The Anatomy of the Atrioventricular Conduction System in Ventricular Septal Defect and Tetralogy of Fallot: Correlations with the Electrocardiogram and Vectorcardiogram

Abstract

The atrioventricular conduction system was studied by a technique of selected serial histological sections in examples of tetralogy of Fallot and ventricular septal defect to correlate the anatomic findings observed with the electrophysiological findings as manifested by the vectorcardiographic pattern. Eight hearts were studied; two examples of each anomaly had electrocardiographic and VCG patterns in the frontal plane similar to A-V canal defects and two examples of each had ECG and VCG patterns usually associated with these lesions. Of the four examples of tetralogy, the two examples with VCG patterns similar to the A-V canal pattern differed from the other examples in that the distance between the A-V node and the origin of left bundle branching was shorter and the fibers destined to become the right bundle branch took an elongated course. The VSD examples offered less striking differences. A short distance from the A-V node to the onset of left bundle branching was seen in both examples with VCG patterns similar to the A-V canal pattern, but one example of VSD with a representative VCG pattern had a similar anatomic configuration. When measurement ratios were compared, the right bundle took its origin at a relatively greater distance from the A-V node in the examples with VCG patterns similar to the A-V canal pattern. The anatomic configuration of those examples of tetralogy and VSD with VCG patterns similar to the A-V canal pattern was such that relatively early conduction to the left bundle branch system could occur.