Which refractory period of atrial and ventricular tissue shortens with pacing, allowing introduction of premature beats?

• A. AERP
• B. VERP
• C. AVNERP
• D. The effective refractory period

Answer: (D)

The effective refractory period is the key concept here. After an action potential, this period represents the functional window during which a premature stimulus cannot propagate. As pacing rate increases, the heart’s ion channels recover more quickly and repolarization occurs sooner, so the ERP shortens. When the ERP shortens, a premature beat can find tissue that has become excitable again and may propagate, allowing premature atrial or ventricular beats to occur. While there are tissue-specific ERPs (atrial or ventricular) and other refractory terms, the phenomenon described—rate-dependent shortening with pacing—relates to the overall effective refractory period.