Which statement best describes reentry as a VT mechanism?

• A. Reentry requires a circuit with slow conduction and a unidirectional block
• B. Reentry is caused by enhanced automaticity
• C. Reentry occurs only in the atria
• D. Reentry is caused by afterdepolarizations

Answer: (A)

Reentry as a VT mechanism relies on a circulating impulse around a pathway that has a key two-part setup: slow conduction and a unidirectional block. In diseased or scarred ventricle, some channels conduct slowly, so an impulse can travel around a loop but not all at once. If one direction around the loop is blocked while the opposite direction is still able to propagate, the impulse can travel around the circuit in one direction. By the time the tissue ahead of the block recovers from refractoriness, the wavefront can re-enter and continue circling, creating a self-sustaining VT. This circuit-based mechanism is why reentrant VT is common around scars and anatomical obstacles.

Enhanced automaticity would produce ectopic beats from a focus rather than a circulating wave; afterdepolarizations are a form of triggered activity, not a sustaining reentrant circuit. Reentry is not limited to the atria; it can occur in the ventricles as well.