Electrocardiographic and Electrophysiological Characteristics of Atrial Tachycardia With Early Activation Close to the His-Bundle.

INTRODUCTION: Radiofrequency (RF) ablation of atrial tachycardia (AT) with earliest activation at the His-bundle may be associated with the risk of AV block, and detection of this AT origin using the electrocardiogram (ECG) would be helpful in planning ablation. Aim of this study was to characterize the P-wave morphology and intracardiac electrograms at the successful ablation site for this group of ATs. METHODS: All consecutive patients undergoing ablation for AT with earliest activation at the His-bundle were included. Twelve-lead ECG and intracardiac electrograms were analyzed. RESULTS: A total of 33 patients underwent successful ablation. The P-wave and the PR interval during AT (cycle length 460 ± 88, range 360-670 milliseconds) were significantly shorter compared to sinus rhythm 87 ± 18 vs. 117 ± 23 and 131 ± 37 vs. 170 ± 47 milliseconds, respectively, P < 0.01. In 28 patients (85%), the P-wave was biphasic (-/+) or triphasic (+/-/+) in the precordial leads, especially V4 -V6 , and in 25 patients (76%) it was biphasic (-/+) or triphasic (+/-/+) in the inferior leads. RF was delivered at the following locations: noncoronary aortic cusp (NCC) in 24 patients, antero-septal left atrium in 4, supero-septal right atrium in 3, left coronary cusp in 1, and between the right coronary cusp and the NCC in 1. Atrial bipolar electrograms at the successful ablation site preceded the P-wave by 38 ± 11 (range 10-60) milliseconds, and AT termination was obtained after a mean RF energy time of 10 ± 8 (range 2-31) seconds. CONCLUSION: A characteristic narrow and biphasic (-/+) or triphasic (+/-/+) P-wave in the inferior and precordial leads reliably identifies the group of AT arising from the para-Hisian region.