Fig. 3.

The major intra-atrial routes at the posterior aspect of the atrial wall. These routes are broad bands or sheets as shown in (C), although they are shown as lines in (A) and (B) to demonstrate the shape of the atrial wall. (A) Posterior aspect of the left atrium (LA). This part is covered by visceral pericardium at the oblique sinus of the pericardium. The branches of the left part of Bachmann’s bundle merge at the posterior wall along with the branches of the middle inter-nodal routes. (B) The posterior wall of the LA shows approaches from inter-nodal routes #1-3. The distal part of L-3 is close to the coronary sinus (CS). The inter-nodal route from the crista terminalis (#3) approaches the atrioventricular node, and the third branch of the first inter-nodal route (#1-3) also approaches the posterior aspect. (C) Myocardial bundles from 3 different routes of the inter-nodal tracts form complex circles at the left atrial wall. Three branches of Bachmann’s bundle (L-1, L-2, L-3), branches of the middle route (#2-2, #2-3), and a branch of the posterior route along the CS join at the left atrial wall, and pulmonary venous orifices are in the center of each circle. Fig. 3B is modified from the authors’ previous publication [25]. Ao, aorta; PT, pulmonary trunk; LAA, left atrial appendage; LUPV, left upper pulmonary vein; RUPV, right upper pulmonary vein; IVC, inferior caval vein; RLPV, right lower pulmonary vein; SVC, superior caval vein; RA, right atrium.