What is VERP?

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

Answer: (A)

VERP stands for the ventricular effective refractory period. It’s the longest interval between a paced beat and a premature stimulus (S1-S2) that fails to produce a ventricular depolarization. In practice, you pace the ventricle with a train of beats, then deliver a premature stimulus at decreasing intervals. The last interval at which the premature beat still fails to capture the ventricle defines VERP. Intervals longer than this will produce capture, while shorter ones will not. This measure reflects how long the ventricular tissue remains temporarily inexcitable after depolarization and is useful for assessing refractoriness, drug effects, and pacing safety.