Children with hypoplastic left heart have poorly developed left ventricles. The reason for the poor development is generally attributed to problems with the mitral valve at the entrance of the left ventricle and the aortic valve at the exit, which may be maldeveloped or directly closed. The left ventricular cavity is small, and the chain reaction is that the ascending aorta is also reduced, and it changes from a large blood vessel to a small blood vessel.
We know that the left ventricle is very important to the human body, and the blood pumped out must support the systemic circulation. A small left ventricle and a small aorta will reduce the blood flow pumped out to the systemic circulation, causing ischemia and hypoxia in the child. In order to maintain a sufficient blood flow to maintain the systemic circulation, the child's heart can only speed up, leading to and aggravating heart failure. This leads to a series of clinical symptoms mentioned above.
To summarize, several links of the left heart system all go wrong due to mutual influence during the development process, so it is called hypoplastic left heart syndrome.
Why do the child's current symptoms not seem serious?
"Because there are multiple atrial septal defects that shunt his blood, and the ductus arteriosus is not closed." Xie Wanying added some of her own speculations.
We have already talked about the situation of the child in the mother's womb in the chapter on atrial septum. The heart and circulatory system in the fetal period is different from that after birth. The same is true for this disease. It is only after the child is born and breathes on his own that we can finally experience the serious consequences of this heart abnormality, and then the symptoms of this disease will gradually appear.
It seems that the best state for the child to avoid ischemia and hypoxia is, theoretically speaking, to return the child's heart and circulatory system to the state it was in the fetal period. The atrial septal defect is large, which is just equivalent to the unclosed wall in the fetal period to do shunt. At the same time, the arterial ductus in the fetal period is not closed, which allows the blood in the pulmonary artery to flow to the aorta to support the systemic circulation as in the fetal period.
As classmate Xie said, this child's heart is exactly like this, no wonder the symptoms are mild.
Can this situation continue?
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The answer is no. First of all, normally, the ductus arteriosus begins to close functionally within a few hours to a few days after birth, and closes anatomically after one or two months, just like the closure of the foramen ovale. Even if it does not close, if this situation lasts for a long time——
"It will not work if we don't have the surgery right away. If we delay any longer, it might turn into pulmonary arterial hypertension. If it turns into pulmonary arterial hypertension, it will be impossible to have the Fontan surgery," said Xie Wanying.
This is to say that according to the above principle, whether it is patent ductus arteriosus or atrial septal defect, shunt support only solves the problem of insufficient blood flow in part of the systemic circulation, but cannot prevent the existence of mixed arterial blood. Mixed blood pumped into the systemic circulation will also cause hypoxia in the body. The Fontan operation is a full cavopulmonary anastomosis, connecting the superior and inferior vena cava directly to the pulmonary artery. This allows only arterial blood with high oxygen content to flow into the heart cavity, avoiding the mixing of arterial blood. The blood pumped out into the systemic circulation is only arterial blood, which can greatly improve the body's hypoxia.
The prerequisite for Fontan surgery is good pulmonary circulation and no pulmonary hypertension. What to do? This is the first-stage surgery for treating hypoplastic left heart, the Norwood surgery, which simply cuts the entire atrial septal defect to expand the communication between the rooms.
Then cut the main pulmonary artery at the bifurcation of the left and right pulmonary arteries, connect the side of the main pulmonary artery to the side of the aorta and expand the aorta.
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