Complete Transposition of the Great Arteries Conotruncal Defects

What is complete transposition of the great arteries, and what type of discordance is present?

Complete transposition of the great arteries, or D-TGA, is a common critical congenital heart defect characterized by ventriculoarterial discordance.

What type of atrioventricular and ventriculoarterial connections are present in D-TGA?

• Atrioventricular concordance: RA → RV and LA → LV

• Ventriculoarterial discordance: RV → aorta and LV → pulmonary artery

Where do the aorta and pulmonary artery arise in D-TGA?

The aorta arises anteriorly from the RV, while the pulmonary artery arises posteriorly from the LV.

What type of circulatory pattern does D-TGA create?

It creates two separate parallel circulatory circuits. Oxygenated blood is pumped back to the lungs, while deoxygenated blood is pumped back to the systemic circulation.

What does the segmental notation Describe in D-TGA?

S,D,D

• S: atrial situs solitus

• D: D-looped ventricles

• D: the aortic valve is rightward and anterior to the pulmonary valve

Please list the 3 structural features of D-TGA and their frequencies.

• Bilateral subarterial conus in 7% of cases

• Bicuspid pulmonary valve with some degree of pulmonary stenosis in 20%

• VSD in approximately 40%–45%

What is the usual coronary artery arrangement in D-TGA, and how often does it occur?

Approximately 65% have the usual arrangement:

• RCA arises from the right aortic sinus.

• LAD and circumflex arteries arise from the left aortic sinus.

What are the 2 most common coronary artery anomalies in D-TGA?

• The circumflex artery arising from the RCA

• A single coronary artery arising from one of the aortic sinuses

What is the conus, and what does it do?

The conus is the infundibulum of the RV. It positions the pulmonary valve and physically separates it from the aortic valve.

Why is there normally fibrous continuity between the mitral and aortic valves?

There is normally no subaortic conus, allowing direct fibrous continuity between the mitral and aortic valves.

What is the prevalence of D-TGA, how common is it among congenital heart lesions, and which sex is affected more often?

• Approximately 0.2 per 1,000 live births

• The 10th most common congenital heart lesion

• The second most common cyanotic CHD after Tetralogy of Fallot

• More common in males than females

Please list the 3 possible risk or causative factors associated with D-TGA.

1. Maternal diabetes

2. Environmental exposure, such as retinoic acid

3. A probable genetic cause

Approximately 10% of patients have a relative with CHD.

What embryologic abnormality causes D-TGA?

D-TGA is a conotruncal abnormality in which the conotruncal septum fails to spiral. This causes the great arteries to run parallel, with the aortic valve positioned rightward and anterior to the pulmonary valve.

Please list the 2 types of D-TGA.

• D-TGA with an intact ventricular septum

• D-TGA with a VSD

What is D-TGA with an intact ventricular septum?

It is the most common type. The ventricular septum is intact, but the aorta and pulmonary artery are switched.

What purpose does the VSD serve in D-TGA with a VSD?

The VSD provides an opening between the ventricles that allows oxygenated and deoxygenated blood to mix.

What additional finding is common with D-TGA and a VSD, and how can the VSD affect the clinical presentation?

Outflow-tract obstruction is common. Because the VSD allows additional mixing, clinical symptoms may be delayed slightly.

Why does D-TGA cause cyanosis, and what determines its severity?

The parallel circulation causes varying degrees of cyanosis after birth. The severity depends on the size of the interatrial communication.

How do the PDA, PFO/ASD, and VSD affect blood mixing in D-TGA?

• A PDA improves mixing when an unrestricted PFO or ASD is present.

• A moderate or large VSD also improves mixing.

• Oxygen saturation is usually higher when a VSD is present.

What ventricular changes occur if D-TGA is not repaired during the first weeks of life?

• The RV becomes hypertrophied.

• The LV loses muscle mass.

• The interventricular septum becomes flattened.

Please list the 4 clinical findings of D-TGA with an intact ventricular septum.

• Severe, progressive cyanosis of the skin, lips, and nail beds within the first 24 hours

• Tachypnea

• Tachycardia

• Poor feeding

How does D-TGA with a VSD usually present?

Infants may initially appear less cyanotic but develop signs of congestive heart failure within the first 3–6 weeks, including:

• Labored breathing

• Excessive sweating

• Failure to gain weight

What is the first major purpose of echo imaging in D-TGA?

Initial imaging determines whether there is adequate mixing of oxygenated and deoxygenated blood.

How is the relationship of the great arteries demonstrated from the subcostal 4-chamber view?

Sweep superiorly from the subcostal 4-chamber view using 2D imaging and then color Doppler to demonstrate the great-artery relationship.

What should be evaluated at the atrial septum from the subcostal 4-chamber view?

Evaluate for left-to-right shunting through the PFO or ASD using:

• 2D imaging

• Color Doppler

• Spectral Doppler

Why should the color scale be lowered below 40 cm/s when looking for VSDs in a newborn with D-TGA?

Pulmonary pressures are still high during the newborn period, which may produce low-velocity VSD flow. Lowering the scale helps detect the VSD.

What great-artery finding should be demonstrated from the subcostal short-axis view?

Demonstrate the parallel arrangement of the great arteries with the transducer marker at 6 o’clock.

What should be assessed from the subcostal bicaval view and during a leftward sweep?

• Use the bicaval view to assess left-to-right shunting through the PFO or ASD with 2D, color, and Doppler.

• Sweep leftward and use a lowered color scale to look for VSDs.

What should be assessed and measured from the parasternal long-axis view?

• LV function

• Outflow-tract anatomy

• Aortic valve annulus diameter

• Pulmonary valve annulus diameter

What additional findings should be assessed from the parasternal long-axis view?

• Mitral-pulmonary fibrous continuity

• VSDs by sweeping through the septum with a lowered color scale

What does the RV inflow view demonstrate in D-TGA?

The RV inflow view demonstrates the aorta and tricuspid valve in the same view.

What should be assessed from the parasternal short-axis view?

• Aortic and pulmonary valve arrangement

• Valve anatomy, including the number of leaflets and stenosis

• Coronary artery anatomy

• Presence of a PDA

How should VSDs be assessed from the parasternal short-axis view?

Sweep through the ventricular septum using a lowered color scale and document the VSD’s:

• Shunt direction

• Velocity

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

• Ventricular function

• VSDs

• Inflow valves

What is the first vessel seen in the apical 5-chamber view, and what should be assessed?

The first vessel is the pulmonary artery arising from the LV. Assess for pulmonary stenosis.

How is the aorta visualized from the apical 5-chamber view?

Turn the transducer toward approximately 5 o’clock to visualize and interrogate the aorta arising from the RV.

What should be evaluated from the suprasternal long-axis view?

• Aortic coarctation

• PDA

What should be assessed from the suprasternal short-axis crab view?

• Aortic arch sidedness

• Systemic venous connections

• Pulmonary venous drainage

What coronary artery findings are commonly associated with D-TGA?

Coronary anatomy is variable. Approximately 65% have normal coronary anatomy, while the most common anomaly is the circumflex artery arising from the RCA, occurring in approximately 13.5%.

What percentage of patients with D-TGA have a VSD, and what are the 4 listed VSD types?

A VSD occurs in approximately 40%.

1. Membranous — 33%

2. Malalignment — 30%

3. Muscular — 25%

4. AV canal defect — 5%

An AV canal defect may include a cleft mitral valve, straddling inflow valve, and inlet VSD

Please list the 3 other common associated defects of D-TGA and their frequencies.

• Bicuspid pulmonary valve with pulmonary stenosis — 20%

• LV outflow-tract obstruction — 10%

• Coarctation of the aorta — 5% when a VSD is present

Please list the 5 less common associated defects of D-TGA.

• Persistent left superior vena cava

• Isolated cleft mitral valve

• Straddling inflow valves

• Partial or total anomalous pulmonary venous return

• Cor triatriatum

Please list the 6 differential diagnoses for D-TGA.

• Congenitally corrected transposition of the great arteries

• Tetralogy of Fallot

• Truncus arteriosus

• Total anomalous pulmonary venous connection

• Tricuspid valve abnormalities

• Hypoplastic left heart syndrome

Please list the 3 surgical procedures used for D-TGA and their indications.

• Jatene arterial switch with LeCompte maneuver: classic D-TGA with an intact septum

• Mustard or Senning atrial switch: classic D-TGA with complex coronary anatomy

• Rastelli repair: D-TGA with a VSD and pulmonary stenosis

What palliative treatments are used before definitive repair of D-TGA with an intact ventricular septum?

• Administration of prostaglandin E1

• Emergent balloon atrial septostomy, which improves oxygen levels

What is performed during the Jatene arterial switch?

• The great arteries are surgically switched.

• The coronary arteries are moved when necessary.

What is performed during the LeCompte maneuver?

The pulmonary arteries are moved anteriorly so that they straddle the aorta.

What defects may be closed during the arterial switch, and what is the surgical mortality?

The ASD, PDA, and VSD are closed when present. Surgical mortality is now less than 5%.

What ventricular findings should be assessed after the Jatene procedure?

• RV and LV function

• Myocardial stunning, which is common during the first few postoperative days

• Regional wall-motion abnormalities, which may indicate coronary artery ischemia

Which structures should be assessed for residual leaks after the Jatene procedure?

• Atrial septum

• Ventricular septum

• PDA

What is the most common short-term complication after the Jatene procedure?

Supravalvular or branch pulmonary artery stenosis is the most common short-term complication, occurring in approximately 30%. Peak Doppler velocity may be greater than 2.0 m/s.

What additional findings should be assessed after the Jatene procedure?

• Semilunar valve regurgitation

• RV systolic pressure

What supravalvular abnormalities should be assessed after an arterial switch?

Look for supravalvular stenosis or dilation associated with regurgitation.

What should be assessed from the subxiphoid views after an arterial switch operation?

Frontal long-axis:

• Atrial and ventricular septa

• Outflow tracts

• Residual ASD or VSD

• Residual outflow-tract obstruction

Sagittal short-axis:

• RV outflow tract

• Ventricular septum

• Descending aorta

• Pulmonary outflow obstruction

• Residual VSD

• Retrograde descending-aortic flow

What should be assessed from the apical views after an arterial switch operation?

Apical 4-chamber:

• AV valve function

• Ventricular size and function

• Regional wall-motion abnormalities, which may suggest coronary stenosis or occlusion

Apical 5-chamber:

• LV outflow tract

• Supravalvular aortic stenosis

• Neoaortic regurgitation

What should be assessed from the parasternal views after an arterial switch operation?

PLAX:

• Neoaortic and neopulmonary outflow

• Residual VSD

• Neoaortic-root dilation and regurgitation

• Neopulmonary stenosis or regurgitation

PSAX:

• Ventricular function

• Septal position

• Residual VSD

• Regional wall-motion abnormalities

• Pulmonary hypertension

High parasternal:

• Branch pulmonary arteries for stenosis

What should be assessed from the suprasternal view after an arterial switch operation?

Assess the aortic arch for residual arch obstruction or a residual PDA.

When is a Mustard or Senning procedure used, and why were atrial-switch operations developed?

It may be used for classic D-TGA with complex coronary anatomy. During the 1950s, approximately 89% of patients with D-TGA died before one year of age, leading to the development of atrial-switch procedures.

What is the difference between the Senning and Mustard baffles?

• Senning: uses atrial tissue to create the baffle

• Mustard: uses pericardial tissue to create the baffle

Where are systemic and pulmonary venous blood directed after an atrial switch?

• SVC and IVC blood is baffled toward the mitral valve.

• Pulmonary venous blood is baffled toward the tricuspid valve.

Which ventricles serve the systemic and pulmonary circulations after an atrial switch?

The circulation is physiologically corrected, but:

• The RV functions as the systemic ventricle.

• The LV functions as the pulmonary ventricle.

How is the pulmonary venous baffle visualized?

Tilt the transducer slightly posteriorly. The pulmonary venous pathway can then be visualized in most patients.

Which parasternal views can be used to evaluate the systemic venous baffle?

• Parasternal long-axis

• Parasternal short-axis

How is the IVC portion of the systemic venous baffle visualized?

From the pulmonary venous baffle view, tilt slightly anteriorly toward a true 4-chamber view until the mitral leaflets are visualized.

Please list the 6 findings assessed after a Mustard or Senning procedure.

• LV outflow-tract obstruction

• Venous baffle obstruction or leak, usually at velocities above 1.5–2.0 m/s

• Atrial baffle leaks

• RV dysfunction because the RV functions systemically

• Inflow-valve regurgitation

• Arrhythmias and pacemakers

What findings suggest pulmonary venous baffle obstruction, where does it usually occur, and which views are used?

• Increasing mitral regurgitation may suggest obstruction.

• It usually occurs where the baffle enters the right atrium.

• Assess with the apical 4-chamber and parasternal short-axis views.

How common is systemic venous baffle obstruction, and after which operation is it more common?

It occurs in approximately 30% of patients and is more common after the Mustard procedure.

What finding suggests systemic venous baffle obstruction, and which views demonstrate it best?

A dilated IVC suggests obstruction. It is best assessed from:

• Parasternal long-axis

• Bicaval

• Subcostal views

What causes a baffle leak, and what symptoms can it produce?

Baffle leaks may occur when sutures separate. Mixing of oxygenated and deoxygenated blood can cause:

• Cyanosis

• Exercise intolerance

• Heart failure

What is the usual shunt direction through an atrial baffle leak, and what chamber changes may develop?

The shunt is usually left to right, from the pulmonary venous atrium to the systemic venous atrium. Progressive LA and LV dilation may develop.

How are baffle leaks identified and treated?

They are identified with color Doppler and may be closed using an occluder device.

How can a baffle leak be confirmed with color Doppler and agitated saline?

• Apical 4-chamber color Doppler demonstrates shunting from the systemic venous atrium to the pulmonary venous atrium.

• Agitated saline confirms interatrial shunting by opacifying the systemic venous atrium and subpulmonary LV while showing flow across the leak.

What should be assessed from the subxiphoid and apical views after an atrial-switch operation?

Subxiphoid:

• IVC limb of the systemic venous baffle

• Pulmonary venous baffle

• Baffle obstruction or leak

Apical:

• AV valves

• Ventricular function

• Systemic and pulmonary venous baffles

• Baffle obstruction or leak

• Pulmonary hypertension using the MR jet

What should be assessed from the parasternal and suprasternal views after an atrial-switch operation?

PLAX:

• SVC limb of the systemic venous baffle

• Ventricular function

• Outflow tracts

• Outflow obstruction and semilunar-valve function

PSAX:

• Pulmonary venous baffle

• Ventricular function

• Outflow tracts

Suprasternal frontal view:

• Proximal SVC

• Branch pulmonary arteries

Suprasternal sagittal view:

• Aortic arch

What should be assessed with TEE after an atrial-switch operation?

Midesophageal 4-chamber:

• Pulmonary venous baffle

• AV valves

• Ventricular function

• Baffle obstruction or leak

• Pulmonary hypertension using the MR jet

Midesophageal bicaval:

• Systemic venous baffle

• Outflow tract

• Baffle obstruction or leak

• Outflow obstruction

• Semilunar-valve function

Transgastric:

• IVC limb of the systemic venous baffle

• Ventricular function

How does the Rastelli procedure route LV blood to the aorta?

The VSD is closed with an intraventricular patch or baffle that directs oxygenated blood from the LV through the VSD and into the aorta.

How does the Rastelli procedure establish pulmonary blood flow?

A conduit is placed between the RV and the pulmonary artery branches.

Why does the RV-to-PA conduit often require replacement?

The conduit does not grow with the child, so it often requires periodic replacement.

What intracardiac structures should be assessed after the Rastelli procedure?

• LV-to-aortic-valve baffle through the VSD

• Aortic valve anatomy

• Residual VSDs

What extracardiac pathway should be assessed after the Rastelli procedure?

Interrogate the RV-to-PA conduit, pulmonary artery, and branch pulmonary arteries for obstruction.

What ventricular findings should be assessed after the Rastelli procedure?

Evaluate the size, function, and degree of hypertrophy of both the RV and LV.