Which ERP defines the longest S1 S2 interval that fails to conduct to the ventricle?

• A. VERP
• B. AERP
• C. AVNERP
• D. AVERP

Answer: (A)

Understanding how the ventricles recover excitability after a beat is tested with the ventricular effective refractory period. In programmed stimulation, you deliver a train of impulses (S1) to steady-state the tissue, then apply a premature impulse (S2) at progressively shorter coupling intervals. The VERP is defined as the longest S1–S2 interval that fails to produce a ventricular response. In other words, it’s the maximum time after S1 at which the ventricle still cannot be activated by S2, reflecting the recovery time of ventricular myocardium. This is distinct from the atrial ERP or AV nodal ERP, which pertain to recovery times in the atria or at the AV node, not the ventricles.