Tetralogy of Fallot vs Transposition of great arteries
How to tell Tetralogy of Fallot and Transposition of great arteries apart when a board question makes them look alike.
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Degree and timing of neonatal cyanosis with oxygen nonresponse requiring ductal-dependent mixing support.
Side by side
Cyanotic spells in infancy with harsh systolic murmur and relief by knee-chest positioning suggest tetralogy of Fallot.
Profound cyanosis shortly after birth with poor oxygen response and little murmur suggests transposition of the great arteries.
Right ventricular outflow obstruction and VSD create right-to-left shunting that worsens during hypercyanotic spells.
Aorta from right ventricle and pulmonary artery from left ventricle create parallel circulations requiring mixing for survival.
Chest radiograph may show boot-shaped heart; echocardiography confirms VSD, overriding aorta, and right ventricular outflow obstruction.
Severe neonatal hypoxemia with egg-on-a-string cardiac silhouette and echocardiographic confirmation of ventriculoarterial discordance supports TGA.
The trap
Mislabeling early profound cyanosis as TOF can delay prostaglandin in TGA. In critically cyanotic newborns with suspected TGA, ductal patency support is urgent before definitive repair.
The repair move
Next best step: start prostaglandin E1 infusion at 0.05 to 0.1 mcg/kg/min to maintain ductal patency, arrange urgent balloon atrial septostomy if mixing is inadequate, and plan arterial switch surgery; for TOF spells use knee-chest positioning, oxygen, morphine, and beta-blockade while preparing definitive repair.
Try a free question
CoreA cyanotic newborn develops severe hypoxemia within hours of birth and remains blue despite 100% oxygen. What is the most likely diagnosis?
Show answer and explanation
Answer: B. Transposition of great arteries. Profound early cyanosis with poor oxygen response is classic for transposition physiology requiring mixing.
Why the other choices are tempting
- A. Incorrect because TOF often presents later with spells and variable cyanosis rather than immediate severe refractory neonatal hypoxemia.
- C. Incorrect because isolated VSD usually causes left-to-right shunt and not immediate profound cyanosis.
- D. Incorrect because PFO alone does not typically produce severe persistent neonatal cyanosis.
- E. Incorrect because bronchiolitis is not a day-1 congenital cyanotic presentation.
Flashcards
Tap a card to flip it.
Which cyanotic congenital lesion classically causes severe hypoxemia in the first days of life requiring immediate mixing support?
Transposition of the great arteries.
What maneuver often improves a tet spell in tetralogy of Fallot?
Knee-chest positioning to increase systemic vascular resistance and reduce right-to-left shunt.
Quick answers
What is the fastest way to tell Tetralogy of Fallot from Transposition of great arteries?
Degree and timing of neonatal cyanosis with oxygen nonresponse requiring ductal-dependent mixing support.
What is the key clue for Tetralogy of Fallot?
Cyanotic spells in infancy with harsh systolic murmur and relief by knee-chest positioning suggest tetralogy of Fallot.
What is the key clue for Transposition of great arteries?
Profound cyanosis shortly after birth with poor oxygen response and little murmur suggests transposition of the great arteries.
What is the common trap with Tetralogy of Fallot vs Transposition of great arteries?
Mislabeling early profound cyanosis as TOF can delay prostaglandin in TGA. In critically cyanotic newborns with suspected TGA, ductal patency support is urgent before definitive repair.