The ductus arteriosus is a physiological vascular channel in fetal life that connects the isthmus of the aorta with the root of the left pulmonary artery. After birth, due to a reduction in pulmonary vascular resistance, a significant decrease in prostaglandin E levels, and an increase in oxygen partial pressure, about 85% of infants experience closure of the ductus arteriosus within the first two months of life. Once closed, the ductus becomes the ligamentum arteriosum. If closure does not occur, the condition is referred to as patent ductus arteriosus (PDA). PDAs can be classified into three morphological types based on their size, length, and shape: tubular, funnel-shaped, and window-like.
Figure 1 Patent ductus arteriosus
Pathophysiology
The pressure in the aorta significantly exceeds that in the pulmonary artery under normal conditions. When the ductus arteriosus remains patent, blood flows continuously from the aorta into the pulmonary artery, creating a left-to-right shunt. The volume of the shunt depends on the diameter of the ductus and the pressure gradient between the aorta and pulmonary artery. The left-to-right shunt leads to an increase in pulmonary blood flow, imposing a volume overload on the left ventricle and causing left ventricular hypertrophy. The increased pulmonary blood flow also elevates pulmonary arterial pressure, triggering reactive spasms in the small pulmonary arteries. Early in the condition, this results in dynamic pulmonary hypertension. With a large or prolonged shunt, intimal thickening, medial smooth muscle hypertrophy, and fibrosis of the small pulmonary arteries occur, leading to lumen narrowing and irreversible pathological changes, eventually culminating in obstructive pulmonary hypertension. Pulmonary vascular resistance and pressure increase markedly during this phase, placing a significant afterload on the right heart and resulting in right ventricular hypertrophy. When pulmonary artery pressure approaches or exceeds aortic pressure, blood flow may become bidirectional or right-to-left. Cyanosis and clubbing of the fingers and toes develop, referred to as Eisenmenger syndrome, which can lead to right heart failure and death.
Clinical Presentation
Patients with a narrow ductus and a small shunt often remain asymptomatic, whereas those with a wide ductus and a large shunt frequently develop congestive heart failure. Symptoms may include irritability, shortness of breath, fatigue, excessive sweating, feeding difficulties, and growth retardation. In cases of severe pulmonary hypertension with the development of a right-to-left shunt, cyanosis of the lower extremities and clubbing of fingers and toes, termed "differential cyanosis," may occur.
Auscultation often reveals a rough, continuous machinery-like murmur at the left second intercostal space near the sternum, with the terminal systolic phase being most prominent. The murmur may radiate to the neck and back, and a continuous thrill is often palpable. When pulmonary hypertension is present, there may be a systolic murmur or disappearance of the murmur, with an accentuated second heart sound at the pulmonary valve. In cases with a large shunt, a mid-diastolic rumbling murmur at the apex due to relative mitral stenosis may be detected. Reduced diastolic pressure leads to widened pulse pressure, accompanied by peripheral vascular signs such as capillary pulsation in the nail bed, bounding peripheral pulses (Water-hammer pulse), and gunshot sounds over the femoral artery.
Auxiliary Examinations
Electrocardiogram
This may appear normal or show signs of left ventricular hypertrophy. With pulmonary hypertension, evidence of both left and right ventricular hypertrophy is often detected.
X-Ray Examination
Findings include cardiac enlargement, a prominent aortic knob, left ventricular enlargement, and increased pulmonary vascularity. Fluoroscopy may show increased pulsations in the hilar arteries, referred to as the “dancing hilum sign.” Severe pulmonary hypertension is suggested by a smaller cardiac silhouette, thickened hilar vessels, and reduced peripheral lung vasculature, known as the "pruned tree sign."
Ultrasound
This may show left atrial and left ventricular enlargement. Anomalies in the ductus arteriosus and abnormal blood flow signals can also be visualized.
Diagnosis
Diagnosis of PDA is generally straightforward for cases with an isolated lesion based on the nature and location of the murmur, associated peripheral vascular signs, and findings from echocardiography, X-ray, and electrocardiography. For more complex cases with additional anomalies, right heart catheterization or aortography may be performed for further clarification. Differential diagnosis includes conditions such as aortopulmonary septal defects, ruptured aortic sinus aneurysms, coronary artery fistulas, or ventricular septal defects with concurrent aortic valve insufficiency.
Treatment
Indications for Surgery
Surgical intervention is recommended for preterm infants and young children who experience recurrent pneumonia, respiratory distress, heart failure, feeding difficulties, or growth retardation. For asymptomatic patients presenting with pulmonary hypertension, elective surgery is advised.
Contraindications for Surgery
Eisenmenger syndrome represents a contraindication for surgical intervention.
In certain complex congenital heart defects, a patent ductus arteriosus (PDA) serves as a compensatory pathway essential for survival, such as in interrupted aortic arch, complete transposition of the great arteries, or pulmonary atresia. In these situations, the ductus arteriosus should not be ligated in isolation, and correction of associated cardiac anomalies must be performed concurrently.
Surgical Techniques
Ligation/Clamping and Division with Suture Repair
This procedure involves accessing the left thoracic cavity via a left posterolateral incision at the fourth intercostal space or using video-assisted thoracoscopic techniques. The mediastinal pleura in the triangle of the ductus arteriosus is dissected, taking care to protect the vagus and recurrent laryngeal nerves. The ductus arteriosus is isolated and, following controlled hypotension, is ligated doubly with coarse sutures or occluded with tantalum clips. Common complications include rupture and hemorrhage from the ductus arteriosus or adjacent aorta and pulmonary artery, injury to the recurrent laryngeal nerve, ductal recanalization, or pseudoaneurysm formation.
Catheter-Based Occlusion
Percutaneous transcatheter occlusion involves accessing the femoral artery and vein via percutaneous puncture under fluoroscopic or ultrasound guidance. The right heart catheter is advanced through the pulmonary artery and ductus arteriosus into the descending aorta, and a device, such as an occluder or a coil, is deployed to close the ductus arteriosus after ensuring its position. This approach is suitable for older patients.
Surgical thoracoscopic occlusion is performed through a small incision at the third intercostal space along the left sternal border, guided by esophageal ultrasound. A catheter is advanced through the pulmonary artery to the ductus arteriosus and aorta, and an occluder device is deployed. This technique is applicable to patients of all ages. It eliminates the risks associated with radiation exposure and vascular injury to the lower limbs. In the event of an occlusion failure, surgical rescue measures are more timely and effective.
Ligation or Internal Closure of the Ductus via Cardiopulmonary Bypass
This procedure is performed through a median sternotomy with the establishment of cardiopulmonary bypass. The ductus arteriosus is dissected and ligated within the pericardial cavity. Alternatively, the pulmonary artery is incised, and after reducing bypass flow temporarily under mild hypothermia, the internal opening of the ductus is either directly sutured or patched for repair. This approach is suitable for patients with concurrent cardiac anomalies requiring simultaneous surgery, as well as cases involving a short, wide ductus with calcification or aneurysmal changes, significant pulmonary hypertension, infective endocarditis, or ductal recanalization after ligation.