Abnormal conduction can be caused by which mechanism?

• A. Reentry
• B. Automaticity
• C. Atrioventricular block
• D. Sinus node dysfunction

Answer: (A)

Reentry is the mechanism that explains abnormal conduction because it creates a self-sustaining loop of activation. An impulse travels through a pathway and, due to a unidirectional block and differences in conduction speed and tissue refractoriness, can re-enter tissue that has recovered excitability. This looping circuit keeps reactivating the heart tissue and produces a faster, abnormal rhythm.

Automaticity describes new impulses arising from non-sinus tissue rather than a looping conduction pathway, while AV block and sinus node dysfunction are disorders of conduction or the primary pacemaker’s performance, not the looping reentrant process. So reentry best accounts for abnormal conduction.