Which pathway repolarizes slowly?

• A. The slow pathway
• B. The fast pathway
• C. Both
• D. Neither

Answer: (A)

In dual AV nodal pathways, the two routes have different electrical properties. Repolarization is how quickly a pathway recovers after an impulse and becomes excitable again. The slow pathway conducts impulses more slowly and has a longer action potential duration with a longer refractory period, largely because its activity relies more on calcium-dependent processes and a prolonged plateau. This causes it to revert to a resting, excitable state more slowly than the fast pathway. The fast pathway, by contrast, repolarizes more quickly and recovers readiness sooner due to a shorter plateau and shorter refractory period. So, among the two, the slow pathway is the one that repolarizes slowly, which is why that pathway stands out in discussions of AV nodal conduction and reentrant circuits.