Patent Ductus Arteriosus (PDA) Pathophysiology & Schematic Diagram

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Patent ductus arteriosus (PDA) is a persistent, abnormal opening between two major blood vessels leading from the heart. Patent ductus arteriosus (PDA) is a condition in which the connecting blood vessel between the pulmonary artery and the aorta in fetal circulation, called the ductus arteriosus, stays open in a newborn baby.

About 3,000 infants are diagnosed with PDA each year in the United States. It is more common in premature infants (babies born too early) but does occur in full-term infants. Premature babies with PDA are more vulnerable to its effects. PDA is twice as common in girls as in boys.

Read the Pathophysiology of Patent Ductus Arteriosus

Patent Ductus Arteriosus (PDA) Pathophysiology & Schematic Diagram

Non-modifiable/Modifiable Factors 

Non-modifiable Factors:

• Genetics: Congenital heart defects appear to run in families and sometimes occur with other genetic problems, such as Down syndrome.
• Age: Patent ductus arteriosus is more common in premature babies. Also, babies with other types of congenital heart defects often have a patent ductus arteriosus.
• Gender: PDA is twice as common in girls as in boys.

Modifiable Factors:

Experiencing any of the following conditions during pregnancy can increase the risk of having a baby with a heart defect.

• Rubella infection: Becoming infected with rubella (German measles) while pregnant can increase the risk of fetal heart defects. The rubella virus crosses the placenta and spreads through the fetus’s circulatory system damaging blood vessels and organs, including the heart.
• Poorly controlled diabetes: Uncontrolled diabetes in the mother in turn affects the fetus’s blood sugar causing various damaging effects to the developing fetus.
• Drug or alcohol use or exposure to certain substances: Use of certain medications, alcohol or drugs, or exposure to chemicals or radiation during pregnancy can harm the developing fetus.
• Presence of other congenital heart defects. Babies with other types of congenital heart defects often have a patent ductus arteriosus.

Signs and Symptoms with Rationale

Signs and symptoms of a patent ductus arteriosus vary with the size of the defect and the gestational age of the infant at birth. A small patent ductus may cause no signs or symptoms, and may go undetected for some time. A larger one can cause signs of heart failure soon after birth. A premature infant may have other problems associated with prematurity, and related testing may uncover a heart defect.

• Murmur: PDA is characterized by a pathognomonic continuous murmur (the whole of systole and diastole), but increases in intensity during systole when the pressure gradient across the PDA is greatest. This can be described as a continuous murmur that waxes and wanes’. Traditionally this has been described as a machinery murmur’. However, such a description is no longer useful as few modern machines produce such a noise. The diastolic component of the murmur can be easily missed if the stethoscope is not placed near to the PDA (high and well forward on the left thorax) – thus mistaking the murmur as only systolic and failing to include PDA in the differential diagnosis. This characteristic machine-like murmur is due to bulging of the aorta and pulmonary artery proximal to the PDA occurs as a result of increased blood volume and turbulent flow leading to a pressure difference between the aorta and pulmonary artery (greatest during systole), and consequently continuous flow through the PDA.

A large patent ductus arteriosus may cause:

• Poor eating, poor growth – due to easy fatigability brought about by decreased blood oxygenation. Continuous shunting of blood causes pulmonary hypertension then congestion of the right ventricle leading to decreased efficiency in pumping blood towards the lungs for oxygenation.
• Enlarged heart – right ventricular hypertrophy – due to continuous shunting of blood that causes pulmonary hypertension then congestion of the right ventricle because of backflow of blood from the lungs
• Tachycardia or other arrhythmia – due to compensation of the heart brought about by the inability to efficiently pump blood out to the lungs.
• Cyanosis - pressure in the pulmonary artery equals or even exceeds that of the aorta. Either the diastolic portion of the murmur or the complete murmur may disappear due to flow reversal (reverse shunting PDA). With this, blood then bypasses the lungs therefore there is no oxygenation of the blood leading to cyanosis.
• Persistent fast breathing or breathlessness – compensation to increase oxygen supply to the body due to decreased oxygenation
• Easy fatigability - due to decreased blood oxygenation. Continuous shunting of blood causes pulmonary hypertension then congestion of the right ventricle leading to decreased efficiency in pumping blood towards the lungs for oxygenation.
• Frequent respiratory infections (eg, colds, pneumonia) – due to decreased blood oxygenation leading to decreased functioning of the immune system to resist infection and of the respiratory system to expel offending microorganisms

Diagnostics for Patent Ductus Arteriosus

PDA is usually diagnosed using non-invasive techniques. Echocardiography, in which sound waves are used to capture the motion of the heart, and associated Doppler studies are the primary methods of detecting PDA. Electrocardiography (ECG), in which electrodes are used to record the electrical activity of the heart, is not particularly helpful as there are no specific rhythms or ECG patterns which can be used to detect PDA.

A chest X-ray may be taken, which reveals the overall size of infant’s heart (as a reflection of the combined mass of the cardiac chambers) and the appearance of the blood flow to the lungs. A small PDA most often shows a normal sized heart and normal blood flow to the lungs. A large PDA generally shows an enlarged cardiac silhouette and increased blood flow to the lungs.

Treatment for Patent Ductus Arteriosus 

Infants without adverse symptoms may simply be monitored as outpatients, while symptomatic PDA can be treated with both surgical and non-surgical methods. Surgically, the DA may be closed by ligation, wherein the DA is manually tied shut, or with intravascular coils or plugs that leads to formation of a thrombus in the DA. Fluid restriction and prostaglandin inhibitors such as indomethacin have also been used in successful non-surgical closure of the DA. This is an especially viable alternative for premature infants.

In certain cases it may be beneficial to the newborn to prevent closure of the ductus arteriosus. For example, in transposition of the great vessels a PDA may prolong the child’s life until surgical correction is possible. The ductus arteriosus can be induced to remain open by administering prostaglandin analogs such as alprostadil (a prostaglandin E₁ analog).

Recent days PDA can be closed by percutaneous interventional method, through femoral vein or femoral artery, a coil can be placed with the help of myocardial forceps to make an embolus, which closes the PDA without open heart surgery.

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