The AV junction region of the heart: A comprehensive study correlating gross anatomy and direct three-dimensional analysis. Part I. Architecture and topography

Abstract

There is little detailed knowledge of the architecture of the AV junction region, the cytoarchitecture of the AV node or of its atrial connections. In the present study, the gross anatomy and topography of intracardiac structures in 21 adult canine hearts were photographically compared in whole and dissected hearts and tissue blocks and serial histologic sections made in three orthogonal planes. There are seven major new findings: 1) A coronary sinus fossa exists at the crux of the heart. It separates the right medial atrial wall (MAW) superoposterior region from the left atrium, its floor is the coronary sinus, and it carries the medial atrionodal bundle and proximal AV bundle on its right wall. 2) The posterior MAW forms two isolated bridges of myocardium as it surrounds the coronary sinus ostium, is isolated from the sinus venarum with crista terminalis and interatrial septum-by the floor of the inferior vena cava, and the narrow bridges link the posterior atrial wall to the mid MAW. 3) The tendon of Todaro has both epicardial and endocardial exposures, terminates in the superoposterior MAW and its medial aspect is adjacent sequentially to the medial atrionodal bundle and proximal AV bundle. 4) Only ordinary myocardium contacts the anulus fibrosus. 5) The ventricular septum's shoulder is humped shape posteriorly, is completely overlaid by anular myocardium and the medial leaflet and is joined by struts of papillary muscle. 6) The membranous septum joins the anterior ventricular septum to the crista supraventricularis, forms part of the posterior noncoronary and right aortic valve sinus walls and encases the right bundle branch. 7) The specialized conduction tissues, the superior, medial and lateral atrionodal bundles, the proximal AV bundle, AV node, distal AV bundle and right bundle branch are subjacent to MAW epicardium outside the right atrium, share regular intracardiac relationships with topographic landmarks and the medial atrionodal bundle, terminal superior atrionodal bundle, the proximal AV bundle and AV node are aligned to the medial leg of Koch's triangle. Thus, atrial myocardium of the AV junction region is that of the MAW. The floor of the inferior vena cava forms a natural barrier to impulse transmission along the full extent of the posterior MAW. The specialized tissues are outside of the MAW. Anatomic landmarks form reliable topographic landmarks for the specialized AV junction region tissues. A knowledge of the association of the specialized conduction tissues with specific regions of the MAW is useful in localizing the tissues and along with the coronary sinus fossa provides several extracardiac approaches.

The AV junction region of the heart: a comprehensive study correlating gross anatomy and direct three-dimensional analysis. Part II. Morphology and cytoarchitecture

“…The Animal Care and Use Committee of Northwestern University approved the protocols for animal and tissue use. Preparation of the hearts was as previously described (55). In brief, the hearts were excised and the right atrium was exposed by using a ventrolateral incision through the AV groove, ventrolateral atrial wall, and superior vena cava.…”

“…1), parallel to the endocardial surface (5 hearts), perpendicular to (4 hearts), or transverse to the long axis of the AV junction region (2 hearts) (see Table 1 in Ref. 55). All sections were mounted on glass microscope slides and selected sections were stained with one of the following: Goldner Trichrome, Mason Trichrome, Verhoff Elastica or hematoxylin-phloxine-safran.…”

“…Photomicrographs of a 0.1-mm ruler, taken at the same magnification, were used for measurements within photomicrographs of the histological sections. Photographs of 10 additional hearts in various stages of dissection described in Part I (55) were studied compared with photographs of the gross hearts used for orthogonal sectioning and photomicrographs of the serial sections. Abbreviations of new terms are listed in Table 1.…”

“…2E in Ref. 55). Figures 2-4 show serial sections of the AV junction region in the three orthogonal planes at regular intervals of ϳ0.25 mm for parallel ( Fig.…”

“…Part I (55) detailed aspects of the gross anatomy and topography. In Part II, details of the histology are presented.…”