4.5c Transposition of Great Arteries (Q20.3)

d(dextro)-transposition of the great arteries (d-TGA) is a structural heart anomaly characterized clinically by cyanosis (usually) and anatomically by an abnormal origin of the great arteries, such that the aorta exits from the right ventricle (instead of the left) and the pulmonary artery exits from the left ventricle (instead of the right) (see Fig. 4.16). d-TGA can occur with or without a ventricular septal defect. These two forms are sometimes called “incomplete” and “complete”
d-TGA, respectively, though these terms are infrequently used and are not particularly useful.

Fig. 4.16. Transposition of great arteries

Transposition of great arteries
Normal heart

Relevant ICD-10 codes

Q20.3 Transposition of great arteries


  • Transposed great arteries can also occur as part of complex heart anomalies such as heterotaxy. Because of this heterogeneity, it is recommended that public health surveillance track separately the simple forms of d-TGA. These can be defined as those with at most a ventricular septal defect and limited valvar involvement, and excludes those cases that, for example, are part of heterotaxy or single ventricle phenotype (Q20.4).
  • Transposed great arteries can occur with double outlet right ventricle (DORV). These cases are often classified, grouped and tracked with DORV rather than with d-TGA.
  • l(levo) transposition of the great arteries (l-TGA, Q20.5) is a different condition, epidemiologically, anatomically and developmentally, and it is not recommended to be included with d-TGA.


Prenatal. d-TGA can be suspected prenatally on a second trimester obstetric anatomic scan – with the outflow tract view being especially important – but can be missed. Prenatally diagnosed or suspected cases should be confirmed postnatally.

Postnatal. Infants with d-TGA present in a variety of ways, depending on the presence or absence of a ventricular septal defect and other intracardiac anomalies. With an intact ventricular septum, infants present early after birth with cyanosis. With a large ventricular septal defect, the cyanosis might not be as apparent, and infants can present (sometimes later) with heart failure because of pulmonary over-circulation.

Newborn screening via pulse oximetry, which is based on the non-invasive detection of low blood oxygen saturation, can detect many cases of d-TGA even before overt signs and symptoms. Echocardiography can provide a firm, specific diagnosis, though other imaging techniques have a role in some cases.

Clinical and epidemiologic notes

As noted, infants present typically early after birth with cyanosis but occasionally – depending on presence and size of the ventricular septal defect and the level of pulmonary vascular resistance – also with congestive heart failure. Rapid clinical deterioration is expected as the ductus arteriosus closes.

d-TGA is considered one of the conotruncal heart defects, like tetralogy of Fallot and interrupted aortic arch type B. However, compared to tetralogy of Fallot, d-TGA is more likely an isolated heart anomaly and less likely to be associated with single-gene conditions or genomic imbalances (e.g. deletion 22q11). Extracardiac anomalies are found in ~10% of cases.

Maternal pregestational diabetes is a well-established modifiable risk factor for d-TGA.

d-TGA occurs with a frequency of approximately 1 in 3000 to 4000 births, and is more common in males.


Q20.3 Transposition of great arteries


  • Q20.3 has also been used for cases of l-TGA, as there is not a specific code for it unless it occurs as part of corrected transposition of the great vessels (Q20.5). For public health surveillance, l-TGA should not be coded with Q20.3 in order to track d-TGA appropriately.
  • d-TGA with ventricular septal defect is best coded with the d-TGA code and with the appropriate ventricular septal defect code.


Q20.2 Double outlet right ventricle
Q20.5 l(levo)-transposition of the great arteries

Checklist for high-quality reporting

d-Transposition of Great Arteries – Documentation Checklist
Describe in detail the clinical and echocardiographic findings:
  • Anatomy – specify intracardiac anomalies, including the presence and type of valvar involvement, of ventricular septal defects, and whether there is evidence of DORV, single ventricle (double inlet left ventricle) or heterotaxy (the latter would make the case not part of simple d-TGA).
  • Procedure – specify whether the cardiac findings are from a prenatal or postnatal echocardiogram, or from other investigations (e.g. catheterization, MRI), surgery or autopsy.
  • Additional cardiac findings – specify any additional findings, including atrial septal defect, atrial isomerism, etc.
  • Look for and document extracardiac birth defects: These are not as common as in other conotruncal defects, but can occur
  • Report whether specialty consultation(s) were done: Report whether the diagnosis was made by a paediatric cardiologist, and whether the patient was seen by a geneticist
  • Report any genetic testing and results(e.g. chromosomal studies, genomic microarray, genomic sequencing).

Suggested data quality indicators

Category Suggested Practices and Quality indicators
Description and documentation Review sample of clinical descriptions for documentation of key elements:
  • Anatomy – presence of ventricular septal defect, other intracardiac and extracardiac anomalies.
  • How cardiac findings were detected (e.g. echocardiography).
  • Who made the diagnosis (e.g. paediatrician, paediatric cardiologist).
  • Specialists who evaluated the child – in particular, if a paediatric cardiologist and geneticist.
  • Key evaluations done, especially genetic testing.
  • Track and evaluate cases of d-TGA with and without ventricular septal defect: A very low proportion of cases with ventricular septal defect might indicate that this commonly associated intracardiac anomaly is being underreported or not documented and coded correctly.
Clinical classification
  • Track proportion of congenital anomalies and syndromes occurring with d-TGA: If < 5%, consider under-ascertainment of these co-occurring conditions.
  • Monitor prevalence: If very low (< 1 per 10 000 births) it suggests under-ascertainment.
  • Compare prevalence among the smallest site/time units: Statistically significant dissimilar results suggest a possible methodological problem in one or more site/time units.