Supraventricular tachycardia (SVT) in children is the most common arrhythmia encountered in pediatrics.

ECG Features of SVT in a Child

1. Heart Rate:

   • Rapid, typically >220 bpm in infants and >180 bpm in older children.

   • Regular rhythm in most cases.

2. P Waves:

   • Often absent or not clearly visible because they are buried in the preceding T wave.

   • If visible, they may appear inverted in leads II, III, and aVF (retrograde conduction).

3. QRS Complex:

   • Narrow QRS complexes (<120 ms) in most cases (orthodromic SVT).

   • Wide QRS complexes can occur with aberrant conduction or pre-existing bundle branch block.

4. RR Interval:

   • Regular intervals; the rhythm is typically regular (unlike irregular rhythms seen in atrial fibrillation).

5. Abrupt Onset and Termination:

   • SVT starts and ends suddenly (paroxysmal).

6. ST-T Changes:

   • May show ST depression or subtle repolarization abnormalities due to the rapid heart rate.

Differential Diagnosis

• Sinus Tachycardia:

  • Gradual onset/offset, identifiable P waves, rate <220 bpm in infants or <180 bpm in children.

• Atrial Flutter:

  • Sawtooth pattern of flutter waves.

• Ventricular Tachycardia:

  • Wide QRS complexes and AV dissociation.

Management During ECG Recognition

1. Assess hemodynamic stability:

   • If unstable (hypotension, poor perfusion, altered mental state), proceed with synchronized cardioversion.

   • If stable, attempt vagal maneuvers (ice to face, blowing into a syringe).

2. Adenosine:

   • If vagal maneuvers fail, administer adenosine IV (0.1 mg/kg, max 6 mg; can increase to 0.2 mg/kg, max 12 mg).

3. Continuous Monitoring:

   • Record ECG during rhythm changes for further evaluation.

Prompt recognition and management of SVT on ECG are crucial to avoid complications and restore normal rhythm.