What is the upper bound of heart rate for sinus tachycardia in infants?

• A. 210 bpm
• B. 220 bpm
• C. 230 bpm
• D. 240 bpm

Answer: (B)

Sinus tachycardia in infants is a regular rhythm driven by the sinus node that simply beats faster in response to physiologic stress. There is a practical ceiling to how fast sinus rhythm can pace in infancy, and that upper limit is about 220 beats per minute. Fevers, crying, or dehydration can push rates upward toward this limit, but rates higher than roughly 220 bpm are unlikely to be sinus in origin and should raise concern for a tachyarrhythmia such as supraventricular tachycardia. Among the options, 220 bpm represents the upper bound for sinus tachycardia; lower values can occur with sinus tachycardia, while higher values are more suggestive of an arrhythmia.