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Ep 3: Transposition of Great Arteries (TGA)

by Neena Jube-DesaiAugust 10, 2020Cardiology

Learning Objectives

By the end of this episode, NICU Grads will be able to:
1. Discuss pathogenesis, presentation, and nonsurgical management of transposition of great arteries (TGA)

Guest Speaker
Gregory Kitley Yurasek, MD FAAP
Pediatric cardiac intensive care specialist
PubMed

Transposition of Great Arteries (TGA)

Types
- Dextro (most common form)
  - Origin of the aorta is anterior and to the right of the origin of the pulmonary artery
  - Creates two parallel circulations
    - Body –> Deoxygenated systemic venous blood –> RA –> RV –> aorta–> body
    - Lung –> Oxygenated pulmonary venous blood –> LA –> LV –> PA –> Lung
  - Presentation (see below)

Reference: Hua N, Yieh L, Dukhovny D, Armsby L. Important considerations in the management of newborns with cyanosis. Neoreviews. 2017;18(4):e258-e264. doi: 10.1542/neo.18-4-e258.

Image Credit: Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities

L-Transposition of the great arteries
- << 1 % of all congenital heart disease (CHD)
- “Congenitally corrected TGA”
- Physiology is normal but anatomy is abnormal
  - Aortic valve is anterior and to the left of pulmonary values and thus levo-transposition (L-TGA) (See picture below)
  - There is ventricular inversion (See picture below)
  - LV sends poorly oxygenated blood from the body to the lungs and RV sends well-oxygenated blood from the lungs to the body
- Clinically present acyanotic with minimal respiratory distress if there is no other cardiac abnormality
- Can present with cyanosis if other cardiac defects present
- Is often associated with complete heart block

*** Note the following is for d-TGA ***

Pathogenesis
- Conotruncal rotational defect
  - TGA is caused by a lack of the normal rotation of the outflow tracts
- Epidemiology
  - Most common cyanotic heart disease presenting in the 1st week of life
  - Comprise 5% of all congenital heart disease and 20% of all cyanotic lesions
  - Male-to-female ratio is 3:1
- Risk Factors
  - In vitro fertilization
  - Maternal diabetes
  - Genetic disorders:
    - CHARGE
    - VACTERL
    - DiGeorge
    - Noonan
    - Turner
    - Williams
    - Marfan
    - Heterotaxy
    - Associated with abnormalities in retinoic acid and laterality genes
  - Infections
    - Toxoplasmosis, rubella, cytomegalovirus, and herpes simplex (TORCH) infections increase the risk of d-TGA
  - + Nuchal translucency (NT)
    - Fetuses with an increased NT have an increased risk for CHD with no particular bias for 1 disorder over another
- Cardiac Association
  - ASD
    - Majority of mixing occurs at this level and is essential for survival
    - Failure of adequate mixing of systemic and pulmonary venous blood due to a restrictive PFO –> persistent severe hypoxemia leading to cardiac arrest if diagnose and treatment do not occur in a timely manner
  - PDA
    - Allows for additional shunting between the aorta (deoxygenated blood) to the PA (oxygenated blood)
  - VSD
    - Not very helpful for promoting mixing as in the newborn SVR is roughly equal to PVR and net flow is driven by difference in vascular resistance
  - Coarctation of the aorta or aortic arch interruption
  - PPHN
    - 12% of cases and with severe PPHN in 5% of cases
    - Mild
      - At rest –> can be asymptomatic
      - Agitated/crying –> increased PVR –> increased R to L shunting –> more exaggerated/severe reversed differential cyanosis with postductal oxygen saturation being higher than preductal saturation
    - Severe
      - At rest –> severely cyanotic
      - Agitated/crying–> increased PVR–> increased R to L shunting –> more exaggerated/severe reversed differential cyanosis with postductal oxygen saturation being generally much higher than preductal saturation
- Noncardiac Association
  - Only 10% of cases are associated with noncardiac malformations
  - Asplenia can be seen in cases where fetus was exposed to retinoic acid or retinoic acid inhibitors
- Presentation
  - Think happy, chubby, blue infant
  - Appear comfortable but cyanotic centrally
  - Degree of cyanosis depends on level of mixing
    - 3 levels where the mixing can occur
      - PFO/ASD
        Best site of arterio-venous admixture occurs at the atrial level
      - PDA
      - VSD
  - Reverse differential cyanosis
  - Respiratory symptoms are generally ABSENT except for occasional tachypnea
  - Heart Sounds
    - No murmur usually
    - Second heart sound is loud and can appear to be single due to the anterior position of the aorta and the posterior position of the PA
  - Perfusion
    - Normal — unless coarctation of the aorta or aortic arch interruption is present
  - Persistent severe hypoxemia leading to cardiac arrest
    - Can occur if highly restrictive PFO is present and TGA is not diagnosed or BAS/surgical intervention are not performed in a timely manner
- Evaluation
  - Prenatal Evaluation & Diagnosis
    - Fetal ECHO
  - Postnatal Evaluation & Diagnosis
    - Cardiac exam
    - Arterial blood gas
    - Hyperoxia test
    - Chest x-ray
      - Chest radiograph may or may not be normal
      - Egg shaped heart
        Is present due to narrow mediastinum that is a direct result of anterior-posterior relationship of the aorta and the main pulmonary artery
      - Pulmonary vascular markings
        Depending on the level of PVR the pulmonary vascular markings vary
    - EKG
      - Usually nonspecific and diagnostically unhelpful
    - ECHO
      - Septum intact? ASD? VSD?
      - PDA?
      - Outflow tracts?
        Parasternal view —> will demonstrate aorta and pulmonary artery in the same view with the outflow vessels notably parallel to one another–> suggesting d-TGA
    - Consult cardiology
  - Medical Management

Obtain central access
- Start oxygen
  - It is a natural pulmonary vasodilator –> increases pulmonary blood flow and pushes blood forward into the LA with the hopes oxygenated blood can shunt across the atrial communication –> RA–> RV out the aorta to reset of the body
- Support respiratory support & minimize metabolic demand
  - To consider intubation
  - To consider sedation
- PGE
  - Prostaglandin should be started prior to an ECHO
    - Indication:
      - Poor arterio-venous admixture
    - MOA:
      - Maintains ductus patency/ reopen a closed duct by directly acting on vascular smooth muscle
      - Increases pulmonary blood flow and as result more blood flow to LA with the hopes oxygenated blood can shunt across the atrial communication –> RA–> RV out the aorta to reset of the body
    - Dosing:
      - Metabolized rapidly infusion must be continuous
      - Initial dose: 0.05-0.1mcg/kg/min
        Can titrate lower to 0.01 and still see effect
    - Route
      - Prefer to be given via central line
      - Can be given via PIV in emergency
    - Adverse effects
      - Apnea
- Consider balloon atrial septostomy (BAS)
  - Enlarges the foramen ovale, allowing saturated blood from the LA to enter the RA and increase the RA saturation
  - Indication:
    - Inadequate arterio-venous mixing
      - Preductal O2 <40% despite O2 administration
      - Metabolic acidosis
      - Increasing tachypnea
      - Poor perfusion
  - Result
    - Successful BAS with improvement
      - Improved O2 saturation by 20 -30% within seconds to minutes
    - Successful BAS with no improvement
      - Consider larger balloon to be used for procedure
      - Must reassess LA blood return
        Optimize oxygenation
        Optimize ventilation
        Address acidosis
        Address anemia
        Mitigate increased PVR
        iNO, ECMO
        May be indicated if the infant fails to respond after balloon septostomy
  - Complications
    - Balloon rupture
    - Failure of the balloon to deflate
    - Injury to the femoral vein, inferior vena cava, hepatic veins, pulmonary veins or mitral valve or perforation of the atria/atrial appendage
    - Atrial flutter
      - May require pacing or electrical cardioversion
    - Air emboli/stroke
      - Can occur while flushing catheter especially given that the right heart provides direct flow to the systemic circulation in patients with d-TGA
- While awaiting an arterial switch operation, it is important to optimize:
  - Mixing of the pulmonary and systemic circulations
  - Balance effective pulmonary and systemic blood flow
    - Excessive pulmonary blood flow–> congestive CHF and poor systemic cardiac output
  - Nutritional status to promote pre & postoperative growth and wound healing
    - At risk of NEC
- Arterial switch operation
  - Requirements:
    - Weigh at least 2.5 – 3kg
      - Increased risk of complications < 2.5kg
    - Optimized lung function
    - Metabolically stable
    - Ability to tolerate ~3 hours of cardiopulmonary bypass during the surgery
  - Timing of surgery
    - Typically 3- 6 DOL if full term infant
  - Surgery consists of:
    - Moving/switching both greater arteries and coronaries
- Post-operative complications
  - Bleeding
  - Cardiac tamponade
  - Arrythmias
  - Low cardiac output syndrome
- Short term prognosis
  - Typically discharged within 2 weeks
- Long term prognosis
  - Morbidity and mortality rates
    - Generally very low
    - Unless associated hypoplastic right ventricle, congenital anomalies, or prematurity is present
  - Need neurology and development follow up
    - Boston Circulatory Arrest Study
      - Study population consisted of 100 infants with d-TGA
      - Monitored at 1, 4, 8, and 16 years of age
      - Results:
        1/3 of these patients had:
        Abnormalities on brain MRI
        Normal IQ but significant number had delays in behavior, language, and speech

Abbreviations
- ASD = Atrial septal defect
- BP = Blood pressure
- HR = Heart rate
- BAS = Balloon atrial septostomy
- CHF= Congestive heart failure
- DOL = Day of life
- ECMO = Extracorporeal membrane oxygenation
- iNO = Inhaled nitric oxide
- LA = Left atrium
- LV = Left ventricle
- NEC = Necrotizing enterocolitis
- PA = Pulmonary artery
- PDA = Patent ductus arterious
- PFO = Patent foreman ovale
- PPHN= Persistent pulmonary hypertension of the newborn
- PVR= Pulmonary vascular resistance
- RA = Right atrium
- RV = Right ventricle
- TGA = Transposition of the great arteries
- VSD = Ventricular septal defect

References:

Dasgupta S, Bhargava V, Huff M, Jiwani AK, Aly AM. Evaluation of the cyanotic newborn: part I—a Neonatologist’s Perspective. Neoreviews. 2016;17(10):e598 LP-e604. doi:10.1542/neo.17-10-e598.
Dasgupta S, Bhargava V, Huff M, Jiwani AK, Aly AM. Evaluation of the cyanotic newborn: part 2—a cardiologist’s perspective. NeoReviews. 2016;17(10):e605-e620. doi: 10.1542/neo.17-10-e605.
Hua N, Yieh L, Dukhovny D, Armsby L. Important considerations in the management of newborns with cyanosis. Neoreviews. 2017;18(4):e258-e264. doi: 10.1542/neo.18-4-e258.
Martin TC. Reverse differential cyanosis: a treatable newborn cardiac emergency. NeoReviews. 2011;12(5):e270-e273. doi: 10.1542/neo.12-5-e270.
Yap SH, Anania N, Alboliras ET, Lilien LD. Reversed differential cyanosis in the newborn: a clinical finding in the supracardiac total anomalous pulmonary venous connection. Pediatr Cardiol. 2009;30:359-362. doi: 10.1007/s00246-008-9314-0
Sims ME. Legal Briefs: Should This Neonate with Transposition of the Great Arteries Have Survived? Neoreviews. 2017;18(11):e674 LP-e676.doi:10.1542/neo.18-11-e674
Richard J. Martin, Avroy A. Fanaroff, Michele C. Walsh. (2015). Fanaroff and Martin’s neonatal-perinatal medicine: diseases of the fetus and infant. Philadelphia, PA: Elsevier/Saunders.
Brodsky, Dara, and Camilia Martin. Brodsky and Martin’s Neonatology Review Series. 3rd ed., Lulu, 2020.
Brodsky, Dara. Neonatology Review: Q&A. 3rd ed., Lulu, 2016.
Chess, Patricia. Avery’s Neonatology Board Review: Certification and Clinical Refresher. 1 ed., Elsevier, 2019.
Polin, Richard A., and Mervin C. Yoder. Workbook in Practical Neonatology. 5th ed., Saunders, 2014.