What is the pathogenesis of patent ductus arteriosus (PDA)?

Updated: Nov 20, 2018
  • Author: Luke K Kim, MD; Chief Editor: Stuart Berger, MD  more...
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Answer

The ductus arteriosus is normally patent during fetal life; it is an important structure in fetal development as it contributes to the flow of blood to the rest of the fetal organs and structure. From the 6th week of fetal life onwards, the ductus is responsible for most of the right ventricular outflow, and it contributes to 60% of the total cardiac output throughout the fetal life. Only about 5-10% of its outflow passes through the lungs.

This patency is promoted by continual production of prostaglandin E2 (PGE2) by the ductus. Closure of the ductus before birth may lead to right heart failure. Prostaglandin antagonism, such as maternal use of nonsteroidal anti-inflammatory medications (NSAIDs), can cause fetal closure of the ductus arteriosus.

Thus, a patent ductus arteriosus (PDA) produces a left-to-right shunt. In other words, it allows blood to go from the systemic circulation to the pulmonary circulation. Therefore, pulmonary blood flow is excessive (see the image below). Pulmonary engorgement results with decreased pulmonary compliance. The reaction of the pulmonary vasculature to the increased blood flow is unpredictable.

Schematic diagram of a left-to-right shunt of bloo Schematic diagram of a left-to-right shunt of blood flow from the descending aorta via the patent ductus arteriosus (PDA) to the main pulmonary artery.

The magnitude of the excess pulmonary blood flow depends on relatively few factors. The larger the internal diameter of the most narrow portion of the ductus arteriosus, the larger the left-to-right shunt. If the ductus arteriosus is restrictive, then the length of the narrowed area also affects the magnitude of the shunt. A longer ductus is associated with a smaller shunt. Finally, the magnitude of the left-to-right shunt is partially controlled by the relationship of the pulmonary vascular resistance (PVR) to the systemic vascular resistance (SVR).

If the SVR is high and/or the PVR is low, the flow through the ductus arteriosus is potentially large. Beginning at the ductus arteriosus, the course of blood flow (through systole and diastole) in a typical patent ductus arteriosus (PDA) with pulmonary overcirculation is as follows: patent ductus arteriosus (PDA), pulmonary arteries, pulmonary capillaries, pulmonary veins, left atrium, left ventricle, aorta, patent ductus arteriosus (PDA). Therefore, a large left-to-right shunt through a patent ductus arteriosus (PDA) results in left atrial and left ventricular enlargement. The pulmonary veins and the ascending aorta can also be dilated with a sufficiently large patent ductus arteriosus (PDA). In addition, if little or no restriction is present at the level of the patent ductus arteriosus (PDA), pulmonary hypertension results.


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