Hypoplastic left heart syndrome Unit 4

What is Hypoplastic Left Heart Syndrome, and why can the LV not act as the systemic ventricle?

HLHS is one of the most severe forms of congenital heart disease. It mainly consists of a hypoplastic left ventricle that is too underdeveloped to function as the systemic ventricle.

What abnormalities can cause the hypoplastic LV in HLHS? List 3

• Aortic stenosis or atresia

• Mitral stenosis or atresia

• Aortic arch hypoplasia

Please list the 4 possible LV findings in HLHS.

• Varying degrees of LV hypoplasia with severely decreased systolic function

• A slit-like LV in mitral and aortic atresia

• Endocardial fibroelastosis

• A non-apex-forming LV

What mitral valve and mitral apparatus abnormalities may occur in HLHS?

There may be mitral atresia or severe mitral stenosis. Papillary muscle and valvar apparatus abnormalities may occur when mitral stenosis is present.

Please list the abnormalities involving the aortic valve, aorta, and aortic arch in HLHS.

• Aortic valve atresia or severe stenosis; the valve may be unicuspid or bicuspid

• A hypoplastic aortic arch

• Coarctation of the aorta, reported in at least 80% of cases

What coronary artery findings may occur in HLHS?

The coronary arteries are usually normal, but coronary ostial atresia or coronary-to-ventricle fistulas may be present.

What findings may be seen in the left atrium and atrial septum?

The left atrium may be small, and a patent foramen ovale is present. Always assess whether the PFO is restrictive.

What happens to the PDA and branch pulmonary arteries, and what is the PDA flow direction?

The PDA and branch pulmonary arteries are enlarged, and color flow through the PDA is right to left.

What right ventricular and tricuspid valve findings may occur in HLHS?

The RV is enlarged and hypertrophied. Tricuspid valve findings include:

• Tricuspid valve dysplasia in up to 50% of cases

• Papillary muscle abnormalities and leaflet tethering

• Tricuspid regurgitation

Please list the 3 typical subtypes of HLHS.

• Aortic atresia with mitral stenosis — AA/MS

• Aortic stenosis with mitral stenosis — AS/MS

• Aortic atresia with mitral atresia — AA/MA

How may the LV appear in the 3 HLHS subtypes?

• Mitral stenosis/aortic stenosis: severe LV hypoplasia with severe LV hypertrophy

• Mitral stenosis/aortic atresia: severe LV hypoplasia with a slit-like LV

• Mitral atresia/aortic atresia: severe LV hypoplasia with a slit-like LV

How severe is HLHS, and what percentage of deaths in CHD patients does it cause?

HLHS is one of the most severe forms of CHD and is the most common cause of death from CHD during the first week of life. It accounts for approximately 20%–25% of deaths in patients with CHD.

What is the prevalence of HLHS, and which sex is more commonly affected?

HLHS affects approximately 0.02% of the population and has a male predominance.

Please list the 3 environmental or epidemiologic factors associated with HLHS

• Increased incidence in certain geographic areas

• Seasonal changes

• Maternal streptococcal infections

How commonly is HLHS associated with genetic abnormalities, what is its family recurrence risk, and which syndrome is strongly associated with it?

HLHS occurs with genetic syndromes and chromosomal abnormalities in up to 30% of cases. The recurrence risk within the same family is up to 2%, and HLHS is strongly associated with Turner syndrome.

Please list the 11 other syndromes or chromosomal abnormalities associated with HLHS.

• Adams-Oliver syndrome

• Beckwith-Wiedemann syndrome

• Jacobsen syndrome

• Kabuki syndrome

• Meckel-Gruber syndrome

• Rubinstein-Taybi syndrome

• Smith-Lemli-Opitz syndrome

• Trisomy 21

• Trisomy 19

• 22q11.2 deletion

• VACTERL

Explain the “No Flow, No Grow” principle in HLHS.

Normal growth and dilation of the left heart require adequate blood flow from the lungs and left atrium. If the fetal mitral or aortic valve develops atresia or stenosis, blood flow decreases. Without enough blood flow and hemodynamic stretch, the LV cannot enlarge and becomes hypoplastic.

Why is systemic circulation ductal-dependent in HLHS, and where does the oxygenated pulmonary venous blood go?

The underdeveloped left heart cannot support systemic circulation, so systemic blood flow depends on the ductus arteriosus. Oxygenated blood enters the left atrium and shunts to the right atrium.

Where does blood mixing occur in HLHS?

Oxygenated blood from the left atrium mixes with desaturated systemic venous blood in the right atrium.

What circulations must the RV supply, and what are the 2 possible pathways for blood leaving the RV?

The RV must pump mixed blood to both the pulmonary and systemic circulations.

1. Blood travels to the lungs through the branch pulmonary arteries.

2. Blood travels to the body through the ductus arteriosus.

What happens when pulmonary vascular resistance decreases after birth?

More RV output travels to the lungs, causing systemic blood flow to decrease. Poor systemic perfusion, metabolic acidosis, and oliguria may develop.

How do the coronary arteries and brain receive blood in HLHS, and what can happen if this blood flow decreases?

Coronary and cerebral perfusion depend on blood passing through the ductus arteriosus and then flowing retrograde through the aortic arch. Decreased blood flow increases the risk of myocardial or cerebral ischemia and may result in hypoxemia.

How can coarctation of the aorta worsen blood flow in HLHS?

Coarctation can interfere with retrograde blood flow to the proximal aorta.

When can symptoms of HLHS appear?

Symptoms may be present at birth or may appear within a few days as the ductus arteriosus begins to close.

Please list the 6 immediate clinical symptoms of HLHS.

• Cyanosis or blue-gray skin

• Rapid breathing, shortness of breath, or flared nostrils

• Pale and clammy skin

• Tachycardia with diminished distal pulses

• Poor feeding with excessive fatigue

• Lethargy, extreme sleepiness, or unresponsiveness

What signs may occur if the baby quickly goes into shock?

• Slow or shallow breathing

• Staring eyes

• Dilated pupils

What murmur may be heard in HLHS, and what causes it?

A soft, nonspecific systolic murmur may be heard. It is caused by the RV driving blood through the low-pressure right-sided circulation.

Please list the 5 possible general ECG findings in HLHS.

• Up to 20% of newborns may have a normal-appearing ECG.

• Prolonged PR intervals

• Wider QRS complexes

• Low left-sided voltages and absent septal Q waves in the inferior and lateral leads

• Right-axis deviation caused by right-sided dominance

What findings may appear on a typical ECG from a patient with HLHS without ventricular preexcitation?

• Long PR interval

• Abnormal right-superior frontal plane axis

• Increased precordial voltages in V1 and V3R

• Decreased precordial voltages in the lateral leads V5–V7

What are the chest X-ray findings of HLHS?

Increased pulmonary vascularity and cardiomegaly.

What should be assessed from the subcostal 4-chamber view?

• Compare the size of the right side with the left side.

• Identify whether the obstruction comes from the mitral valve, aortic valve, or aortic arch.

• Compare the enlarged pulmonary artery with the hypoplastic arch.

Why is the subcostal 4-chamber view important for assessing the atrial septum, and what should be evaluated?

It is the best view for interrogating the interatrial septum. Evaluate the:

1. Number of atrial communications

2. Size

3. Location

4. Degree of restriction

Include color and Doppler assessment.

How large should the PFO or ASD be, and in which direction will the interatrial septum bow?

The PFO or ASD is recommended to be more than one-half the length of the septum, and the interatrial septum will bow into the right atrium.

What can be evaluated from the subcostal PSAX view?

Most of the aortic arch can be visualized. Decreased pulsatility indicates stenosis above the sampled area, and reversal of flow from the PDA may be seen.

What LV and LA findings should be assessed from the PLAX view?

• Determine the size of the LV.

• Measure the LV dimensions.

• Look for endocardial fibroelastosis.

• Measure the diameter of the left atrium.

What additional structures should be assessed from the PLAX view?

Define and interrogate any VSDs and measure the hypoplastic aorta.

What should be assessed from the PSAX RV inflow and RV outflow views?

• RV inflow: Assess RV and tricuspid valve function and look for TR.

• RV outflow: Assess the pulmonary artery, which may be dilated because of increased flow.

What should be assessed at the PSAX great-vessel level regarding the aorta and great arteries?

• Measure the aortic root and ascending aorta.

• Determine the size of these structures.

• Confirm that the great arteries are normally related.

How should the PDA and VSD be evaluated at the PSAX great-vessel level?

Evaluate the size and shunt direction of both the PDA and VSD using:

1. 2D imaging

2. Color Doppler

3. Spectral Doppler

What additional findings should be assessed at the PSAX great-vessel level?

• Look for pulmonary regurgitation.

• Assess the pulmonary valve for stenosis and regurgitation.

• Evaluate the coronary artery anatomy.

What does the PSAX ventricular-level view demonstrate?

It demonstrates the size discrepancy between the ventricles and allows assessment of ventricular function.

What should be assessed initially from the apical 4-chamber view?

• Show the size discrepancy between the ventricles.

• Define whether the subtype is AS/MS, AA/MS, or AA/MA.

• Look for color flow through the aorta.

What LV findings should be assessed from the apical 4-chamber view?

• LV size

• LV function

• Endocardial fibroelastosis

• Coronary fistulas

What left atrial and pulmonary venous findings should be assessed?

Assess left atrial size and pulmonary venous drainage. Use color and pulsed-wave Doppler on all pulmonary veins.

What right ventricular and tricuspid valve findings should be assessed?

• RV size, function, and morphology

• Tricuspid valve morphology and chordal attachments

• Severity of tricuspid regurgitation

What additional right-sided structures should be assessed?

Assess the main pulmonary artery with Doppler and evaluate right atrial size and morphology.

Which parts of the aorta should be evaluated and measured?

Evaluate the morphology of the ascending aorta, arch, and descending aorta. Measure the:

1. Ascending aorta

2. Transverse arch

3. Aortic isthmus

4. Descending aorta

How should coarctation or interrupted aortic arch be assessed?

Rule out coarctation or interrupted aortic arch using color and spectral Doppler. Look for retrograde flow in the ascending and abdominal aorta.

What systemic venous structures should be demonstrated?

Demonstrate systemic venous drainage and look for:

1. Innominate vein

2. Levoatriocardinal vein

3. Persistent left superior vena cava

Use color and Doppler.

How should PDA and PFO flow be quantified?

Assess PDA and PFO flow and measure the peak and mean velocities across the shunts.

What Doppler findings should be used to assess systemic blood flow and coarctation?

Look for retrograde flow in the ascending and abdominal aorta and Doppler the descending aorta for coarctation.

How should RV function be quantified?

Interrogate the TR jet, calculate RV fractional area change, and perform tissue Doppler imaging on all walls.

What Doppler measurement may help evaluate the single RV, and what information does it provide?

The RV dP/dt can be measured from the continuous-wave Doppler tracing of the tricuspid regurgitation jet. It provides systolic and diastolic information.

Please list the 4 associated defects of HLHS.

• Coarctation of the aorta

• Persistent left superior vena cava

• Levoatriocardinal veins

• Pulmonary venous abnormalities, although these are rare

Please list the 3 differential diagnoses for HLHS.

• Critical aortic stenosis

• Coarctation of the aorta

• Single ventricle

What is the goal of emergent treatment, and how are the PFO and PDA kept open?

The goal is to maintain patency of the PFO and PDA.

• The atrial communication is maintained or enlarged through atrial septostomy.

• Prostaglandin E1 is given to keep the PDA open.

What is the ideal arterial oxygen saturation, and when does multistage surgery begin?

The ideal arterial oxygen saturation is 75%–85%. Multistage surgery is required, beginning during the first week of life.

Please list the 3 main components of the Stage 1 Norwood procedure.

• Oversewing the pulmonary artery

• Construction of the neoaorta

• Establishing controlled pulmonary blood flow through either a BT shunt or Sano shunt

What is the difference between the BT shunt and the Sano shunt?

• BT shunt: connects the innominate artery to the right pulmonary artery.

• Sano shunt: creates a conduit from the RV to the branch pulmonary arteries.

What is hybrid Stage 1 palliation, and when may it be used?

The hybrid procedure avoids cardiopulmonary bypass and open-heart surgery during the neonatal period. It may be used for high-risk neonates or to delay more complex surgery.

Please list the 3 components of the hybrid procedure.

• Bilateral pulmonary artery banding

• Ductus arteriosus stenting

• Atrial septal manipulation

When is the Stage 2 bidirectional Glenn or hemi-Fontan performed, and what occurs?

It is performed at approximately 4–6 months. The SVC is anastomosed to the pulmonary artery, and the aortopulmonary shunt is closed.

When is Stage 3 performed, what procedure is completed, and where is the IVC directed?

Stage 3 is performed at approximately 2–3 years. The Fontan, also called Norwood III, is completed, and the IVC is directed to the pulmonary artery through a modified Fontan procedure.

Why may an HLHS patient eventually be placed on the heart-transplant list?

The RV must function as the systemic pumping chamber, even though it is not designed to support systemic circulation long-term.

Please list the 8 postoperative findings that should be assessed by echo.

• RV dysfunction or severe TR

• Neoaortic aneurysms

• Neoaortic insufficiency

• Patency and flow through the BT, Sano, Glenn, or Fontan pathways

• Thrombi

• Inflow valve regurgitation

• Branch pulmonary artery sizes

• Aortic arch size