Tetralogy of Fallot (TOF) is a congenital heart defect which is classically understood to involve four anatomical abnormalities (although only three of them are always present). It is the most common cyanotic heart defect, and the most common cause of blue baby syndrome.
Tetralogy of Fallot causes low oxygen levels in the blood. This leads to cyanosis (a bluish-purple color to the skin).
The classic form includes four defects of the heart and its major blood vessels:
- Ventricular septal defect VSD
- Pulmonary Infundibular Stenosis
- Overriding aorta
- Right ventricular hypertrophy
Tetralogy of Fallot is rare, but it is the most common form of cyanotic congenital heart disease. Patients with tetraology of Fallot are more likely to also have other congenital defects.
The cause of most congenital heart defects is unknown. Many factors seem to be involved.
Factors that increase the risk for this condition during pregnancy include:
- Alcoholism in the mother
- Diabetes
- Mother who is over 40 years old
- Poor nutrition during pregnancy
- Rubella or other viral illnesses during pregnancy
Children with tetralogy of Fallot are more likely to have chromosome disorders, such as Down syndrome and DiGeorge syndrome (a condition that causes heart defects, low calcium levels, and poor immune function).
Symptoms
- Blue color to the skin (cyanosis), which gets worse when the baby is upset
- Clubbing of fingers (skin or bone enlargement around the fingernails)
- Difficulty feeding (poor feeding habits)
- Failure to gain weight
- Passing out
- Poor development
- Squatting during episodes of cyanosis
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| Chest X-Ray of child with Teratology of fallot |
Diagnosis
A physical examination with a stethoscope almost always reveals a heart murmur.
Tests may include:
Before more sophisticated techniques became available, chest x-ray 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.
The abnormal "coeur-en-sabot" (boot-like) appearance of a heart with tetralogy of Fallot is classically visible via chest x-ray, although most infants with tetralogy may not show this finding.Absence of interstitial lung markings are another classic finding in tetralogy.
Additional anomalies
In addition, tetralogy of Fallot may present with other anatomical anomalies, including:
- stenosis of the left pulmonary artery, in 40% of patients
- a bicuspid pulmonary valve, in 40% of patients
- right-sided aortic arch, in 25% of patients
- coronary artery anomalies, in 10% of patients
- a foramen ovale or atrial septal defect, in which case the syndrome is sometimes called a pentalogy of Fallot
- an atrioventricular septal defect
- partially or totally anomalous pulmonary venous return
- forked ribs and scoliosis
Treatment
Surgery to repair tetralogy of Fallot is done when the infant is very young. Sometimes more than one surgery is needed. When more than one surgery is used, the first surgery is done to help increase blood flow to the lungs.
Surgery to correct the problem may be done at a later time. Often only one corrective surgery is performed in the first few months of life. Corrective surgery is done to widen part of the narrowed pulmonary tract and close the ventricular septal defect.
Prognosis:
Most cases can be corrected with surgery. Babies who have surgery usually do well. More than 90% survive to adulthood and live active, healthy, and productive lives. Without surgery, death usually occurs by the time the person reaches age 20.
Patients who have continued, severe leakiness of the pulmonary valve may need to have the valve replaced.
Regular follow-up with a cardiologist to monitor for life-threatening arrhythmias is recommended.
Complications
- Delayed growth and development
- Irregular heart rhythms (arrhythmias)
- Seizures during periods when there is not enough oxygen
- Death
Treatment
Emergency
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 (100%) 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.
Palliative surgery
palliative surgical procedure, which involved forming an anastomosis between the subclavian artery and the pulmonary artery. 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 Potts shunt and the Waterston-Cooley shunt 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
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 aGore-Tex patch or a homograft. Additional reparative or reconstructive surgery may be done on patients as required by their particular cardiac anatomy.
References
- Webb GD, Smallhorn JF, Therrien J, Redington AN. Congenital heart disease. In: Bonow RO, Mann DL, Zipes DP, Libby P, eds. Braunwald's Heart Disease: A Textbook of Cardiovascular Medicine, 9th ed. Philadelphia, Pa: Saunders Elsevier; 2011: chap 65.
- Cheng TO (1995). "Pentalogy of Cantrell vs pentalogy of Fallot". Tex Heart Inst J 22 (1): 111–2. PMC 325224. PMID 7787464.
- Boshoff D, Budts W, Daenen W, Gewillig M (January 2005). "Transcatheter closure of a Potts' shunt with subsequent surgical repair of tetralogy of fallot". Catheter Cardiovasc Interv 64 (1): 121–3. DOI:10.1002/ccd.20247. PMID 15619282.
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