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 North American Society of Pacing and electrophysiology

Atrial tachycardias are regular atrial rhythms at a constant rate ≥ 100 beats, min-1 originating outside the sinus node region. The mechanism can be focal or macroreentrant. Electrocardiographically, flutter refers classically to a pattern of regular tachycardia with rate ≥ 240 beats, min-1 (cycle length ≤ 250 ms) lacking an isoelectric baseline between deflections. Neither rate nor lack of isoelectric baseline are specific of any tachycardia mechanism. Focal atrial tachycardia is characterized by origin of activation from a circumscribed area with centrifugal spread to both atria. It can be due to enhanced automaticity, triggered activity or microreentry (very small reentry circuits). Inappropriate sinus tachycardia is a form of atrial tachycardia originating along the superior aspect of the crista terminalis (in the 'sinus node region') at rates above the physiological range, but with no relationship to metabolic or physiological demands. Macroreentrant atrial tachycardia is an atrial tachycardia due to a reentry circuit of large size with fixed and/or functional barriers. These circuits can be entrained during atrial pacing. Well characterized macroreentrant atrial tachycardias include Typical atrial flutter Reverse typical atrial flutter Lesion macroreentrant tachycardia Lower loop flutter Double wave reentry Right atrial free wall macroreentry without atriotomy Left atrial macroreentrant tachycardia Atypical atrial flutter is only a descriptive term for an atrial tachycardia with an ECG pattern of continuous undulation of the atrial complex, different from typical or reverse typical flutter, at a rate ≥ 240 beats, min-1. If the mechanism can be elucidated, either through conventional mapping and entrainment, or with special multipoint mapping techniques, description of the mechanism should accompany the term atypical flutter, otherwise it should be stated that the mechanism is unknown.