Tetralogy of Fallot (TOF) is an abnormality of the heart and major blood vessels, which may be found in babies.
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It’s one of the most complex heart problems, as there are four different abnormalities (hence the term ‘tetralogy’):
•A large ventricular septal defect – one of the more serious types of hole in the heart, in which there is a connection between the two main pumping chambers of the heart (ventricles)
•Narrowing of the pulmonary valve (pulmonary stenosis) – this means the heart has to work harder to pump blood into the lungs to collect oxygen
•Right ventricular hypertrophy – thickening of the muscle wall of the right ventricle
•A displaced aorta – the major blood vessel that takes blood out of the heart and directs it around the body
Although these are the main problems, every child is different and there may be all sorts of other abnormalities.
Tetralogy of Fallot occurs in approximately 400 per million live births.
It was described in 1672 by Niels Stensen, in 1773 by Edward Sandifort, and in 1888 by the French physician Étienne-Louis Arthur Fallot, for whom it is named.
Tetralogy of Fallot symptoms vary, depending on the extent of obstruction of blood flow out of the right ventricle and into the lungs. Signs and symptoms may include:
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*A bluish coloration of the skin caused by blood low in oxygen (cyanosis)
*Shortness of breath and rapid breathing, especially during feeding
*Loss of consciousness (fainting)
*Clubbing of fingers and toes — an abnormal, rounded shape of the nail bed
*Poor weight gain
*Tiring easily during play
*A heart murmur
Sometimes, babies with tetralogy of Fallot will suddenly develop deep blue skin, nails and lips after crying, feeding, having a bowel movement, or kicking his or her legs upon awakening. These episodes are called “Tet spells” and are caused by a rapid drop in the amount of oxygen in the blood. Toddlers or older children may instinctively squat when they are short of breath. Squatting increases blood flow to the lungs. Tet spells are more common in young infants, around 2 to 4 months old.
Seek medical help if you notice that your baby has the following symptoms:
*Bluish discoloration of the skin
*Passing out or seizures
If your baby becomes blue (cyanotic), immediately place your child on his or her side and pull the knees up to the chest. This helps increase blood flow to the lungs.
The cause of TOF isn’t fully understood. While a baby is in the womb, something interferes with the development of the heart and major blood vessels.
Its cause is thought to be due to environmental or genetic factors or a combination. It is associated with chromosome 22 deletions and DiGeorge syndrome.
Specific genetic associations include:
It occurs slightly more often in males than in females.
Embryology studies show that it is a result of anterior malalignment of the aorticopulmonary septum, resulting in the clinical combination of a VSD, pulmonary stenosis, and an overriding aorta. Right ventricular hypertrophy results from this combination, which causes resistance to blood flow from the right ventricle.
Although no specific single genetic abnormality has yet been found to explain every case, genetics often do play a part in these types of malformations (known as conotruncal abnormalities). In some children, a particular genetic problem can be identified, such as DiGeorge syndrome, where a small piece of chromosome 22 is lost or deleted.
Some researchers have suggested that TOF is caused by an autosomal recessive gene that has yet to be identified and which has variable penetrance (that is, it doesn’t always cause disease).
However, this is far from proven and TOF has also been linked to environmental factors such as certain medications or alcohol taken by the mother while pregnant.
Whatever the cause, in those families who have a child with TOF, the risk of a second child being born with the condition is only increased very slightly.
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:
*A viral illness in the mother, such as rubella (German measles), during pregnancy
*A mother older than 40
*A parent with tetralogy of Fallot
*Babies who are also born with Down syndrome or DiGeorge syndrome
The abnormal “coeur-en-sabot” (boot-like) appearance of a heart with tetralogy of Fallot is easily visible via chest x-ray, and before more sophisticated techniques became available, this was the definitive method of diagnosis. Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.
Emergency management of tet spells:
Prior to corrective surgery, children with tetralogy of Fallot may be prone to consequential acute hypoxia (tet spells), characterized by sudden cyanosis and syncope. These may be treated with beta-blockers such as propranolol, but acute episodes may require rapid intervention with morphine to reduce ventilatory drive and a vasopressor such as epinephrine, phenylephrine, or norepinephrine to increase blood pressure. Oxygen is effective in treating spells because it is a potent pulmonary vasodilator and systemic vasoconstrictor. This allows more blood flow to the lungs. There are also simple procedures such as squatting and the knee chest position which increases aortic wave reflection, increasing pressure on the left side of the heart, decreasing the right to left shunt thus decreasing the amount of deoxygenated blood entering the systemic circulation.
The condition was initially thought untreatable until surgeon Alfred Blalock, cardiologist Helen B. Taussig, and lab assistant Vivien Thomas at Johns Hopkins University developed a palliative surgical procedure, which involved forming an anastomosis between the subclavian artery and the pulmonary artery (See movie “Something the Lord Made”). It was actually Helen Taussig who convinced Alfred Blalock that the shunt was going to work. This redirected a large portion of the partially oxygenated blood leaving the heart for the body into the lungs, increasing flow through the pulmonary circuit, and greatly relieving symptoms in patients. The first Blalock-Thomas-Taussig shunt surgery was performed on 15-month old Eileen Saxon on November 29, 1944 with dramatic results.
The Potts shunt and the Waterston-Cooley shunt are other shunt procedures which were developed for the same purpose. These are no longer used.
Currently, Blalock-Thomas-Taussig shunts are not normally performed on infants with TOF except for severe variants such as TOF with pulmonary atresia (pseudotruncus arteriosus).
Total surgical repair:
The Blalock-Thomas-Taussig procedure, initially the only surgical treatment available for Tetralogy of Fallot, was palliative but not curative. The first total repair of Tetralogy of Fallot was done by a team led by C. Walton Lillehei at the University of Minnesota in 1954 on a 11-year-old boy. Total repair on infants has had success from 1981, with research indicating that it has a comparatively low mortality rate.
Total repair of Tetralogy of Fallot initially carried a high mortality risk. This risk has gone down steadily over the years. Surgery is now often carried out in infants one year of age or younger with less than 5% perioperative mortality. The open-heart surgery is designed (1) to relieve the right ventricular outflow tract stenosis by careful resection of muscle and (2) to repair the VSD with a Gore-Tex patch or a homograft. Additional reparative or reconstructive surgery may be done on patients as required by their particular cardiac anatomy
Untreated, Tetralogy of Fallot rapidly results in progressive right ventricular hypertrophy due to the increased resistance on the right ventricle. This progresses to heart failure (dilated cardiomyopathy) which begins in the right heart and often leads to left heart failure. Actuarial survival for untreated Tetralogy of Fallot is approximately 75% after the first year of life, 60% by four years, 30% by ten years, and 5% by forty years.
Patients who have undergone total surgical repair of Tetralogy of Fallot have improved hemodynamics and often have good to excellent cardiac function after the operation with some to no exercise intolerance (New York Heart Association Class I-II). Surgical success and long-term outcome greatly depends on the particular anatomy of the patient and the surgeon’s skill and experience with this type of repair.
Ninety percent of patients with total repair as infants develop a progressively leaky pulmonary valve as the heart grows to its adult size but the valve does not. Patients also may have damage to the electrical system of the heart from surgical incisions if the middle cardiac nerve is accidentally tapped during surgery. If the nerve is touched, it will cause abnormalities as detected by EKG and/or arrhythmias.
Long-term follow up studies show that patients with total repair of TOF are at risk for sudden cardiac death and for heart failure. Therefore, lifetime follow-up care by an adult congenital cardiologist is recommended to monitor these risks and to recommend treatment, such as interventional procedures or re-operation, if it becomes necessary.
The use of antibiotics is no longer required by cardiologists and varies from case to case.
Disclaimer: This information is not meant to be a substitute for professional medical advise or help. It is always best to consult with a Physician about serious health concerns. This information is in no way intended to diagnose or prescribe remedies.This is purely for educational purpose.
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