Patent ductus arteriosus
|Patent ductus arteriosus|
|Other names||Ductus arteriosus|
|Diagram of a cross-section through a heart with PDA|
|Specialty||Cardiac surgery, paediatrics|
|Symptoms||Shortness of breath, failure to thrive, tachycardia, heart murmur|
|Complications||Congestive heart failure, Eisenmenger's syndrome, pulmonary hypertension|
|Risk factors||Preterm birth, congenital rubella syndrome, chromosomal abnormalities, genetic conditions|
|Diagnostic method||Echocardiography, Doppler, X-ray|
|Prevention||Screening at birth, high index of suspicion in neonates at risk|
The ductus arteriosus is a fetal blood vessel that closes soon after birth. In a PDA, the vessel does not close and remains "patent" (open), resulting in an irregular transmission of blood between the aorta and the pulmonary artery. PDA is common in newborns with persistent respiratory problems such as hypoxia, and has a high occurrence in premature newborns. Premature newborns are more likely to be hypoxic and have PDA due to underdevelopment of the heart and lungs.
A PDA allows a portion of oxygenated blood from the left heart to flow back to the lungs by flowing from the aorta (which has higher pressure) to the pulmonary artery. If this shunt is substantial, the neonate becomes short of breath: the additional fluid returning to the lungs increases lung pressure, leading to pulmonary hypertension, which in turn increases the energy required to inflate the lungs. This uses more calories than normal and often interferes with feeding in infancy. This condition, as a constellation of findings, is called congestive heart failure.
In some congenital heart defects (such as in transposition of the great vessels) a PDA may need to remain open, as it is the only way that oxygenated blood can mix with deoxygenated blood. In these cases, prostaglandins are used to keep the DA open and NSAIDs should not be administered, until surgical correction of the heart defect is completed.
Signs and symptoms
Common symptoms include:
- tachycardia (a heart rate exceeding the normal resting rate)
- respiratory problems
- dyspnea (shortness of breath)
- continuous "machine-like" (also described as "rolling-thunder" and "to-and-fro") heart murmur (usually from aorta to pulmonary artery, with higher flow during systole and lower flow during diastole)
- cardiomegaly (enlarged heart, reflecting ventricular dilation and volume overload)
- left subclavicular thrill
- bounding pulse
- widened pulse pressure
- increased cardiac output
- increased systolic pressure
- poor growth
- differential cyanosis, i.e. cyanosis of the lower extremities but not of the upper body.
Patients typically present in good health, with normal respirations and heart rate. If the PDA is moderate or large, widened pulse pressure and bounding peripheral pulses are frequently present, reflecting increased left ventricular stroke volume and diastolic run-off of blood into the (initially lower-resistance) pulmonary vascular bed. Prominent suprasternal and carotid pulsations may be noted secondary to increased left ventricular stroke volume.
- Preterm birth
- Congenital rubella syndrome
- Chromosomal abnormalities (e.g., Down syndrome)
- Genetic conditions such as Loeys-Dietz syndrome (would also present with other heart defects), Wiedemann-Steiner syndrome, and CHARGE syndrome.
PDA is usually diagnosed using noninvasive 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 no specific rhythms or ECG patterns can be used to detect PDA.
A chest X-ray may be taken, which reveals overall heart size (as a reflection of the combined mass of the cardiac chambers) and the appearance of blood flow to the lungs. A small PDA most often accompanies a normal-sized heart and normal blood flow to the lungs. A large PDA generally accompanies an enlarged cardiac silhouette and increased blood flow to the lungs.
In the developing fetus, the DA is the vascular connection between the pulmonary artery and the aortic arch that allows most of the blood from the right ventricle to bypass the fetus' lungs, which are fluid-filled and compressed. During fetal development, this shunt protects the right ventricle from pumping against the high resistance in the lungs, which can lead to right ventricular failure if the DA closes in utero.
When the newborn takes his or her first breath, the lungs open and pulmonary vascular resistance decreases. After birth, the lungs release bradykinin to constrict the smooth muscle wall of the DA and reduce blood flow as it narrows and then completely closes. In most newborns with a patent ductus arteriosus, the blood flow is reversed from that of in utero flow; i.e., the blood flow is from the higher-pressure aorta to the now lower-pressure pulmonary arteries.
In normal newborns, the DA is substantially narrowed within 12–24 hours after birth, and seals completely after three weeks. The primary stimulus for closure of the DA is an increase in neonatal blood oxygen content. Withdrawal from maternal circulating prostaglandins also contributes to ductal closure. The residual scar tissue from the fibrotic remnants of the DA, called the ligamentum arteriosum, remains in the normal adult heart.
Some evidence suggests that indomethacin administration on the first day of life to all preterm infants reduces the risk of developing a PDA and the complications associated with PDA. Indomethacin treatment in premature infants also may reduce the need for surgical intervention.
Neonates 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 (though support in premature infants is mixed), either manually tied shut, or with intravascular coils or plugs that leads to formation of a thrombus in the DA.
Because prostaglandin E2 is responsible for keeping the DA open, NSAIDs (which can inhibit prostaglandin synthesis) such as indomethacin or a special form of ibuprofen have been used to initiate PDA closure. Recent findings from a systematic review concluded that, for closure of a PDA in preterm and/or low birth weight infants, ibuprofen is as effective as indomethacin. It also causes fewer side effects (such as transient renal insufficiency) and reduces the risk of necrotising enterocolitis. A review and meta-analysis showed that paracetamol may be effective for closure of a PDA in preterm infants. A recent network meta-analysis that compared indomethacin, paracetamol and ibuprofen at different doses and administration schemes among them found that a high dose of oral ibuprofen may offer the highest likelihood of closure in preterm infants.
While indomethacin can be used to close a PDA, some neonates require their PDA be kept open. Keeping a ductus arteriosus patent is indicated in neonates born with concurrent heart malformations, such as transposition of the great arteries. Drugs such as alprostadil, a PGE-1 analog, can be used to keep a PDA open until the primary defect is corrected surgically.
If left untreated, the disease may progress from left-to-right shunt (acyanotic heart) to right-to-left shunt (cyanotic heart), called Eisenmenger's syndrome. Pulmonary hypertension is a potential long-term outcome, which may require a heart and/or lung transplant. Another complication of PDA is intraventricular hemorrhage.
Since PDA is usually identified in infants, it is less common in adults, but it can have serious consequences, and is usually corrected surgically upon diagnosis.
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