Fallot tetralogy
This congenital heart defect is caused by a maldevelopment of certain areas of the right ventricle. It is characterised by four main features: First, a narrowing of the muscle at the exit of the right ventricle; second, a narrowing of the valve of the pulmonary artery; third, a large hole between the two chambers of the heart (ventricular septal defect); and fourth, abnormal positioning of the aorta that ‘rides’ over the VSD, as well as a thickening of the muscles of the right ventricle caused by the narrowing of the pulmonary artery. The combination of these 4 features is known as ‘tetralogy of Fallot’.
There is usually also a connection between the two atria (atrial septal defect, ASD), and the aortic arch is often located on the right side.
Background
It is a congenital heart malformation that accounts for approximately 5% of all congenital heart defects and is also the most common cyanotic heart defect. It is named after the French pathologist Étienne-Louis Arthur Fallot, who described it. It consists of four heart defects occurring together (Greek ‘tetra’, four), hence tetralogy. In English it is called ‘Tetralogy of Fallot’ and abbreviated as TOF. The abbreviation TOF is now also commonly used in German-speaking countries.
One consequence of this heart defect is an undersupply of oxygen to the body, which leads to a blue colouration of the skin and mucous membranes. Fallot referred to the malformation as maladie bleue (roughly ‘blue disease, blue evil’).
The characteristics of Fallot's tetralogy cause mixed blood to flow from the right and left ventricle into the aorta, which leads to undersaturation, a cyanosis. On the other hand, critically little blood can also flow into the lungs, which can lead to so-called ‘hypoxia attacks’, a life-threatening situation. Without surgery, all children die by the age of 10.
Symptoms
If the heart defect is not known prenatally, it is usually diagnosed by the ever-present heart murmur and generalised cyanosis (blue colouring, mainly visible on the lips), although this may not be visible in all children at first.
Other symptoms may include a rapid heartbeat, poor growth behaviour, loss of appetite, muscle weakness and fainting spells.
Some babies have such severe constriction of the muscles below the pulmonary artery that they are characterised by seizures with severe hypoxia; these children need medication, sometimes even cardiac catheterisation.
After birth, all babies with TOF must therefore initially be monitored for a few days and remain under close outpatient paediatric cardiological control until the operation, which is usually performed in the 5th-6th month of life.
Therapy
Medication:
If children are affected early, beta-blockers must be given to relax the muscles below the pulmonary artery.
Cardiac catheterisation:
In some cases, children need a balloon dilation of the pulmonary artery or a vascular support (‘stent’) in the right ventricular outflow tract.
Operation:
Through an incision (dashed line) in the right ventricle, which is extended beyond the outflow tract into the trunk of the pulmonary artery (pulmonary artery, PA), the surgeon can view the muscle mass in the outflow tract and the VSD. The thickened muscle masses are excised and the VSD is closed with a patch (VSD patch). The atrophied pulmonary valve is either repaired or cut out and the entire outflow tract is then closed with a patch and thus widened. Sometimes it is necessary to replace the pulmonary valve with a human (so-called ‘homograft’) or animal valve.
The aim of the operation has been achieved
The right ventricle can now pump blood into the pulmonary arteries with far less force because the thickened muscle masses and the pulmonary valve, which is too small, have been reconstructed or cut out and the entire outflow tract has been widened beyond the narrow trunk of the pulmonary artery with a patch. The risk of cyanosis attacks is averted because the VSD has been closed with a patch. This prevents deoxygenated blood from the right ventricle from entering the aorta, which now only transports oxygen-rich blood.
The circulatory systems are separated, the cyanosis has disappeared and the children usually have normal heart function and can take part in all leisure activities and sports.
Forecast
The prognosis for children after surgery is generally good, but it is often necessary to perform a new operation on the pulmonary artery years later as it does not grow with the child. Annual check-ups are usually sufficient.
Nowadays there are very many adults with this heart defect who were operated on as children. Most of them are doing very well, many affected women have given birth to healthy children; many patients are also very active in sports.
A long-term problem can be pulmonary artery stenosis or inability to close, which can result in the need for replacement (by cardiac catheterisation or surgery).
Some patients also have cardiac arrhythmias, often years after the operation, which may necessitate drug therapy or the implantation of pacemakers/defibrillators
