Transposition of the Great Arteries
Introduction to Transposition of the Great Arteries
Transposition of the Great Arteries (TGA) is a congenital heart defect where the two main arteries leaving the heart - the pulmonary artery and the aorta - are connected to the wrong ventricles. This results in two separate circuits of blood flow, leading to insufficient oxygenation of the body.
Key points:
- Incidence: Approximately 1 in 3,500-5,000 live births
- Accounts for 5-7% of all congenital heart defects
- More common in males (ratio 2:1)
- Considered a cyanotic congenital heart defect
- Without intervention, mortality rate is high in the first year of life
TGA can be classified into two main types:
- D-TGA (Dextro-TGA): The most common form, where the aorta arises from the right ventricle and the pulmonary artery from the left ventricle.
- L-TGA (Levo-TGA or Congenitally Corrected TGA): A rarer form where the ventricles are also transposed, resulting in physiologically correct but anatomically incorrect circulation.
Anatomy and Pathophysiology of TGA
Anatomical Features:
- Aorta arises from the right ventricle (anteriorly positioned)
- Pulmonary artery arises from the left ventricle (posteriorly positioned)
- Coronary arteries usually arise from the anterior facing sinus
Pathophysiology:
In TGA, the systemic and pulmonary circulations run in parallel rather than in series:
- Deoxygenated blood returns to the right atrium and is pumped to the body via the aorta
- Oxygenated blood returns to the left atrium and is recirculated to the lungs via the pulmonary artery
- Survival depends on mixing of oxygenated and deoxygenated blood through:
- Patent foramen ovale (PFO) or atrial septal defect (ASD)
- Ventricular septal defect (VSD)
- Patent ductus arteriosus (PDA)
- Without adequate mixing, severe hypoxemia and acidosis develop rapidly
Associated Anomalies:
- VSD (in about 50% of cases)
- Left ventricular outflow tract obstruction (15-20%)
- Abnormal coronary artery patterns (in about 5%)
- Coarctation of the aorta
Clinical Presentation of TGA
The clinical presentation of TGA depends on the degree of mixing between the two circulations and the presence of associated defects:
Neonatal Period:
- Cyanosis apparent within hours of birth
- Tachypnea and respiratory distress
- Poor feeding and lethargy
- Absence of murmur in isolated TGA
Physical Examination:
- Central cyanosis, not improving with oxygen administration
- Tachycardia and tachypnea
- Single S2 heart sound
- Murmur may be present if associated VSD or LVOTO exists
Presentation in TGA with VSD:
- May present later due to better mixing
- Congestive heart failure signs may develop over weeks
- Systolic murmur at left sternal border
Presentation in TGA with LVOTO:
- May mimic severe pulmonary stenosis or atresia
- Systolic ejection murmur along left sternal border
- Potential for rapid decompensation
Diagnosis of TGA
Diagnosis of TGA involves a combination of clinical suspicion and imaging studies:
1. Prenatal Diagnosis:
- Fetal echocardiography can detect TGA as early as 18-22 weeks gestation
- Allows for planned delivery at a tertiary care center
2. Postnatal Diagnosis:
- Pulse Oximetry Screening: Low oxygen saturation not improving with oxygen administration
- Hyperoxia Test: Lack of significant improvement in PaO2 with 100% oxygen
- Chest X-ray:
- "Egg on a string" appearance
- Narrow mediastinum
- Absent thymic shadow
- ECG: Right ventricular hypertrophy (RVH) in the first week of life
- Echocardiography:
- Diagnostic modality of choice
- Demonstrates the parallel arrangement of great arteries
- Assesses associated defects and coronary artery anatomy
- Cardiac Catheterization:
- May be needed for detailed coronary anatomy
- Useful for preoperative assessment in complex cases
- CT or MRI: May provide additional anatomical details in complex cases
Management of TGA
Management of TGA requires a multidisciplinary approach involving neonatologists, pediatric cardiologists, and cardiac surgeons:
1. Initial Stabilization:
- Prostaglandin E1 infusion to maintain ductal patency
- Supplemental oxygen as needed
- Correction of acidosis and electrolyte imbalances
- Mechanical ventilation if required
2. Balloon Atrial Septostomy (BAS):
- Emergency procedure to improve mixing at atrial level
- Performed at bedside under echocardiographic guidance
- Bridges to definitive surgical repair
3. Definitive Surgical Repair:
- Arterial Switch Operation (ASO):
- Procedure of choice for D-TGA
- Typically performed within first 2 weeks of life
- Involves switching the great arteries and reimplanting coronary arteries
- Atrial Switch Operations (historical):
- Senning or Mustard procedures
- Redirect blood flow at atrial level
- Largely replaced by ASO due to long-term complications
- Rastelli Procedure:
- For TGA with VSD and pulmonary stenosis
- Involves intracardiac baffle and RV-to-PA conduit
4. Post-operative Care:
- Close monitoring in pediatric cardiac ICU
- Management of potential complications (arrhythmias, low cardiac output)
- Anticoagulation as needed
Long-term Outcomes of TGA
Long-term outcomes for patients with TGA have dramatically improved with advances in surgical techniques:
After Arterial Switch Operation:
- Survival rates >90% at 20 years
- Most patients have normal exercise capacity and quality of life
- Potential long-term issues:
- Neoaortic root dilation and regurgitation
- Pulmonary artery stenosis
- Coronary artery stenosis or occlusion
- Arrhythmias
After Atrial Switch Operations:
- Long-term survival lower than ASO
- Right ventricular failure is a major concern
- Higher incidence of arrhythmias and sudden cardiac death
- Baffle obstruction or leaks may occur
Follow-up:
- Lifelong cardiology follow-up is essential
- Regular echocardiography and ECG monitoring
- Exercise stress testing to assess functional capacity
- Cardiac MRI for detailed assessment of anatomy and function
- Counseling regarding pregnancy and contraception for female patients
With appropriate management and follow-up, many patients with repaired TGA can lead normal, productive lives. However, they remain at risk for long-term complications and require ongoing specialized cardiac care.
Transposition of the Great Arteries
- What is Transposition of the Great Arteries (TGA)?
A congenital heart defect where the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle - What percentage of congenital heart defects is TGA?
Approximately 5-7% - Which gender is more commonly affected by TGA?
Males (2:1 ratio compared to females) - What is the primary embryological defect in TGA?
Abnormal spiral septation of the cardiac outflow tract - What is the characteristic clinical sign of TGA in newborns?
Severe cyanosis within the first few hours or days of life - Which diagnostic test is considered the gold standard for diagnosing TGA?
Echocardiogram - What is the classic chest X-ray finding in TGA?
"Egg-on-side" appearance due to a narrow mediastinum - Which ECG finding is common in patients with TGA?
Right axis deviation and right ventricular hypertrophy - What is the name of the emergency procedure used to improve oxygenation in newborns with TGA?
Balloon atrial septostomy (Rashkind procedure) - Which medication is used to keep the ductus arteriosus open in TGA before surgical repair?
Prostaglandin E1 - What is the preferred age for surgical repair of TGA?
Within the first 2 weeks of life - What is the name of the current standard surgical repair for TGA?
Arterial switch operation (ASO) - What is the mortality rate for the arterial switch operation in experienced centers?
Less than 5% - Which genetic syndrome is associated with a higher incidence of TGA?
Heterotaxy syndrome - What is the risk of recurrence of TGA in offspring if a parent has TGA?
Approximately 2-3% - What is the most common long-term complication after arterial switch operation?
Pulmonary artery stenosis - Which coronary artery complication can occur after arterial switch operation?
Coronary artery stenosis or occlusion - What is the recommended follow-up interval for patients after TGA repair?
Annual follow-up with a cardiologist specializing in congenital heart disease - Which imaging modality is often used for long-term follow-up of TGA patients?
Cardiac MRI or CT angiography - What is the name of the older surgical technique used for TGA repair before the arterial switch operation?
Atrial switch operation (Mustard or Senning procedure) - Which ventricle functions as the systemic ventricle in patients who underwent atrial switch procedures?
Right ventricle - What is the life expectancy for patients with repaired TGA using the arterial switch operation?
Near-normal life expectancy, but long-term data is still being collected - Which complication can occur due to chronic right ventricular dysfunction in patients with atrial switch repairs?
Right ventricular failure and tricuspid regurgitation - What is the most common arrhythmia in patients who underwent atrial switch procedures?
Atrial arrhythmias (flutter or fibrillation) - Which non-invasive test is used to assess exercise capacity in TGA patients?
Cardiopulmonary exercise testing - What is the name of the procedure used to assess coronary artery patency in TGA patients?
Coronary angiography - Which biomarker is used to assess ventricular function in TGA patients?
B-type natriuretic peptide (BNP) - What is the recommended frequency of cardiac imaging in adults with repaired TGA?
Every 2-3 years, or more frequently if clinically indicated - Which pregnancy-related complication is more common in women with repaired TGA?
Increased risk of arrhythmias and right ventricular dysfunction (in those with atrial switch repairs) - What is the name of the condition where TGA occurs with a ventricular septal defect and pulmonary stenosis?
Taussig-Bing anomaly
Further Reading
- AHA Scientific Statement on Diagnosis and Management of Neonates with Complex Congenital Heart Disease
- Transposition of the Great Arteries - New England Journal of Medicine
- Long-term outcomes after the arterial switch operation for transposition of the great arteries
- Transposition of the Great Arteries - NCBI
