What is the most common dysrhythmia in children and its characteristics in newborns and children?

• A. Sinus Tachycardia: Variable R-R interval; <220 bpm infants; <180 bpm children
• B. SVT: Consistent R-R interval; >200 bpm infants; >180 bpm children
• C. Atrial flutter: Regular rhythm; rate <150 in infants
• D. Bradycardia: Sinus bradycardia; heart rate depends on age

Answer: (A)

Supraventricular tachycardia is the most common dysrhythmia seen in children. It presents as a rapid, regular rhythm with a narrow QRS complex. In newborns, the ventricular rate from SVT is typically over 200 beats per minute, while in older children it is usually over 180 beats per minute. The rhythm remains consistently regular, so the R-R interval is steady beat to beat. P waves are often not clearly visible because they may be buried in the preceding QRS or occur just after it due to retrograde conduction. This pattern distinguishes SVT from sinus tachycardia, which is a normal physiologic response with regular rhythm but not a primary reentrant tachycardia, and from other rhythms like atrial flutter or bradycardias, which have different characteristic features and are less commonly encountered as the primary pediatric dysrhythmia.