Surgical significance of morphological variations in the atrial septum in atrioventricular septal defect for determination of the site of penetration of the atrioventricular conduction axis

Introduction to the Congenital Heart Defects: Anatomy of the Conduction System

The position and course of the conduction system in congenital heart disease are intricately tied to the underlying congenital malformation. Although only subtle differences exist between the anatomy of the conduction axis for simple congenital heart lesions and normal anatomy, almost every patient with congenital heart disease harbors some important anatomic variation. This article summarizes the body of literature by retaining original classical concepts and by attempting to translate the available knowledge into useful points for the congenital heart disease specialist. This discussion spans the entire spectrum of simple to complex congenital heart disease.

Development of the cardiac conduction system in atrioventricular septal defect in human trisomy 21

In patients with atrioventricular septal defect (AVSD), the occurrence of nonsurgical AV block has been reported. We have looked for an explanation in the development of the AV conduction system. Human embryos with AVSD and trisomy 21 and normal embryos were examined (age 5-16 wk gestation). Antibodies to human natural killer cell-1 (HNK-1), muscle actin (HHF-35), and collagen VI were used to delineate the conduction system. As in normal hearts, HNK-1 transiently stains the AV conduction system, the sinoatrial node, and parts of the sinus venosus in AVSD. A large distance is present between the superior and inferior node-like part of the right AV ring bundle, comparable to 6-wk-old normal hearts. The definitive inferior AV node remains in dorsal position from 7 wk onward and does not appose to the superior node-like part as seen in normal hearts. Furthermore, in AVSD, a transient third HNK-1-positive "middle bundle" branch that is continuous with the retroaortic root branch and the superior node-like part can be identified, and thus the AV conduction system forms a figure-of-eight loop. At later stages, the AV node remains in dorsal position close to the coronary sinus ostium with a long nonbranching bundle that runs through thin fibrous tissue toward the ventricular septum. The formation of the AV node and the ventricular conduction system in AVSD and Down syndrome differs from normal development, which can be a causative factor in the development of AV conduction disturbances.