2011 Group Project 6

From Embryology
Note - This page is an undergraduate science embryology student group project 2011.
2011 Projects: Turner Syndrome | DiGeorge Syndrome | Klinefelter's Syndrome | Huntington's Disease | Fragile X Syndrome | Tetralogy of Fallot | Angelman Syndrome | Friedreich's Ataxia | Williams-Beuren Syndrome | Duchenne Muscular Dystrolphy | Cleft Palate and Lip

Tetralogy of Fallot



In 1671, Niels Stenson was the first to describe Tetralogy of Fallot anatomically. However, the precise descriptions of the anatomy of Tetralogy of Fallot was done in 1784 by William Hunter at St Georges Hospital Medical School in London. His description is as follows [1]:

“…the passage from the right ventricle into the pulmonary artery, which should have admitted a finger, was not so wide as a goose quill; and there was a hole in the partition of the two ventricles, large enough to pass the thumb from one to the other. The greatest part of the blood in the right ventricle was driven with that of the left ventricle into the aorta, or great artery, and so lost all the advantage which it ought to have had from breathing”[2]

Hunter’s description of the defected heart’s anatomy along with its resulting physiology was further specified and advanced by Etienne-Louis Fallot. However it was Maude Abbott from Canada who coined the term ‘Tetralogy of Fallot’ in 1924. The first procedures for Tetralogy of Fallot were around from the 1950s. Due the advances in the areas of ‘diagnosis, perioperative and surgical treatment and postoperative care’, children born with Tetralogy of Fallot now have a great chance to survive to adulthood[3]

In retrospective studies it shows how surgical procedures have improved because in the 1950’s to today’s times, the mortality rate from surgery dropped from 50% to less than 2%. It was in 1945 that Blalock and Taussig explained the ‘systemic artery-to-pulmonary artery shunt’ and in 1954 that Varco and Lillehei repaired a TOF heart whilst doing a open-heart surgery.[4]

During such surgeries in the past the surgeons will actually now put a shunt between the pulmonary artery and a systemic artery of a child with Tetralogy of Fallot as this will allow some improvement to the oxygenation of the blood in the infant. It will be later when the individual grows up that the shunt will be removed then the heart will be repaired. Now surgeons prefer to repair the heart in the initial operation to repair the infants heart. [5]


Tetralogy of Fallot makes up around 7%-10% of Cardiac Congenital Defects as studies show that it occurs in 3 out of 10000 live births that are delivered. After the Neonatal age, Tetralogy of Fallot is the most frequent cause of cyanotic heart disease. Moreover, Tetralogy of Fallot slightly affects more males then females.[6]

From studies conducted in regards to mortality rates in respect to congenital heart disease in the US between 1979-2005, there was a 40% reduction in mortality that was linked to Tetralogy of Fallot. It is thought that this reduction in mortality was associated to the ‘earlier recognition and treatment of heart failure and arrythmia’ which allowed this change to occur.[7]

Signs and Symptoms

The most important sign of TOF patients is Cyanosis. This is when the lips, fingernails and skin of the patient turns into a bluish colour. Sometimes babies who have TOF can enter into ‘tet spells’, in which there is a sudden drop in oxygen saturation of the blood, causing the baby to turn blue. These tets spells become apparent when the baby does certain activities such as crying. In addition to the tet spells the baby could pass out, become unresponsive to their parents calling or touch, can develop fatigue and finally have dyspnoea. Furthermore, children of TOF would develop fatigue quickly and possibly pass out, thus surgeons now repair TOF hearts during infancy and not at adult to prevent such events.[8]

Another common sign of TOF is heart murmur which occurs due to the defected heart’s abnormal blood flow through it. However it should be mentioned that heart murmur is not a hallmark for Congenital Heart Defects as many hearts of healthy children also have murmurs.Furthermore, children of TOF don’t grow at the rate of normal children as whilst breastfeeding in infancy, the babies would get tired quicker and whilst the infant grows up, normal functionability of the heart and oxygen saturated blood is needed for proper growth. Finally, TOF children may also have clubbing. [9]

It should also be mentioned that pulmonary insufficiency symptoms developed from a TOF heart varies in the degree of pulmonary insufficiency found in that individual. Thus the symptoms that could be presented are of a wide range which could from decline in function to palpitations. Moreover, late symptoms could also develop from the insufficiency which includes right heart failure, exertional dyspnea, syncope and palpitations. In an event of which right ventricular failure occurs, signs to indicate it include elevated jugular venous pressure, ascites, hepatomegaly, jugular venous distension and peripheral edema.[10]


Pathophysiology and Abnormalities

Diagnostic Tests


Medical therapy:

Medical therapy is usually used to prepare the infant/adult for surgery, the degree of therapy depends upon the degree of cyanosis.

Acute cyanosis: knee chest positions, providing oxygen & intravenous morphine

Severe cyanosis: intravenous propranolol

Asymptomatic patients: no particular medical treatments


Today Tetralogy of fallot can only be treated with open-heart surgery, This is usually performed before 6 months of age and has a

  • low mortality rate of 2%, and
  • High long term survival rate of 85-90%
The goal of surgery is to be able to treat the four congenital abnormalities. It is also advantageous to perform this surgery at an early age and not wait until the child is older, however the specific timming of the operation is still under some controversy. 

Today, Transatrial and transatrial-transpulmonary surgical approaches are the most common in patients of all ages, having a survival rate of more than 99%.

Factors that increase the risk of surgery include: Low birth weight, young/old age, severe annular hypoplasia, simultaneous cardiac anomalies, major associated anomalies etc

In the surgery itself, the surgeon:

  • Widens the narrowed pulmonary blood vessels and the pulmonary valve itself, hence allowing for greater blood flow to the lungs.
  • Repairs the ventricular septal defect using a patch to cover the hole in the septum.

Fixing these two defects also solves the other two defects (the hypertrophy of the right ventricle wall and provides oxygenated blood to the aorta). Surgery is carried out during infancy, the incision heals in roughly 6 weeks.


Future Directions



  1. <pubmed>19683809</pubmed>
  2. <pubmed>19683809</pubmed>
  3. <pubmed>19683809</pubmed>
  4. <pubmed>21251297</pubmed>
  5. <pubmed>21048055</pubmed>
  6. <pubmed>20091166</pubmed>
  7. <pubmed>19853711</pubmed>
  8. http://www.nhlbi.nih.gov/health/health-topics/topics/tof/signs.html
  9. http://www.nhlbi.nih.gov/health/health-topics/topics/tof/signs.html
  10. <pubmed>21048055</pubmed>

2011 Projects: Turner Syndrome | DiGeorge Syndrome | Klinefelter's Syndrome | Huntington's Disease | Fragile X Syndrome | Tetralogy of Fallot | Angelman Syndrome | Friedreich's Ataxia | Williams-Beuren Syndrome | Duchenne Muscular Dystrolphy | Cleft Palate and Lip