Mechanisms of atrial flutter and atrial fibrillation: distinct entities or two sides of a coin?

1. Introduction fundamental features that determine whether the atrial tachyarrhythmia becomes atrial flutter or atrial fibrillation There has been a long recognized clinical interrelation-often will be the atrial flutter cycle length, i.e. the cycle ship between atrial flutter and atrial fibrillation. Patients length of a stable atrial reentrant circuit which develops. If who primarily manifest atrial flutter commonly also exit is critically short, it will create fibrillatory conduction perience atrial fibrillation and vice versa [1,2]. Both are and clinical atrial fibrillation; if it is sufficiently long, it very common as a temporary atrial tachyarrhythmia shortly will result in 1:1 activation of the atria by the reentrant after open heart surgery, and often in the same patient [3]. circuit, with resulting clinical atrial flutter. Critical to the And some antiarrhythmic agents, notably class IC drugs, latter consideration is the increasing recognition that atrial IA drugs and amiodarone, used to suppress atrial fibrilla-flutter may be due to macroreentrant circuits which are tion not uncommonly 'convert' recurrences of atrial tach-different than that responsible for typical and reverse yarrhythmia to atrial flutter [4–6]. Are these clinical typical atrial flutter [8–11]. associations mere coincidences, or do they reflect an important underlying similar pathophysiology and even similar mechanism(s)? Data derived largely from a series 2. The mechanism of classical atrial flutter—the of unconnected studies in animal models and patients importance of block between the venae cavae seemingly point to a clear interrelationship between the two, suggesting, if not indicating, that they are two sides of On the basis of studies in experimental animals and on a coin. vector analysis of electrocardiograms in humans, Lewis Classical atrial flutter, now called typical and reverse and colleagues [12] concluded that atrial flutter was the typical atrial flutter [7], is well recognized to be due to a result of circus movement in the atria. Their experimental macro-reentrant mechanism, in which the reentrant wave studies included mapping (quite limited) of induced atrial front travels up the inter-atrial septum and down the right flutter in normal canine atria (Fig. 1) [12]. From these atrial free wall or vice versa, respectively [1,7]. Critical to studies, Lewis and colleagues [12] concluded that atrial the development and maintenance of this reentrant circuit flutter was due to reentry around their great veins. But are the lateral boundaries, one being fixed (anatomic), the Lewis had great difficulty inducing atrial flutter in the tricuspid valve annulus, and the …