Which of the following is NOT a criterion to initiate and sustain reentry tachycardia?

• A. Different conduction velocities
• B. Unidirectional block
• C. Two pathways
• D. Increased automaticity

Answer: (D)

Reentry tachycardia relies on a circulating electrical circuit around an obstacle. For the circuit to start and keep going, you typically need at least two conducting pathways around that obstacle, a region of unidirectional block so the impulse can travel in one direction and then re-enter, and differences in conduction properties (conduction velocity and refractoriness) so the tissue on the path returns to excitability at just the right moment to be re-excited. These conditions create a self-sustaining loop.

Increased automaticity, while it can generate ectopic beats, does not by itself form or sustain a reentrant circuit. It involves spontaneous depolarization of automatic cells rather than the looping path with block and timing that reentry requires. That’s why increased automaticity is not a criterion for initiating and sustaining reentry tachycardia.