Patent Ductus Arteriosus (PDA) – persisting communication between aorta and pulmonary artery

Patent Ductus Arteriosus (PDA) – persisting communication between aorta and pulmonary artery

Patent ductus arteriosus (PDA) is a communication between the pulmonary artery, the blood vessel carrying deoxygenated blood to the lungs and aorta, the largest blood vessel arising from the heart which carries oxygenated blood to the whole body. Ductus arteriosus is a structure present in fetal life and its function is to shunt relatively deoxygenated blood coming from the upper part of the body to the descending aorta. This blood reaches the placenta for oxygenation. After birth, when the infant takes the first breath, pulmonary vascular resistance or resistance offered by the blood vessels in the lung, falls rapidly and pressures in the pulmonary artery falls.

This occurs due to the rapid expansion of the lungs with the first breath and increase in the oxygen concentration in the lungs. Blood vessels in the lung responds to oxygen by dilatation or enlargement of the lumen, which causes the resistance to blood flow to come down. This leads to reversal of blood flow from aorta to pulmonary artery across the ductus arteriosus. The mature ductus responds to the high oxygen content of blood from the aorta after birth and starts constricting or narrowing. Functional closure of ductus occurs within 72 hours of birth. Full anatomical or structural closure takes a little longer. In premature infants, the ductus does not respond to oxygen and remains open. That is why premature babies have more incidence of PDA. The more the prematurity, the higher the chance of PDA.

Though the premature ductus does not respond to oxygen, it is responsive to prostaglandin. Prostaglandin keeps the ductus patent. Prostaglandin inhibitors can be used to close the premature ductus medically, in premature infants. This does not work in mature infants. In certain complex congenital heart diseases, it is essential to maintain the patency of the ductus to improve oxygenation. In such instances, patency of the ductus is maintained by giving a continuous infusion of prostaglandins. This is useful in both ductus dependant pulmonary circulation and ductus dependant systemic circulation.

PDA produces left to right shunting of blood and causes dilatation of the left atrium and left ventricle, the left upper and left lower chambers of the heart. If the shunt is large, it can cause heart failure in infancy. In the long term, shunt through the PDA leads to pulmonary hypertension, increase in the blood pressure in vessels of the lung, and irreversible pulmonary vascular obstructive disease (obstruction in the small vessels of the lung). When the pulmonary hypertension is severe, it causes reversal of shunt across the ductus (Eisenmenger Syndrome).