The atrioventricular conduction system in persistent common atrioventricular canal defect: correlations with electrocardiogram.

SUMMARY Serial histologic sections of the atrioventricular (A-V) conduction system were studied in four hearts with persistent common A-V canal, and the anatomic findings were related to the abnormal ECG pattems. Two hearts were examples of the partial form and two of the complete form of A-V canal. The major anatomic abnormalities were: (1) postero-inferior displacement of the A-V node; (2) relatively short distances between the A-V node and the origin of the left bundle branching; (3) marked postero-inferior displacement of the left bundle branching system; and (4) relative hypoplasia of the anterior (superior) left bundle branches. The anatomic configuration of the A-V conduction system in A-V canal could result in relatively early impulse propagation to the posterior aspect of the ventricular septum as suggested by reported electrophysio-logic studies. The anatomic findings are considered to be related closely to the known ECG patterns of A-V canal. Congenital heart disease T HE ELECTROCARIOGRAPHIC (ECG) and vectorcardiographic (VCG) patterns in patients with persistent common atrioventricular canal defects (A-V canal) are considered to be distinctive in the presence of a fully developed left ventricle.1-5 Although these pattems were once thought to be the result of left ventricular hypertrophy, experimental evidence6-9 suggests that they are the result of anomalous A-V conduction which might be related to anatomic abnormalities in the A-V conduction system. In this Left bundle branches study, the morphologic configuration of the A-V conduction system of-heArts with either partial or complete forms of A-V canal'0 was studied in an effort to determine whether anatomic characteristics could be associated with the known electrophysiologic abnormalities. Methods Four examples of A-V canal were studied; two were the partial form and two were the complete form. In all four instances, schematic analysis of the scalar ECG revealed a superiorly oriented counterclockwise QRS loop or a figure-of-eight QRS loop lying on the isoelectric line in the frontal plane, the initial portion of which was counterclockwise in direction (fig. 1).