In a reentrant circuit, what is the excitable gap?

In a reentrant circuit, what is the excitable gap?

• A. The portion of tissue that is ready to be depolarized as the wavefront circulates
• B. The time between successive heartbeats
• C. The dead tissue region blocking conduction
• D. The refractory period of the circuit

Answer: (A)

The main idea is that a reentrant loop keeps going only if there is tissue inside the circuit that has recovered from refractoriness and can be depolarized by the circulating wavefront. The excitable gap is that recovered, ready-to-fire portion of tissue as the wavefront moves around the loop. It is the window where excitation can occur; behind it, tissue remains refractory and cannot be depolarized yet. If this gap is too small or closes, the wavefront runs into still-refractory tissue and conduction fails, terminating the reentry. The other options describe the overall cycle timing, a fixed scar block, or the refractory period itself, none of which define the functional, propagating window that the excitable gap represents.

The main idea is that a reentrant loop keeps going only if there is tissue inside the circuit that has recovered from refractoriness and can be depolarized by the circulating wavefront. The excitable gap is that recovered, ready-to-fire portion of tissue as the wavefront moves around the loop. It is the window where excitation can occur; behind it, tissue remains refractory and cannot be depolarized yet. If this gap is too small or closes, the wavefront runs into still-refractory tissue and conduction fails, terminating the reentry. The other options describe the overall cycle timing, a fixed scar block, or the refractory period itself, none of which define the functional, propagating window that the excitable gap represents.