Generality
The tetralogy of Fallot is a congenital heart disease, which alters the structure of the heart and compromises its normal functioning. Affected patients present, from birth, with a bluish appearance: it is the so-called cyanosis.
The only effective therapy is surgery, which aims to resolve heart abnormalities. Without this operation, the patient cannot lead a normal life.
A brief reference to the anatomy of the heart
Before describing the tetralogy of Fallot, it is useful to remember some anatomical elements of the heart. With the help of the image, readers are reminded that:
- The heart is divided into two halves, right and left. The right heart is composed of the right atrium and the right ventricle below. The left heart is composed of the left atrium and the left ventricle below. Each atrium is connected to the underlying ventricle by means of a valve.
- The right atrium receives non-oxygenated blood through the hollow veins, and pushes it into the right ventricle.
- The right ventricle pumps blood into the pulmonary artery, which leads the blood to the lungs. In the lungs, the blood is charged with oxygen.
- The left atrium receives oxygenated blood, returning from the lungs, through the pulmonary veins, and pushes it into the left ventricle.
- The left ventricle pumps oxygenated blood to the organs and tissues of the human body, through the aorta .
What is the tetralogy of Fallot
The tetralogy of Fallot is a malformation of the heart, characterized by four anatomical anomalies. This malformation is congenital, that is, present at the time of birth, and alters the normal flow of blood that passes through the human body.
The bluish aspect, that is the cyanosis, of the patient is one of the characteristic signs of the tetralogy of Fallot.
Now let's see what are the anatomical anomalies of the heart responsible for cyanosis.
THE FOUR ANATOMICAL ANOMALIES. PATHOPHYSIOLOGY
- Narrowing (or stenosis) of the pulmonary valve and of the right ventricle portion surrounding the valve itself.
Effect: reduces the flow of blood entering the pulmonary artery and then reaches the lungs.
Consequences: there is a stagnation of blood in the right ventricle and the proportion of oxygenated blood is lower than the normal quota.
- Interventricular septal defect . The interventricular septum separates the right ventricle from the left. The defect consists of a hole in the septum.
Effect: the two ventricles communicate with each other.
Consequences: the stagnation of non-oxygenated blood from the right ventricle and mixes with the oxygenated blood (mixed blood) of the left ventricle. It is the so-called " shunt from right to left".
NB: in medicine, the term shunt indicates a hole or a passage, which allows the transfer of a liquid from one compartment to another.
- Biventricular origin of the aorta (aorta a cavaliere) . The aorta occupies a different position than a normal heart. It is slightly shifted to the right. Therefore, also because of the hole present in the interventricular septum, it communicates directly with the right ventricle.
Effect: the mixed blood (oxygenated and non-oxygenated) takes the aorta and reaches the tissues of the human body.
Consequences: cyanotic color.
- Hypertrophy of the right ventricle . Due to the stenosis of the pulmonary valve, more force is needed to push the non-oxygenated blood into the lungs. To do this, the muscle of the ventricle grows and strengthens.
Effect: the ventricle wall thickens.
Consequences: the muscle of the ventricle loses elasticity and stiffens.
Epidemiology
The incidence of tetralogy of Fallot is 1 case every 3, 600 newborns. It is the congenital malformation of the most common heart, among those that cause cyanosis. It affects men and women equally.
Causes
The precise cause of the tetralogy of Fallot is unknown. However, two types of favoring factors are suspected:
- Genetic factors
- Environmental factors
To determine the cardiac malformation associated with the tetralogy of Fallot, environment and genetics can act individually, or combine and act in concert.
GENETIC FACTORS
The tetralogy of Fallot is very often associated with some genetic diseases:
- DiGeorge syndrome
- Down syndrome
- Maternal phenylketonuria
The following table shows the main characteristics of the aforementioned genetic diseases:
| Genetic disease | Site of the mutation | Type of mutation |
| DiGeorge syndrome | Chromosome 22 | Absence (deletion) of a portion of chromosome 22 |
| Down syndrome | Chromosome 21 | Trisomy, that is three copies of chromosome 21 |
| Phenylketonuria | Chromosome 12 | Point mutation of some DNA bases |
ENVIRONMENTAL FACTORS
A relationship has been observed between some environmental circumstances and the tetralogy of Fallot. They are:
- Maternal alcoholism. The child becomes ill with fetal alcohol syndrome
- Some viral diseases of the mother, which arise during pregnancy (for example, rubella)
- Mother over the age of 40
- Taking a hydantoin by a pregnant woman to alleviate epileptic seizures. The child is born with fetal hydantoin syndrome
WHEN DOES MALFORMATION COME? WHAT DOES IT DETERMINE?
The malformation arises in the pre-natal age, ie before birth. Thanks to modern diagnostic techniques, it has been identified which process originates the four cardiac anomalies of the tetralogy of Fallot. This is an incorrect alignment of the aortic-pulmonary septum, during the embryonic phase of heart formation (the aortic-pulmonary septum is the cut that separates the right heart from the left heart; it distinguishes the aorta from the pulmonary arteries and separates the two ventricles).
An incorrect alignment of the aortic-pulmonary septum determines the first three abnormalities described above. The fourth anomaly, hypertrophy of the right ventricle, is a consequence of the other three.
Symptoms, signs and associations
As mentioned, the anatomical anomalies of the heart determine the formation and release of mixed blood (oxygenated and non-oxygenated) into the circulation. The mixed blood, reaching the tissues of the human body, determines the main sign of the tetralogy of Fallot: cyanosis .
The other typical symptoms / signs of the tetralogy of Fallot are numerous. Therefore, to facilitate understanding, it was decided to divide them into:
- General
- cardiac
- Ophthalmologicals
SYMPTOMS AND GENERAL SIGNS
Cyanosis determines the bluish aspect ( cyanotic color ) of the patient, whether newborn or adult. The greater the transfer of non-oxygenated blood from the right ventricle to the left ventricle (" shunt from right to left"), the greater the cyanotic complexion. When cyanosis is severe, it causes asphyxiated crises (due to lack of oxygen in the blood), the outcome of which is lethal.
Other general symptoms / signs are:
- Low birth weight
- agitation
- Growth and delayed puberty
- Dyspnea, breathlessness and fatigue. In particular, during lactation or after prolonged crying
- Tendency to take a squatting position. The patient realizes he is breathing better and feels relief
- Weeping facies, due to lack ( agenesis ) or hypoplasia of the depressor muscle of the corner of the mouth.
SYMPTOMS AND HEART SIGNS
These are revelations that are auscultated by the cardiologist. They are puffs, or noises, that come from the malformed heart; of these noises, the pulmonary systolic murmur (ie that generated by the passage of blood through the stenotic pulmonary valve) is the most important. In fact, based on its intensity, the cardiologist can estimate the degree of stenosis and the extent of the interventricular hole .
Further details - Evaluation criteria for pulmonary systolic murmur:
- The lower the sound intensity of the pulmonary systolic murmur, the greater the stenosis and the amount of blood transferred in the left ventricle. The cyanotic complexion is more intense.
- Conversely, the louder the murmur is, the smaller the stenosis and the amount of blood transferred in the left ventricle. The cyanotic complexion is less intense.
SYMPTOMS AND OPHTHALMOLOGICAL SIGNS
In patients with tetralogy of Fallot, congestion of the blood vessels of the retina may be observed.
OTHER ASSOCIATED DISORDERS
In association with the tetralogy of Fallot, other anomalies may occur, cardiac or not. One of these is pulmonary atresia . Very serious, it consists in the complete obstruction of the tract which allows blood to escape from the right ventricle, that is the pulmonary artery. The only way forward is that created by the interventricular hole: the transfer of blood (" shunt from right to left") is complete and the cyanosis becomes severe.
The following table shows the main associated disorders:
| Abnormalities associated with the tetralogy of Fallot: | Percentage of appearance |
| Defect of the atrial septum (with its appearance, we speak of pentalogy of Fallot) | 10% |
| Aortic arch positioned to the right (instead of to the left) | 25% |
| Bicuspid pulmonary valve | 60% |
| Coronary artery abnormalities | 10% |
| Pulmonary atresia (or pseudo arterial trunk) | unknown |
| Scoliosis | unknown |
Diagnosis
The cyanotic complexion at birth and the pulmonary systolic murmur are already two valid clues, which suggest the tetralogy of Fallot.
Today, to have a confirmation of these suspicions, different tests can be used. At one time, instead, the alternatives were few and we relied on chest radiography, with its limitations and contraindications. Therefore, the possible tests for the diagnosis of the tetralogy of Fallot are:
- Fetal and trans-thoracic echocardiography
- Electrocardiogram (ECG)
- Pre-natal ultrasound and tri-tests
- Blood tests
- Chest x-ray
- Oxygen level measurement
- Cardiac catheterization
FETAL AND TRANS-THORACIC ECOCARDIOGRAPHY
Echocardiography is the examination of choice for the tetralogy of Fallot. The advantages of this diagnostic test are: speed, absence of harmful radiation and the possibility of performing it in the pre-natal age ( fetal echocardiography ).
Through echocardiography, fetal and trans-thoracic, the physician obtains a comprehensive description of the internal anatomy of the heart: state of the interventricular septum, stenosis of the pulmonary valve, position of the aorta, hypertrophy of the right ventricle.
ELECTROCARDIOGRAM
The ECG trace clearly shows right ventricular hypertrophy. Advantages: it is not invasive.
NB: right ventricular hypertrophy occurs later and becomes more severe with time, as it is a consequence of the first three anomalies.
PRE-CHRISTMAS AND TRI TEST ECOGRAPHY
Pre-natal ultrasound and three tests are two tests performed on pregnant mothers, in order to assess the presence, in the fetus, of possible chromosomal abnormalities. One of these anomalies is Down syndrome, a condition often associated with the tetralogy of Fallot.
Advantages: it is not harmful, neither for the mother nor for the fetus.
BLOOD TESTS
It is quite common for patients to have a large number of red blood cells ( erythrocytosis ). In this regard we proceed with a simple blood test.
CHEST RADIOGRAPHY
Once, in the absence of modern techniques, it was the most reliable examination. From the radiographic images, the heart of a patient with tetralogy of Fallot assumes a shape similar to a boot (" heart-shaped boot ").
Disadvantages: emission of harmful ionizing radiation.
MEASUREMENT OF OXYGEN LEVEL
Through a sensor applied to a finger of the hand, the oxygen levels in the blood are evaluated.
Advantages: it is not invasive.
CARDIAC CATHETERISM
Cardiac catheterization uses catheters that pass through vessels and cavities of the heart. Provides information on the anatomy of the internal cavities of the heart and on the levels of oxygen present in the blood.
Disadvantages: it is invasive. Catheters can damage the blood vessel wall.
Therapy
The tetralogy of Fallot forcedly requires surgery . In fact, the malformation of the heart is not compatible with a normal life.
There are two types of intervention:
- Intracardiac repair . It is the main and decisive operation.
- The palliative procedure . It is an operation with temporary effects.
Furthermore, the most severe cases require emergency therapy . It is essential to save the life of the newborn before subjecting it to surgery.
EMERGENCY THERAPY
Infants and children with severe cyanosis and with asphyxiated seizures require some emergency care. Interventions to be performed immediately, as patients' lives are at high risk. In such circumstances, therapeutic measures consist of oxygen therapy and the administration of certain drugs: beta-blockers, morphine, vasopressors and prostaglandin E1 . With different mechanisms, these drugs promote blood oxygenation and attenuate asphyxial crises.
INTRACARDIAN REPAIR
Intracardiac repair is the only therapy that can resolve cardiac malformations of the tetralogy of Fallot.
The operation takes place with an open heart.
It is advisable to practice it on patients at least one year old. In the first months of life, in fact, the heart must develop, so an intervention, at this stage, could be useless and dangerous. However, some serious cases impose an operation even at the sixth or ninth month of life.
The procedure consists of:
- Stenosis reduction
- Application of a Gore-Tex "patch" to the interventricular septum hole
If successful:
- Increasing levels of circulating oxygenated blood
- Cyanosis and asphyxial crises is reduced
THE PALLIATIVE PROCEDURE
The palliative procedure is a non-conclusive surgical operation. It is, in fact, a temporary measure, waiting for the child's heart to grow and be ready for intracardiac repair.
The procedure involves the application of a bypass, or shunt, which connects the aorta to the pulmonary artery. This communication is also called anastomosis and promotes blood flow to the lungs. When you decide to intervene with intracardiac repair, the bypass is removed.
Prognosis
The importance of surgery is underlined by the following statistical data regarding the survival of unoperated patients:
- 75% exceed the first year of life
- 60% reach 4 years of life
- 30% exceed 10 years of life
- 5% survive over 40 years
To these percentages, it must be added that an untreated child suffers from a delayed development and that every physical activity (even moderate) creates anxiety. It therefore appears evident that life is strongly conditioned by the malformation of the heart.
The prognosis of tetralogy of Fallot improves significantly when patients undergo surgery. In fact, most patients, after surgery, no longer show any symptoms and lead a normal life. However, family members are advised to subject the young patient to periodic checks, so as to prevent post-operative complications.
The success of the intervention depends on the severity of the stenosis of the pulmonary valve and on the experience of the surgeon regarding the intracardiac repair of the tetralogy of Fallot.
