In typical AVNRT, the repolarization time of the fast pathway is longer than that of the slow pathway.

• A. Longer
• B. Shorter
• C. Equal
• D. Unknown

Answer: (A)

In AVNRT there are two pathways within the AV node, each with its own recovery time after activation. The fast pathway has a longer repolarization time than the slow pathway, so it stays non-excitable for a longer period after being activated. This difference in recovery is what allows a self-sustaining reentrant loop: the impulse travels antegradely through the slow pathway to the ventricles, and then, as the fast pathway recovers from its longer refractory period, the impulse travels retrogradely through the fast pathway back toward the atria, completing the circuit. If the fast pathway didn’t have a longer repolarization time, the timing wouldn’t favor this stable reentry, and the tachycardia would be less likely to sustain.