Which pathway repolarizes quickly?

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

Answer: (A)

In the AV node, two pathways exist with different conduction and recovery properties. Repolarization speed refers to how quickly a pathway can recover after an action potential, i.e., how short its refractory period is. The slow pathway has a shorter refractory period, so it repolarizes and becomes excitable sooner than the fast pathway. The fast pathway, by contrast, conducts impulses quickly but remains refractory longer, taking more time to repolarize. So, the pathway that repolarizes quickly is the slow pathway. This quick recovery of the slow pathway helps determine which route is available to conduct impulses at different timings and is important in understanding dual AV nodal physiology and related arrhythmias.