Two Obstructive “Pink Baby” Lesions
Introduction
Congenital stenotic lesions are easiest to understand by asking:
Where is the narrowing?
Which ventricle is pumping against it?
And is enough blood still reaching the body or the lungs?
Aortic Stenosis and Pulmonary Stenosis are both primarily obstructive congenital cardiac defects.
They are usually placed in the “pink baby” group because the principal problem is obstruction to blood flow rather than mixing of oxygenated and deoxygenated blood.
In Aortic Stenosis, the left ventricle must pump against obstruction to systemic outflow.
In Pulmonary Stenosis, the right ventricle must pump against obstruction to pulmonary outflow.
Both can range from mild disease with little physiological effect to severe neonatal obstruction requiring urgent intervention. (www.heart.org)
Aortic Stenosis
What is Aortic Stenosis?
Aortic Stenosis is narrowing of the pathway through which blood leaves the left ventricle and enters the aorta.
Normally:
Left ventricle → Aortic valve → Aorta → Body
If this pathway becomes narrowed, the left ventricle must generate greater pressure to eject blood through the obstruction.
This creates a pressure gradient across the narrowed area and increases the workload placed upon the left ventricle. (www.heart.org)
Where Can the Obstruction Occur?
Congenital aortic outflow obstruction can occur at three principal levels:
Subvalvar
Valvar
Supravalvar
The precise anatomical level matters because the underlying abnormality and surgical treatment are different.
Valvar Aortic Stenosis
Valvar Aortic Stenosis is the common congenital form.
The valve itself is abnormal.
A normal aortic valve usually has three cusps.
Congenital valves may instead be:
- bicuspid;
- unicuspid;
- thickened;
- dysplastic;
- or have fused commissures.
These abnormalities prevent the valve from opening normally. (www.heart.org)
Bicuspid Aortic Valve
A Bicuspid Aortic Valve — BAV has two functional valve leaflets rather than three.
Some bicuspid valves function almost normally during childhood.
Others become stenotic or regurgitant.
Bicuspid valve disease is important because it may also be associated with:
- dilation of the ascending aorta;
- Coarctation of the Aorta;
- and progressive valve disease later in life. (www.heart.org)
Subaortic Stenosis
In subvalvar or subaortic stenosis, the obstruction lies below the aortic valve within the left ventricular outflow tract.
It may consist of:
- a fibrous membrane;
- a fibromuscular ridge;
- or a longer tunnel-like narrowing.
The aortic valve itself may initially be structurally normal.
However, the high-velocity jet created by the obstruction can damage the valve over time and contribute to aortic regurgitation.
Supravalvar Aortic Stenosis
In supravalvar aortic stenosis, the narrowing occurs above the aortic valve, commonly at the sinotubular junction of the ascending aorta.
This is a different anatomical lesion from valvar stenosis and is particularly associated with Williams syndrome.
The coronary arteries arise below the obstruction, so severe supravalvar disease can expose the coronary circulation to unusually high proximal pressure.
What Happens to the Left Ventricle?
The left ventricle must generate sufficient pressure to overcome the obstruction.
This produces pressure overload.
The ventricular muscle responds by becoming thicker.
This is called:
Left Ventricular Hypertrophy — LVH
Initially, hypertrophy helps generate greater pressure.
However, severe or longstanding hypertrophy can reduce ventricular compliance and impair filling.
Eventually ventricular function may deteriorate. (www.heart.org)
Why is the Baby Usually Pink?
In uncomplicated Aortic Stenosis, pulmonary venous blood still reaches:
Left atrium → Left ventricle → Aorta
The blood entering the systemic circulation is therefore normally oxygenated.
The problem is how much blood can get through the obstruction, not whether the blood contains oxygen.
The child is consequently usually acyanotic.
Critical Neonatal Aortic Stenosis
Critical Aortic Stenosis is a very different situation.
The left ventricle may be unable to generate adequate systemic output through the severely narrowed valve.
Systemic circulation may then become dependent upon the Ductus Arteriosus.
Blood may travel:
Right ventricle → Pulmonary artery → PDA → Aorta
to maintain systemic perfusion.
This is therefore a duct-dependent systemic circulation.
As the ductus closes, the baby may deteriorate rapidly with:
- poor systemic perfusion;
- metabolic acidosis;
- weak pulses;
- oliguria;
- tachypnoea;
- and cardiovascular collapse.
Severely affected infants require urgent treatment. (www.heart.org)
Initial Management of Critical Aortic Stenosis
A critically obstructed neonate may require:
- Prostaglandin E1 to maintain ductal patency;
- ventilatory support;
- correction of acidosis;
- inotropic support;
- and urgent intervention.
The objective is to maintain systemic perfusion while the left ventricular outflow obstruction is relieved.
Diagnosis of Aortic Stenosis
Echocardiography
Echocardiography assesses:
- valve morphology;
- location of obstruction;
- pressure gradient;
- left ventricular hypertrophy;
- ventricular function;
- aortic regurgitation;
- and associated abnormalities.
Doppler echocardiography is particularly useful for estimating the velocity and pressure gradient across the obstruction.
Balloon Aortic Valvuloplasty
For suitable congenital valvar Aortic Stenosis, balloon valvuloplasty is commonly used.
A catheter-mounted balloon is positioned across the aortic valve.
The balloon is inflated to separate or stretch the fused valve leaflets.
This reduces obstruction and improves left ventricular outflow. (www.heart.org)
One important limitation is that improving valve opening can increase aortic regurgitation.
The procedure is therefore a balance between relieving stenosis and preserving valve competence.
Surgical Aortic Valvotomy
Surgery may be required when:
- catheter treatment is unsuitable;
- the valve anatomy is complex;
- there is significant associated disease;
- or previous balloon treatment has been inadequate.
The fused commissures can be surgically divided to improve valve opening.
Aortic Valve Replacement
Some patients ultimately require valve replacement.
Options can include:
- mechanical valve replacement;
- biological valve replacement;
- or the Ross procedure.
The choice depends upon age, anatomy, previous operations and long-term considerations. (www.heart.org)
The Ross Procedure
In the Ross procedure:
the patient’s own pulmonary valve is removed and placed in the aortic position.
Thus:
Pulmonary valve → Aortic position
A donor homograft or conduit is then used to reconstruct the pulmonary outflow tract.
The pulmonary autograft has the advantage of living tissue and potential for growth in younger patients.
However, the operation converts a single-valve problem into a circulation involving two surgically altered valve positions.
Pulmonary Stenosis
What is Pulmonary Stenosis?
Pulmonary Stenosis is narrowing of the pathway carrying blood from the right ventricle towards the lungs.
Normally:
Right ventricle → Pulmonary valve → Pulmonary artery → Lungs
With stenosis:
Right ventricle → Narrowed outflow → Pulmonary artery
The right ventricle must generate greater pressure to overcome the obstruction. (www.heart.org)
Where Can Pulmonary Stenosis Occur?
As with Aortic Stenosis, pulmonary obstruction can occur at different levels.
These include:
Subvalvar
Valvar
Supravalvar
or within the:
main or branch pulmonary arteries. (NCBI)
Valvar Pulmonary Stenosis
Valvar stenosis is the commonest isolated form.
The pulmonary valve leaflets may be fused, forming a small central opening.
When the right ventricle contracts, the abnormal valve can bulge into the pulmonary artery.
This is often described as doming of the pulmonary valve.
Dysplastic Pulmonary Valve
Not all pulmonary stenosis is caused by commissural fusion.
Some valves are thickened and dysplastic.
This pattern is particularly associated with Noonan syndrome.
Dysplastic valves may respond less well to balloon valvuloplasty than thin, doming valves because there may be less commissural fusion available to split. (NCBI)
Subvalvar Pulmonary Stenosis
Subvalvar pulmonary obstruction occurs within the right ventricular outflow tract.
Muscular narrowing of the infundibulum is particularly familiar in Tetralogy of Fallot.
The obstruction may therefore form part of a more complex congenital cardiac defect rather than occurring in isolation.
Supravalvar and Branch Pulmonary Artery Stenosis
Obstruction can also occur above the pulmonary valve within:
- the main pulmonary artery;
- right pulmonary artery;
- left pulmonary artery;
- or multiple peripheral pulmonary arterial branches.
These lesions behave differently from valvar stenosis and may require balloon angioplasty, stenting or surgical reconstruction rather than valvuloplasty.
What Happens to the Right Ventricle?
Pulmonary obstruction creates right ventricular pressure overload.
The right ventricle must generate increasing pressure to push blood through the narrowing.
The ventricular muscle therefore thickens.
This produces:
Right Ventricular Hypertrophy — RVH
In severe disease, right ventricular pressure can approach or exceed systemic pressure.
Right ventricular function may eventually deteriorate. (www.heart.org)
Why is Pulmonary Stenosis Usually a Pink Baby Lesion?
In mild or moderate Pulmonary Stenosis, enough blood still reaches the lungs to become oxygenated.
Pulmonary venous blood returns normally to the left side of the heart and then reaches the systemic circulation.
Systemic oxygen saturation therefore remains normal.
The main physiological problem is right ventricular pressure overload, not cyanosis.
Critical Pulmonary Stenosis
Critical neonatal Pulmonary Stenosis is different.
If the obstruction is extremely severe, insufficient blood can pass from the right ventricle to the lungs.
Pulmonary circulation may then become duct-dependent.
Blood reaches the lungs through:
Aorta → PDA → Pulmonary artery
The infant may become cyanosed because pulmonary blood flow is inadequate.
This places critical Pulmonary Stenosis at the boundary between the “pink” and “blue” categories. (www.heart.org)
Right-to-Left Atrial Shunting
Severe Pulmonary Stenosis can cause right atrial pressure to rise.
If a PFO or ASD is present, blood may cross:
Right atrium → Left atrium
This allows deoxygenated blood to enter the systemic circulation.
The baby then becomes cyanosed.
Thus:
mild/moderate Pulmonary Stenosis = usually pink
critical Pulmonary Stenosis = potentially blue
Balloon Pulmonary Valvuloplasty
For suitable valvar Pulmonary Stenosis, balloon valvuloplasty is usually the principal catheter intervention.
A catheter is advanced across the pulmonary valve.
A balloon is inflated to separate fused valve commissures and enlarge the opening.
Most suitable children can be treated using this technique. (www.heart.org)
Pulmonary Regurgitation After Treatment
Relieving the obstruction can leave the pulmonary valve less competent.
Some degree of pulmonary regurgitation may therefore develop after balloon or surgical valvotomy.
Over many years, significant regurgitation can cause:
- right ventricular dilation;
- exercise intolerance;
- arrhythmias;
- and eventually right ventricular dysfunction.
Long-term follow-up therefore remains important even after successful treatment.
Surgical Pulmonary Valvotomy
Surgery may be required when:
- the valve is severely dysplastic;
- balloon valvuloplasty is unsuccessful;
- the anatomy is unsuitable for catheter treatment;
- or associated cardiac abnormalities require surgery.
The surgical objective is to increase the size of the pulmonary valve opening while preserving as much valve function as possible.
Transannular Patch
Where obstruction involves both the pulmonary annulus and right ventricular outflow tract, surgical enlargement may require a patch extending across the pulmonary valve annulus.
This is known as a transannular patch.
It relieves obstruction very effectively but often sacrifices pulmonary valve competence.
This technique is particularly familiar from repair of severe Tetralogy of Fallot.
Comparing Aortic and Pulmonary Stenosis
The two lesions are almost mirror images physiologically.
Aortic Stenosis
Obstruction after the left ventricle
causes:
Left ventricular pressure overload → LV hypertrophy → reduced systemic output if severe
Pulmonary Stenosis
Obstruction after the right ventricle
causes:
Right ventricular pressure overload → RV hypertrophy → reduced pulmonary blood flow if severe
The important difference is what lies beyond the obstruction.
A severe aortic obstruction threatens systemic perfusion.
A severe pulmonary obstruction threatens pulmonary blood flow and oxygenation.
Clinical Presentation
Mild Disease
Children may be entirely asymptomatic.
The lesion may be discovered because of a cardiac murmur.
More Significant Aortic Stenosis
Symptoms can include:
- poor feeding in infants;
- breathlessness;
- exercise intolerance;
- chest pain;
- dizziness;
- syncope;
- or heart failure.
More Significant Pulmonary Stenosis
Symptoms can include:
- exercise intolerance;
- breathlessness;
- fatigue;
- right-sided heart failure;
- and, in severe neonatal disease, cyanosis. (www.heart.org)
The Murmur
Both lesions produce turbulent flow across a narrowed outflow tract.
This creates an ejection systolic murmur.
Aortic Stenosis is classically heard most strongly in the aortic area and may radiate towards the neck.
Pulmonary Stenosis is typically heard at the upper left sternal edge.
The exact murmur depends upon severity and anatomy.
Anaesthetic and Theatre Considerations
The principal physiological issue in both lesions is ventricular pressure loading.
For Aortic Stenosis, important considerations include:
- maintaining coronary perfusion;
- preserving preload;
- avoiding severe hypotension;
- maintaining sinus rhythm;
- and understanding the degree of LV hypertrophy and dysfunction.
A severely hypertrophied left ventricle can be particularly dependent upon adequate diastolic coronary perfusion.
For Pulmonary Stenosis, attention focuses upon:
- right ventricular preload;
- right ventricular function;
- pulmonary vascular resistance;
- systemic pressure;
- and maintaining adequate pulmonary flow.
A severely pressure-loaded right ventricle can deteriorate rapidly if pulmonary vascular resistance rises substantially.
Cardiopulmonary Bypass
Surgical treatment may require cardiopulmonary bypass for:
- surgical valvotomy;
- valve repair;
- valve replacement;
- RV outflow reconstruction;
- subaortic membrane resection;
- supravalvar reconstruction;
- or associated congenital abnormalities.
The operation depends upon the precise level of obstruction.
Long-Term Follow-Up
Both Aortic and Pulmonary Stenosis require continued congenital cardiology surveillance.
After treatment, patients may develop:
- recurrent stenosis;
- valve regurgitation;
- ventricular hypertrophy;
- ventricular dilation;
- arrhythmias;
- or progressive ventricular dysfunction.
Aortic valve disease in particular may continue to evolve throughout life, while treated Pulmonary Stenosis may later become predominantly a problem of pulmonary regurgitation. (www.heart.org)
Aortic and Pulmonary Stenosis in One Sentence
Aortic Stenosis obstructs blood leaving the left ventricle for the body, while Pulmonary Stenosis obstructs blood leaving the right ventricle for the lungs.
Both are usually Pink Baby lesions because oxygenation remains preserved until obstruction becomes critical.
Key Points
Aortic and Pulmonary Stenosis are primarily obstructive congenital lesions, not shunt lesions.
Aortic Stenosis causes left ventricular pressure overload.
Pulmonary Stenosis causes right ventricular pressure overload.
Both may occur at:
- subvalvar;
- valvar;
- or supravalvar level.
Congenital valvar Aortic Stenosis is often associated with abnormal cusp development, including bicuspid or unicuspid valves. (www.heart.org)
Valvar Pulmonary Stenosis is commonly treated using balloon pulmonary valvuloplasty. (www.heart.org)
Suitable valvar Aortic Stenosis can also be treated using balloon valvuloplasty. (www.heart.org)
Critical neonatal Aortic Stenosis may produce duct-dependent systemic circulation.
Critical Pulmonary Stenosis may produce duct-dependent pulmonary circulation and cyanosis.
The pink/blue classification therefore reflects physiology rather than simply the anatomical name of the lesion.
Glossary of Terms
Afterload
The resistance or pressure against which a ventricle must pump.
Stenotic outflow lesions increase ventricular afterload.
Aortic Regurgitation
Backward leakage of blood through the aortic valve from the aorta into the left ventricle during diastole.
It may occur after treatment of congenital Aortic Stenosis.
Aortic Stenosis — AS
Narrowing of the left ventricular outflow pathway towards the aorta.
Aortic Valve
The semilunar valve between the left ventricle and aorta.
Balloon Angioplasty
A catheter procedure in which a balloon is inflated inside a narrowed blood vessel to enlarge it.
Balloon Valvuloplasty
A catheter procedure in which a balloon is inflated across a narrowed valve to increase the valve opening.
Bicuspid Aortic Valve — BAV
A congenital aortic valve with two functional cusps instead of the normal three.
Critical Aortic Stenosis
Severe neonatal obstruction of left ventricular outflow that may prevent adequate systemic blood flow and make systemic circulation duct-dependent.
Critical Pulmonary Stenosis
Severe obstruction of right ventricular outflow causing inadequate pulmonary blood flow, potentially producing cyanosis and duct-dependent pulmonary circulation.
Ductus Arteriosus
The normal foetal vascular connection between the pulmonary artery and aorta.
It may become essential after birth in critical obstructive congenital heart disease.
Dysplastic Valve
A valve with abnormally thickened or malformed leaflets rather than simple fusion of the commissures.
Ejection Systolic Murmur
A murmur produced by turbulent forward blood flow during ventricular contraction, commonly heard in outflow tract stenosis.
Left Ventricular Hypertrophy — LVH
Thickening of the left ventricular myocardium in response to increased pressure workload.
Left Ventricular Outflow Tract — LVOT
The pathway through which blood leaves the left ventricle towards the aortic valve and aorta.
Noonan Syndrome
A genetic syndrome commonly associated with congenital heart abnormalities, particularly dysplastic Pulmonary Stenosis and hypertrophic cardiomyopathy.
Pressure Gradient
The difference in pressure across a narrowed valve or vessel.
Greater obstruction usually produces a larger gradient, although ventricular function and blood flow also influence the measured value.
Pressure Overload
An increased workload caused by a ventricle pumping against abnormally high resistance.
Prostaglandin E1 — PGE1
A medication used to maintain patency of the Ductus Arteriosus in duct-dependent congenital cardiac lesions.
Pulmonary Regurgitation
Backward leakage of blood through the pulmonary valve into the right ventricle.
It can occur following treatment of Pulmonary Stenosis.
Pulmonary Stenosis — PS
Narrowing of the right ventricular outflow pathway towards the pulmonary circulation.
Pulmonary Valve
The semilunar valve separating the right ventricle from the pulmonary artery.
Pulmonary Vascular Resistance — PVR
Resistance to blood flow through the pulmonary circulation.
Right Ventricular Hypertrophy — RVH
Thickening of the right ventricular myocardium in response to increased pressure workload.
Right Ventricular Outflow Tract — RVOT
The pathway through which blood leaves the right ventricle towards the pulmonary valve and pulmonary arteries.
Ross Procedure
An operation in which the patient’s own pulmonary valve is transferred to the aortic position, with the pulmonary outflow reconstructed using a donor valve or conduit.
Stenosis
Abnormal narrowing of a valve, vessel or outflow tract.
Subaortic Stenosis
Obstruction within the left ventricular outflow tract below the aortic valve.
Subvalvar Stenosis
A narrowing located below a valve.
Supravalvar Stenosis
A narrowing located above a valve.
Systemic Perfusion
Delivery of blood to the body’s organs and tissues.
Critical Aortic Stenosis can severely compromise systemic perfusion.
Transannular Patch
A surgical patch placed across a valve annulus to enlarge a narrowed outflow tract.
It is commonly associated with reconstruction of severe right ventricular outflow obstruction.
Unicuspid Aortic Valve
A congenital aortic valve with a single functional cusp or opening.
It can cause severe congenital Aortic Stenosis.
Valvotomy
Surgical or catheter-based opening of a stenotic valve.
Williams Syndrome
A genetic condition associated particularly with supravalvar Aortic Stenosis and characteristic vascular abnormalities.
