Conotruncal anomaly characterized by ventriculoarterial discordance.
Aorta arises from morphologic right ventricle (RV); pulmonary artery (PA) arises from morphologic left ventricle (LV).
Categorized into two primary types based on atrioventricular connections, ventricular looping, and spatial relationship of great arteries: Dextro-TGA (D-TGA) and Levo-TGA (L-TGA/CC-TGA).
Dextro-Transposition of the Great Arteries (D-TGA)
Morphology and Hemodynamics
Atrioventricular concordance (right atrium RA connects to RV; left atrium LA connects to LV).
Ventriculoarterial discordance (RV connects to aorta; LV connects to PA).
Survival dependent on mixing of oxygenated and deoxygenated blood via atrial, ventricular, or great vessel communications.
D-TGA Subtypes (Classification by Associated Lesions)
Subtype
Anatomic Features
Pathophysiology & Clinical Presentation
D-TGA with Intact Ventricular Septum (IVS)
Isolated/simple TGA; no VSD.
Hypoxemia within first days of life following ductus arteriosus closure. Survival entirely dependent on patent foramen ovale (PFO)/atrial septal defect (ASD) and patent ductus arteriosus (PDA) for mixing.
D-TGA with Ventricular Septal Defect (VSD)
VSD present, typically perimembranous.
Increased pulmonary blood flow. Severity of cyanosis determined by degree of mixing at ventricular level. Congestive heart failure develops around 4-10 weeks of age.
D-TGA with VSD and Pulmonary Stenosis (LVOTO)
Associated with subaortic stenosis or dynamic/acquired left ventricular outflow tract obstruction (LVOTO).
Mimics Tetralogy of Fallot physiology, but obstruction is in the LV. Results in left-to-right anatomic shunting with limited effective pulmonary blood flow.
Diagnosis
Prenatal / Fetal Echocardiography
Aneuploidy rarely associated; extracardiac anomalies generally absent except situs anomalies.
Four-chamber view often normal.
PA arises from LV centrally, bifurcates into branch pulmonary arteries.
Aorta arises from RV anteriorly.
Great vessels exhibit parallel orientation.
Abnormal “three-vessel view” demonstrates overlapping ductal and aortic arches (“I” sign or two-vessel view).
Restrictive atrial septum evaluation critical: identified by hypermobile septum, bowing >50%, lack of swinging motion, or pulmonary vein flow reversal during systole.
Chest Radiograph (CXR): Classic “egg on a string” appearance; narrow mediastinal silhouette; absent thymic shadow.
Electrocardiogram (ECG): Right axis deviation; right ventricular hypertrophy.
Echocardiography: Gold standard. Subcostal view confirms posterior PA arising from LV and anterior aorta arising from RV. Parasternal short-axis shows semilunar valves as two circles (aorta anterior/rightward). Evaluates mixing lesions (PFO, VSD, PDA) and coronary artery anatomy.
Surgical Management
Preoperative Palliation: Balloon atrial septostomy (Rashkind procedure) for restrictive atrial septum to improve mixing and reduce LA pressure.
D-TGA (IVS or small VSD): Arterial switch operation (ASO). Pulmonary artery and aorta transected and switched; coronary arteries transferred from aortic to pulmonary root.
D-TGA with VSD and LVOTO:
Rastelli procedure: VSD patch connects LV to aorta; native PA transected/oversewn; RV-to-PA extracardiac conduit placed.
Réparation à l’Etage Ventriculaire (REV): Infundibular septum resected; intraventricular baffle placed; native PA directly implanted to RV without conduit.
Nikaidoh procedure: Aortic root and coronary arteries translocated entirely to LV; biventricular outflow tract reconstruction.
Historical/Alternative Operations: Mustard or Senning procedures (atrial switch) using pericardial or autologous atrial baffles to redirect venous flow. Used historically or if ASO contraindicated.
Congenitally Corrected Transposition of the Great Arteries (CC-TGA / L-TGA)
Morphology and Hemodynamics
Atrioventricular discordance (RA connects to morphologic LV; LA connects to morphologic RV).
Ventriculoarterial discordance (morphologic LV connects to PA; morphologic RV connects to aorta).
Aorta positioned anterior and leftward to PA (Levo-transposition).
Systemic venous blood routed: RA → LV → PA → Lungs.
Physiologically “corrected” circulation; presentation dependent on associated anomalies.
Morphologic RV functions as systemic ventricle, prone to eventual failure under systemic pressures.
CC-TGA Subtypes (Classification by Associated Lesions)
Isolated CC-TGA occurs in only 10-20% of cases. 80-90% present with associated structural defects:
Associated Lesion
Incidence
Pathophysiologic Impact
Ventricular Septal Defect (VSD)
60-80%
Typically perimembranous. Large VSDs lead to systemic-level pressures in both ventricles and congestive heart failure.
Pulmonary Outflow Obstruction
50%
Variable severity (mild to pulmonary atresia). Co-existing VSD and pulmonary stenosis mimics Tetralogy of Fallot physiology.
Left-sided Tricuspid Valve (TV) Anomalies
90%
Ebstein-like anomaly of the systemic TV; apical displacement of septal leaflet; dysplasia. Results in progressive systemic TV regurgitation, LA dilation, and heart failure.
Conduction System Abnormalities
~40% AV Block
Displaced, unstable AV node. Up to 40% born with or develop complete AV block; risk increases ~2% annually.
Diagnosis
Chest Radiograph (CXR): Straight left upper border of cardiac silhouette formed by ascending aorta. Levocardia without cardiomegaly typical in isolated/mild disease; progressive cardiomegaly correlates with severe TV regurgitation.
Electrocardiogram (ECG): Ventricular inversion reflected by absent Q waves in precordial lead V6; abnormal Q waves in III, aVR, aVF, V1; upright T waves across precordium. Frequently shows AV block.
Echocardiography: Demonstrates AV and VA discordance. Parasternal short-axis verifies anterior and levo-positioned (leftward) aortic valve. Long-axis views essential for sub-pulmonary obstruction evaluation.
Cardiac Magnetic Resonance (CMR) / Angiography: Flat, sagittally positioned interventricular septum separating right-sided LV and left-sided RV. CMR indicated for quantification of systemic RV size, volume, and function, including late gadolinium enhancement (LGE) for fibrosis.
Surgical Management
Indications: Declining systemic RV function, worsening systemic TV regurgitation, or symptomatic heart failure. Symptomatic CC-TGA with severe TV insufficiency requires TV replacement.
Conventional (Physiologic) Repair: Closure of VSD or relief of pulmonary stenosis without altering the morphologic RV’s role as the systemic pump. High risk of postoperative complete AV block.
Double Switch Operation: Anatomic repair to restore morphologic LV as systemic ventricle. Includes atrial switch (Senning/Mustard) plus arterial switch (ASO) or Rastelli procedure (if VSD/pulmonary stenosis present).
Comparative Summary: D-TGA vs. L-TGA
Feature
D-TGA (Complete TGA)
L-TGA (CC-TGA)
Atrioventricular Connection
Concordant
Discordant (Ventricular Inversion)
Ventriculoarterial Connection
Discordant
Discordant
Aortic Position
Anterior, Rightward (D-loop)
Anterior, Leftward (L-loop)
Systemic Ventricle
Morphologic Right Ventricle (Pre-repair)
Morphologic Right Ventricle
Pulmonary Circulation
Parallel, isolated circuits
”Corrected”, in-series physiological flow
Neonatal Presentation
Severe cyanosis, ductal/PFO dependent
Often asymptomatic unless associated lesions present
