Heart abnormality with false connections of the blood vessels
All of these abnormalities are very rare. One distinguishes between purely abnormal inlets and such that result from an absent or abnormal separation of the outflow tract.
Transposition of the great vessels (TGA)
While the cause of TGA (5%) is unknown, an increased risk is associated with maternal diabetes mellitus.
In a TGA, the aorta arises completely out of the right ventricle and the pulmonary arteries from the left one. From an embryologic point of view, the rotation of the aorto-pulmonary septum of 180o did not take place. The hemodynamic of the TGA is characterized by the parallel connection of the two circulatory systems that permit no oxygen intake or release. Such a circulation situation can only be survived when in addition to the TGA a mixing of O2 enriched pulmonary venous blood with the systemic venous blood via a crossed shunt can take place. Such shunt connections at the atrium level are an open foramen ovale or an atrium septum defect, at the ventricle level a VSD, and at the vessel level an open ductus arteriosus.
Double inlet ventricle
With an incidence of 2% this is a rare malformation of the heart. In this cardiac abnormality one or both av-valves empty into a common ventricle (see name). In addition, a rudimentary outflow tract mostly still exists that is connected with the main chamber via a VSD. This rudimentary cardiac chamber has no connection to the av-valve and thus cannot form an inflow tract or a cavum during cardiac development. The great arteries can diverge from the associated ventricle in either a normal way or transposed. The cause of this defect is probably an atrophy of the crista prima that occurs too late and thus the right conus septum cannot fuse with the dorsal av-septum.
Complete pulmonary vein inlet errors
In an early stage of development connections exist between the pulmonary vein and somatic vein systems. When the junctions of the pulmonary veins with the left atrium are unsuccessful, the pulmonary veins thereby empty into the somatic circulation system. This abnormality is also rare (2%).
Truncus arteriosus communis
In this cardiac abnormality only one arterial vessel, the truncus arteriosus communis, emerges from the heart and the two ventricles are connected with each other via a large VSD. Most often the truncus arteriosus straddles it, so that it receives blood from both ventricles. The pulmonary artery emerges dorsally and the aorta ventrally, since here the formation of the conus septum failed to take place. The outflow tract is divided by the truncus septum only in the upper part. In this cardiac abnormality only a common valve, the truncus valve, has formed. This also is a very rare cardiac abnormality.