Repeated USMLE Questions Step 1- 285

A 16-month-old boy is brought to the clinic by his mother who is concerned that her boy turns blue and becomes short of breath several times during last three months. During these episodes, he becomes irritable and stays in squatting position until he relieves. Cardiac examination reveals systolic ejection murmur over the upper right sternal border. X-ray shows boot-shaped heart.

What is the most likely diagnosis?

A- Tetralogy of Fallot

B- Total anomalous pulmonary venous return

C- Transposition of the great arteries

D- Tricuspid atresia

E- Truncus arteriosus


This is a case of cyanotic heart disease. As we may all know, congenital heart diseases are classified into cyanotic and non-cyanotic heart diseases. Also, cyanotic heart diseases are further classified into early and late cyanotic depending upon if they are diagnosed early in the neonatal period or later. Total anomalous pulmonary venous connection, transportation of the great vessels, tricuspid atresia and truncus arteriosus are examples of early cyanotic congenital heart diseases which show right after birth. Tetralogy of Fallot is usually revealed later on or after the neonatal period due the development of right-to-left shunt through the ventricular septal defect.

Fallot of Tetralogy is characterized by ventricular septal defect, pulmonary stenosis, right ventricular hypertrophy and overriding aorta. Sometimes, as in this case, it appears later after the neonatal period and it causes “tet spells” which are episodes of cyanosis, dyspnea, irritability and loss of consciousness. Some kids develop natural relief by squatting which increases venous return to the heart leading to relief of these episodes.

The correct answer is A

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