Which feature is essential for a reentrant tachycardia circuit?

Which feature is essential for a reentrant tachycardia circuit?

• A. Dead cell in the middle
• B. Depolarization wavefront
• C. Excitable gap on outside
• D. Unidirectional block

Answer: (D)

The thing that makes a reentrant tachycardia possible is a unidirectional block that shapes a looping path for the impulse. When conduction can proceed in one direction but is blocked in the opposite direction, the wavefront can travel around a circuit and, after the tissue ahead has recovered from its refractory period, re-enter it to continue propagating. That one-way block is what creates the closed loop needed for sustained reentry. Without a unidirectional block, the impulse would either go through in all directions and extinguish, or would not form a closed circuit at all, so the tachycardia cannot be sustained. An excitable gap and other features matter for the timing and maintenance of the circuit, but the defining element that enables the circulating pathway is this one-way block. A dead cell center or simply the presence of a depolarization wavefront doesn’t by itself establish the looping, and while an excitable gap is important for perpetuation, it doesn’t replace the essential role of the unidirectional block.

The thing that makes a reentrant tachycardia possible is a unidirectional block that shapes a looping path for the impulse. When conduction can proceed in one direction but is blocked in the opposite direction, the wavefront can travel around a circuit and, after the tissue ahead has recovered from its refractory period, re-enter it to continue propagating. That one-way block is what creates the closed loop needed for sustained reentry.

Without a unidirectional block, the impulse would either go through in all directions and extinguish, or would not form a closed circuit at all, so the tachycardia cannot be sustained. An excitable gap and other features matter for the timing and maintenance of the circuit, but the defining element that enables the circulating pathway is this one-way block. A dead cell center or simply the presence of a depolarization wavefront doesn’t by itself establish the looping, and while an excitable gap is important for perpetuation, it doesn’t replace the essential role of the unidirectional block.