UNIT 3 Congenitally corrected transposition of great arteries

Explain congenitally corrected transposition of the great arteries and why blood still travels in the correct direction.

Congenitally corrected transposition of the great arteries, or CCTGA, is a cardiac structural abnormality with double discordance:

1. Atrioventricular discordance

2. Ventriculoarterial discordance

Because there are 2 abnormal connections, the blood is redirected back into the correct circulation.

Describe the blood-flow pathway in CCTGA.

1. Systemic venous blood enters the right atrium

2. The right atrium connects through the mitral valve to the morphologic LV

3. The morphologic LV pumps blood into the pulmonary artery

4. Oxygenated blood returns to the left atrium

5. The left atrium connects through the tricuspid valve to the morphologic RV

6. The morphologic RV pumps blood into the aorta

Simple reminder:
The ventricles and great arteries are both switched, so circulation is physiologically corrected.

List the 3 morphologic variants of CCTGA.

• Usual CCTGA arrangement with an intact ventricular septum and levocardia

• CCTGA with a VSD and LV outflow tract obstruction or pulmonary stenosis

• CCTGA with mirror-image anatomy and dextrocardia

What relationship do the tricuspid and mitral valves have with the ventricles in CCTGA?

Each AV valve remains connected to its corresponding morphologic ventricle:

• Tricuspid valve goes with the morphologic RV

• Mitral valve goes with the morphologic LV

Where are the morphologic ventricles located and what circulation does each one support?

• The morphologic LV becomes the subpulmonary ventricle

• The morphologic RV becomes the subaortic or systemic ventricle

What is abnormal about the tricuspid valve in CCTGA?

The tricuspid valve is located on the left side and is almost always abnormal. Because it functions as the systemic AV valve, it is exposed to high systemic pressures and may develop regurgitation.

What happens to the subpulmonary infundibulum in CCTGA?

There is no normal subpulmonary infundibulum. It is replaced by mitral valve–pulmonary valve fibrous continuity.

What happens to the membranous septum in CCTGA?

The membranous septum becomes enlarged and may contribute to outflow tract obstruction.

Describe the coronary artery anatomy in CCTGA.

The coronary arteries follow the anatomy of their respective morphologic ventricles, although a single coronary artery is common.

Are the systemic and pulmonary veins normally connected in CCTGA?

Yes. The systemic and pulmonary veins usually connect normally to their corresponding atria.

Describe the position of the aorta and pulmonary artery in CCTGA.

The aorta is positioned anterior and leftward of the pulmonary artery.

How do the proximal portions of the great arteries course?

They run parallel rather than crossing normally.

Why is the conduction system abnormal in CCTGA?

Leftward looping causes malalignment between the atrial and ventricular septa. This disrupts the normal conduction pathway and changes the position and course of the AV node and bundle of His.

What percentage of patients may develop third-degree AV block?

Approximately 50% may develop third-degree AV block.

How common is CCTGA?

CCTGA is uncommon and makes up approximately 0.5% of all congenital heart defects

What is the usual Van Praagh classification for CCTGA?

S, L, L

Explain the embryologic cause of CCTGA.

Abnormal leftward looping of the heart tube causes:

1. Atrioventricular discordance

2. Ventriculoarterial discordance

Where does the cardiac apex point in most patients with CCTGA?

The apex points to the left in approximately 75% of patients.

Why can the systemic right ventricle eventually fail in CCTGA?

The morphologic RV is heavily trabeculated and designed to pump against the low-pressure pulmonary circulation. In CCTGA, it must pump against the high-pressure systemic circulation.

Over time, the systemic pressure load can cause:

1. Progressive RV dilation

2. RV systolic dysfunction

3. Heart failure

Why does systemic tricuspid regurgitation develop in CCTGA?

The left-sided tricuspid valve functions as the systemic inflow valve. It is not designed to tolerate systemic pressure over a lifetime.

This may cause:

1. Annular dilation

2. Tricuspid regurgitation

3. Progressive systemic RV volume overload

4. Worsening RV failure

Why can complete heart block occur in CCTGA?

Complete heart block can occur because the AV node and bundle of His have an abnormal location and an elongated conduction pathway.

How may CCTGA present clinically?

CCTGA may remain undetected until adulthood. Many patients are asymptomatic and are diagnosed during routine chest X-ray or ECG evaluation.

List the 2 common presenting symptoms of CCTGA.

• Cyanosis

• Dyspnea

List the 4 main causes of symptoms in CCTGA.

• Systemic RV failure

• Systemic tricuspid valve failure or regurgitation

• LV outflow tract obstruction

• Large VSD

What effect does LV outflow tract obstruction have in CCTGA?

Because the morphologic LV pumps to the lungs, LVOTO is a subpulmonary obstruction.

It can:

1. Reduce pulmonary blood flow

2. Alter right-sided pressure

3. Alter left-sided volume

4. Contribute to cyanosis

What percentage of patients with CCTGA have associated defects?

More than 90% have associated defects.

List the 7 associated defects of CCTGA.

• Ebstein anomaly of the systemic tricuspid valve —

• VSD —

• Dextrocardia or mesocardia —

• Right aortic arch —

• Aortic coarctation

• Subpulmonary outflow tract obstruction

Describe the VSD commonly associated with CCTGA.

The VSD is commonly:

1. Membranous or perimembranous

2. Large

3. Nonrestrictive

How common is subpulmonary outflow tract obstruction in CCTGA?

It occurs in approximately 50% of patients.

What causes subpulmonary outflow tract obstruction?

It may be caused by:

1. A fibrous ridge

2. An aneurysm arising from excessive membranous septal tissue

List the 5 beginning steps of the subcostal evaluation for CCTGA.

• Begin by establishing visceral situs

• Sweep to determine the cardiac position in the chest

• Perform segmental analysis of the atria

• Identify the morphologic ventricles

• Determine the great-artery connections

What venous connections should be demonstrated?

Both:

1. Pulmonary venous connections

2. Systemic venous connections

How should the great-artery connections be determined?

Use 2D sweeps and color Doppler to follow each ventricle into its connected great artery.

List the 5 features used to identify the morphologic RV.

• More apical position of the tricuspid valve septal leaflet hinge point

• Trileaflet tricuspid valve

• Chordal attachments to the ventricular septum

• Moderator band

• Irregular, heavily trabeculated endocardial surface

• Crescent-shaped ventricular cavity

How can the morphologic LV be differentiated from the morphologic RV?

The morphologic LV typically has:

1. Smoother endocardial walls

2. Fine trabeculations

3. No moderator band

4. A more elliptical cavity

5. A mitral valve without chordal attachment to the septum

Why may obtaining a normal PLAX view be difficult in CCTGA?

The abnormal ventricular and great-artery positions change the usual heart orientation, so the transducer may need to be moved more laterally.

What may be visualized by moving the PLAX view more laterally?

The parallel course of the great arteries.

List the 3 main PLAX assessment goals.

• Demonstrate the parallel great arteries

• Assess for VSDs

• Evaluate the enlarged membranous septum and outflow tracts

Why are VSDs commonly perimembranous in CCTGA?

The abnormal outflow alignment creates a large membranous septal region, making perimembranous VSDs common.

List the 4 assessment goals from PSAX.

• Demonstrate the orientation of the semilunar valves

• Demonstrate the coronary arteries

• Evaluate ventricular morphology and function

• Assess for VSDs

What inflow-valve feature should be evaluated?

Look for AV-valve chordal attachments to the septum to help identify the tricuspid valve and morphologic RV.

List the 5 assessment goals from the apical views.

• Identify the morphologic ventricles

• Confirm atrioventricular discordance

• Evaluate ventricular function

• Evaluate the outflow tracts for location and obstruction using color and spectral Doppler

• Assess systemic tricuspid valve morphology and regurgitation

Which ventricle requires especially careful functional assessment?

The systemic morphologic RV, because it may progressively dilate and fail.

List the 9 major echocardiographic findings of CCTGA.

• Atrioventricular discordance

• Ventriculoarterial discordance

• Morphologic RV on the left side

• Morphologic LV on the right side

• Left-sided tricuspid valve

• Aorta anterior and leftward of the pulmonary artery

• Parallel great arteries

• Systemic RV dilation or dysfunction

• Systemic tricuspid regurgitation

List the 6 associated findings that should be evaluated on echo.

• VSD location, size, and shunt direction

• Subpulmonary LVOTO

• Systemic tricuspid valve regurgitation

• Ebstein-like tricuspid valve abnormality

• Aortic arch abnormalities

• Cardiac position, including dextrocardia or mesocardia

List the 2 main differentials for CCTGA.

• D-transposition of the great arteries

• Ebstein’s anomaly

What is the major difference between CCTGA and D-TGA?

CCTGA has both AV and ventriculoarterial discordance, so blood flow is physiologically corrected. D-TGA has ventriculoarterial discordance without AV discordance, creating parallel circulations.

How are asymptomatic patients without major associated defects managed

They may require lifelong monitoring by a congenital cardiologist.

List the 3 medication classes used when ventricular weakness or volume/pressure overload causes heart failure.

• ACE inhibitors

• Beta blockers

• Diuretics

What percentage of patients with CCTGA may require a pacemaker?

Approximately 45% may need a pacemaker for heart block.

When may an ICD be used?

An implantable cardioverter-defibrillator may be used in patients with:

1. Moderate-to-severe systemic RV dysfunction

2. Increased risk for dangerous ventricular arrhythmias

What are the 2 general surgical approaches for CCTGA?

• Physiologic repair

• Anatomic or double-switch repair

What is repaired during a physiologic repair?

Associated defects are corrected while the morphologic RV remains the systemic ventricle.

This may include:

1. VSD closure

2. Relief of pulmonary or subpulmonary obstruction

3. Systemic tricuspid valve repair or replacement

What is the disadvantage of physiologic repair?

The morphologic RV continues pumping against systemic pressure, so systemic RV failure and systemic tricuspid regurgitation may still progress.

What is the goal of a double-switch repair?

The goal is to make the morphologic LV the systemic ventricle and the morphologic RV the pulmonary ventricle.

What are the 2 stages or components of a double-switch repair?

• Atrial redirection

• Ventricular or arterial redirection

What is the purpose of the atrial switch?

The atrial switch redirects systemic and pulmonary venous blood to the opposite ventricles.

Which procedures may be used for the atrial switch?

• Mustard procedure

• Senning procedure

Explain the Rastelli component of CCTGA repair.

The Rastelli procedure includes:

1. An LV-to-aorta baffle routed through the VSD

2. An RV-to-pulmonary artery conduit

What is the goal of the Rastelli procedure?

It redirects the morphologic LV to the aorta so the LV becomes the systemic ventricle

What is done during an arterial switch or Jatene procedure?

The aorta and pulmonary artery are transected and reconnected to the appropriate ventricles.

This establishes the morphologic LV as the systemic ventricle.

List the 10 most important findings of CCTGA.

• Atrioventricular discordance

• Ventriculoarterial discordance

• Physiologically corrected blood flow

• Morphologic LV pumps to the pulmonary artery

• Morphologic RV pumps to the aorta

• Left-sided systemic tricuspid valve

• Aorta is anterior and leftward of the pulmonary artery

• Great arteries run parallel

• Systemic RV failure and tricuspid regurgitation may develop

• Heart block and associated defects are common