How is the fast pathway defined?

• A. A pathway that naturally has fast conduction but repolarizes slowly
• B. A pathway that naturally has slow conduction but repolarizes quickly
• C. A pathway that naturally has fast conduction and fast repolarization
• D. A pathway that naturally has slow conduction and slow repolarization

Answer: (A)

The fast pathway is defined by fast conduction velocity coupled with a relatively long refractory period. In dual AV nodal pathways, the fast pathway conducts quickly but takes longer to repolarize, meaning it has a slower recovery. This combination distinguishes it from the slow pathway, which conducts slowly but repolarizes quickly (shorter refractory). The option describing fast conduction with slow repolarization fits this pattern best. The other descriptions mix in slow conduction or fast repolarization, which do not characterize the fast pathway.