Unlike sinus tachycardia, reentry supraventricular tachycardia in infants is characterized by:

• A. A pulse rate that varies with activity
• B. An unvarying pulse rate
• C. Low blood pressure
• D. Chest pain

Answer: (B)

In reentry SVT in infants, the heart rate tends to be very rapid but strikingly regular, staying essentially the same regardless of activity or crying. This regularity is a hallmark because the electrical circuit driving the tachycardia keeps a steady pace, unlike sinus tachycardia, where the rate changes with autonomic input and situations like fever, dehydration, or exertion. So the pulse remains unvarying in reentry SVT, even as the child’s activity level changes. Chest pain is uncommon in infants, and while blood pressure can be affected if the situation progresses, it doesn’t define the pattern. That steady, unchanging rate is what sets reentry SVT apart.