The ductus arteriosus is a short arterial segment in the fetus that connects the origin of the main pulmonary artery to the aorta below the left subclavian artery. The ductus usually closes within the first hours of life. In cases where it persists, its wall often shows changes that suggest it is a primary anomaly that prevents it from following its natural course toward closure.
Patent ductus arteriosus has an incidence of less than 1 in every 1,000 live births, and is higher in premature infants. In most cases, it is an isolated anomaly, but it can accompany other congenital malformations, primarily aortic coarctation, ventricular septal defect, pulmonary stenosis, and aortic stenosis.
What are the consequences of a patent ductus arteriosus?
In the fetus, with collapsed lungs and no breathing, the lungs need little blood, so most of the blood flow passes from the pulmonary artery to the aorta through the ductus arteriosus. When the child begins to breathe at birth, increases the amount of blood to the lungs, and flow through the ductus arteriosus reverses, causing blood to flow from the aorta to the pulmonary artery. The consequences that these changes can produce depend on the diameter of the ductus arteriosus and the pressure difference between the aorta and the pulmonary artery.
When flow through the ductus arteriosus is limited, there is no significant overload, and the child can develop as a normal child. When it is large, however, the aorta’s blood overload into the pulmonary artery can cause pulmonary hypertension, and pulmonary edema.
Pulmonary hyperflow leads to volume overload of the left atrium, left ventricle, and ascending aorta, which dilate. Increased volume and pressure in the left atrium can cause the foramen ovale (natural hole in the interatrial septum) to become incompetent, allowing the blood to pass from the left atrium to the right atrium. Chronic volume overload on the arteries of the lungs can lead to thickening and stiffness of the arterial wall. Over time, it can diminish the flow through the ductus arteriosus and even reverse itself if the pressure in the pulmonary artery exceeds that of the aorta.
What symptoms does patent ductus arteriosus cause?
- In most cases, the ductus is not very large and does not cause symptoms. In these cases, it is diagnosed by auscultation of the characteristic murmur.
- In ductus arteriosus with a significant flow, heart failure can occur in infancy, sometimes even in newborns. In these cases, a child may be found with developmental delay, showing tachypnea (rapid breathing), intercostal or subcostal retraction, and hepatomegaly (enlarged liver).
- If the ductus arteriosus does not cause heart failure in the first 6 months of life, it is very rare for it to do so later. When it is discovered in an older child or adult, it is usually an incidental finding in an asymptomatic patient.
- The child with significant patent ductus shows a heart murmur and a prominent arterial pulse. In advanced cases, increased pulmonary vascular resistance can reverse the flow (venous blood from the pulmonary artery passes to the aorta), leading to cyanosis (bluish or purple skin color) and clubbing (clubbed fingers).
- Large ductus arteriosus, which causes significant heart failure in newborns or infants, can lead to death at these ages. Death in older children and adults can be due to heart failure or endocarditis (infection of the ductus arteriosus). In adults, the ductus arteriosus can also dilate and calcify, sometimes even rupturing.
How is the diagnosis made?
The electrocardiogram is normal when the ductus arteriosus is small. When it is large, it is usually normal at birth, and signs of left atrial and left ventricle enlargement subsequently appear. In some cases, left bundle branch block occurs. Right ventricle enlargement is observed later in the process, when pulmonary hypertension has already developed, and signs of biventricular enlargement are then found. In advanced stages, right atrial enlargement also occurs. Some patients present with supraventricular tachyarrhythmias, especially atrial fibrillation.
Chest x-ray shows dilation of the left cavities and aorta. Depending on the severity of the flow through the ductus, signs of pulmonary hyperflow will vary from case to case. Some patients develop pulmonary edema. In advanced cases, signs of pulmonary arterial hypertension may be present.
Echocardiogram is the most useful technique for diagnosing the ductus arteriosus. It is often possible to visualize it and determine its size. It is usually seen as a small tube connecting the aorta below the left subclavian artery to the distal portion of the pulmonary trunk, immediately above the left pulmonary branch.
Very narrow ducts may not be visible, but in these cases, typical turbulent flow is frequently detected with Doppler. Color Doppler demonstrates turbulent flow in the pulmonary artery, which with continuous Doppler is typically shown as a high-velocity curve, commonly continuous and with its maximum peak in systole.
Other imaging techniques, such as computed tomography, magnetic resonance imaging, and isotopic studies, are also useful for diagnosing the ductus, its consequences, and associated heart disease. Current cine techniques with computed tomography and magnetic resonance imaging can also provide hemodynamic data.
Cardiac catheterization is rarely performed in the ductus, as echocardiogram information is habitually sufficient. It is only indicated when there are diagnostic doubts or if there are other defects that require it.
What is the treatment for patent ductus arteriosus?
Initial treatment for a child with patent ductus arteriosus and heart failure is with medication. Preventing infective endocarditis with antibiotics should be used in all cases where indicated.
The classic treatment of choice is surgical closure of the ductus arteriosus, which can be performed at any age, even in newborns, as the technique has a low incidence of complications and death. However, it is not usually indicated for ductus arteriosus with insignificant flow. Closure by catheterization is also possible, using membranes or umbrellas to occlude the ductus arteriosus. However, this technique also has risks, such as device embolism and problems associated with catheterization. Closure can also be performed by thoracoscopy, which is achieved by inserting tubes without having to open the chest. Any of these techniques can be effective, successfully eliminating the flow in most cases. In some patients, a residual flow remains, which is commonly mild.
If ductal infection occurs, treatment is based on antibiotics. In these cases, ductal closure should be delayed for several months after the infection has healed, as the ductal cavity may remain edematous and friable for some time.
