AV Nodal Re-entrant Tachycardia (AVNRT)

In AVNRT, a re-entry circuit may be present in or near the AV node and may cause episodes of tachycardia. An episode may last from a few seconds to as long as a few hours. AVNRT most commonly affects young and middle-aged adults who do not have heart disease.

AVNRT is the most common form of SVT – supraventricular tachycardia, a fast heart rhythm involving the top part of the heart and/or the normal connection between the top and bottom parts of the heart. AVNRT involves a short circuit that is actually part of the normal pathway (the AV node) that takes the heartbeat from the top to the bottom of the heart. Instead of having one AV node, patients with AVNRT have two: a fast pathway and a slow pathway. The SVT occurs when the heartbeat blocks in one pathway and then goes down the other slowly enough so that when it reaches the far end of the first pathway, it can turn around and come up it back to the top again and then back down again – and so on like a dog chasing its tail. Usually, the slow pathway conducts electrical impulses to the bottom of the heart and the fast pathway conducts it to the top. But in rare cases, the circuit consists of the fast pathway to the bottom and the slow pathway to the top or even two different slow pathways. Usually these different pathways are very near the main part of the AV node, but they may occur at some distance either on the right or left side of the heart.