AV Nodal Reentrant Tachycardia (AVNRT) MCQ — NEET PG Practice Question | NEETPGAI
AV Nodal Reentrant Tachycardia (AVNRT)
medium
stethoscope Medicine
A 28-year-old woman presents to the emergency department with sudden-onset palpitations, lightheadedness, and a sensation of neck pounding. Her vital signs show a regular heart rate of 160 bpm. 12-lead ECG during the episode reveals a narrow-complex regular tachycardia with retrograde P waves appearing immediately after the QRS complex, creating a pseudo-S wave in the inferior leads. The resting ECG between episodes is completely normal with no delta waves. The rhythm shown in the diagram marked **A** is suspected. Which of the following is the PRIMARY pathophysiological mechanism underlying this arrhythmia?
A. Triggered activity from enhanced automaticity of the AV nodal region due to catecholamine sensitivity
B. Accessory pathway-mediated reentry with antegrade conduction down the accessory pathway and retrograde conduction through the AV node
C. Atrial automaticity with variable AV nodal conduction block producing a regular narrow-complex tachycardia
D. Reentry confined to the AV node via dual pathways with antegrade conduction through the slow pathway and retrograde conduction through the fast pathway
Explanation
Why option 1 is correct
The clinical presentation—sudden-onset palpitations with neck pounding, narrow-complex regular tachycardia at 160 bpm, retrograde P waves immediately after QRS (pseudo-S in inferior leads), and normal resting ECG without delta waves—is pathognomonic for typical (slow-fast) AVNRT. The mechanism marked A in the diagram depends critically on DUAL AV NODAL PHYSIOLOGY: a critically timed premature atrial complex blocks in the fast pathway (which is refractory), conducts antegrade down the SLOW pathway (long conduction time, short refractory period), and then finds the fast pathway recovered—it conducts retrograde up the fast pathway, completing a reentry circuit entirely within the AV nodal region. This produces the characteristic very short RP interval (<70 ms) with retrograde P waves simultaneous with or immediately after QRS. The absence of delta waves on baseline ECG rules out an accessory pathway. (2019 ACC/AHA/HRS SVT Guidelines; Harrison's 21e Ch 247)
Why each distractor is wrong
Option 2 (Accessory pathway-mediated reentry): This describes orthodromic AVRT in Wolff-Parkinson-White syndrome (marked B in the diagram), not AVNRT. AVRT requires an accessory pathway and would show a delta wave on baseline ECG; the RP interval in orthodromic AVRT is ≥70 ms (longer than typical AVNRT) because the impulse must travel down a separate accessory pathway. This patient's normal resting ECG excludes WPW.
Option 3 (Atrial automaticity with variable AV block): This describes atrial flutter or atrial tachycardia (marked C in the diagram), not AVNRT. Atrial flutter typically shows sawtooth flutter waves and variable AV conduction; atrial tachycardia shows visible P waves distinct from the QRS. AVNRT is a reentrant mechanism, not an automatic one, and the P waves are retrograde (not ectopic atrial).
Option 4 (Triggered activity from enhanced automaticity): This mechanism is not responsible for AVNRT. Triggered activity (early or delayed afterdepolarizations) may underlie some atrial or ventricular arrhythmias but does not explain the dual-pathway reentry circuit that characterizes AVNRT. The arrhythmia is reproducibly initiated and terminated by AV nodal conduction properties, not automaticity.
High-YieldNEET PG
AVNRT = most common SVT (60% of SVTs); depends on dual AV nodal pathways (slow pathway antegrade, fast pathway retrograde); produces very short RP interval with pseudo-S/pseudo-R' on ECG; normal baseline ECG (no delta wave) distinguishes from WPW/AVRT.
2019 ACC/AHA/HRS SVT Guidelines; Harrison's Principles of Internal Medicine 21e Ch 247
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