One of the hallmark ECG clues for typical AV nodal reentrant tachycardia (AVNRT) is the appearance of a small, sharp pseudo-r’ deflection in lead V1. Although it looks like a tiny terminal R’ wave, it is not part of ventricular depolarization. Instead, it represents retrograde atrial activation occurring immediately after ventricular depolarization.

Unfamiliar with AVNRT? Read more & watch the AVNRT blog post here.

1. The Anatomical Basis: Dual Pathways of the AV Node

In typical AVNRT, the reentrant loop forms within the AV node and perinodal tissue, utilizing two distinct conduction pathways:

• Slow pathway: Posterior–inferior, located near the coronary sinus ostium

• Fast pathway: Anterior–superior, located near the compact node

During sinus rhythm:

• Atrial impulses preferentially travel down the fast pathway.

During AVNRT:

• The impulse travels anterograde through the slow pathway (slow conduction)

• Then retrograde through the fast pathway (rapid conduction back to the atria)

This produces a near-simultaneous activation of the ventricles and atria.

2. Why the Retrograde P Wave Gets Hidden

Because retrograde conduction occurs rapidly through the fast pathway, the atria depolarize:

**• Very shortly after the ventricles depolarize

• With the atria activated from the septum upward**

This timing means that the retrograde P wave falls inside or immediately after the QRS complex, where it becomes visually obscured.

But depending on the lead orientation, part of that hidden P wave becomes visible — and that’s where the pseudo-r’ comes from.