Which of the following is a characteristic of AVNRT?

• A. Short RP tachycardia
• B. Wide QRS
• C. P waves clearly visible before QRS
• D. P waves after QRS

Answer: (A)

AVNRT is a reentrant tachycardia that involves retrograde atrial activation through the AV node. Because the atria are activated back through the AV node, the P waves often appear very soon after the QRS or are even hidden in the QRS, making the interval from the QRS to the next P wave (RP interval) short. This short RP tachycardia is a characteristic hallmark of AVNRT, and the tachycardia is typically narrow-complex since ventricular activation follows the normal His-Purkinje system.

Wide QRS would point away from AVNRT, suggesting ventricular origin or aberrant conduction. P waves clearly before the QRS would imply an atrial source or a different mechanism, not the classic AVNRT picture. P waves after the QRS can occur in AVNRT, but the defining feature to identify AVNRT is the short RP interval.