Conducting tissues in congenitally corrected transposition with situs inversus

Three cases of congenitally corrected transposition in situs inversus individuals were characterised by visceroatrial situs inversus, atrioventricular discordance, and ventiruloarterial discordance: one case was studied clinically, and the other 2 were necropsy specimens. The disposition of the atrioventricular conducting tissues was established in each case, in the living patient by intraoperative mapping, and in the necropsy specimens by histopathological investigation. In all, the connecting atrioventricular bundle arose from a normally situated posterior atrioventricular node, normally related to the landmarks of the atrial septum. Though anterior nodes were identified in the necropsy specimens, as reported in congenitally corrected transposition in situs individuals, they differed from those in the latter situation in that they made no atrioventricular connection. These findings have obvious surgical importance. It is suggested that the posterior connection is related to the good septal alignment in these cases which lacked significant septal defects. Posterior connections are not necessarily present in all situs inversus individuals with corrected transposition, particularly when there are malalignment ventricular septal defects: further studies are required in such cases.