The dissection of the atrioventricular node, bundle and bundle branches in the human heart.

The A-V node, bundle and bundle branches were grossly dissected in 41 human hearts. The method for this dissection is described. Given also are the sizes of the individual structures with advancing age. These structures grow more slowly than the remainder of the myocardium. T HE dissectability of the A-V node, bundle, and bundle branches in the human heart has been questioned. Retzer1 originally performed the dissection, which was confirmed by Tawara,2 Keith and Flack,3 Curran,4 Walls,5 and Kistin.6 On the other hand, Holmes7 and Mahaim8 doubted its dissectability, and Glomset and Glomset's9 and Glomset and Birge's10 description of the gross dissection varied from that of other authors. Accordingly, we undertook to dissect these structures in man and to study their gross morphology in various age groups. MATERIAL AND METHOD OF DISSECTION Forty-one formalin-fixed hearts of various ages, exhibiting no evidence of pathologic change, were dissected as indicated in the accompanying table 1, by the following method of dissection: The pars membranacea is first inspected as to its anatomy. The pars membranacea normally consists of two parts: (1) an atrioventricular part, between the right atrium and left ventricle, and (2) an inter-ventricular part. The relative sizes of these two parts varies markedly. The pars membranacea is roughly triangular, with proximal, distal and superior angles. At the proximal angle the central fibrous body is palpated. The coronary sinus, limbus, eustachian valve, medial tricuspid leaflet, septal band of the crista supraventricularis, muscle bundle of Lancisi, and moderator band are identified (fig. lA). The chordae tendineae of the medial part of the anterior tricuspid leaflet are now cut and these portions of leaflet detached at their ring base and from the pars membranacea and central fibrous body (fig. iB). The atrial endocardium is removed from the region bounded by the eustachian valve, the coronary sinus, and the denuded valve ring attachment. This reveals a thin sheet of muscle cours-ing obliquely or at right angles to the base of the tricuspid valve. After cutting, the A-V node becomes evident, embedded in a varying amount of fat in the adult (not present in the child). Fat tissue posterior to this area is removed, revealing the ramus septi fibrosi coursing from its origin in the right (occasionally the left) coronary artery to enter the region of the node (fig. 2E). The right layer of the posterior aspect of the pars membranacea (near its junction with the …