Physiologically, a PDA allows for oxygenated blood (“red blood”) to pass from the aorta backwards into the lungs. The effect is an increase in the total amount of blood that flows to the lungs. The amount is primarily determined by the size of the patent ductus arteriosus. A large PDA can allow for a significant increase in blood flow into the lungs; a small PDA often results in a negligible increase.
The cause of a patent ductus arteriosus is not always known. The presence of a PDA in a premature baby is understandable, given that the ductus arteriosus is meant to be open in the womb prior to birth. In full term babies and older children, a patent ductus arteriosus is caused by the absence of the normal constriction of the elastic tissue in the wall of the blood vessel.
PDA Signs and Symptoms
Symptoms from a patent ductus arteriosus are related to excess blood flow to the lungs. They are usually seen in children or babies with large PDA's, but may be absent in the setting of moderate size defects as well. Small PDA's rarely if ever produce symptoms. In children who develop symptoms, the most common finding is rapid breathing. This may be more obvious during times of exertion, such as feeding in an infant. Other symptoms in infants include sweating with exertion, poor feeding due to fatigue, and poor weight gain. PDA’s may also predispose to an increased risk of lung infections such as pneumonia.
Diagnosis of a patent ductus arteriosus can be made in a number of different ways. A child with a PDA often comes to attention due to the presence of a heart murmur. This simply refers to the sound that blood is making as it flows from the aorta into the lungs. There are many other different causes of heart murmurs, including normal causes. An echocardiogram uses sound waves to visualize the intracardiac structures and is the easiest way to diagnose the size and location of a PDA. Occasionally a cardiac catheterization may be necessary to assess the lung blood pressures or the amount of shunting through a PDA.
There is a wide spectrum of treatment options for a child or infant with a patent ductus arteriosus. Small PDA’s detected in the first few days of life often close spontaneously. Even in cases where a small PDA remains open, specific therapy is often unnecessary. In children with larger PDA’s who are symptomatic, medication may help those symptoms. The most commonly used medicine is furosemide (Lasix), a diuretic that works by decreasing excess lung fluid caused by the extra blood flow to the lungs. Furosemide may be given anywhere from 1 to 4 times daily. Side effects are uncommon; abnormalities of electrolytes can occasionally be seen with larger doses. Another medication frequently used in the setting of a large PDA is digoxin (Lanoxin). Digoxin increases calcium levels in heart cells, thereby improving overall heart function.
Intervention to close a PDA may be necessary in selected cases. This most commonly occurs in the setting of a large or moderate size communication. Indications for intervention in infancy include symptoms unresponsive to medication, elevated blood pressure in the lungs, and significant dilation of the heart due to excess blood flow. Usually the need for intervention in infancy becomes clear by 6-12 months of age, and often much earlier. The most common form of intervention for older infants and children is PDA device closure in the cardiac catheterization laboratory. A catheter (a long thin tube) is placed into the heart through a blood vessel in the leg. A device is then positioned in PDA, effectively closing it from the inside. In general, the procedure is both safe and effective in the vast majority of cases. Surgery for a patent ductus arteriosus is usually reserved for premature and small infants. Surgery is equally effective as a cardiac catheterization but entails a thoracotomy scar and a longer hospital stay in most cases.
The prognosis for a child with a patent ductus arteriosus is generally very good. The vast majority of babies and children who require intervention tend to do well long-term. Almost all can lead normal healthy lives with normal activity levels.