AVNRT

          AVNRT - AV Nodal Reentrant Tachycardia is one of the most common forms of tachycardias that originates in the upper chambers of the heart. AVNRT is a reentry tachycardia that is contained within the AV node. In many people, the AV node has two pathways, one faster pathway along with a secondary slower pathway. These pathways must connect with each other at the top and bottom of the AV node. The pathway that has a faster conduction speed takes longer to recover to the point where it can accept a new signal. The slower pathway recovers more quickly and can accept a new signal ealier than the pathway that conducts faster. If an early signal happens in the time period when the fast pathway is not ready to recieve a new signal but the slow pathway is, then the early signal will travel down the slow pathway only. When the early signal reaches the lower connection, it is possible that the faster pathway is now ready to conduct a signal. If this happens and the fast pathway has the ability to conduct a signal back against the normal direction of conduction, the early signal will split with part of it travelling down into the ventricles along the normal conduction paths. The other part of the signal will return backwards, or retrograde, up the fast pathway. When this signal reaches the top of the node where the upper connection between the two pathways is located, it will travel back down the slow pathway while part of the signal also conducts back up into the atrium. The circuit is now in a loop that will continue until something changes and the circuit is interrupted.