Transposition of Great Arteries (TGA)

Definition and Clinical FeaturesTop

Two different conditions are classified under the transposition complexes: complete transposition of great arteries (or d-TGA) and so-called congenitally corrected transposition of great arteries (CCTGA or l-TGA).

1. In patients with complete TGA, there is atrioventricular concordance and ventriculoarterial discordance. Obviously, this situation is not compatible with life, unless adequate mixing of the venous and arterial blood takes place. Newborns become progressively cyanotic with the physiologic closure of the ductus arteriosus and survival is dependent on mixing of blood, either through existing communications (such as a ventricular septal defect [VSD], atrial septal defect [ASD], and patent ductus arteriosus [PDA]) or by catheter or surgical interventions to create shunting (at the atrial level). Unoperated patients have >90% mortality in the first year of life; hence, almost all adult patients have had a surgery, usually early in childhood (atrial switch operation, arterial switch operation, or Rastelli repair).

2. In patients with congenitally corrected TGA, there is both atrioventricular and ventriculoarterial discordance. The majority of the patients (>95%) have associated cardiac abnormalities including VSDs, systemic tricuspid valve abnormalities, and pulmonary or subpulmonary stenosis. There is also a significant risk of development of complete heart block with a rate of ~2% per year.

3. Symptoms: The majority of patients have had previous operations. Rarely, a patient with previously unrecognized isolated congenitally corrected TGA is seen with presyncope or syncope. Patients may develop progressive dyspnea, fatigue, and decreased exercise tolerance as the function of the systemic ventricle deteriorates. Most patients with a previous atrial switch operation develop atrial arrhythmias and may present with palpitations and presyncope. Patients who have had the arterial switch operation may present with signs or symptoms of ischemia related to the coronary artery stenosis.

4. Signs (details on surgical interventions: see Treatment, below):

1) Patients after the atrial switch: Previous sternotomy is present. A right parasternal lift is felt. Auscultation usually reveals a normal first heart sound and a single loud second heart sound. There may be a pansystolic murmur related to systemic tricuspid regurgitation (note that in these patients the anatomic right ventricle supports systemic circulation: it is subaortic and the atrioventricular valve that allows inflow into this ventricle is a tricuspid valve).

2) Patients after the arterial switch: Usually these patients have relatively normal examination findings with the exception of the previous sternotomy. However, particular attention should be paid to the presence of a diastolic murmur associated with neoaortic regurgitation. A systolic ejection murmur may also be heard, which is associated with right ventricular outflow tract obstruction.

3) Patients after the Rastelli operation: Usually there is a systolic thrill associated with the flow through the conduit. Auscultation reveals a loud systolic murmur from the conduit. The duration of time in systole occupied by the murmur is helpful in detecting significant conduit obstruction. This may be associated with a systolic thrill. A diastolic murmur may be heard due to conduit regurgitation.

4) Patients with congenitally corrected TGA: The majority of these patients have undergone the classic repair and have a previous sternotomy scar. The jugular venous pressure is usually normal except in patients with complete heart block, where an intermittent cannon a wave is seen. Usually a right parasternal lift is present. Auscultation reveals a normal first heart sound with a single loud second heart sound. A third heart sound or a fourth heart sound may be present depending on the function of the systemic ventricle. There may be a holosystolic murmur, which is related to systemic atrioventricular valve regurgitation.

DiagnosisTop

Diagnostic Tests

1. Electrocardiography (ECG): In patients with complete transposition after the atrial switch operation, ECG may show junctional rhythm at varying rates. Signs of right ventricular hypertrophy and right atrial overload are present. In patients after the arterial switch operation, ECG is usually normal. However, special attention should be paid to signs of ventricular hypertrophy (both left and right) and evidence of ischemia and infarction. In patients with CCTGA, there may be complete heart block present. Typically, there are Q waves present in leads V1 to V2 and absent in leads V5 to V6. This reflects the initial right-to-left septal depolarization in patients with ventricular inversion (this should not be mistaken for previous anteroseptal myocardial infarction).

2. Chest radiography: In patients with complete transposition after the atrial switch operation, radiography shows a narrow vascular pedicle with a cardiac silhouette that is somewhat oblong. Following the arterial switch, radiography is usually normal (with the exception of evidence of previous sternotomy). In patients with CCTGA, radiography usually shows evidence of cardiomegaly. There is an abnormal contour to the left heart border, which reflects the left-sided ascending aorta.

3. Echocardiography: In patients after the atrial switch operation, echocardiography is used to assess the size and function of the systemic right ventricle as well as the degree of systemic atrioventricular valve regurgitation. Baffle obstruction or leak can be assessed by echocardiography with or without the use of IV agitated bubble contrast. In patients after the arterial switch operation, echocardiography may be entirely normal. However, the assessment of aortic stenosis or regurgitation as well as aortic dimensions are important. Similarly, the degree of pulmonary stenosis and pulmonary regurgitation should be documented. In patients after Rastelli operation, the main echocardiographic index is the degree and progression of conduit stenosis or regurgitation. In patients with CCTGA, echocardiography provides the size and function of the systemic ventricle; these patients will have more important degrees of systemic atrioventricular valve regurgitation and echocardiography can provide information with regards to its severity and progression when compared with previous studies.

TreatmentTop

Medical Treatment

There are currently no data to support the use of angiotensin-converting enzyme inhibitors (ACEIs), beta-blockers, angiotensin receptor blockers (ARBs), or aldosterone antagonist therapy in this population of patients with systemic right ventricular dysfunction. However, many practitioners extrapolate evidence from trials on left heart failure and use some or all of those agents; guidelines do not support this pattern of practice.

Surgical Intervention

1. Complete TGA: There are 3 major operative procedures for patients with complete transposition:

1) Atrial switch operation: Two similar operations (Mustard and Senning procedures). The goal of both operations is to redirect blood at the atrial level to provide physiologic correction. Hence, the systemic venous return is directed via the atrial baffle through the mitral valve to the subpulmonic left ventricle, and the pulmonary venous flow is redirected through the tricuspid valve to the systemic right ventricle.

2) Arterial switch operation (Jatene procedure): This provides both anatomic and physiologic correction, as the great arteries are switched. The arterial switch operation has been in widespread use since the late 1970s and for the most parts has replaced the atrial switch operations.

3) Rastelli operation: This is reserved for patients with VSD and pulmonary or subpulmonary stenosis. In this operation blood is redirected through the VSD to the aorta via an artificial tunnel, while a valved conduit connects the right ventricle to the pulmonary artery. In these patients, the morphologic left ventricle supports the systemic circulation.

2. Congenitally corrected TGA with pulmonary stenosis and VSD: These patients usually have undergone a classic repair in childhood, where the VSD is closed with left ventricle to pulmonary artery valved conduit placement (in those with subpulmonary or pulmonary stenosis).

Follow-UpTop

Many patients with transposition of great arteries have complex issues and should be seen regularly by a specialist with expertise in adult congenital heart disease. In general, these patients need a serial follow-up of systemic right ventricular function as well as the assessment of baffle patency (patients with complete transposition after the atrial switch operation and those with CCTGA) with different imaging modalities (echocardiography, radionuclide angiography, or magnetic resonance imaging [MRI]).