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

Abstract

IN RECENT YEARS the morphological features of the major portions of the atrioventricular (A-V) conduction system of human hearts that were afflicted with various congenital anomalies have been described. [1][2][3][4][5][6] These reports have contrasted the anatomy of the A-V conduction system in examples of ventricular septal defect (VSD) and tetralogy of Fallot with that configuration found in defects of the persistent atrioventricular (A-V) canal type.7 8The vectorcardiographic (VCG) pattern found in the A-V canal has been considered to be characteristic.9-12 It is now known, however, that various congenital heart defects have a similar vectorcardiographic pattern, including occasional examples of VSD and tetralogy of Fallot.13-l5 Therefore, a study was made of the morphology of the A-V conduction system in instances of VSD and tetralogy of Fallot that had frontal plane VCG patterns similar to those usually found in the A-V canal. An effort was made to find a characteristic or characteristics of the anatomy of the conduction system that might be associated with the unusual VCG pattern observed in these examples. Material Tetralogy of Fallot Of 78 examples of tetralogy in which autopsy was performed from 1958 through 1962, five (6.4%) were associated with preoperative VCG From the Mayo Clinic and Mayo Foundation, Rochester, Minnesota. This investigation was supported in part by Training Grant HTS-5515 from the National Institutes of Health, U. S. Public Health Service. patterns similar to the A-V canal pattern, that is, an initially counterclockwise QRS loop in the frontal plane with the mean axis directed superiorly and to the left (fig. 1A). Two of these cases were studied; these were designated cases Al and A2. Two other examples of tetralogy (cases A3 and A4), which had VCG patterns more representative of tetralogy, also were studied (fig. 1C). None of the four examples selected had ventricular septal defects of the A-V canal type.8 The defects in all four cases were located in similar positions in the ventricular septum. Ventricular Septal Defect Seventy-nine examples of isolated VSD of the usual type came to autopsy from 1958 through 1962. Seven of the 79 (8.9%) had preoperative VCG patterns similar to the A-V canal pattern and two of these (cases Bi and B2) were studied (fig . 1B). Two other examples (cases B3 and B4) in which the VCG patterns were more typical of VSD also were studied ( fig. 1D). None of these four examples had the morphological features of VSD of the A-V canal type.8 Methods The morphology of the conduction system in each of the eight cases studied was reconstructed with the use of a previously established technique of multiple histological sections.5 The blocks of tissue for sectioning included the atrial and ventricular septa on each side of the atrioventricular rings and included the atrioventricular node, the common bundle of His, and the proximal portions of the right and left bundle branches. The more peripheral bundle branches were not studied.The tissue blocks were sectioned at ...

Clinical Use of Electrocardiography in Adults With Congenital Heart Disease

“…64 In adults, baseline sinus rhythm is the rule, with P waves of normal axis, duration, and amplitude, although somewhat peaked. 67 The QRS axis is typically normal or displaced to the right with right ventricular hypertrophy. In the presence of a right bundle-branch block, criteria for right ventricular hypertrophy include an RЈ in V 1 Ն15 mm and right-axis deviation of the initial vector representing unblocked forces.…”

“…68 Left-axis deviation should raise suspicion for an associated AVCD, although left anterior hemiblock is present in 5% to 10% of adults. 67 Right bundle-branch block is expected after repair, even in the absence of a ventriculotomy incision. 67 Early QRS lengthening after repair results from surgical injury to the right bundle branch and myocardium, 69 whereas later broadening reflects right ventricular dilation.…”

“…67 Right bundle-branch block is expected after repair, even in the absence of a ventriculotomy incision. 67 Early QRS lengthening after repair results from surgical injury to the right bundle branch and myocardium, 69 whereas later broadening reflects right ventricular dilation. 70 Independent ECG predictors of ventricular tachycardia and sudden death include a QRS interval Ն180 ms (risk ratio 8.8) and annual increase in QRS duration (risk ratio 1.1 for each 1-ms increase per year).…”

Differential diagnosis of congenital heart disease in the first 3 months of life: Significance of a superior (left) QRS axis

“…These workers had earlier shown similar patterns of origin of the left bundle branch in hearts with isolated VSDs and Fallot's tetralogy exhibiting a superior axis. In these hearts they again concluded that the distribution of the left bundle branch favoured initial activation of the posterior septum (Feldt, DuShane, and Titus, 1966). Few detailed studies of the conduction tissue have been made in the other anomalies presently studied which possessed superior axes.…”

“…The defect displaces the conducting elements posteriorly so that they ramify as a continuous sheet, mainly over the posterior septum. The position of the conducting tissue is based on personal sttudies (R. H. Anderson, unpublished observations), together with the works of Feldt et al, 1966, and Demoulin and Kulbertus (1972. posteriorly by the defect, and that the left bundle branch was distributed principally to the posterobasal portion of the septum (Fig.…”