right-to-left shunt in the heart, microbubbles can be detected in the middle cerebral artery.

5. What should I do if an echocardiogram shows patent foramen ovale?

In most cases, patent foramen ovale is discovered during physical examination or routine examination. Since the shunt of foramen ovale is very small, it generally does not increase the load on the heart and does not have a significant effect on hemodynamics. Therefore, most people have no obvious clinical symptoms and do not need treatment. In a few cases, patent foramen ovale may be associated with certain diseases, such as unexplained ischemic stroke, transient ischemic attack, migraine, etc. This situation mostly occurs in relatively young adults (generally less than 60 years old), and its mechanism of occurrence is not completely clear. Current studies believe that: when the right atrial pressure increases, there is a shunt from the right atrium to the left atrium, and microemboli or vasoactive substances pass through the foramen ovale to the left heart system and then to the cerebral artery, thereby causing related neurological symptoms. At this time, detailed examination and evaluation are required. Commonly used examination methods include transcranial Doppler ultrasound, transthoracic echocardiography, transesophageal echocardiography, and right heart acoustic angiography. After a detailed evaluation, if there is a definite indication, transcatheter foramen ovale closure can be considered. For people who are found to have a patent foramen ovale and are at risk of related diseases, whether treatment is needed and the treatment method need to be individually evaluated based on the patient's condition, risk factors, etc. It should neither be ignored nor over-treated.