Introduction
Congenital cardiac disease can appear extraordinarily complicated.
The terminology alone can be intimidating. ASD, VSD, PDA, AVSD, PVR, SVR, shunts, stenoses, atresias and anomalous vascular connections can rapidly turn what is fundamentally a problem of blood flow into something that appears almost impenetrable.
At one end of the spectrum are explanations written for parents and relatives. These quite correctly concentrate on explaining a child’s condition in understandable, non-technical language.
At the other end are specialist texts written for paediatric cardiologists, congenital cardiac surgeons, cardiac anaesthetists, perfusionists and intensivists. These assume a considerable existing knowledge of embryology, anatomy and cardiovascular physiology.
There is a considerable space between the two.
This work is intended to occupy that space.
It is aimed primarily at healthcare professionals, students and theatre practitioners who encounter congenital cardiac patients but who do not necessarily require the depth of knowledge expected of a specialist neonatal congenital cardiac surgeon or paediatric cardiac anaesthetist.
The purpose is therefore not simply to describe what the abnormality looks like, but to understand:
What has gone wrong anatomically?
What does that do to blood flow?
How does the child compensate?
And what are we trying to achieve when we repair it?
Pink Babies and Blue Babies
One of the simplest ways of beginning to understand congenital heart disease is to divide patients into two broad physiological groups: the pink baby and the blue baby.
A pink baby has sufficient oxygenated blood reaching the systemic circulation to avoid obvious central cyanosis. These conditions are traditionally described as acyanotic congenital heart defects.
A blue baby has deoxygenated blood entering the systemic circulation and may therefore develop visible cyanosis.
Coarctation of the aorta is traditionally classed as an acyanotic obstructive congenital heart defect rather than a shunt lesion. (Merck Manuals)
The important problem is not that the blood lacks oxygen.
The problem is that the blood cannot easily get past an obstruction in the aorta.
In severe neonatal disease, however, the physiology can become considerably more complicated because systemic blood flow may depend upon a patent ductus arteriosus.
Body
What is Coarctation of the Aorta?
Coarctation of the Aorta — CoA — is a congenital narrowing of part of the aorta.
The aorta is the major artery carrying oxygenated blood from the left ventricle to the systemic circulation.
In CoA, one section of the aorta is abnormally constricted.
The narrowing most commonly occurs in the region of the aortic isthmus, close to where the ductus arteriosus joins the descending aorta.
The consequence is straightforward:
The left ventricle must generate sufficient pressure to force blood through the narrowed segment.
Blood pressure therefore rises proximal to the obstruction while pressure and flow distal to the narrowing may be reduced. (www.heart.org)
This explains one of the classic clinical findings in coarctation:
higher blood pressure in the arms than in the legs.
Normal Aortic Anatomy
Blood leaves the left ventricle through the aortic valve and enters the ascending aorta.
The aorta then forms the aortic arch.
Three major arterial branches normally arise from the arch:
- the brachiocephalic artery;
- the left common carotid artery;
- and the left subclavian artery.
The arch then curves posteriorly and continues as the descending thoracic aorta.
The region between the origin of the left subclavian artery and the descending aorta is known as the aortic isthmus.
It is within or close to this region that coarctation most commonly occurs.
The Relationship With the Ductus Arteriosus
Understanding the ductus arteriosus is particularly important in neonatal coarctation.
During foetal life, the ductus arteriosus connects the pulmonary artery to the descending aorta.
Because pulmonary vascular resistance is high before birth, much of the right ventricular output bypasses the lungs and enters the descending aorta through the ductus.
Consequently, severe narrowing of the aortic isthmus may have relatively little effect upon the foetus.
Blood can still reach the descending aorta through the ductus arteriosus.
This changes after birth.
As the lungs expand, pulmonary vascular resistance falls and the ductus begins to constrict.
If there is severe coarctation, the infant may suddenly lose an important alternative route supplying blood to the lower body.
For this reason, critical coarctation can be duct-dependent. Keeping the ductus open with prostaglandin can be vital until definitive treatment is performed. (Merck Manuals)
Why Does Coarctation Occur?
The precise cause of coarctation is not completely understood.
One explanation relates to tissue from the ductus arteriosus extending into the wall of the adjacent aorta.
As the ductus constricts after birth, this tissue may also constrict and contribute to narrowing of the aortic lumen. The American Heart Association notes that ductal tissue can extend into the aorta and constrict as the ductus closes. (www.heart.org)
Other developmental explanations involve abnormal flow through the foetal aortic arch, producing underdevelopment of portions of the arch.
In reality, coarctation probably represents a spectrum of developmental abnormalities rather than one single mechanism.
Anatomy of Coarctation
The anatomy varies enormously.
At one extreme there may be a relatively short, discrete narrowing.
At the other there may be significant hypoplasia involving a long segment of the transverse arch or isthmus.
This matters because two patients both described as having “coarctation” may therefore have quite different anatomical problems and require different repairs.
Historically, coarctation was sometimes classified as preductal, ductal or postductal, depending upon the relationship of the narrowing to the ductus arteriosus.
Although these terms can still be encountered, modern descriptions generally concentrate more upon the actual anatomy of the aortic arch and the extent of hypoplasia.
The Physiology
Imagine placing a clamp partly across a hosepipe.
Pressure increases before the obstruction.
Flow beyond the obstruction decreases.
Coarctation produces essentially the same problem.
The left ventricle ejects blood into the ascending aorta.
It must then generate greater pressure to force that blood through the narrowed section.
This leads to:
Higher pressure proximal to the coarctation
and
Lower pressure and reduced pulsatility distal to it.
The proximal circulation includes the arteries supplying the head and upper limbs.
The distal circulation supplies the abdomen, kidneys and lower limbs.
This creates the characteristic difference between upper- and lower-body perfusion.
Effects on the Left Ventricle
The left ventricle normally pumps against systemic vascular resistance.
Coarctation creates an additional fixed obstruction.
The ventricle must therefore work harder and generate higher systolic pressure.
Over time the myocardium can respond by becoming thicker.
This is left ventricular hypertrophy.
The physiological principle is the same as any muscle working against increased resistance.
Initially this may allow the ventricle to maintain cardiac output.
Eventually severe or prolonged obstruction can contribute to ventricular dysfunction and heart failure.
Coarctation in the Newborn
Severe neonatal coarctation can initially be deceptive.
While the ductus arteriosus remains open, blood may continue to reach the descending aorta through the pulmonary artery and ductus.
The baby may consequently appear relatively well shortly after birth.
Then the ductus begins to close.
Systemic blood flow distal to the coarctation can deteriorate rapidly.
The infant may develop:
- poor feeding;
- tachypnoea;
- lethargy;
- poor peripheral perfusion;
- metabolic acidosis;
- oliguria;
- weak or absent femoral pulses;
- heart failure;
- and ultimately cardiovascular collapse.
The timing can therefore be dramatic.
A baby who appeared well during the first day or two of life can become critically unwell as ductal closure progresses.
This is one reason obstructive left-sided congenital lesions can sometimes be missed by oxygen-saturation screening alone; coarctation is among the lesions that pulse-oximetry screening may fail to detect. (Merck Manuals)
Duct-Dependent Systemic Circulation
In severe coarctation, the descending aorta may depend upon blood crossing the ductus arteriosus.
This gives rise to the concept of a duct-dependent systemic circulation.
The ductus, which would normally be expected to close after birth, becomes temporarily essential for survival.
The immediate priority is therefore not to encourage closure.
It is to keep it open.
An intravenous infusion of prostaglandin E1 can be used to maintain or reopen ductal patency while the infant is stabilised and definitive treatment planned. (Merck Manuals)
This is a useful example of why understanding foetal circulation is so important in congenital heart disease.
A vessel that is normally expected to disappear after birth can become a life-saving pathway when another part of the circulation has failed to develop normally.
The Older Child
Less severe coarctation may not present during the neonatal period.
A child may grow apparently normally while progressively developing the characteristic haemodynamic effects of the obstruction.
Presentation may include:
- hypertension detected during routine examination;
- strong upper-limb pulses;
- weak or delayed femoral pulses;
- headaches;
- exertional leg discomfort or fatigue;
- or a cardiac murmur.
Some children and adolescents are diagnosed only because a blood pressure measurement is unexpectedly high. (www.heart.org)
This is why examination of the femoral pulses remains an important part of paediatric cardiovascular assessment.
Radiofemoral Delay
One of the classic physical signs of coarctation is radiofemoral delay.
Normally the femoral arterial pulse should be readily palpable and occur almost simultaneously with the radial pulse.
In significant coarctation, the pressure wave reaching the lower limbs is delayed and diminished.
The examiner may therefore feel a strong radial pulse followed fractionally later by a weaker femoral pulse.
This reflects the obstruction between the upper- and lower-body arterial circulation.
Blood Pressure
Another important finding is a difference in blood pressure between the upper and lower limbs.
Pressure above the coarctation may be elevated.
Pressure below it may be reduced.
Consequently:
Arm blood pressure > leg blood pressure.
This pressure gradient provides an important clue to both diagnosis and severity.
However, blood-pressure measurements must always be interpreted together with imaging and the clinical condition of the patient.
Collateral Circulation
If coarctation develops gradually or persists into later childhood or adulthood, the body may attempt to bypass the obstruction.
Collateral arteries enlarge and create alternative pathways allowing blood to travel from vessels above the coarctation to vessels below it.
Important collateral pathways can involve the subclavian, internal thoracic and intercostal arteries.
These collateral vessels can become remarkably enlarged.
In older patients this may produce characteristic rib changes on chest radiographs because enlarged intercostal arteries progressively erode the undersurface of the ribs — the classic appearance of rib notching.
This is essentially the body’s attempt at building a vascular diversion around the obstruction.
Associated Cardiac Abnormalities
Coarctation should not automatically be considered an isolated lesion.
It may occur alongside other congenital abnormalities.
One particularly important association is bicuspid aortic valve, in which the aortic valve has two functional leaflets rather than the normal three. The American Heart Association notes that bicuspid aortic valve is frequently associated with CoA. (www.heart.org)
Other associated abnormalities can include:
- ventricular septal defect;
- abnormalities of the mitral valve;
- hypoplasia of the aortic arch;
- subaortic obstruction;
- and other left-sided obstructive lesions.
Coarctation can therefore form part of a broader pattern of abnormal development of the left side of the heart and aortic arch.
Diagnosis
Echocardiography
Echocardiography is central to diagnosis in infants and children.
It allows assessment of:
- the anatomy of the aortic arch;
- the site of narrowing;
- flow velocity through the obstruction;
- left ventricular function;
- associated intracardiac abnormalities;
- and ductal flow in the newborn.
CT and MRI
Cross-sectional imaging with CT or MRI can provide detailed anatomical information about the aortic arch and descending aorta.
This becomes particularly useful in older children and adults and during long-term surveillance following repair.
The American Heart Association recommends lifelong follow-up, including periodic imaging of the repaired aorta because recurrent narrowing and aneurysmal dilation can occur. (www.heart.org)
Treatment of the Critically Ill Neonate
The critically ill neonate requires stabilisation before definitive repair.
Management may include:
- prostaglandin infusion to maintain ductal patency;
- respiratory support where required;
- correction of metabolic acidosis;
- careful management of systemic perfusion;
- inotropic support when necessary;
- and urgent involvement of the congenital cardiac team.
One important principle is that these babies can have profoundly abnormal systemic perfusion despite appearing relatively well oxygenated.
A saturation monitor tells us about oxygen saturation.
It does not tell us whether sufficient blood is reaching the kidneys, bowel or lower body.
Surgical Repair
Unlike many intracardiac congenital defects, isolated coarctation can frequently be repaired without opening the heart itself.
Cardiopulmonary bypass is therefore not always required.
The surgical approach depends upon the anatomy of the lesion, the patient’s size and whether there is associated arch hypoplasia or additional cardiac disease.
Several techniques are used.
Resection and End-to-End Anastomosis
The narrowed section of aorta is removed.
The two healthy ends are then joined together.
In concept:
narrow section out — normal ends together.
This is one of the fundamental surgical approaches to discrete coarctation.
Extended End-to-End Anastomosis
Where the narrowing involves a longer portion of the arch or is associated with isthmic hypoplasia, a more extensive incision and reconstruction may be required.
The descending aorta is joined to a larger portion of the aortic arch, producing a wider reconstructed channel.
Subclavian Flap Repair
Historically, part of the left subclavian artery could be opened and used as a flap to enlarge the narrowed aortic segment.
The technique sacrifices or alters the normal proximal left subclavian circulation and is used less commonly than in the past.
Nevertheless, it remains important historically and explains why the left subclavian artery features prominently in descriptions of older coarctation repairs.
Patch Aortoplasty
The narrowed section may be opened longitudinally and enlarged using a patch.
This widens the lumen without completely removing the affected segment.
Patch techniques have historically included synthetic material and biological tissue.
Catheter Treatment
Some coarctations can be treated in the cardiac catheter laboratory.
A balloon can be passed across the narrowed section and inflated to enlarge it.
In older children and adults, a stent may be positioned across the coarctation to hold the vessel open.
Catheter techniques are particularly important in treating recoarctation following previous surgical repair and are also widely used in suitable older patients. (www.heart.org)
The choice between surgery and catheter intervention depends upon age, anatomy, previous repairs and local congenital cardiac expertise.
Anaesthetic and Theatre Considerations
From the theatre perspective, coarctation is fundamentally a problem of differential perfusion.
The anaesthetic team must consider what is happening both above and below the obstruction.
Blood pressure measured in the right arm reflects pressure proximal to the coarctation.
It does not necessarily reflect perfusion pressure in the lower body.
Monitoring therefore needs to be interpreted in relation to the anatomy.
For surgical repair, arterial pressure monitoring may be used to assess proximal pressure while additional monitoring provides information about distal perfusion.
Temperature, urine output, acid-base status and lactate can provide further evidence of systemic perfusion.
During aortic cross-clamping, blood flow to tissues below the clamp may be reduced.
The surgical and anaesthetic teams must therefore balance adequate proximal pressure with protection of distal organs.
Particular concern surrounds perfusion of:
- the spinal cord;
- kidneys;
- abdominal viscera;
- and lower limbs.
The exact monitoring and surgical strategy depends upon the child’s anatomy and the repair being undertaken.
The Spinal Cord
The descending thoracic aorta contributes to arterial supply of the spinal cord through segmental vessels.
Interruption of blood flow during aortic cross-clamping therefore carries a potential risk of spinal cord ischaemia.
This is one reason clamp time, distal perfusion and arterial pressure are carefully managed during repair.
Neurological injury following modern paediatric coarctation repair is uncommon, but the underlying anatomical risk remains important to understand.
After Repair
Successful correction removes the major mechanical obstruction.
However, repair should not be interpreted as meaning that the patient has ceased to have congenital heart disease.
Coarctation requires lifelong surveillance.
Potential long-term problems include:
- persistent systemic hypertension;
- recurrent narrowing or recoarctation;
- aneurysmal dilation at or near the repair;
- associated aortic valve disease;
- and abnormalities elsewhere within the aorta.
Persistent hypertension is particularly important and may remain even after apparently successful anatomical repair. (www.heart.org)
The repaired patient therefore requires continuing congenital cardiac follow-up.
Coarctation in One Sentence
If the entire condition had to be reduced to one physiological description:
Coarctation of the aorta is an obstruction to systemic blood flow that produces high pressure before the narrowing, reduced pressure beyond it, and increased workload on the left ventricle.
In the newborn, one additional question becomes critical:
Is the lower body dependent upon the ductus arteriosus for blood flow?
Once those two concepts are understood, the majority of the physiology of coarctation begins to make sense.
Key Points
Coarctation is a narrowing of the aorta, usually close to the ductus arteriosus.
It is traditionally described as an acyanotic obstructive congenital heart defect.
The left ventricle must generate increased pressure to overcome the obstruction.
Blood pressure is typically higher above the coarctation than below it.
Severe neonatal coarctation may be duct-dependent.
Closure of the ductus in a critically obstructed infant can cause rapid cardiovascular deterioration.
Prostaglandin E1 can maintain ductal patency before definitive treatment.
Weak femoral pulses, radiofemoral delay and an arm-to-leg blood-pressure difference are important clinical signs.
Treatment may involve surgical reconstruction, balloon angioplasty or stent implantation.
Even after successful repair, lifelong congenital cardiac follow-up is required because hypertension, recoarctation and aortic abnormalities can occur. (www.heart.org)
Glossary of Terms
Acyanotic
A congenital cardiac condition in which sufficient oxygenated blood reaches the systemic circulation to prevent characteristic central cyanosis.
Aorta
The principal systemic artery carrying blood from the left ventricle to the body.
Aortic Arch
The curved portion of the aorta between the ascending and descending aorta from which the major arteries supplying the head and upper limbs arise.
Aortic Isthmus
The portion of the aorta around the junction between the distal arch and descending aorta, close to the attachment of the ductus arteriosus.
Bicuspid Aortic Valve — BAV
A congenital abnormality in which the aortic valve has two functional leaflets rather than the usual three.
It is commonly associated with coarctation.
Coarctation of the Aorta — CoA
A congenital narrowing of part of the aorta that obstructs systemic blood flow.
Collateral Circulation
Alternative vascular pathways that enlarge or develop to allow blood to bypass an obstruction.
Cyanosis
Bluish discoloration of the skin or mucous membranes associated with an increased concentration of deoxygenated haemoglobin within arterial blood.
Ductus Arteriosus
A normal foetal vascular connection between the pulmonary artery and descending aorta.
Duct-Dependent Systemic Circulation
A condition in which adequate systemic blood flow depends upon continued patency of the ductus arteriosus.
Critical coarctation may produce this physiology.
End-to-End Anastomosis
A surgical technique in which a diseased vascular segment is removed and the two remaining ends are joined together.
Hypertension
Abnormally elevated arterial blood pressure.
Left Ventricular Hypertrophy — LVH
Thickening of the left ventricular myocardium in response to sustained increased workload or pressure.
Patent Ductus Arteriosus — PDA
Persistence of the ductus arteriosus after birth.
In critical coarctation, temporary maintenance of ductal patency may be essential to systemic perfusion.
Prostaglandin E1 — PGE1
A medication used in duct-dependent congenital heart disease to maintain or restore patency of the ductus arteriosus.
Radiofemoral Delay
A delay and reduction in the femoral pulse compared with the radial pulse, caused by obstruction between the arterial supply of the upper and lower body.
Recoarctation
Recurrent narrowing of the aorta following previous repair of coarctation.
Stenosis
Abnormal narrowing of a valve, vessel or opening.
Systemic Vascular Resistance — SVR
The resistance against which the left ventricle pumps blood into the systemic circulation.
Sources
This revised piece was checked against contemporary descriptions from the American Heart Association and current professional congenital-heart references. The AHA’s Coarctation of the Aorta information was last reviewed on 14 April 2026. (www.heart.org)
