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Tetralogy of Fallot
Additional recommended knowledge
Primary four malformations
As classically described, tetralogy of Fallot involves four heart malformations which present together:
There is anatomic variation between the hearts of individuals with tetralogy of Fallot. The degree of right ventricular outflow tract obstruction varies between patients and is generally determines clinical symptoms and disease progression. Tetralogy of Fallot may present with other anatomical anomalies, including:
Tetralogy of fallot with pulmonary atresia or pseudotruncus arteriosus is a severe variant in which there is complete obstruction of the right ventricular outflow tract and absence of the pulmonary trunk. In these individuals, there is complete right to left shunting of blood. The lungs are perfused via extensive collaterals from the systemic arteries.
Epidemiology and etiology
Tetralogy of Fallot occurs in approximately 3 to 6 per 10,000 births and represents 5-7% of congenital heart defects. 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. It occurs slightly more often in males than in females.
Embryology studies show that it is a result of anterior malalignment of the conal 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.
Tetralogy of Fallot results in low oxygenation of blood due to mixing of oxygenated and deoxygenated blood in the left ventricle through the VSD and preferential flow of both oxygenated and deoxygenated blood from the ventricles through the aorta because of obstruction to flow through the pulmonary valve. This is known as a right-to-left shunt.
Children with tetralogy of Fallot may develop acute severe cyanosis or hypoxic "tet spells". The precise mechanism of these episodes is in doubt, but presumably results from an increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body.
The primary symptom is low blood oxygen saturation with or without cyanosis from birth or developing in the first year of life. Without cyanosis, the baby is referred to as a "pink tet". Other symptoms include a heart murmur which may range from almost imperceptible to very loud, difficulty in feeding, failure to gain weight, retarded growth and physical development, dyspnea on exertion, clubbing of the fingers and toes, and polycythemia.
Tet spells are characterized by a sudden, marked increase in cyanosis, syncope, and may result in hypoxic brain injury and death.
Often a simple chest x-ray is enough to determine the presence of this condition. The heart may present with a "boot-like" appearance, rather than the symmetric appearance of a normal heart. The most common method to diagnose this condition , or any other congenital heart defect, is with echocardiography. It is quick, involves no radiation and is very specific.
Tetralogy of Fallot is treated on two levels: with immediate emergency care for hypoxic or "tet" spells and with corrective surgery.
Emergency management of tet spells
Consequential acute hypoxia may be treated with beta-blockers such as propranolol, but acute episodes may require rapid intervention with morphine to reduce ventilatory drive and phenylephrine to increase blood pressure. Oxygen is ineffective in treating hypoxic spells because the underlying problem is lack of blood flow through the pulmonary circuit and not alveolar oxygenation. There are also simple procedures such as 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 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 Pott shunt and the Waterson procedure are other shunt procedures which were developed for the same purpose.
Currently, Blalock-Thomas-Taussig shunts are not normally performed on infants with TOF except for severe variants such as TOF with pulmonary atresia.
Total surgical repair
The Blalock-Taussig procedure was the only surgical treatment until the first total repair was performed in 1954. Between 1944 and when total repair became available at major surgical centers in the early 1960s, many infants and children were treated with Blalock-Taussig procedures.
The total repair was performed by C. Walton Lillehei at the University of Minnesota in 1954 on a 10-month boy. Total repair initially carried a high mortality risk which has consistently improved over the years. Surgery is now often carried out in infants 1 year of age or younger with a <5% perioperative mortality. The surgery generally involves making incisions into the heart muscle, relieving the right ventricular outflow tract stenosis by careful resection of muscle, and repairing the VSD using a Gore-Tex or Dacron patch or a homograft. Additional reparative or reconstructive work may be done on patients as required by their particular anatomy.
Patients who have undergone "total" repair of tetralogy of Fallot often have good to excellent cardiac function after the operation with some to no exercise intolerance and have the potential to lead normal lives. 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.
Untreated, tetralogy of Fallot results in progressive right ventricular hypertrophy and dilatation due to the increased resistance on the right ventricle. The dilated cardiomyopathy progresses to right heart failure, usually with accompanying 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 with repaired tetralogy of Fallot have the potential to lead normal lives with continued excellent cardiac function, with some considerations:
Current techniques for total surgical repair greatly improve the hemodynamic function of the heart with tetralogy of Fallot but do not provide a lifetime correction of the defect. Ninety percent of patients with total repair as infants develop a progressively leaky pulmonary valve as the heart grows to its adult size. Patients also may have some degree of residual right outflow stenosis and damage to the electrical system of the heart from surgical incisions, causing abnormalities as detected by EKG and/or arrhythmias.
Long-term follow up studies show that this patient population is 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.
Antibiotic prophylaxis is indicated during dental treatment in order to prevent infective endocarditis.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Tetralogy_of_Fallot". A list of authors is available in Wikipedia.|