Atriofascicular Accessory Pathways
Uncommon accessory pathways presenting decremental properties and inserting into the right ventricle have been described as Mahaim pathways, and these fibers are distinct form of preexcitation. Those anomalous pathways are subdivided into three types, and
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29
Yukio Sekiguchi
Keywords
Atriofascicular pathway • Mahaim fiber • Paroxysmal supraventricular tachycardia
29.1 Introduction Around 1940, Mahaim firstly reported the existence of Mahaim fibers which connected His bundle or the atrioventricular node to the ventricle anatomically [1–3]. Although some reports were published about these fibers after his report, no one knew the electrophysiological characteristics of them at that time. In 1975, Lev et al. described that Mahaim fibers histologically passed from the atrioventricular node to the left and to the right side of the posterior ventricular septum [4], and these pathways might play a role in the genesis of the preexcitation [5, 6]. In same year, Anderson proposed that Mahaim fibers might be classified into two anatomical types [7]. One was nodoventricular (NV) fibers connecting between the atrioventricular node and the ventricle, and the other was fasciculoventricular (FV) fibers connecting between the His bundle or the bundle branches and ventricle. However, there were rare cases having NV fibers or FV fibers, and the demonstration of reentrant circuit during reciprocating tachycardias might be difficult [6, 8]. In 1988, Tchou proposed that an accessory pathway which behaved a typical NV fiber actually arose directly from the right atrium and inserted into the right bundle branch, named as atriofascicular accessory pathway [9]. Many data have supported this proposal [10–12], and most accessory pathways with anterograde decremental conduction properties referred to as Mahaim fibers have been recognized as originating from the right lateral atrium in these days. Y. Sekiguchi, M.D. Cardiovascular Division, Faculty of Medicine, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8575, Japan e-mail: [email protected]
29.2 C lassification of Mahaim Fibers in Cardiac Arrhythmias Uncommon accessory pathways presenting decremental properties and inserting into the right ventricle have been frequently described as Mahaim pathways, and these fibers are distinct form of preexcitation. Recently, these anomalous pathways are subdivided into three types (Fig. 29.1), and it is said that most of those pathways in fact originate from the right atrial free wall near the tricuspid annulus and terminate in the distal right bundle branch, which is called as atriofascicular pathways. The most important feature in Fig. 29.1 is that the circuit of atriofascicular pathway includes right atrial muscle, in contradistinction to other circuit of Mahaim pathways. By using this feature, atriofascicular pathways can be ruled out of other Mahaim pathways. The differential diagnosis between atriofascicular pathway and other Mahaim pathways are noted in the following section. This Fig. 29.1 also indicates that Mahaim fibers including atriofascicular pathways can play a role of only anterograde pathway when macro reentrant reciprocating tachycardia occurs. These pathways typically conduct only in the anterograde direction.
29.3 Electrocardiographic Characteristics of Atriof
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