Basic Mechanisms of Atrial Fibrillation and Atrial Flutter

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Abstract
Basic mechanisms of atrial fibrillation and atrial flutter are considered. Experimental data support the concept that atrial fibrillation is due to multiple, simultaneously circulating reentrant wave fronts of the leading circle type. Studies of atrial fibrillation in patients have been limited, but are consistent with this notion. Atrial flutter is generally accepted as being due to reentry. Several reentrant mechanisms of atrial flutter are discussed, principally in experimental animal models. Atrial flutter may result from atrial lesions that, depending on their extent, cause circulation of the reentrant wave front either around the lesion or around the tricuspid valve annulus. In addition, atrial flutter can result from a functionally determined reentrant circuit in the free wall of the right atrium. Studies in patients suggest that atrial flutter most often is due to reentrant excitation in the right atrium, with the atrial flutter reentrant wave front traveling in a caudocranial direction in the atrial septum and in a craniocaudal direction in the right atrial free wall. Furthermore, the reentrant circuit seems to revolve around an anatomical (inferior vena cava) and functional (atrial septum) obstacle and has at least one area of slow conduction located inferiorly in the reentrant circuit, probably in the area of the coronary sinus orifice. (Cardiol Rev 1993;1:16-23)

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