Which pacing modality is used to determine the ventricular effective refractory period (VERP)?

• A. Ventricular extrastim pacing
• B. Atrial extrastim pacing
• C. Ventricular pacing at a fixed cycle length
• D. His bundle pacing

Answer: (A)

The ventricular effective refractory period is about how long the ventricular tissue remains unexcitable after a depolarization. To measure it, you need to probe the ventricle with premature impulses and see when they can or cannot propagate. This is achieved with ventricular extrastimulus pacing: you pace the ventricle with a basic drive train and then deliver a premature ventricular stimulus at progressively shorter coupling intervals. The point at which the premature impulse fails to propagate defines the VERP. Using extrastimuli from the ventricle isolates the ventricular tissue’s refractoriness, whereas pacing from the atrium would assess atrial refractoriness, pacing at a fixed cycle length doesn’t test how the ventricle responds to premature beats, and His bundle pacing targets the conduction system rather than measuring ventricular refractoriness.