Classification of atrial flutter and regular atrial tachycardia according to electrophysiologic mechanism and anatomic 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

Regular atrial tachycardias classically are classified into flutter or tach ycardia, depending on the rate and presence of a stable baseline on the EGG . However, current understanding of electrophysiology atrial tachycardias m akes this classification obsolete, because it does not correlate with mecha nisms, The proposed classification is based on electrophysiologic mechanism s, defined by mapping and entrainment, Radiofrequency ablation of a critica l focus or isthmus can afford proof. Focal tachycardias are characterized b y radial spread of activation and endocardial activation not covering the w hole cycle. Ablation of the focus of origin interrupts the tachycardia. The mechanism of focal firing is difficult to ascertain by clinical methods. M acroreentrant tachycardias are characterized by circular patterns of activa tion that cover the whole cycle. Fusion can be shown during entrainment on the ECG or by multiple endocardial recordings. Ablation of a critical isthm us interrupts the tachycardia. Macroreentry can occur around normal structu res (terminal crest, eustachian ridge) or around atrial lesions. The anatom ic bases of these tachycardias must be defined, to guide appropriate treatm ent. Atria flutter is a mere description of continuous undulation on the EG G, and only some strictly defined typical flutter patterns correlate with r ight atrial macroreentry bounded by the tricuspid valve, terminal crest, an d caval vein orifices. This classification should be considered open, as so me classically described tachycardias, such as reentrant sinus tachycardia, inappropriate sinus tachycardia, and type II atrial butter, cannot be clas sified accurately. Furthermore, the possibility of fibrillatory conduction makes the limits with atrial fibrillation still ill defined.