Tetralogy of Fallot

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Not to be confused with Teratology.
Tetralogy of Fallot
Tetralogy of Fallot.svg
Diagram of a healthy heart and one with tetralogy of Fallot
Classification and external resources
Specialty Cardiac surgery, pediatrics
ICD-10 Q21.3
ICD-9-CM 745.2
OMIM 187500
DiseasesDB 4660
MedlinePlus 001567
eMedicine emerg/575
Patient UK Tetralogy of Fallot
MeSH D013771
[[[d:Lua error in Module:Wikidata at line 863: attempt to index field 'wikibase' (a nil value).|edit on Wikidata]]]

Tetralogy of Fallot (TOF) is a congenital heart defect which is classically understood to involve four anatomical abnormalities of the heart (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.[1] TOF is usually a right-to-left shunt, in which higher resistance to right ventricular outflow results in more severe cyanosis symptoms.[2]

TOF is treated with corrective surgery, usually within the first year of life, but presents with long-term problems including arrhythmia, pulmonary regurgitation, and re-operation.[3]

In the United States, the prevalence of TOF is 3.9 per 10,000 live births and accounts for 7-10% of congenital heart diseases.[4] It was described in 1672 by Niels Stensen, in 1773 by Edward Sandifort, and in 1888 by the French physician Étienne-Louis Arthur Fallot, after whom it is named.[5]

Signs and symptoms

Digital clubbing with cyanotic nail beds in an adult with tetralogy of Fallot

Tetralogy of Fallot results in low oxygenation of blood due to the mixing of oxygenated and deoxygenated blood in the left ventricle via the ventricular septal defect (VSD) and preferential flow of the mixed blood from both ventricles through the aorta because of the obstruction to flow through the pulmonary valve. This is known as a right-to-left shunt. The primary symptom is low blood oxygen saturation with or without cyanosis from birth or developing in the first year of life. If the baby is not cyanotic then it is sometimes referred to as a "pink tet."[6] 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.

Children with tetralogy of Fallot may develop "tet spells." The precise mechanism of these episodes is in doubt, but presumably results from a transient increase in resistance to blood flow to the lungs with increased preferential flow of desaturated blood to the body. Tet spells are characterized by a sudden, marked increase in cyanosis followed by syncope, and may result in hypoxic brain injury and death. Older children will often squat during a tet spell, which increases systemic vascular resistance and allows for a temporary reversal of the shunt.

Cause

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 develops progressively from resistance to blood flow through the right ventricular outflow tract.

Pathophysiology

Primary four malformations

"Tetralogy" denotes a four-part phenomenon in various fields, including literature, and the four parts the syndrome's name implies are its four signs. This is not to be confused with the similarly named teratology, a field of medicine concerned with abnormal development and congenital malformations, which thereby includes tetralogy of Fallot as part of its subject matter.

As such, by definition, tetralogy of Fallot involves four heart malformations which present together:

Tetralogy of Fallot
Normal heart
Condition Description
A: Pulmonary Infundibular Stenosis A narrowing of the right ventricular outflow tract. It can occur at the pulmonary valve (valvular stenosis) or just below the pulmonary valve (infundibular stenosis). Infundibular pulmonic stenosis is mostly caused by overgrowth of the heart muscle wall (hypertrophy of the septoparietal trabeculae),[11] however the events leading to the formation of the overriding aorta are also believed to be a cause. The pulmonic stenosis is the major cause of the malformations, with the other associated malformations acting as compensatory mechanisms to the pulmonic stenosis.[12] The degree of stenosis varies between individuals with TOF, and is the primary determinant of symptoms and severity. This malformation is infrequently described as sub-pulmonary stenosis or subpulmonary obstruction.[13]
B: Overriding aorta An aortic valve with biventricular connection, that is, it is situated above the ventricular septal defect and connected to both the right and the left ventricle. The degree to which the aorta is attached to the right ventricle is referred to as its degree of "override." The aortic root can be displaced toward the front (anteriorly) or directly above the septal defect, but it is always abnormally located to the right of the root of the pulmonary artery. The degree of override is extremely variable, with 5-95% of the valve being connected to the right ventricle.[11]
C: ventricular septal defect (VSD) A hole between the two bottom chambers (ventricles) of the heart. The defect is centered around the most superior aspect of the ventricular septum (the outlet septum), and in the majority of cases is single and large. In some cases thickening of the septum (septal hypertrophy) can narrow the margins of the defect.[11]
D: Right ventricular hypertrophy The right ventricle is more muscular than normal, causing a characteristic boot-shaped (coeur-en-sabot) appearance as seen by chest X-ray. Due to the misarrangement of the external ventricular septum, the right ventricular wall increases in size to deal with the increased obstruction to the right outflow tract. This feature is now generally agreed to be a secondary anomaly, as the level of hypertrophy tends to increase with age.[14]

There is anatomic variation between the hearts of individuals with tetralogy of Fallot. Primarily, the degree of right ventricular outflow tract obstruction varies between patients and generally determines clinical symptoms and disease progression.

Presumably, this arises from an unequal growth of the aorticopulmonary septum. The aorta is too large, thus "overriding," and this "steals" from the pulmonary artery, which is therefore stenosed. This then prevents ventricular wall closure, therefore VSD, and this increases the pressures on the right side, and so the R ventricle becomes bigger to handle the work.

Additional anomalies

In addition, tetralogy of Fallot may present with other anatomical anomalies, including:

  1. stenosis of the left pulmonary artery, in 40% of patients
  2. a bicuspid pulmonary valve, in 60% of patients
  3. right-sided aortic arch, in 25% of patients
  4. coronary artery anomalies, in 10% of patients
  5. a patent foramen ovale or atrial septal defect, in which case the syndrome is sometimes called a pentalogy of Fallot[15]
  6. an atrioventricular septal defect
  7. partially or totally anomalous pulmonary venous return
  8. forked ribs and scoliosis

Tetralogy of Fallot with pulmonary atresia (pseudotruncus arteriosus) is a severe variant[16] in which there is complete obstruction (atresia) of the right ventricular outflow tract, causing an absence of the pulmonary trunk during embryonic development. In these individuals, blood shunts completely from the right ventricle to the left where it is pumped only through the aorta. The lungs are perfused via extensive collaterals from the systemic arteries, and sometimes also via the ductus arteriosus.

Diagnosis

A CXR (Chest X-Ray) of a child with tetralogy of Fallot

Congenital heart defects are now diagnosed with echocardiography, which is quick, involves no radiation, is very specific, and can be done prenatally.

Before more sophisticated techniques became available, chest x-ray was the definitive method of diagnosis. 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.[17] Absence of interstitial lung markings secondary to pulmonary oligaemia are another classic finding in tetralogy,[18] as is the pulmonary bay sign.

Treatment

Tet spells

Prior to corrective surgery, children with tetralogy of Fallot may be prone to consequential acute hypoxia, tet spells, characterized by dyspnea, cyanosis, agitation, and syncope. This may initiated by any event leading to decreased oxygen saturation or that causes decreased systemic vascular resistance, leading to increased venous return, which in turn leads to increased shunting through the ventral septal defect. These may be treated with beta-blockers such as propranolol, but acute episodes require rapid intervention with morphine or intranasal fentanyl[19] to reduce ventilatory drive, a vasopressor such as ketamine, phenylephrine, or norepinephrine to increase systemic vascular resistance, and IV fluids for volume expansion. Oxygen (100%) may be effective in treating spells because it is a potent pulmonary vasodilator and systemic vasoconstrictor. This allows more blood flow to the lungs by decreasing shunting of deoxygenated blood from the right to left ventricle through the VSD. There are also simple procedures such as squatting and the knee chest position which increase systemic vascular resistance and decrease right-to-left shunting of deoxygenated blood into the systemic circulation.[20]

Palliative surgery

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 a side to end anastomosis between the subclavian artery and the pulmonary artery. This first surgery was depicted in the film Something the Lord Made.[21] 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[22] and the Waterston-Cooley shunt[23][24] 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 an 11-year-old boy.[25] Total repair on infants has had success from 1981, with research indicating that it has a comparatively low mortality rate.[26]

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.

Epidemiology

Tetralogy of Fallot occurs approximately 400 times per million live births[27] and accounts for 7 to 10% of all congenital heart abnormalities.

Prognosis

Untreated, tetralogy of Fallot rapidly results in progressive right ventricular hypertrophy due to the increased resistance caused by narrowing of the pulmonary trunk. This progresses to heart failure which begins in the right ventricle and often leads to left heart failure and dilated cardiomyopathy. Mortality rate depends on the severity of the tetralogy of Fallot. If left untreated, TOF carries a 35% mortality rate in the first year of life, and a 50% mortality rate in the first three years of life. Untreated TOF also causes delayed growth and development, including delayed puberty.

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 depend 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 later in adulthood. They require, therefore, follow up in specialized Adult Congenital Heart Disease centres. 55% are present.

Notable cases

See also

References

  1. ↑ Breitbart R, Fyler, D. Tetralogy of Fallot. In Nadas' Pediatric Cardiology, 2ed, Ed. Keane, Locke, & Fyler, Philadelphia: Saunders-Elsevier, 2006, p. 559.
  2. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ synd/2281 at Who Named It?
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  11. ↑ 11.0 11.1 11.2 Gatzoulis MA, Webb GD, Daubeney PE. (2005) Diagnosis and Management of Adult Congenital Heart Disease. Churchill Livingstone, Philadelphia. ISBN 0-443-07103-9.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Anderson RH, Weinberg. The clinical anatomy of tetralogy of Fallot. Cardiol Young. 2005 15;38-47. PMID 15934690.
  14. ↑ Anderson RH, Tynan M. Tetralogy of Fallot – a centennial review. Int J Cardiol. 1988 21; 219-232. PMID 3068155.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  16. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  17. ↑ http://radiopaedia.org/articles/tetralogy-of-fallot
  18. ↑ http://www.scribd.com/shawn_robinson_2/d/74194438/67-Tetralogy-of-Fallot p290
  19. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  20. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  21. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  22. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  23. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  24. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  25. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  26. ↑ Lua error in package.lua at line 80: module 'strict' not found..
  27. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  28. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  29. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  30. ↑ http://www.bookcouncil.org.nz/writers/mceldowney.html
  31. ↑ http://www.msnbc.msn.com/id/41455377/ns/business-business_of_super_bowl_xlv/

External links

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