The anatomic electrophysiologic basis of AV node re-entry tachycardia is dual AV node conduction pathways. AV node re-entry tachycardia is most likely to occur with which of the following electrophysiologic aberrations?

A. Proximal antegrade block in the slow conduction pathway.
B. Proximal retrograde block in the slow conduction pathway.
C. Proximal antegrade block in the fast conduction pathway.
D. Proximal retrograde block in the fast conduction pathway.

Ans: C