Which refractory period of the AV node lengthens with pacing, and results in blocking of conduction to the ventricles?

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

Answer: (D)

The effective refractory period is the time after an impulse when that tissue cannot be re-excited, and in the AV node this period lengthens as pacing rate increases. As pacing gets faster, the AV node takes longer to recover, so an incoming atrial impulse may arrive while the node is still refractory, blocking conduction to the ventricles. This rate-dependent lengthening of the AV nodal refractory period explains why ventricles fail to follow every atrial beat at higher pacing rates. The other terms point to atrial or ventricular tissue, or to AV nodal specifics, but the general effective refractory period captures the mechanism of rate-related AV block in this context.