Which of the following statements accurately describes stimulation during the excitable gap of a reentrant circuit?

• A. It prolongs the tachycardia
• B. It accelerates the rhythm
• C. It triggers ventricular fibrillation
• D. When the stimulus hits the excitable gap it breaks the rhythm

Answer: (D)

The key idea is that a reentrant tachycardia runs as a circulating impulse around a loop that contains an excitable gap—tissue that has recovered enough to be excited again. If a premature stimulus arrives right in that excitable gap, it can be captured and propagate in a way that collides with the ongoing impulse in the circuit, creating bidirectional block and disrupting the loop. This interruption stops the reentrant circuit, effectively terminating the tachycardia and returning rhythm to normal or a slower rhythm.

So, stimulating during the excitable gap is most likely to break the abnormal rhythm rather than prolong it, accelerate it, or trigger chaotic activity like ventricular fibrillation under typical circumstances.