A 4-month-old infant with cyanotic spells and a systolic murmur best heard at the left sternal border most likely has which condition?

A 4-month-old infant with cyanotic spells and a systolic murmur best heard at the left sternal border most likely has which condition?

• A. Apnea
• B. Congestive heart failure
• C. Coarctation of the aorta
• D. Cyanotic spell related to tetralogy of Fallot

Answer: (D)

Episodes of cyanosis in an infant, especially when accompanied by a systolic murmur best heard along the left sternal border, point to tetralogy of Fallot and its characteristic Tet spells. In TOF, a combination of four defects—ventricular septal defect with malaligned path, infundibular (RV outflow tract) stenosis, an overriding aorta, and right ventricular hypertrophy—reduces blood flow to the lungs and promotes right-to-left shunting. The result is sudden drops in arterial oxygen that cause the spells. The systolic murmur at the left lower sternal border comes from the obstruction of the right ventricular outflow tract; that murmur reflects the degree of RVOT obstruction, which is central to TOF physiology. During a spell, increased right-to-left shunting worsens cyanosis, and the patient may become rapidly more hypoxic, often triggered by crying or feeding. The age fits, as these spells commonly begin in infancy. Other options don’t fit as well because apnea lacks the chronic murmur pattern and the characteristic episodic cyanosis; congestive heart failure would present with tachypnea, poor feeding, and hepatomegaly rather than discrete cyanotic spells; coarctation of the aorta typically shows diminished femoral pulses and upper-limb hypertension rather than cyanotic spells with a left sternal border murmur.

Episodes of cyanosis in an infant, especially when accompanied by a systolic murmur best heard along the left sternal border, point to tetralogy of Fallot and its characteristic Tet spells. In TOF, a combination of four defects—ventricular septal defect with malaligned path, infundibular (RV outflow tract) stenosis, an overriding aorta, and right ventricular hypertrophy—reduces blood flow to the lungs and promotes right-to-left shunting. The result is sudden drops in arterial oxygen that cause the spells.

The systolic murmur at the left lower sternal border comes from the obstruction of the right ventricular outflow tract; that murmur reflects the degree of RVOT obstruction, which is central to TOF physiology. During a spell, increased right-to-left shunting worsens cyanosis, and the patient may become rapidly more hypoxic, often triggered by crying or feeding. The age fits, as these spells commonly begin in infancy.

Other options don’t fit as well because apnea lacks the chronic murmur pattern and the characteristic episodic cyanosis; congestive heart failure would present with tachypnea, poor feeding, and hepatomegaly rather than discrete cyanotic spells; coarctation of the aorta typically shows diminished femoral pulses and upper-limb hypertension rather than cyanotic spells with a left sternal border murmur.