With this defect both normally developed atriums are available in the heart but they open into a single ventricular chamber. This common chamber rarely consists of just merged right and left ventricles not separated by a septum and as for the rest of the properly developed ones (it would have been easier with such a picture). In the vast majority of cases the common ventricle has anatomical structure either of the left or right one and the second underdeveloped ventricle remains in the form of a small chamber connected with the main ventricle with a huge ventricular septal defect.
Aorta and pulmonary artery, the great vessels, may diverge both from the main, common ventricle, and from this little one called "emissarium".
Therefore the group of defects which are called "single ventricle" brings together a large variety of options. Hence there is a wide range of clinical manifestations.
From the point of view of the blood flow things are not all that bad: the flows are mixed in a common chamber and there is no expressed oxygen undersaturation, and hence, slight cyanosis is present, if there is at all. In this case, however, the ventricle is working at a double load, which eventually leads to a thickening of its wall muscle (including unnecessary residual septum) and muscle bulk under the aorta (i.e., to subaortic stenosis). This occurs in the course of time.
After birth, if there are no other changes in the heart, the pressure is equal in both circles, and this can result in irreversible pulmonary hypertension. Cyanosis such as in Tetralogy of Fallot can develop when there is additional interference with pulmonary circulation.
But nevertheless, children with a single ventricle are usually not critically ill immediately after birth and if no measures are taken or if the defect is treated conservatively, they can live for 10 years or more. However their condition can be misleading and if the right moment is missed the surgical treatment would be impossible. And it is necessary to understand what for you can be offered an additional palliative surgery while in your opinion there is no extra need. There can be a number of such surgeries and finally they are aimed not only at elimination of life-threatening symptoms but also at preparing the vasculature of both circuits to their final separation, i.e. to Fontan operation which was discussed in the previous chapter about tricuspid atresia. Everything mentioned in this chapter is related to the patients with a single ventricle and while the patients with a single ventricle require timely surgical aid to prevent possible complications and to prepare the whole circulatory system to the new potential conditions, in tricuspid atresia the heart is naturally prepared to exist without a right ventricle.
As it was mentioned in the chapter about the major ventricular septal defects, the child can be recommended to undergo pulmonary artery banding to prevent pulmonary hypertension even in the first month of life if the defect is diagnosed immediately after birth.
In a few months but during the first year of life, a bidirectional anastomosis should be applied between superior vena cava and pulmonary artery forwarding venous blood from the upper half of the body directly to the lungs. If evident subaortic stenosis is present – it should be eliminated and a single ventricle should be created with unimpeded arterial inflow into aorta.
And the last step is Fontan operation after which the venous blood flows into pulmonary vessels and the single ventricle works for the systemic circuit. Fontan operation can be done later, at 4 years or older but there is no point to delay for a long time.