The AVNRT (atrioventricular nodal re-entrant tachycardia) mechanism involves a dual-pathway AV node. In typical (slow-fast) AVNRT, the P wave relationship to QRS is:

• A P wave precedes QRS by PR interval >200 ms
• B P wave follows QRS by >200 ms (long RP tachycardia)
• C No P wave visible at any lead
• D P wave buried in or immediately after QRS (RP <70 ms, pseudo-R' in V1 or pseudo-S in inferior leads) ✓

Explanation

In typical (common) AVNRT, antegrade conduction uses the slow pathway and retrograde uses the fast pathway. Because retrograde atrial activation occurs nearly simultaneously with ventricular depolarisation, P waves are buried in or immediately follow the QRS complex (RP interval <70–90 ms). This produces characteristic pseudo-R' deflection in V1 (retrograde P mimicking RSR') or pseudo-S wave in inferior leads — diagnostic ECG clues. Atypical AVNRT (fast-slow) has long RP interval (RP > PR).

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.