A 3-week-old infant with irritability, pallor, poor feeding; afebrile; heart rate 240/min while asleep. The most likely diagnosis is:

A 3-week-old infant with irritability, pallor, poor feeding; afebrile; heart rate 240/min while asleep. The most likely diagnosis is:

• A. Supraventricular tachycardia
• B. Premature ventricular contractions
• C. Sinus tachycardia
• D. Cyanotic heart defect

Answer: (A)

In infants, a very rapid heart rate that persists even when the baby is asleep points to a tachyarrhythmia rather than a normal physiologic response. Supraventricular tachycardia is the most common sustained tachyarrhythmia in early infancy and often presents with irritability, pallor, poor feeding, and a heart rate in the 220–300 bpm range. The infant described has a rate of 240/min with afebrile status, which fits SVT well because fever is not driving the tachycardia and the symptoms reflect reduced cardiac output during a rapid rhythm. Premature ventricular contractions would produce irregular rhythm with isolated beats rather than a sustained rate this high. Sinus tachycardia due to fever or distress is unlikely here given the lack of fever. Cyanotic heart defects usually present with cyanosis and other signs of poor oxygenation or heart failure, not just isolated tachycardia. Therefore, the most likely diagnosis is supraventricular tachycardia.

In infants, a very rapid heart rate that persists even when the baby is asleep points to a tachyarrhythmia rather than a normal physiologic response. Supraventricular tachycardia is the most common sustained tachyarrhythmia in early infancy and often presents with irritability, pallor, poor feeding, and a heart rate in the 220–300 bpm range. The infant described has a rate of 240/min with afebrile status, which fits SVT well because fever is not driving the tachycardia and the symptoms reflect reduced cardiac output during a rapid rhythm. Premature ventricular contractions would produce irregular rhythm with isolated beats rather than a sustained rate this high. Sinus tachycardia due to fever or distress is unlikely here given the lack of fever. Cyanotic heart defects usually present with cyanosis and other signs of poor oxygenation or heart failure, not just isolated tachycardia. Therefore, the most likely diagnosis is supraventricular tachycardia.