Electrophysiological features of atrial tachycardia arising from the atrioventricular annulus.

Atrial tachycardia (AT) arises from various sites in the atrium and the mechanisms are nonuniform. McGuire et al. reported that the cells around the atrioventricular annuli resembled nodal cells in their cellular electrophysiology. The purpose of this study was to delineate the electrophysiological features of AT arising from the atrioventricular (AV) annulus (AVAT). The study included five patients with six AVATs that were abolished by the radiofrequency energy delivery. The location of the AV annuli was defined by using the AV ratio of the local electrograms and the amplitude of the ventricular electrograms, in addition to the anatomic findings under fluoroscopic guidance. The tachycardia cycle lengths were 403 +/- 117 ms. An AV ratio of the electrograms at the successful ablation sites was 0.4 +/- 0.4 at the tricuspid annulus and 1.5 +/- 0.3 at the mitral annulus. Small doses (mean 3.2 +/- 1.8 mg) of adenosine triphosphate could terminate all the tachycardia episodes for five of the ATs without the development of AV nodal conduction block. The successful ablation sites were located at the right mid-septum in 1 AT, right posteroseptum in 2 ATs, right posterolateral region in 1 AT, and left anteroseptum in 2 ATs. These findings suggest that the cells with nodal-type action potentials around both annuli might play an important role in the genesis of AVAT.