Prenatal therapy of congenital heart disease

Pathology description

Congenital heart disease (CHD) is a problem that occurs while the heart is still forming and will be present at birth. Defects can affect different parts of the heart (chambers, septa and valves) and blood vessels. 

CHD are the most frequent human malformations, and those most associated with other defects, syndromes and chromosomal abnormalities. In most cases, the specific cause of CHD, which usually has a multifactorial origin, is unknown.

Known risk factors include having a family history of congenital heart disease (especially having previously had a child with a CHD), genetic and environmental factors (such as some drugs), maternal diabetes, maternal alcohol or drug use, and exposure to industrial chemicals.

Diagnosis

Once a CHD that is amenable to be treated before birth is diagnosed, we have to confirm that it is occurring in isolation by performing an exhaustive ultrasound study to rule out other malformations and an amniocentesis to rule out associated genetic anomalies. 

The next step is to perform a complete study of the anatomy and function of the fetal heart using echocardiography. In this way we will be able to identify those cases that present a disease serious enough to consider prenatal treatment. Such cases are those that, left to evolve, will be accompanied by a progressive deterioration that will condition a severe ventricular hypoplasia, cardiac failure or severe pulmonary hypertension.

We must also confirm that the fetal heart is within a "recoverable" time, that is, at a time when prenatal therapy could improve the growth and ventricular function of the heart, thereby increasing the chances of having a biventricular circulation postnatally and minimizing secondary lesions in the brains and lungs of affected children. 

Once the study is completed, the situation is discussed in detail with the parents, who always have the final say on the treatment.

Treatment

Most CHDs pose no problem for the growth and development of the baby while in the womb of the pregnant woman, since the placenta performs the basic functions necessary for the development of the baby. Therefore, CHD is best treated after birth, as it is possible to offer a postnatal treatment for practically all types of CHD. However, in some cases fetal therapy is highly recommended to complement postnatal therapy or in cases where the CHD would lead to the death of the fetus before birth.  

There are some CHDs in which the anatomy and function of the heart worsens throughout pregnancy, which can cause heart failure and stillbirth. If these CHDs are treated by fetal surgery at the time of diagnosis, when the fetus is still too premature to be born, we can avoid death during pregnancy and improve the surgical options for the baby after birth, achieving a curative postnatal treatment and therefore an improvement in the prognosis in the medium and long term. 

In such severe cases of CHD, fetal therapy does not aim at the definitive intrauterine correction of the defect nor the replacement of postnatal treatment, but is performed to prevent the death of the fetus or to improve the surgical options after birth and the future quality of life of the baby. 

Although most CHDs can be corrected with surgery, and therefore cured, with excellent results both in terms of mortality and long-term evolution, there are still very severe CHDs that cannot be corrected after birth. In such cases, only palliative options can be offered, which are therefore not curative, and that have suboptimal results in the short, medium and long term. 

What CHDs are likely to be treated before birth?

They are those in which the main problem is a reduction in the passage of blood through the semilunar valves (which control the outflow of blood to the aorta and pulmonary arteries) or the foramen ovale (a natural opening of the fetal heart through which blood circulates).

The reduction of the passage of blood due to a CHD supposes: 

• A reduction in the growth and function of the ventricle (one of the chambers of the heart through which blood circulates), which may become too small to function after birth (ventricular hypoplasia). 
• An excessive increase in pressure in the heart, which leads to the development of hydrops fetalis (accumulation of fluid in other parts of the body) and fetal death during pregnancy. 
• A decrease in blood flow in other organs of the fetus (brain, lungs) that will produce irreversible secondary lesions in them, such as neurodevelopmental problems or pulmonary hypertension. 

There are three CHDs that reduce the passage of blood and are amenable to be treated before birth: 

• Critical aortic valve stenosis (narrowing of the valve that controls the outflow of blood from the heart). 
• Critical stenosis/pulmonary valve atresia (narrowing of the valve that controls the outflow of blood from the heart). 
• Foramen ovale restriction (narrowing of the hole that connects the two atria, which are chambers of the heart through which blood circulates). 

In these cases, fetal surgery before birth can be corrective or curative, allowing a biventricular circulation (as occurs in a healthy heart) with a much better quality of life. However, a postnatal surgery will be palliative, that is, not curative, and will condition what we call a univentricular circulation (a heart that works with only one ventricle) with a poor prognosis. 

In case of fetal therapy, if the pathology is an aortic or pulmonary stenosis, a valvuloplasty will be performed (to open the valve), while if it is a foramen ovale restriction it will be an atrial septostomy (to enlarge the foramen ovale). 

Both types of procedures are performed with the same methodology:  

• The intervention is performed under ultrasound control through a needle of just over 1 mm (in a similar way to how an amniocentesis is done). Local anaesthesia is used for the pregnant woman at the site of the puncture with a mild sedation, as well as fetal anaesthesia that we administer intramuscularly (in the fetal thigh or arm). 
• Needle insertion into the fetal heart is controlled by ultrasound. After passing through the pregnant woman's abdomen, the uterine wall, the amniotic cavity and the fetal chest, the needle is inserted into the heart to look for the valve or the foramen ovale. 
• The devices necessary for the intervention are inserted through the needle. 
• A small expandable tube (stent) is placed in the foramen ovale.  
• After checking for improvement in blood flow through the valve or foramen ovale, the needle is removed. 

What appointments are needed for fetal surgery?

An in-patient admission of the pregnant woman will initially last 1–2 days and afterwards weekly check-ups with examination and ultrasound will be required, and she will have to maintain a low-activity lifestyle mainly at home until the end of pregnancy, especially for the first 3-4 weeks after the intervention. 

In general, it is recommended that the baby is born at term, that is, when it is due, and that the start of delivery is spontaneous. For most heart defects, the more mature the baby is and the more it weighs at birth, the better. This means that it is a setback if the baby is born prematurely.

Although in some infrequent cases it may be necessary for the fetus to be born by caesarean section, in the vast majority of cases the pregnant woman can have a natural birth. In such cases the baby will need specialized care immediately after birth, so it is advisable that the delivery takes place in SJD Barcelona CHildren's Hospital. The paediatric Heart Area service will follow the postnatal evolution of the baby. 

During pregnancy, you will receive the support of nurses specialized in fetal medicine, not only on a technical level but also on an emotional level throughout the process. In addition, we can put you in contact with other families who have gone through the same experience. This is very positive and helps to humanize and understand the problem in a much more intuitive way and without the difficulties that sometimes arise when receiving only technical information from professionals.