SUSTAINED ATRIAL TACHYCARDIA IN ADULT PATIENTS - ELECTROPHYSIOLOGICALCHARACTERISTICS, PHARMACOLOGICAL RESPONSE, POSSIBLE MECHANISMS, AND EFFECTS OF RADIOFREQUENCY ABLATION

Background Mechanisms and electropharmacological characteristics in ad ult patients with atrial tachycardia (AT) are not well described. We p roposed that a combination of electropharmacological characteristics, recording of monophasic action potential, and effects of radiofrequenc y ablation could further determine the mechanisms and achieve a new cl assification in adults with various types of AT because they were impo rtant in regard to the correlation between mechanisms and pathophysiol ogy, clinical syndrome, and responses to specific pharmacological or n onpharmacological therapies. Methods and Results Thirty-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 act ion potential, serial drug test, response to Valsalva maneuver, endoca rdial mapping technique, and radiofrequency ablation were performed. S even patients had automatic AT provocable with isoproterenol; neither initiation nor termination was related to programmed electrical stimul ation. The other 29 patients had AT initiated or terminated by electri cal stimulation and mechanisms related to triggered activity or reentr y; nine of them needed isoproterenol to facilitate initiation of AT, a ssociated with delayed afterdepolarization in monophasic action potent ial. All responded to adenosine (15 to 60 mu g/kg) and Valsalva maneuv er. Dipyridamole terminated AT and decreased the slope of afterdepolar ization. Afterdepolarization was not found in the patients with automa tic or reentrant AT. In 40 of 41 (98%), AT was ablated successfully, w ith late recurrence in 2 of 40 (5%) (follow-up, 18+/-4 months). Conclu sions This study demonstrates the diverse mechanisms and electropharma cological characteristics of AT in adults. Furthermore, radiofrequency ablation of various types of AT could achieve high success and low re currence rates.