Definition

  • Discordant ventriculoarterial connection.

Incidence

  • Four times more in males
  • Predisposing factors-
    • Maternal diabetes
    • Maternal exposure to sex hormones
    • Multiparity

Embryology

  • Theory of conal inversion
    • Subaortic conus persists while subpulmonic conus is absorbed.
    • So aorta comes anterior and is connected to the anterior ventricle which is the RV.

Classification

  • Simple TGA-
    • No associated anomaly
    • Some authorities include VSD, PDA and LVOTO also under simple TGA.
  • Complex TGA-
    • Associated anomalies

Pathology

  • D of D-TGA refers to D loop of ventricle.
  • Aortic position-
    • Usually anterior and right (two-thirds)
    • Less commonly anterior or anterior and left
    • Rarely posterior
  • Coronary anomalies-
    • LCx from RCA- 16%
    • Single RCA- 4%
    • Single LCA- 2%
  • Associated anomalies-
    • VSD alone- 30%
    • VSD + LVOTO- 10%
    • LVOTO alone- 5%
    • PDA
    • Mitral anomalies
    • Juxtaposition of atrial appendages
  • VSD- subaortic or muscular.
  • LVOTO-
    • 15% at birth, 30% later
    • Usually associated with VSD
    • Dynamic or fixed    
  • PDA-
    • Half of infants have PDA which closes by one month.
    • Persists less commonly
  • Mitral anomalies-
    • Cleft, straddling etc
    • Usually functionally insignificant
  • Juxtaposition of atrial appendages
    • Left sided
    • Male preponderance is lost

Hemodynamics

  • Basics-
    • Systemic and pulmonary circulations are in parallel.
    • Effective systemic blood flow is equal to effective pulmonary blood flow.
    • Inter-circulatory mixing
      • By ASD, VSD or PDA- usually by VSD
      • Poor, good or balanced
  • Poor mixing
    • Cyanosis from birth
    • Metabolic acidosis
    • No heart failure
  • Good mixing
    • Heart failure from birth
    • No cyanosis
  • Balanced mixing
    • No heart failure or cyanosis at birth
    • May change to poor mixing if VSD/ASD/PDA becomes smaller
  • Good mixing becoming cyanotic-
    • PDA closing at one month
    • VSD or ASD becoming smaller
    • PVOD (pulmonary vascular obstructive disease)
    • LVOTO

Clinical features

  • Cyanosis or heart failure from birth.
  • Heart failure decreasing and cyanosis increasing-
    • PDA closing at one month
    • ASD or VSD decreasing in size
    • PVOD- PDA with PVOD can cause reverse differential cyanosis and necrotizing enterocolitis
    • LVOTO- Dynamic obstruction can cause cyanotic spells
  • Hypoglycemia, hypocalcemia
  • Single loud S2-
    • A2 is loud as aorta is anterior
    • P2 is not heard even in high pulmonary blood flow situations
  • PES may be heard in high pulmonary blood flow situations
  • VSD, LVOTO and PDA may cause murmurs. If these are not present, there are no murmurs (simple TGA with intense cyanosis at birth is characteristically murmurless).

ECG

  • Cyanotic cases- RVH, right axis deviation
  • HF cases- BVH, normal axis or just right axis
  • Left axis- AVCD with TGA

Chest X-ray

  • Egg on side-
    • Narrow superior mediastinum-
      • Absent thymus
      • Anteroposterior great vessels
    • Cardiomegaly
  • Cardiomegaly and increased pulmonary vasculature
    • Absent in poor mixing cases
    • Prominent in good mixing cases
    • Right sided vascularity may be more as MPA may be directed to right
  • Right aortic arch
    • TGA in general- 8%
    • TGA + VSD + PS- 15%

Echocardiography

  • Double circle in PSAX. Aorta is right and anterior.
  • Aorta and MPA are parallel.
  • Fetal echo can diagnose.

Cath study

  • If PA pressure cannot be measured, find pulmonary vein wedge pressure.
  • Laid back balloon occlusion aortic root angiogram to find coronary anomalies.

Natural history

  • 1 year survival-
    • Poor mixing- 4% (1 month- 20%)
    • VSD- 30%
    • VSD with LVOTO- 70%
  • Surviving child with TGA-
    • VSD with PVOD- more common
    • VSD with LVOTO- less common
  • Large VSD-
    • Grade 3 to 4 Heath-Edwards
      • 20% at 2 months
      • 80% at 1 year

Management

  • Medical
    • PG E1
    • Balloon atrial septostomy- success means 10% increase in saturation
  • Arterial switch in first month of life itself along with closure of ASD, VSD or PDA.
  • For TGA + VSD + PS- Rastelli procedure.