How does a His-refractory PVC affect AVNRT?

• A. It will terminate tachycardia
• B. It will not break tachycardia because arrhythmia is only in the AVN
• C. It will transiently modify tachycardia but not terminate
• D. It will cause ventricular fibrillation

Answer: (B)

In AVNRT the reentrant circuit is within or immediately around the AV node, so the ventricles are just downstream of the circuit and do not participate in driving or sustaining the tachycardia. For a ventricular event to terminate AVNRT, it would typically need to perturb the circuit via retrograde conduction into the AV node and atria to reset or block the loop.

A His-refractory PVC means the premature ventricular beat occurs when the His bundle is refractory, so there is no retrograde conduction from the ventricles back into the AV node to interact with the reentrant circuit. Because retrograde interaction with the AV nodal circuit is blocked, the tachycardia continues unchanged. A single His-refractory PVC is unlikely to cause ventricular fibrillation, and since the ventricles aren’t part of the AVNRT mechanism, the tachycardia isn’t terminated by this event.

Thus, the tachycardia persists because the arrhythmia is confined to the AV node and cannot be interrupted by a ventricle-originating beat that cannot reach the atrial side.