Patent arterial ductus: When the heart resists closing

A persistent ductus arteriosus is a somewhat common birth defect that occurs when the heart doesn't adapt properly to the start of breathing after birth. Like a Shadock, the heart starts pumping again and again... into the void or nearly so.

Adaptation of the fetal cardiovascular anatomy

During pregnancy, the fetus's lungs are not functional, and oxygen reaches it directly from the mother through the placenta attached to the umbilical cord. The fetal heart is, therefore, somewhat different from the adult heart to prevent the blood from unnecessarily seeking oxygen in the lungs. There are two cardiac shunts or circulatory pathways through which the majority of blood flow occurs:

1. The foramen ovale, which allows communication between the two atria of the heart.

2. The ductus arteriosus, which allows blood to circulate directly between the pulmonary artery and the aorta without passing through the lungs.

Fig. 1 : Fetal circulation (https://www.stanfordchildrens.org/en/topic/default?id=blood-circulation-in-the-fetus-and-newborn-90-P02362)

These two shunts also help to exercise the heart muscles and develop them properly.

At birth, the baby takes its first breath, and its lungs become functional. It no longer relies on its mother to supply oxygen but captures oxygen through its pulmonary system and the blood vessels within it. Several changes occur in the cardiac and pulmonary systems, leading the baby's anatomy to readjust to this new way of extracting oxygen.

The pressure decreases in the lungs, allowing the pulmonary microcirculation to establish itself. This results in a reversal of pressure between the right and left atria and enables a gradual functional closure of the foramen ovale. Simultaneously, the pressure in the aorta increases, reversing the pressure trend between it and the pulmonary artery. This leads to a change in the direction of the shunt, allowing oxygenated blood from the aorta to mix with deoxygenated blood from the pulmonary artery. At the same time, the oxygen pressure, indicating how much oxygen the baby's lungs are absorbing, goes up in the aorta due to the baby breathing on its own. The modification of these parameters, combined with a decrease in the concentrations of molecules called prostaglandins, causes the smooth muscles in the walls of the ductus arteriosus to contract, eventually leading to its closure in the hours following birth. After a few weeks, the ductus arteriosus has typically transformed into a ligament called the ligamentum arteriosum.

When everything doesn't go as planned

It is, however, possible that events do not unfold in this way. The shunts then remain open, leading to the establishment of a left-to-right shunt over time, meaning oxygenated blood (in the left side of the heart) passes into deoxygenated blood (in the right side of the heart).

In the case of non-closure or partial closure of the ductus arteriosus beyond 3 months of life, it is referred to as Persistent Ductus Arteriosus or PDA. This is a congenital malformation that occurs in 1 case out of 2000 to 1 case out of 5000 according to studies. This condition is common, especially in premature and very premature babies. Given that the lungs are not mature, it is easy to understand that the necessary adaptations to changes in heart anatomy cannot occur correctly.

The causes of this heart defect are not clear in all cases, but several possible factors are identified: prematurity, infections transmitted from the mother to the baby at birth or late in pregnancy, environmental factors (such as the mother taking medications or giving birth at high altitudes), or even multifactorial genetic predispositions (although no single gene has been identified).

Real marathon runners!

The consequences of the persistent circulation between the aorta and the pulmonary artery depend on the diameter of the canal but can be significant. Indeed, if the residual opening is very small, there will often be no symptoms. However, the larger the opening, the more significant the blood flow from the aorta to the pulmonary artery. In other words, already oxygenated blood joins non-oxygenated blood to be unnecessarily reoxygenated in the lungs. The oxygenated flow reaching the organs is reduced, requiring the heart to constantly pump and send enough oxygenated blood to the body. Overall, the child feels as if they are continuously running or doing sports. Over time, this leads to an overload of work for the left heart and the onset of symptoms of heart failure. Among them are delayed growth and/or a plateau in weight gain, shortness of breath in mundane situations, and an elevated heart rate. The child may also develop pulmonary hypertension, which also leads to right heart failure. But the most common indicator that often leads medical professionals to refer to a pediatric cardiologist is the detection of a heart murmur, the characteristics of which evolve depending on the severity of the PDA. Echocardiography performed by a pediatric cardiologist confirms or refutes the suspicion of a PDA. Various parameters such as the diameter of the canal, the blood velocity in the arterial canal, or the volume of the left heart can be assessed, providing valuable information to characterize the PDA and guide the physician in deciding on treatment.

Medication or Surgery Treatments?

Two types of management are considered depending on whether the child is premature or full-term.

Medication treatments involve the use of non-steroidal anti-inflammatory drugs, , with indomethacin being the most commonly used molecule. As mentioned earlier, the closure of the ductus arteriosus is related to the modification of physical parameters between the lungs and the heart, but also to the decrease in the presence of molecules called prostaglandins. These anti-inflammatory drugs have the ability to reduce prostaglandin concentrations and thus help close the ductus. These drugs are only indicated for premature infants as they are ineffective in full-term infants.

The second solution is closure through catheterization. This is a semi-invasive method that aims to insert a small device (several forms are available) to block the ductus using a catheter. The catheter is inserted through the femoral artery (at the top of the thigh) and travels through the vessels to the heart to deposit the prosthesis. Once in place, the body will naturally generate a kind of scar tissue around the device. Thus, the ductus will be permanently closed. In 2021, this technique was used for the first time in a premature baby with a device specially designed for preterm infants.

Fig. 2 : Examples of devices used for the closure of a PDA by catheterization (https://www.cardiovascular.abbott/us/en/hcp/products/structural-heart/structural-interventions/amplatzer-pda.html)

In very rare cases, open surgery may be necessary to access the duct and close it. After treatment with medication or catheterization, symptoms naturally regress in the majority of cases, and the condition doesn’t reoccur.

Techniques are evolving, and dedicated medical devices are becoming increasingly effective. Therefore, PDA is not inevitable. An early diagnosis and appropriate management will restore the situation and overcome the nature that sometimes does not perfectly follow established rules.