Which tissue has the fastest conduction velocity?

• A. AV Node
• B. Purkinje Fibers
• C. Atrial Myocardium
• D. Ventricular Myocardium

Answer: (B)

Purkinje fibers have the fastest conduction velocity. They are specialized conducting pathways with large-diameter fibers and abundant gap junctions, which greatly reduce intercellular resistance and allow the impulse to travel rapidly from the His bundle through the ventricles. The rapid phase 0 upstroke in these fibers, driven by strong sodium current and tight cell-to-cell coupling, lets the impulse sweep through the Purkinje network quickly so the ventricles depolarize essentially in unison.

In contrast, the AV node is built for delay—the tissue is small in diameter with fewer gap junctions and uses calcium-based conduction, producing a slow impulse transmission to provide atrial-ventricular delay. Atrial and ventricular myocardium conduct more slowly than Purkinje fibers because of smaller diameter and less direct coupling, leading to slower spread of the impulse compared with the Purkinje system.