Chapter 2580: The Defective Wall

Another important reason is that the physical examination items of this era are too simple. The heart examination in the check-ups that children undergo annually at school, as required by the state, mostly involve an electrocardiogram and a chest X-ray, some don’t even include an electrocardiogram. Lacking instrumental detection, doctors attempt to detect subtle heart issues using a simple stethoscope: Hmm, the doctors who can do this are practically divine.

Moreover, relying solely on an electrocardiogram and a chest X-ray is very limited in diagnosing heart disease.

Take the simplest example, a 16-year-old girl in bed 12 with an atrial septal defect.

This condition is a congenital disease, meaning it is present from birth, starting as an anomaly from embryonic development. Interestingly, many cases of this congenital disease are diagnosed in adulthood, making it a common cardiac deformity in adults. What does this indicate? It indicates that it is hard to detect and cannot be identified without precise medical detection instruments. To be precise, a cardiac ultrasound is needed.

Why can’t this condition be detected in time with an electrocardiogram and chest X-ray? Let’s talk about its pathogenesis.

The atrial septum is like a wall, and as the name suggests, it is located between the left and right atrium. The wall’s function is to block, and the atrial septum blocks the blood of the left atrium and the right atrium, preventing the blood of these two atria from mixing.

The name atrial septal defect is more descriptive, as it illustrates the characteristics of this condition: the wall is defective. A defective wall appears either as a hole, one, two, or several holes, or directly as a missing part of the wall.

Since the cause of this condition is congenital, we need to start by discussing how the atrial septum develops.

In the process of constructing the atrial septum, an initial wall called the primary septum is first built. If there is an anomalous defect during the construction of the primary septum, the gap left is called a primary foramen. If the primary foramen is not filled in, it is called a primary foramen atrial septal defect. This is one type of atrial septal defect.

According to the description above, the primary septum needs to be completely constructed, thus preventing the illness. The issue lies in the fact that the process of constructing the atrial septum takes place during the fetal stage in the Uterus.

During the fetal stage, there is a significant issue: the fetus receives oxygen and other nutrients through the placenta, rather than its own pulmonary circulation. Therefore, the right atrium and left atrium of the fetus need to be connected so that blood rich in oxygen and nutrients from the placenta can directly flow into the fetus’ left atrium and left ventricle, and then circulate through the entire systemic circulation to nourish the whole body.

So, the atrial septum must not seal off the entire wall; what should be done?

In this case, a hole is deliberately left in the initial wall, which later develops and is referred to as the secondary foramen.

The secondary foramen is useful for the baby during the fetal stage, but it’s unnecessary after birth and should ideally close, as leaving it open can lead to problems. The body prepares for this by developing another wall on the primary wall called the secondary septum, which acts like a patch to close the hole. By now, the secondary foramen has another name that many mothers have heard of: the well-known foramen ovale.

In summary, during the fetal stage, to maintain the connection between the left and right atria, the secondary septum and the primary septum do not fuse. This allows blood to enter the right atrium through the foramen ovale and then pass through the gap between the primary and secondary septa to the left atrium.