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

Abstract

Time for primary review 23 days. There has been a long recognized clinical interrelationship between atrial flutter and atrial fibrillation. Patients who primarily manifest atrial flutter commonly also experience atrial fibrillation and vice versa [1,2]. Both are very common as a temporary atrial tachyarrhythmia shortly after open heart surgery, and often in the same patient [3]. And some antiarrhythmic agents, notably class IC drugs, IA drugs and amiodarone, used to suppress atrial fibrillation not uncommonly ‘convert’ recurrences of atrial tachyarrhythmia to atrial flutter [4–6]. Are these clinical associations mere coincidences, or do they reflect an important underlying similar pathophysiology and even similar mechanism(s)? Data derived largely from a series of unconnected studies in animal models and patients seemingly point to a clear interrelationship between the two, suggesting, if not indicating, that they are two sides of a coin. Classical atrial flutter, now called typical and reverse typical atrial flutter [7], is well recognized to be due to a macro-reentrant mechanism, in which the reentrant wave front travels up the inter-atrial septum and down the right atrial free wall or vice versa, respectively [1,7]. Critical to the development and maintenance of this reentrant circuit are the lateral boundaries, one being fixed (anatomic), the tricuspid valve annulus, and the other almost always being functional, a line of block between the venae cavae. We shall develop the theme that one of the fundamental features that determines whether an atrial tachyarrhythmia becomes sustained atrial flutter or atrial fibrillation is the development of the line of block between the venae cavae. We shall also develop the theme that another of the fundamental features that determine whether the atrial tachyarrhythmia becomes atrial flutter or atrial fibrillation often will be the atrial flutter cycle length, i.e. the cycle length of a stable … * Tel.: +1-216-844-7690; fax: +1-216-844-7196 alw2{at}po.cwru.edu