Tetralogy of Fallot – what is it, and how can it be treated?

Tetralogy of Fallot is a congenital cardiac condition. It is associated with various genetic disorders including 22q11 deletion syndrome, DiGeorge syndrome and Down’s syndrome.

Fallot’s tetralogy has four constituent parts:

  • A (usually large) ventricular septal defect (VSD – a hole in the wall dividing the lower two chambers of the heart). More than one VSD may be present;
  • A pulmonary artery (the artery which takes de-oxygenated blood to the lungs) which is narrowed at its base. The degree of narrowing varies from patient to patient;
  • A large, overriding aorta (the body’s main artery which supplies oxygenated blood). In Fallot’s, the aorta straddles the two pumping chambers. The aorta therefore receives an admixture of oxygenated and de-oxygenated blood from the left and right chambers respectively, rather than solely oxygenated blood;
  • A hypertrophic (highly muscled) right ventricle. This happens as a consequence of the other three defects, which create the fourth component over time. A hypertrophic pumping chamber is likely to make matters worse over time. This is because the muscle has to expand into the space which would otherwise be filled with de-oxygenated blood, and that in turn means that the muscles have to work even harder to compensate.

How tetralogy of Fallot affects people

The precise point at which tetralogy of Fallot is detected depends upon the degree and type of symptoms manifested. Typically, children suffering from this condition will exhibit symptoms in the first year (quite possibly in the first month) of life:

  • The cardinal sign is linked to low blood oxygen saturation levels and is in the form of cyanosis (literally, blueness) either from birth, or occurring over the first year of life. Cyanosis is normally noticeable around the lips and on the fingers.
  • A heart murmur may be present. If present, it can be quite pronounced.
  • There can be problems with feeding (babies with the condition can go blue during or after a feed). This can in turn lead to problems with weight gain, and associated difficulties with physical development.
  • There can be problems with breathing on exertion. Grunting may be present (this can also be marked after feeds).
  • There can be acute spells of hypoxia (lack of oxygen) which result in dizziness, shortness of breath, and loss of consciousness.

How Tetralogy of Fallot can be diagnosed and treated

Diagnosis is usually made by performing an echocardiogram – a form of ultrasound. Ultrasound devices are very good at detecting anomalies in blood flow, and may assist in detecting structural issues (including holes) affecting the heart’s chambers. They can also allow a reasonably precise assessment of interruptions of blood flow caused by impedances such as pulmonary stenosis. (narrowing of the pulmonary artery)

It may be necessary to clarify the diagnosis by further investigation – possibly including a cardiac catheterisation. During this procedure, a camera is threaded up blood vessels towards the heart and imaging of the affected areas is then performed.

Once the diagnosis has been made and clarified, treatment is surgical. A primary repair (i.e. corrective surgery) may be attempted following diagnosis. Alternatively, a separate procedure (usually a Blalock-Taussig shunt – form of surgical communication between the systemic blood supply and the deoxygenated blood which is sent to the lungs) may be performed, with the aim of facilitating growth and with surgical correction to be performed at a later date.

The longer a repair is left, the more likely it is that hypertrophy (thickening of the muscle) in the right ventricle will be pronounced.

Corrective surgery will aim to achieve:

  • closing of VSD(s), usually with a patch;
  • narrowing at the base of the pulmonary artery will be surgically corrected;
    relocation of the aorta so that it is connected solely to the left ventricle.

Corrective surgery will normally be conducted on cardiopulmonary bypass (i.e., the body will be supplied with oxygenated blood from a machine), including a period during which the heart will be stopped. During this section of the procedure, the aorta is clamped and a preservative solution known as cardioplegia is periodically washed around the heart, with the aim of preserving cardiac tissue. The surgeon will aim to perform the repair swiftly and thoroughly, in order to minimise problems associated with prolonged time spent on bypass and aortic cross-clamps. These include an increased risk of mortality and brain damage.

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