Tetralogy of Fallot (ToF)
Tetralogy of Fallot (ToF) is the most frequently occurring cyanotic (blue baby syndrome) heart defect. Tetralogy of Fallot is named after a French physician, Etienne Fallot in 1888 (also described earlier by Niels Stenson 1672) and is called a tetralogy (four parts) because there are four features that are commonly seen. The four heart abnormalities which typically occur together are:
- Right ventricular hypertrophy–The right ventricle becomes enlarged due to an excess workload that occurs in Tetralogy of Fallot. The normal right ventricle is much thinner and less muscular than the left ventricle. It normally pumps the blood into a low pressure system that goes to the lungs but in ToF it works much harder to pump blood into the lungs because the other heart defects obstruct blood flow in the pulmonary valve and sometimes just below the valve. The obstruction must be overcome by pumping harder and the muscle of the right ventricle responds to this workload by becoming thicker. The enlarged right heart can be seen on a chest xray as well as echo-cardiograms and other heart tests.
- Overriding aorta–The aorta which is the main artery coming from the left ventricle is located in an abnormal position in Tetralogy of Fallot. It is moved somewhat towards the right ventricle outflow region and that is why it is referred t as an overriding aorta. The aortic valve and aorta are actually in communication with or attached to the right ventricle. The amount that the aorta is overriding the right ventricle varies greatly from patient to patient.
- Pulmonic stenosis–Normally, the blood exits the right ventricle through the pulmonic valve which sends the blood to the pulmonary artery and the lungs. In Tetralogy of Fallot, the pulmonic valve opening is narrowed. Narrowing can also occur just before blood gets to the pulmonic valve. The narrowed openings are responsible for the right ventricle muscle enlargement that is part of Tetralogy of Fallot.
- Ventricular Septal Defect or “VSD”– The wall or septum between the right and left ventricles has a hole in it in Tetralogy of Fallot. The hole or defect is usually a large one
Symptoms that Tetralogy of Fallot patients usually have include:
Sudden Hypercyanotic Attacks (Tet Spells)–Patients with Tetralogy of Fallot have episodes where they suddenly turn a blue color due to a lack of oxygen in their bloodstream. The cause of inadequate oxygen in the bloodstream is obstruction of blood flow to the pulmonary arteries which normally send blood to the lungs where it should be getting oxygenated. When the patient has an less blood flow through the lungs due to high 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 VSD and overriding aorta, the blue color of the hypercyanotic spell is seen. The blue color indicates hemoglobin molecules in the blood are not bound to oxygen. The hypercyanotic (Tet) spells can be severe and may lead to death or organ damage.
Cyanosis–Many patients with Tetralogy of Fallot have lower than normal oxygen levels in their bloodstream most of the time. The low oxygen levels result in a bluish lip and skin color because the deoxygenated blood is blue in color. The patient’s body manufactures extra red blood cells as a way to cope with the low oxygen content of the blood. The extra red blood cells cause a thicker than normal blood–the condition is called polycythemia (meaning “many cells”).
Dyspnea with exertion–The lower than normal oxygen content of the blood causes the patients to get out of breath easily since their blood oxygen levels gets used up quickly when the patient is physically active.
Reduced Growth of the patient –A side effect of Tetralogy of Fallot is often a reduction in growth of the body. This is termed “failure to thrive”
Treatment for Tetralogy of Fallot is medical for management of Hypercyanotic (Tet) spells. Eventually surgery should be done to provide a long term correction to the condition.
- The medical treatments of Tet spells aim to slow the heart rate and raise the systemic blood pressure in order to force the deoxygenated venous blood to flow into the narrow pulmonary valve and pulmonary vessels. Propranolol is used to slow the heart rate and decrease right to left heart shunt. Also the squatting position 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 complicated procedures that seek to simply relieve the pulmonary circuit obstructions. The first surgical treatment that was done to treat Tetralogy of Fallot was the Blalock-Taussig shunt. The Blalock-Taussig shunt connects a large arterial branch from the aorta to the left pulmonary artery in order to bypass the pulmonary valve narrowing.
More successful complete surgical correction is now possible. Long term results are much better than in the past, although additional surgeries are sometimes needed because of scarring and changes at the site of 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 fare much better and may live fairly normal lives. The surgically corrected patients continue to have an increased risk of cardiac problems and death for the remainder of their lives.
