REVIEW Atrial Tachycardias Encountered in the Context of Catheter Ablation for Atrial Fibrillation Part II: Mapping and Ablation S ´ EBASTIEN KNECHT, M.D.,*,† GEORGE VEENHUYZEN, M.D.,‡ MARK D. O’NEILL, M.B.B.CH., D.PHIL.,* MATTHEW WRIGHT, M.B.B.S., PH.D.,* ISABELLE NAULT, M.D.,* RUKSHEN WEERASOORIYA, M.B.B.S.,* SHINSUKE MIYAZAKI, M.D.,* FR ´ ED ´ ERIC SACHER, M.D.,* M ´ EL ` EZE HOCINI, M.D.,* PIERRE JA ¨ IS, M.D.,* and MICHEL HA ¨ ISSAGUERRE, M.D.* From the *Hˆ opital Cardiologique du Haut-L´ evˆ eque and the Universit´ e Victor Segalen Bordeaux II, Bordeaux, France; †CHU Brugmann, Bruxelles, Belgique; and ‡Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada Over the past decade, there has been an exponential increase in the number of catheter ablation procedures performed for atrial fibrillation (AF). While for paroxysmal AF, proximal pulmonary vein isolation is sufficient in the majority of cases, ablation of persistent and longstanding AF requires an extensive surgical-like procedure. This approach is correlated with a high rate of AF termination; however, this is achieved at the cost of at least one atrial tachycardia (AT) during the index procedure or during the patient’s follow-up in the vast majority of cases. As these ATs are often multiple, complex, and frequently more symptomatic than AF, they constitute the last and frequently the most difficult step in ablation for patients with persistent AF. This review concentrates on the practical approaches to the treatment of AT in the context of AF ablation and provides an algorithm that aims at facilitating mapping and ablation strategies using conventional electrophysiological tools. (PACE 2009; 32:528–538) atrial tachycardia, electrophysiology-clinical, ablation, mapping, atrial fibillation Introduction Over the past decade, as our understanding of some of the mechanisms underlying atrial fibril- lation (AF) has improved, there has been an ex- ponential increase in the number of ablation pro- cedures performed for this indication. While for paroxysmal AF, proximal pulmonary vein (PV) isolation is sufficient in most cases, 1–4 ablation of persistent and longstanding AF is associated with an extensive surgical-like procedure. 5–8 This extensive ablation approach is associated with a high rate of AF termination and long-term mainte- nance of sinus rhythm; however, this is at the cost of at least one atrial tachycardia (AT) during the index procedure or during the patient’s follow-up in the vast majority of cases. 9–12 These ATs are of- ten resistant to antiarrhythmic medication and fre- quently more symptomatic than the original AF. Additionally, they tend to be multiple and com- Address for reprints: S´ ebastien Knecht, M.D., Service de Ryth- mologie, H ˆ opital Cardiologique du Haut-L´ evˆ eque, Avenue de Magellan, 33604 Bordeaux-Pessac, France. Fax: 33-5-57-65-65- 09; e-mail: sebastien.knecht@chu-brugmann.be Received September 16, 2008; revised October 28, 2008; ac- cepted November 2, 2008. plex, and as such they constitute the final frontier in ablation of persistent AF. This review focuses on the practical approach of AT in the context of previous AF ablation, and provides an algorithm that aims at facilitat- ing mapping and ablation strategies using conven- tional electrophysiological tools. Definitions: AT or AF? The distinction between AT and AF can gen- erally be easily discerned from the 12-lead elec- trocardiogram (ECG). During AT, a monomorphic regular P wave is present, while during AF there is variation of the P-wave morphology and cy- cle length, even during “organized” AF. 13 If any doubt persists after ECG analysis, three catheters (at least) are required to differentiate between these arrhythmias during the electrophysiological study: one in the right atrium, one in the left atrium (LA), and one in the coronary sinus (CS). AF can be defined by beat-to-beat variability in cycle length and morphology, whereas AT behaves as a 100% consistent organized atrial rhythm and endocar- dial activation sequence in both atria. While the distinction between “disorganized AF” and AT is obvious, the main difficulty resides in the distinc- tion between “organized AF” and AT, which is C 2009, The Authors. Journal compilation C 2009 Wiley Periodicals, Inc. 528 April 2009 PACE, Vol. 32