What is retrograde AVNERP defined as?

• A. The longest S1 H2 or H1 H2 that fails to conduct to the atrium
• B. The shortest S1 H2 interval with retrograde conduction
• C. The time from atrial stimulus to atrial activation
• D. The total conduction time of the AV node during antegrade conduction

Answer: (A)

Retrograde AVNERP represents the upper limit of retrograde conduction through the AV node. In a programmed-stimulation test, you pace the atrium with a train (S1) and then deliver a premature stimulus (H2) to probe retrograde conduction back to the atria. The longest S1-H2 interval that still fails to produce atrial activation defines the retrograde refractory period of the AV node. In other words, it’s the maximum S1-H2 interval at which retrograde conduction does not occur. Shorter intervals may still conduct retrogradely; longer intervals cannot.

This is distinct from the actual retrograde conduction time (the interval when retrograde conduction does happen) and from antegrade AV nodal conduction measures, which assess forward conduction to the ventricles rather than back to the atria.