A 5-year-old child presents with recurrent episodes of paroxysmal supraventricular tachycardia. ECG during sinus rhythm is normal with no delta wave. Which of the following is the most common mechanism underlying this arrhythmia?
- A Automaticity in the atrial myocardium
- B Re-entry within the AV node (AVNRT) ✓
- C Re-entry involving an accessory pathway
- D Triggered activity in the His-Purkinje system
Correct answer: B. Re-entry within the AV node (AVNRT)
Explanation
In children with structurally normal hearts and no evidence of pre-excitation (normal ECG in sinus rhythm), AV nodal re-entrant tachycardia (AVNRT) is the most common mechanism of paroxysmal SVT. Accessory pathway-mediated re-entry (orthodromic AVRT) typically shows no delta wave on baseline ECG (conceptible pathway) but is slightly less common than AVNRT in young children without structural heart disease. Automatic atrial tachycardia and triggered activity are less common mechanisms.
Reference: Nelson Textbook of Pediatrics, 21st ed.
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