Which arrhythmia is suggested by a rapid heart rate with a regular rhythm in an infant?

• A. Supraventricular tachycardia
• B. Ventricular tachycardia
• C. Atrial fibrillation
• D. Sinus tachycardia

Answer: (A)

Rapid, regular tachycardia in an infant most often points to a supraventricular tachycardia. The key clue is a very fast but steady rhythm, usually with a narrow QRS complex and no clearly visible P waves because they’re often buried in the QRS or aligned in a way that makes them hard to see. In infants, a rate above roughly 220 beats per minute during rest is a classic threshold suggesting SVT, most commonly AV nodal reentrant tachycardia.

If the rhythm were ventricular tachycardia, you’d expect a wide, abnormal QRS and a rhythm that can be regular but is generated from the ventricles rather than the atrioventricular node. Atrial fibrillation would produce an irregularly irregular rhythm with no single predictable rate. Sinus tachycardia, while it can be fast, keeps normal P waves and a rhythm that follows physiologic cues (like fever or stress) and usually isn’t sustained at such extreme rates.