A classification of atrial flutter and regular atrial tachycardia according to electrophysiological mechanisms and anatomical bases. A Statement from a Joint Expert Group from the Working Group of Arrhythmias of the European Society of Cardiology and the

Current classifications of regular atrial tachycardias have been based exclusively on the ECG. Differentiation between atrial flutter and atrial tachycardia depends on a rate cut-off around 240–250/min and the presence of isoelectric baselines between atrial deflections in atrial tachycardia, but not in atrial flutter. However, atrial tachycardia mechanisms, defined by electrophysiological studies and radiofrequency catheter ablation, do not correlate with electrocardiographic (ECG) patterns as defined currently, and a certain amount of confusion is evident in the literature at the time of assigning appropriate terms to specific arrhythmias. The current ECG classification is obsolete for this purpose, creating the need for a mechanistic classification of atrial tachycardias. Terms and definitions employed were not very important when only electrical cardioversion and/or empirical antiarrhythmic drug therapy were available. Unfortunately, knowledge of the electrophysiological properties of the atrial tachycardia mechanism is still too incomplete to guide antiarrhythmic drug choice, and selective drugs are not available to effectively target each tachycardia mechanism and component. However, radiofrequency ablation offers specific