In terms of tissue readiness, how is the excitable gap best described?

• A. The region that cannot be excited
• B. The portion of tissue that can be excited
• C. The central circuit
• D. The boundary tissue

Answer: (B)

The excitable gap is the portion of tissue that can be excited. In a reentrant rhythm, tissue just ahead of the advancing wavefront has recovered from refractoriness and is ready to depolarize again, forming the gap through which the next impulse can propagate. This readiness to be excited allows the wavefront to continually re-enter the circuit and sustain the tachycardia. If there were no excitable tissue ahead, the wavefront couldn’t advance and the reentrant circuit would terminate. The region that cannot be excited is the refractory tissue, not the excitable gap; the central circuit refers to the loop itself, and boundary tissue isn’t a standard descriptor.