Tetralogy of Fallot (ToF) is the most frequently seen cyanotic (blue baby syndrome) heart abnormality. Tetralogy of Fallot is named after the French physician, Etienne Fallot in 1888 (also described in 1672 by Niels Stenson ) and is called a tetralogy because there are four main features that are commonly observed. The four heart defects which typically occur together are:
1. Right ventricular enlargement-The right ventricle becomes hypertrophied due to an excess workload that occurs in Tetralogy of Fallot. The normal right ventricle is much less muscular than the left ventricle. It normally pumps the blood into the low pressure pulmonary system that goes to the lungs but in Tetralogy of Fallot it works much harder to pump blood into the pulmonary vessels because the other heart defects obstruct blood flow in the pulmonary valve and sometimes just before the valve. The obstruction must be overcome by the right ventricle(RV)pumping harder and the muscle of the RV responds to this increased workload by becoming thicker and more muscular. The enlarged right ventricle can be seen on a chest xray as well as echocardiograms and other heart studies.
2. Overriding aorta-The aorta which is the main large artery arising from the left ventricle is located in an abnormal place in Tetralogy of Fallot. It is moved towards the right ventricle outflow region and that is why it is referred t as an "overriding aorta". The aortic valve and aorta are in communication with or attached to the right ventricle. The amount that the aorta overrides the right ventricle greatly varies from patient to patient.
3. Pulmonic Valve stenosis-Normally, the blood leaves the right ventricle through the pulmonary valve which sends the blood to the pulmonary artery and the lungs. In Tetralogy of Fallot, the pulmonary valve opening is smaller. Narrowing can also occur just before blood gets to the pulmonary valve. The smaller openings are responsible for the right ventricle muscle enlargement that is part of Tetralogy of Fallot.
4. Ventricular Septal Defect or "VSD"- The wall between the right and left ventricles has a hole or defect in Tetralogy of Fallot. The hole is usually a large one.
Symptoms that Tetralogy of Fallot patients generally include:
*Hypercyanotic Attacks (Tet Spells)-Patients with Tetralogy of Fallot have spells where they suddenly turn a blue color due to a low oxygen in their bloodstream. The main cause of inadequate oxygen in the bloodstream is obstruction of blood flow to the pulmonary arteries which are supposed to send blood to the lungs where it should be picking up oxygen. When the patient has an less blood flow through the lungs due to elevated resistance in the pulmonary blood vessels, the patient turns blue. During a Tet spell, much of the blood goes directly from the right heart to the left heart through the ToF defects such as the Ventricular Septal Defect and the overriding aorta, the blueish color of the hypercyanotic spell is observed. The blue color means hemoglobin molecules in the blood are not bound to oxygen(deoxygenated hemoglobin is blue in color). The hypercyanotic (Tet) spells can be quite severe and may lead to death or organ damage.
*Cyanosis-Usually patients with Tetralogy of Fallot have lower than normal oxygen levels in their bloodstream. The lower oxygen levels cause the bluish lip and skin color because the deoxygenated blood is blue in color. The patient's body makes extra red blood cells as a way to deal with the lower oxygen levels in the blood. The extra red blood cells result in a thicker than normal blood-the condition is referred to as polycythemia (meaning "many cells").
*Dyspnea with exertion-The lower than normal oxygen levels of the blood cause the patients to get short of breath easily because their blood oxygen supply gets used up quickly when the patient is physically active.
*Reduced Growth of the patient -Infants with ToF may be slow to grow. This side effect of Tetralogy of Fallot is termed "failure to thrive"
The treatment for Hypercyanotic (Tet) spells in Tetralogy of Fallot is medical management. Surgery should be done to provide a long term correction to the condition.
The medical treatments for Tet spells aims to slow the heart rate and raise the systemic blood pressure in order to push the deoxygenated venous blood flow into the small pulmonary valve and pulmonary vessels. Propranolol is used to slow the heart rate and decrease right to left heart shunt. Patients with Tet spells often assume a squatting position which increases the amount of blood returning to the right heart from the veins and helps reduce hypercyanotic spells.
The surgical treatments for Tetralogy of Fallot range from complete corrective surgery to less complex procedures that simply relieve the pulmonary circuit obstructions. The original surgical treatment that was done to treat Tetralogy of Fallot was the Blalock-Taussig shunt. The Blalock-Taussig shunt works by connecting a large arterial branch from the aorta(the left subclavian artery) to the left pulmonary artery in order to bypass the pulmonic valve narrowing.
Successful complete surgical correction is now possible. Long term results are much better than in the past. Often additional surgeries are needed because of scarring and other changes near the defects that are repaired.
In the past (and in poor countries) where surgery may be unavailable Tetralogy of Fallot leads to congestive heart failure symptoms and premature death. About one third of patients survive ten years if left untreated. Surgically treated patients can live fairly normal lives. The surgically corrected patients continue to have an increased risk of cardiac problems and sudden death for the remainder of their lives.
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