AV junctional re-entrant tachycardias, including those associated with AV nodal bypass tracts, are a distinct and common cause of supraventricular tachycardias. Their characteristics are shown here and on the next page.
It is important to recognize that these re-entrant tachycardias frequently occur in the absence of underlying heart diseases. Their onset is abrupt and usually initiated by an atrial premature beat with a long PR interval, although rarely, a ventricular premature beat may initiate the arrhythmia. They can be terminated by drugs or maneuvers which slow or block conduction in either pathway of the re-entry circuit, although it is most often the AV nodal pathway. This is accomplished by maneuvers which increase vagal tone, such as a sudden increase in blood pressure, direct carotid sinus massage, the valsalva maneuver or the administration of beta-adrenergic blocking agents. It is also accomplished by drugs which directly inhibit AV nodal conduction. These include adenosine and the calcium channel blocking agents.