What is persistent ductus arteriosus
'Congenital' is an adjective used to refer to medical conditions present at birth.
Persistent ductus arteriosus is also known as patent ductus arteriosus.
Both versions of the name of this condition are commonly abbreviated to PDA. It is therefore referred to as any of the following:
- Persistent ductus arteriosus
- Patent ductus arteriosus, or
Persistent ductus arteriosus (PDA) is a congenital heart condition in which the arterial duct - also called the ductus arteriosus (labelled "Patent Ductus Arteriosus" in the diagram below), which is a normal part of the foetal* heart, 'persists' i.e. fails to fails to 'close' or 'disconnect' in the usual time-frame soon after birth.
Above: Diagram of the heart showing the patent ductus arteriosus (Ductus Arteriosus Diagram)
What is the ductus arteriosus ?
The ductus arteriosus is a normal fetal* structure. Before birth it connects the pulmonary artery of the fetus* to its descending aorta. The function of the ductus arteriosus is to prevent blood from reaching the lungs (of the fetus) because fetal* lungs are in a collapsed non-functional state - obviously, as they have no source of air. The ductus arteriosus directs blood to the fetal aorta, from which it passes on to the rest of the fetus via the developing systemic circulation.
Note: Fetal blood bypasses the non-functional fetal lungs (which oxygenate blood only after birth). Instead a fetus receives blood that is already oxygenated when it reaches the fetus, from its mother, via the placenta.
After birth the ductus arteriosus 'tube' normally closes, resulting in the structure of the adult human heart, which consists of the "2 circuits" characteristic of a double circulation system, i.e. systemic circulation and pulmonary circulation (there is also coronary circulation, which is the circulation of blood in the blood vessels of the heart muscle).
When does the ductus arteriosus cease to function ?
When a baby takes its first breath a spasm (in this case a sudden, involuntary contraction of muscle in the heart) invokes blood flow to the newly inflated (via the first breath) and now functional, lungs. Closure of the ductus arteriosus is initiated (that is, the process is started) by an abrupt contraction of the muscular wall of the ductus when the newborn takes his or her first breath. Although functional closure of the ductus arteriosus generally happens within about 10-18 hours of the birth of a normal full-term infant, it is thought to take about three weeks before the closure is permanent, i.e. until it cannot re-open.
The condition 'Persistent ductus arteriosus (PDA)' also called 'Patent ductus arteriosus (PDA)' applies
if the ductus arteriosus fails to close after an extended period of time beyond that normally expected.
E.g. according to patient.co.uk:
"True persistence of a patent ductus arteriosus (PDA) is often taken as one persisting after 3 months of age."
After the ductus arteriosus has closed following birth the tissues that formed it become the ligamentum arteriosum.
What if the ductus arteriosus does not close ?
After birth, so when blood flow is no-longer supplied through the placenta, the presence of an 'open' ductus arteriosus is effectively a 'leak'.
This produces a left-to-right 'shunt', meaning that it permits blood to go from the systemic circulation (intended for the tissues of the body) to the pulmonary circulation (blood flow to the lungs).
The continuing functional existance of the ductus arteriosus permits blood to flow from
- the systemic circulation - which is the network of blood vessels that conveys oxygenated blood from the heart via arteries, arterioles and capillaries to the tissues of the body, and enables de-oxygenated blood to return to the heart via capillaries, venules and veins,
- the pulmonary circulation - which is the shorter circuit conveying de-oxygenated blood to the lungs, where it is oxygenated at gas exchange surfaces (see also features of exchange surfaces), then returned to the heart as oxygenated blood to supply the systemic circulation circuit.
The result of the continuing functional existance of the ductus arteriosus after it would normally close following birth is too much ('excessive') pulmonary blood flow, while the amount of blood flowing through the systemic circulation to organs, limbs, etc. is correspondingly reduced.
How serious a problem is a persistent ductus arteriosus ?
In some cases the effects of a PDA can be so slight that there are no symptoms, or symptoms that only become apparent much later in life. In other cases, a PDA can require monitoring and possibly intervention.
A key issue is the magnitude of the excess pulmonary blood flow, i.e. the left-to-right shunt due to the PDA. That is, does it amount to a very small 'leak' or is it large and therefore potentially severe?
The amount of excess pulmonary blood flow and therefore the severity of the PDA varies according to
- the internal diameter of the narrowest part of the ductus arteriosus
- the larger the diameter, the greater the left-to-right shunt.
- the length of the narrowest part of the ductus arteriosus
- if the ductus arteriosus is relatively narrow then the length of the narrowest section also affects the magnitude of the the left-to-right shunt (the longer the narrow section, the smaller the left-to-right shunt, i.e. the less serious the PDA).
- vascular resistance (resistance to flow needed push blood) in different parts of the cardiovascular system, specifically the relationship between pulmonary vascular resistance (PVR) and systemic vascular resistance (SVR)
- if PVR is low and/or SVR is high, the left-to-right shunt is greater than otherwise.
If the shunt is substantial, the newborn child ("neonate") can become short of breath due to the additional fluid going to the lungs increasing lung pressure to the extent that the baby has increasing difficulty inflating its lungs. The greater than normal effort required to inflate the lungs can consume more energy than is usually required for breathing, resulting in less energy from the baby's food being available for growth and development.
Symptoms of Persistent Ductus Arteriosus
Signs and symptoms of persistent ductus arteriosus vary with the size and therefore effect of the PDA (see above), the age of the child and the presence (or not) of any other heart problems.
Some cases of persistent ductus arteriosus are asymptomatic, i.e. there are no symptoms. Where present, examples of symptoms of PDA include:
- heart murmur (an 'extra' or unusual sound heard during the heartbeat)
- rapid heart rate
- signs of effort required to breathe e.g. breathlessness, shortness of breath, fast breathing
- poor weight gain / poor growth
- bluish or dusky skin tone or turns dusky/blue when eating or crying.
This is not a complete list. Any, not necessarily all, of the above might apply.
In case of concern expert advice should be sought from an appropriately qualified professional.
Treatment of Persistent Ductus Arteriosus
To be added shortly ...