Which of the following best describes AVNRT features?

• A. Short RP tachycardia with narrow QRS and P waves hidden in QRS
• B. Long RP tachycardia with wide QRS
• C. P waves clearly visible before QRS
• D. P waves after QRS

Answer: (A)

AVNRT is a reentrant tachycardia that uses pathways within or near the AV node. Ventricular activation occurs through the normal His-Purkinje system, so the QRS is narrow. The atrial activation is retrograde and occurs very soon after the QRS, often being hidden in the QRS or appearing just after it, which makes the RP interval short. This combination—a rapid, narrow-complex tachycardia with P waves that are not clearly seen within the rhythm strip—is the classic AVNRT presentation.

Other patterns don’t fit as well: a long RP with wide QRS suggests a different mechanism (like VT or antidromic AVRT), and P waves clearly before the QRS points to atrial pacing or a different atrial tachycardia. So the description of a short RP tachycardia with a narrow QRS and P waves hidden in the QRS is the best match for AVNRT.