Tetralogy of Fallot: Causes, Pathophysiology, Risk Factors, Investigation & Management

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The combination of four heart defects that are present at birth causes Tetralogy of Fallot. These defects, which affect the structure of the heart, cause oxygen-poor blood to flow out of the heart and into rest of the body. Infants and children with tetralogy of Fallot usually have blue-tinged skin due to low oxygen level in their body.

Tetralogy of Fallot is often diagnosed during infancy or soon in later life, However, tetralogy of Fallot may be not detected until later in life, depending on the severity of the defects and symptoms. But early diagnosis followed by appropriate treatment, most children with tetralogy of Fallot live relatively normal lives, though they’ll need regular medical care and may have restrictions on exercise.

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Epidemiology of Tetralogy of Fallot

Tetralogy of Fallot occurs in approximately 400 per million live births. TOF is the most common cyanotic congenital heart defect and is estimated to account for 4% to 9% of congenital heart defects overall, or in the range of 0.262 to 0.392 per live births.

Causes of Tetralogy of Fallot

Tetralogy of Fallot occurs during fetal growth when the fetus’s heart is developing. While factors such as poor maternal nutrition, viral illness or genetic disorders may increase the risk of this condition, in most cases tetralogy of Fallot is unknown.

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The four abnormalities that make up the tetralogy of Fallot include:

  • Pulmonary valve stenosis

This is narrowing of the pulmonary valve, the flap that separates the right ventricle of the heart from the pulmonary artery, the main blood vessel leading to the lungs. Constriction of the pulmonary valve reduces blood flow to the lungs. The narrowing may also affect the muscle beneath the pulmonary valve.

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  • Ventricular septal defect

This is a hole in the wall that separates the two lower chambers (ventricles) of the heart. The hole allows deoxygenated blood in the right ventricle, blood that has circulated through the body and is en route to the lungs to replenish its oxygen supply, to flow into the left ventricle and mix with oxygenated blood fresh from the lungs. Blood from the left ventricle also flows back to the right ventricle in an inefficient manner. This ability for blood to flow through the ventricular septal defect dilutes the supply of oxygenated blood to the body and eventually can weaken the heart  

  • Overriding aorta

Normally the aorta, the main artery leading out to the body, branches of the left ventricle. The aorta shifts slightly to the right and lies directly above the ventricular septal defect. In this position the aorta receives blood from both the right and left ventricles, mixing the oxygen-poor blood from the right ventricle with the oxygen-rich blood from the left ventricle.

  • Right ventricular hypertrophy

The overworking of heart’s pumping action causes the muscular wall of the right ventricle to enlarge and thicken. Over time this may cause a heart to stiffen, become weak and eventually fail.

Rare some babies who have tetralogy of Fallot will have a hole in their heart’s upper chambers (atrial septal defect), as well. When this occurs, the condition is known as pentalogy of Fallot.

Pathophysiology of Tetralogy of Fallot

The large Ventricular septal defect associated with this defect leads to equal pressures in the R and L ventricles. The amount of pulmonary blood flow and, therefore, the amount of cyanosis, will depend on the degree of pulmonary stenosis. Even with mild pulmonary stenosis, there is usually enough obstruction to pulmonary flow that these infants have some decrease in pulmonary blood flows. In some individuals there is such minimal obstruction that they are not cyanotic thus, the term “pink tets” is often used to describe them.

Risk factors of Tetralogy of Fallot

While the exact cause of tetralogy of Fallot is unknown, several factors may increase the risk of a baby being born with this condition. These include:

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  • A viral illness in the mother, such as rubella, during pregnancy
  • Maternal alcoholism
  • Poor nutrition
  • A mother older than 40 years
  • A parent with tetralogy of Fallot
  • Clinical features
  • A bluish coloration of the skin caused by blood flow in oxygen
  • Shortness of breath and rapid breathing, especially during feeding
  • Loss of consciousness
  • Clubbing of fingers and toes- an abnormal, rounded shape of the nail bed
  • Poor weight gain
  • Tiring easily during play
  • Irritability
  • Prolonged crying
  • A heart murmur

Investigations

  • Physical examination by the physicians
  • Chest X-ray: a typical sign of tetralogy of Fallot on an X-ray is a “boot-shaped” heart because the right ventricle is enlarged
  • Blood test: complete blood count. In tetralogy of Fallot, the number of red blood cell may be abnormally high as the body attempts to increase the oxygen level in the blood.
  • Electrocardiogram (ECG): a test that records the electrical activity of the heart shows abnormal rhythms and detects the heart muscle stress.

Cardiac Catheterization: a cardiac catheterization is an invasive procedure that gives very detailed information about the structures of the heart.  A contrast dye is injected to clearly visualize the structure of the heart.

Management

Surgery is the only and most effective treatment for tetralogy of Fallot. There are two types of surgery, including intracardiac repair or a temporary procedure that uses a shunt. Most babies and children will have intracardiac repair.

Intracardiac repair

Tetralogy of Fallot treatment for most babies involves a type of open-heart surgery called intracardiac repair. During the first year of life performs this surgery.

Temporary surgery

Occasionally babies need to undergo a temporary surgery before having intracardiac repair. If a baby was born prematurely or has pulmonary arteries that are underdeveloped doctors will create a bypass (shunt) between the aorta and pulmonary artery. This bypass increases blood flow to the lungs. Doctors remove the stunt when the baby is ready for intracardiac repair.

Complications

All babies with tetralogy of Fallot need corrective surgery. Without treatment, a baby may not grow and develop properly. He/she is also at increased risk of various complications, such as infective endocarditis, an inflammation of the inner lining of the heart caused by a bacterial infection.

Untreated cases of tetralogy of Fallot usually develop severe complications over time, which may result in death or disability by early adulthood.

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Prognosis

Tetralogy of Fallot is left untreated then it rapidly results in progressive right ventricular hypertrophy due to the increased resistance in the right ventricle. This progresses to heart failure which begins in the right heart and often leads to left heart failure.

Patients who have undergone total surgical repair of tetralogy of Fallot have improved hemodynamics and often have well to excellent cardiac function after the operation with some to no exercise intolerance. 90% of patients with total repair as infants develop a progressively leaky pulmonary valve later in adulthood. They require, therefore, follow up in specialized Adult Congenital Heart Disease centers.

 The binaural beats meditation for cardiovascular disease (sound therapy treatment of heart repair) Check the below video.

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