Posterior extensions of the human compact atrioventricular node: a neglected anatomic feature of potential clinical significance.

BACKGROUND: Catheter ablation procedures have revived interest in the detailed anatomy of the specialized atrioventricular (AV) septal junctional area. The compact AV node usually is considered to have a blunt posterior end. The objective of this study was to reconstruct the human compact AV node in relation to the landmarks of Koch's triangle, with emphasis on its posterior extension. METHODS AND
RESULTS: In 21 hearts obtained from autopsies, the AV nodal septal junctional area was removed en bloc, serially sectioned, and reconstructed. None of the hearts showed a blunt posterior ending of the compact AV node; 13 showed posterior extensions on both the right and left sides; 7 had a rightward posterior extension only; and 1 heart showed a single leftward extension. Hence, a rightward posterior extension was present in 20 of 21 hearts. Furthermore, in 16 of these 20 hearts, the rightward extension continued to the level of the coronary sinus ostium; in 7, the bundle extended beyond this anatomic landmark. The mean length of the right posterior extension was 4.4+/-2.0 mm; that of the leftward posterior extension was 1.8+/-0.9 mm. Superimposed onto the slope of the muscular AV septum, viewed from the right atrium, the rightward extension ran close to the tricuspid annulus with the leftward extension positioned superiorly.
CONCLUSIONS: The human compact AV node contains rightward and leftward posterior extensions, with the right extension close to the tricuspid annulus. It is tempting to speculate that these extensions are involved in "slow pathway" conduction.