Left atrial impulse formation in atrial flutter.

Although the underlying mechanism of atrial flutter has not yet been conclusively determined (Katz and Pick, 1960), the available evidence in-creasingly favours the "unifocal " versus the "circus movement " theory (Beilet, 1963). While this arrhythmia may be produced experimentally by an appropriate stimulation of any atrial area (Scherf, Blumenfeld, and Yildiz, 1963), the precise location of the discharging focus in clinical in-stances of flutter remains hypothetical. Data per-taining to this problem derive essentially from theoretical considerations based on the direction of P waves as recorded in the limb and cesophageal leads. Thus, it is held that in the "common type" of flutter, characterized by inverted P waves in leads II, II, and aVF, the impulses originate in the caudal region of the atria (Prinzmetal et al., 1952), most probably in the atrio-ventricular (A-V) node