A 6-year-old girl with fever presents lethargy and tachycardia. Her heart rate is 170 beats/min and varies with activity. The cardiac monitor shows a narrow complex tachycardia with a rate of 150-170. After applying high-flow oxygen, what is the next best step?

• A. Begin synchronized cardioversion
• B. Establish vascular access and administer a 20-mL/kg normal saline bolus
• C. Administer amiodarone
• D. Administer aspirin

Answer: (B)

In pediatrics, always judge stability and the likely cause of tachycardia. A fever with a high heart rate that varies with activity and presents as a narrow complex rhythm in a child often points to sinus tachycardia from fever and dehydration rather than a dangerous reentrant arrhythmia. After giving oxygen, the most appropriate next step is to restore intravascular volume with an isotonic saline bolus (about 20 mL/kg). This helps correct dehydration, improves perfusion, and can reduce the heart rate by addressing the underlying stress on the body.

Medications like amiodarone or aspirin aren’t indicated for a febrile, sinus-origin tachycardia, and synchronized cardioversion is reserved for unstable tachyarrhythmias with poor perfusion or ongoing hemodynamic collapse. If the patient remains tachycardic after fluids or develops signs of instability, reevaluate and consider other interventions based on the rhythm and clinical status.