What is the definition of AERP?

• A. The longest S1 S2 that fails to capture the atrium
• B. The longest S1 S2 that captures the atrium
• C. The shortest S1 S2 that fails to capture the atrium
• D. The maximum S1 S2 that conducts to the atrium

Answer: (A)

The main concept is the atrial effective refractory period, which is the longest interval between a drive beat and a premature stimulus that fails to produce atrial activation. In practice, you pace the atrium with a steady S1 drive and then deliver an extrastimulus S2; you vary the S1–S2 interval to find the point at which the atrium stops responding. The AERP is specifically the longest S1–S2 interval that fails to capture the atrium, meaning it defines how long the tissue remains refractory after a beat. This is not about the longest interval that successfully conducts, nor the shortest interval that fails, and it isn’t a measure of conduction time to the atrium.