SECTION XII - Congenitally Corrected Transposition of the Great Arteries

Part I - Background Information

This condition involves atrioventricular discordance and ventriculoarterial discordance (double discordance). Systemic venous return to the right atrium enters the morphological left ventricle, which ejects blood into the pulmonary artery. Pulmonary venous return is to the left atrium and then via the morphological right ventricle to the aorta. The circulation is physiologically corrected but the systemic circulation is supported by the morphologic right ventricle (hence the term 'ventricular inversion' that has been used for this condition).

Congenitally corrected transposition may exist in the setting of univentricular heart, but this is not considered further here.

It is rare (< 1% of CHD) but accounts for a high percentage of cyanotic patients undergoing surgery as adults. Associated anomalies occur in up to 98% in some series and consist of VSD (75% of cases), pulmonary or subpulmonary stenosis (75% of cases) and systemic (tricuspid) valve anomalies (Ebstein-like in 30% of cases). Congenital complete heart block occurs in 5%.

 
Part II - Prevalence and Genetics

A large survey did not show an elevated rate of cardiac malformations in parents (0.6%) or siblings (0.8%) of patients with different forms of TGA (178). Although single case reports of chromosome 22q11 deletion in cases of TGA exist, a large study did not confirm this association (179).

 
Part III - History and Management of Unoperated Patients

Patients with no associated abnormalities may survive until the 6th or 7th decade and may go unrecognized until problems arise. Progressive systemic (tricuspid) AV valve regurgitation and systemic (right) ventricular dysfunction which may present as acute pulmonary edema tend to occur from the 4th decade onwards. The presence of significant systemic tricuspid AV regurgitation impacts negatively on the survival of this patient population (180). Atrial arrhythmias are common from the 5th decade onwards. In addition to congenital complete atrioventricular block, acquired complete atrioventricular block continues to develop at 2% per year (181), and is especially common at the time of heart surgery. Pulmonary (mitral) AV valve regurgitation may occasionally occur and subpulmonary (morphological left) ventricular dysfunction or outflow tract obstruction may also develop and progress.

The outcome of patients with pulmonary stenosis/VSD who have a balanced pulmonary circulation (without excessive pulmonary blood flow on the one hand or excessive pulmonary stenosis on the other hand) is similar with or without operation.

 
Part lV - Diagnostic Workup

An adequate diagnostic workup:

• Documents the anatomy described above.
• Identifies and quantitates associated abnormalities which may influence management (VSD, pulmonary/subpulmonary stenosis, systemic (tricuspid) AV valve regurgitation, ventricular function and AV block).

The diagnostic workup should include at a minimum:

• A thorough clinical assessment.
• ECG.
• Chest x-ray.
• Echo-Doppler examination by an appropriately trained individual.
• Exercise or cardiopulmonary testing with oximetry.

The diagnostic workup may require:

• TEE examination to assess ventricular function, AV valve regurgitation and pulmonary outflow tract if this information is not provided by a TTE study, particularly in the operated patient. These patients are often very difficult to image on TTE because of a poor echo window.
• A complete heart catheterization to assess the hemodynamics, especially in the operated patient who has a conduit between the left ventricle and pulmonary artery or the unoperated patient who is being considered for surgery.
• Coronary angiography in patients at risk of coronary artery disease or if the patient is over the age of 40 years and surgery is planned.
• Holter monitor for AV block and atrial arrhythmia assessment.
• Nuclear cardiology assessment of ventricular function. Radionuclide angiography and MRI usually report better RV function than does echocardiography.
• MRI to evaluate ventricular volumes, ventricular function, or conduit function.
• CBC, ferritin, clotting profile, renal function, and uric acid if the patient is cyanosed (See Management of the Cyanotic Patients - Section XVI).

 
Part V - Indications for Intervention

Patients with a VSD and pulmonary outflow tract obstruction are frequently cyanotic and may have been palliated with systemic-to-pulmonary artery shunts in childhood. Significant cyanosis (< 90%) in the absence of severe pulmonary hypertension should be an indication for intracardiac repair.

The following situations may warrant intervention: The presence of VSD. Pulmonary or subpulmonary stenosis (pullback gradient at cath > 60 mmHg). The presence of moderate or greater systemic (tricuspid) AV valve regurgitation. Complete AV block which requires pacemaker implantation for symptoms, progressive or profound bradycardia or poor exercise heart rate response. Symptomatic deterioration.
Grade: C	Level: V	Refs: 167,181-186

The following situations may warrant re-intervention: Residual VSD. Stenosis across a prior left ventricle-to-pulmonary artery conduit (pullback gradient at cath > 60mmHg). Moderate or worse systemic (tricuspid) AV valve regurgitation following prior surgical repair. Deteriorating systemic (right) ventricular function. Failing pacemaker. Important pulmonary/subpulmonary stenosis.
Grade: C	Level: V	Refs: 187-189

 
Part VI - Interventional Options

Patients who require intervention or re-intervention should be treated by ACHD cardiologists and congenital heart surgeons with appropriate experience.
Grade: C	Level: V	Refs: 18,19

Occasional patients may be unsuitable for repair because of small pulmonary arteries, small systemic (right) ventricles or straddling AV valves and may require palliative shunt procedures.

VSD closure alone is almost always done in childhood with the VSD patch placed to avoid atrioventricular block.

Balloon dilation of pulmonary stenosis may lead to complete AV block and is not recommended.

Repair may involve implantation of a valved conduit from the pulmonary (left) ventricle to the pulmonary artery and repair of the VSD(s). Alternatively, the Ilbawi approach involves tunnelling the left ventricle to the aorta, a right ventricle-to-pulmonary artery conduit and an atrial switch (Mustard) with/without a bi-directional cavo-pulmonary anastomosis. Thus the morphological left ventricle and mitral valve support the systemic circulation. Adult data is lacking regarding the use of the Ilbawi approach (in the setting of VSD and pulmonary stenosis) or a double switch (i.e. Mustard operation and an arterial switch if there is no pulmonary stenosis). Such procedures should still be considered experimental in adult patients.

Patients with systemic (tricuspid) regurgitation presenting for surgery will usually require valve replacement. Repair is usually impractical because the valve is usually morphologically abnormal. Surgery should be performed before systemic ventricular function deteriorates. The Ilbawi approach, leaving the regurgitant tricuspid valve on the pulmonary side may be an option but is still experimental in the adult.
Grade: C	Level: V	Refs: 182,186

Patients with deteriorating systemic (right) ventricular function (which commonly appears after surgical repair) should be treated aggressively with medical therapy but may need to be considered for transplantation. Deterioration may be rapid. The role of ACE inhibitors and beta-blockers in preserving systemic right ventricular function is as yet unknown but many patients are treated empirically with afterload reduction while clinical trial data is awaited.

Complete AV block is not uncommon after surgery and necessitates pacing.

In isolated pulmonary/subpulmonary stenosis, direct enlargement of the outflow tract and valve is seldom possible because of the wedging of the outflow tract and the close relation to the conducting system and left coronary artery, and a pulmonary (left) ventricle-to-pulmonary artery conduit is required.

 
Part VII - Interventional Outcomes

Of patients with congenitally corrected transposition operated or unoperated who reach adulthood, median survival is 40 years. Survival is better if there are no associated anomalies but the overall survival of these patients is still very poor compared to the general population (190). Usual causes of death are sudden (presumed arrhythmic) and progressive ventricular dysfunction with systemic (tricuspid) AV valve regurgitation.

Following surgical repair of VSD and/or subpulmonary stenosis, rapidly progressive systemic (tricuspid) AV valve regurgitation is well recognized. Medical therapy is often tried, but valve replacement is usually required.

 
Part VIII - Arrhythmias

Atrial fibrillation is common in operated patients and may be related to systemic (tricuspid) AV valve regurgitation.

If atrial fibrillation occurs, both anticoagulants and antiarrhythmic therapy are usually required. Back-up pacing may also be necessary. Reparative surgery at the tricuspid valve level does not seem to prevent recurrence of atrial arrhythmias (191).

Complete atrioventricular block requires the insertion of a permanent pacemaker. The optimal modality is DDD but is not always possible. Active fixation electrodes are required.

Transvenous pacing should be avoided if there are intracardiac shunts since paradoxical emboli may occur. Epicardial leads are preferred under these circumstances. For the same reason, venous thromboemboli from any source are a potential hazard. Anticoagulants should be used if a source of venous thromboembolism is found.
Grade: C	Level: V	Ref: 11

 
Part IX - Pregnancy

Pregnancy may be associated with a marked deterioration in systemic right ventricular function and/or the development or worsening of systemic (tricuspid) AV valve regurgitation. In two series of 19 and 22 patients with CCTGA a total of 105 pregnancies were reported (192,193). There were no maternal deaths, but substantial maternal morbidity and fetal losses were observed. Close supervision of such pregnant patients is recommended.

 
Part X - Follow-up

All patients should have regular cardiology follow up by an ACHD cardiologist. Particular attention should be paid to: Ventricular function (deteriorating systemic ventricular function may require consideration of afterload reduction and/or transplantation). Systemic (tricuspid) AV valve regurgitation. Complete AV block. Atrial fibrillation.

Grade: Consensus