Critical Assessment of the Concepts and Misconceptions of the Cardiac Conduction System over the Last 100 Years: The Personal Quest of Robert H. Anderson

Figures

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  Figure 1. Atrioventricular node and penetrating bundle: The histological sections, stained using the trichrome technique, show the features of the atrioventricular node (A) and the insulation provided to produce the penetrating atrioventricular bundle (B). The sections were made using an adult human heart.

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  Figure 2. The compact node and the last connection: The sections, again stained using the trichrome technique, show the last connections to the atrioventricular node from the central part of the atrial septum (A) as opposed to the mitral vestibule (B). The section shown in Panel A is from the same series of sections as shown for the atrioventricular node and penetrating bundle in Figure 1. Both sections are taken from adult human hearts.

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  Figure 3. Nodo-ventricular and fasciculo-ventricular pathways: The sections are again stained using the trichrome technique. (A) shows a nodo-ventricular connection in an infant human heart, while (B) shows multiple fasciculo-ventricular connections in an adult human heart.

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  Figure 4. Nodo-ventricular and fasciculo-ventricular pathways: Both sections were taken from human hearts shown at autopsy to exhibit Ebstein’s malformation. (A) shows a direct nodoventricular connection between the inferior rightward extention of the atrioventricular (AV) node and the crest of the ventricular septum, while (B) shows a fasciculo-ventricular connection given off from the conduction axis prior to the origin of the right bundle branch. The sections were stained using the trichrome technique.

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  Figure 5. Mönckeberg and Aschoff’s criteria for a conducting tract: The histological section shows the crest of the ventricular septum in a human heart stained using the trichrome technique. The right bundle branch is insulated by a sheath of fibrous tissue, colored green. This makes it possible to distinguish the bundle from the adjacent myocardium, and follow the bundle in serial sections. Thus, the structure satisfies all of the criteria established by Mönckeberg and Aschoff [3,4] for recognition as a conducting tract.

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  Figure 6. Absence of specialized tracts within atrial walls: The section is taken from a human of 35 weeks. It shows the entirety of the walls of the right atrium, with the section again stained using the trichrome technique. Even at the low power of magnification used to show the features of the right atrium, it is possible to recognize the tail of the sinus node and the atrioventricular node. The atrial walls, however, do not contain any insulated tracts comparable to the right bundle branch (see Figure 5). Only when assessing the entirety of the atrial myocardium in this fashion, using serial histological sections, is it justifiable to draw any conclusions regarding the presence or absence of “specialized” tracts responsible for conduction. When using the criteria established by Mönckeberg and Aschoff [3,4], which retain their validity for histological studies, examination of serial sections shows that there are no such tracts.