Which of the following is an example of an anatomic abnormality that can cause abnormal conduction?

• A. Congenital accessory pathways
• B. Degenerative disease
• C. Atherosclerotic plaque
• D. Postoperative scar

Answer: (A)

Abnormal conduction often stems from an anatomic substrate that provides an alternate route for impulses. Congenital accessory pathways are classic examples: these are extra muscular connections that link atrial tissue directly to ventricular tissue, bypassing the normal AV node. Because impulses can travel through this bypass tract, conduction can occur outside the usual slow AV nodal pathway, leading to preexcitation and potentially reentrant tachyarrhythmias. This discrete, persistent anatomical connection from birth makes it a quintessential substrate for abnormal conduction.

Degenerative disease of the conduction system involves gradual loss or impairment of the nodes or His‑Purkinje tissue, which slows or blocks conduction but isn’t an extra conduction pathway. Atherosclerotic plaque affects the vessels rather than the conduction tissue itself, so it alters perfusion rather than providing a direct conduction substrate. Postoperative scar is an anatomic change that can disrupt conduction, but the classic, congenital example of a discrete conduction pathway that causes abnormal conduction is the accessory pathway.