The Conducting Tissues in Congenitally Corrected Transposition

The histopathological findings are reported in 11 cases of congenitally corrected transposition. For the purposes of this investigation, only hearts with a well-formed septum separating two ventricular sinuses were classed as corrected transposition. We did not, therefore, study any examples of single ventricle with inverted outlet chamber. Five of the cases formed the basis of a preliminary report, in which the distribution of conducting tissues in the anomaly was shown to differ from that reported in previous investigations. The six new cases confirmed this distribution. Thus, in all cases, the connecting atrioventricular node was anteriorly situated in the right atrium at the lateral junction of pulmonary and mitral valves. An anteriorly situated bundle descended into the morphologically left ventricle (right-sided) and encircled the anterolateral quadrant of the pulmonary outflow tract before descending on the anterior septum and bifurcating. The bundle branches were inverted. This distribution was observed in specimens with intact septa (three cases) and in specimens with ventricular septal defects (eight cases). In the latter cases the conducting tissues were related to the anterior quadrants of the defects. One case was of particular interest since the posterior node in the position of the normal atrioventricular node also made contact with the ventricles via a posterior bundle. In all other specimens this node was hypoplastic and did not have ventricular connections. It is considered that this finding provides a link with previous descriptions of posterior conducting tissue in congenitally corrected transposition. The findings are discussed with relation to the development of complete heart block in this anomaly.