Patent Ductus Arteriosus (PDA) Workup

The diagnosis of patent ductus arteriosus (PDA) is almost always based on careful clinical evaluation, including physical examination showing the characteristic murmur, typical electrocardiographic (ECG) abnormalities, radiographic changes, and echocardiographic/Doppler findings.

Echocardiography is the primary diagnostic study used to evaluate and diagnose patent ductus arteriosus (PDA). Chest radiography may provide some helpful information. Laboratory tests are generally not helpful in the workup of patent ductus arteriosus (PDA). Magnetic resonance angiography and cardiac computed tomography are alternative, more novel, diagnostic tools.

CBC and metabolic panel

A complete blood cell (CBC) count with differential and a chemistry profile are obtained to determine the overall health of the child. However, findings are usually within reference ranges in patients with this condition. Polycythemia may be present if the child has other congenital heart defects.

Pulse oximetry/ABG

Pulse oximetry/arterial blood gas (ABG) analysis usually demonstrate normal saturation because of pulmonary overcirculation. A large ductus arteriosus could cause hypercarbia and hypoxemia from congestive heart failure (CHF) and air space disease (atelectasis or intra-alveolar fluid/pulmonary edema).

In the event of pulmonary artery hypertension (PAH), right-to-left intracardiac shunting of blood, hypoxemia, cyanosis, and acidemia may be present.

The echocardiographic findings are typically diagnostic for patent ductus arteriosus (PDA). High velocity jets of turbulent flow in the pulmonary artery can be reliably detected by color flow Doppler imaging; this technique is sensitive in detecting even the small PDA. Relying on alternative imaging techniques to make the diagnosis of this condition is unusual. Additionally, echocardiography provides important diagnostic information regarding associated congenital cardiovascular malformations.

By 2-dimensional (2-D) echocardiography, the aortic end of the patent ductus arteriosus (PDA) is localized first, and then it is tracked back to the pulmonary artery. Precisely documenting the size, shape, and course of the ductus is difficult.

The patent ductus arteriosus (PDA) can be seen most easily in the parasternal short axis view and from the suprasternal notch. The classic patent ductus arteriosus (PDA) connects the junction of the main pulmonary artery and the left pulmonary artery with the aorta just below and opposite the left subclavian artery.

If no other abnormalities are present, Doppler echocardiography reveals continuous flow from the aorta into the main pulmonary artery. If the magnitude of the left-to-right shunt is large, continued flow around the aortic arch into the ductus arteriosus in diastole and flow reversal in the descending aorta are evident. Also, variable levels of continuous flow in the branch pulmonary arteries related to the magnitude of the shunt are observed. As the shunt magnitude increases, increased flow in the pulmonary veins is evident and the left atrium enlarges. With a small or moderate-sized patent ductus arteriosus (PDA), the left ventricular size is often normal, but as shunt magnitude increases, the left ventricular diastolic size also increases. (Qp/Qs can be calculated using Doppler velocity and left ventricular/right ventricular (LV/RV) outflow tract dimensions.)

One study evaluated the internal color Doppler diameter of the PDA and the pulsed Doppler flow pattern in 197 echocardiograms from 104 infants (gestational age < 31 wk). The data noted that while ductal diameter varied widely, it was significantly associated with flow patterns. Because results from the 2 methods may result in different treatment decisions, the use of both echocardiographic parameters may be helpful in managing preterm infants with PDA.^[3]

Findings on chest radiographs range from normal to those consistent for congestive heart failure (CHF). Cardiomegaly may be present with or without CHF.

If significant left-to-right shunt through the patent ductus arteriosus (PDA) is present, the pulmonary arteries, pulmonary veins, left atrium, and left ventricle are enlarged on chest films. Also, the ascending aorta may be prominent.

Usually, chest radiographic findings are normal until the magnitude of the ratio of pulmonary to systemic circulation (QP/QS) exceeds 2:1. Prominence of the main pulmonary artery segment is an early sign of increased pulmonary artery pressure and flow. With marked pulmonary overcirculation, pulmonary edema may occur. Accentuated peripheral pulmonary vascular markings and increased pulmonary venous markings may be noted. In elderly individuals, the patent ductus arteriosus (PDA) may calcify and may be visible on a standard radiograph.

Studies have shown that chest radiographs have limited predictive value in determining which infants will benefit from ligation.

With a small patent ductus arteriosus (PDA), the electrocardiographic (ECG) findings are typically normal. Left ventricular hypertrophy may be present with a larger PDA. Left atrial enlargement may also be present with large shunts. In the presence of significant pulmonary hypertension, there may be evidence of right ventricular hypertrophy.

In the neonate, especially the premature neonate with a large patent ductus arteriosus (PDA), T-wave inversion and ST segment depression may be present, suggesting ischemia or a supply-demand mismatch. This is thought to be related to increased myocardial work due to the left-to-right shunt and pulmonary overcirculation in the face of low aortic and coronary diastolic blood pressure due to the runoff of blood from the aorta into the pulmonary arteries.

Cardiac catheterization and angiography is not indicated for the uncomplicated patent ductus arteriosus (PDA). Color-flow Doppler mapping is more sensitive than cardiac catheterization in detecting a small patent ductus arteriosus (PDA). However, cardiac catheterization may be required for confirmation of clinical diagnosis in children with pulmonary hypertension and/or associated congenital cardiovascular malformations; response to pulmonary vasodilators can be important in planning operative intervention.

Cardiac catheterization may be used as a therapeutic procedure for coil embolization/occluder and to demonstrate the following:

• The shunt
• The amount of the shunt
• The pulmonary pressure
• Other coexisting cardiac abnormalities

During right heart catheterization, the measured oxygen saturation is increased in the pulmonary artery, except in Eisenmenger syndrome. The shunt (Qp/Qs) and the pulmonary vascular resistance (PVR) can be calculated to determine the size of the ductus and the presence of pulmonary vascular pathology.

Selective angiography is the definitive tool for determining the presence and size of the ductus. Angiography is also used to define the intracardiac anatomy when other defects are suspected.

Very rarely, a biopsy may be performed in severe cases. Histologic findings include the following:

• The walls of the ductus contain intima, media, and adventitia
• The medial layer of the structure is composed of longitudinal smooth muscle in the inner layer and circumferentially arranged smooth muscle in the outer layers; this is in contrast to true arterial structures, which contain a medium primarily composed of circumferential elastic fibers; these layers of smooth muscle contain concentric loose lamina of elastic tissue and a network of tiny thin-walled vessels.
• The intimal layer is irregularly thickened and contains a considerable amount of mucoid material