Variable morphology of ventricular septal defect in double inlet left ventricle

The morphologic characteristics of ventricular septal defect (VSD) relative to the disposition of the atrioventricular conduction axis were studied (as far as was possible from gross observation) in 33 hearts with double inlet left ventricle. The hearts were separated into 4 groups. The hearts had either right-sided or left-sided rudimentary right ventricles (RV) coexisting with either ventriculoarterial (VA) concordance or discordance, respectively. Significant differences were noted in the morphology of the VSD according to these patterns. With right-sided rudimentary RV and VA concordance the anatomy was similar to that of classic tricuspid atresia, with an extensive outlet septum in the roof of the defect. With left-sided rudimentary RV and VA concordance, 2 further patterns were seen. In 1 pattern the arrangement was similar to that found with VA discordance. In the other, there was a pinhole VSD, a grossly hypoplastic right ventricle and a complete subaortic infundibulum in the dominant left ventricle. With VA discordance the morphology was broadly similar be the rudimentary RV right-sided or left-sided. The outlet septum was much less extensive than in the arrangement with right-sided RV and VA concordance. Minimal differences related to the formation of the right margin of the defect, which always carried the conduction axis on its left ventricular aspect. These differences dictated the "safest margins" of the defect should its excision be required during life. Basically, the left margin of the apical trabecular septum can most safely be excised.