Junctional Tachycardia

IN THE ABSENCE of functioning anomalous connection between atria and ventricles, the A-V junction serves as the only link between these structures, allowing the atrial impulse to be transmitted to the ventricles. The A-V junction may be defined as consisting of the atrial approaches to the A-V node, the A-V node itself, and the penetrating portion of the His bundle. Total transection of the A-V junction at any point should produce A-V block, and stimulation in the presence of a normal His-Purkinje system should produce a narrow QRS. The electrophysiologic function of the A-V junction is primarily that of conduction. However, in addition, the A-V junction possesses intrinsic automaticity, allowing it to serve as a subsidiary pacemaker in the event of failure of proximal impulse formation or propagation. Under pathologic conditions, the A-V junction can serve as an ectopic pacemaker, or as a site of reentry.