BackgroundMechanisms and electropharmacological characteristics in adult patients with atrial tachycardia (AT) are not well described. We proposed that a combination of electropharmacological characteristics, recording of monophasic action potential, and effects of radiofrequency ablation could further determine the mechanisms and achieve a new classification in adults with various types of AT because they were important in regard to the correlation between mecha-nisms and pathophysiology, clinical syndrome, and responses to specific pharmacological or nonpharmacological therapies.Methods and ResultsThirty-six patients (11 female, 25 male; mean age, 57±13 years) with AT were referred for electropharmacological studies and radiofrequency ablation. Resetting response pattern, entrainment phenomenon, recording of monophasic action potential, serial drug test, response to Valsalva maneuver, endocardial mapping technique, and radiofrequency ablation were performed. Seven patients had automatic AT provocable with isoproterenol; neither initiation nor termination was related to programmed electrical stimulation. The other 29 patients had AT initiated or terminated by electrical stimulation and mechanisms related to triggered activity or reentry; nine of them needed isopro-terenol to facilitate initiation of AT, associated with delayed afterdepolarization in monophasic action potential. All responded to adenosine (15 to 60 μg/kg) and Valsalva maneuver. Dipyridamole terminated AT and decreased the slope of afterdepolarization. Afterdepolarization was not found in the patients with automatic or reentrant AT. In 40 of 41 (98%), AT was ablated successfully, with late recurrence in 2 of 40 (5%) (follow-up, 18±4 months).ConclusionsThis study demonstrates the diverse mechanisms and electropharmacological characteristics of AT in adults. Furthermore, radiofrequency ablation of various types of AT could achieve high success and low recurrence rates.