A description of a very unusual formation of the human heart



Wait, isn’t there only one type of human heart?  Yes there is one standard model for the human heart.  However this model can have many variations in structure and pumping function.  Hearts with this condition are not normal, and are considered to be diseased. While it’s true that normal hearts can become diseased and dysfunctional over time, sometimes hearts can be diseased and dysfunctional at birth.  The topic of this article is Tetralogy of Fallot. This condition is more commonly known as TOF.


More about TOF

When talking about the human heart and it’s general condition, there are two basic categories:  normal and diseased. Of diseased hearts, there are two main categories: acquired and congenital.  An acquired heart disease is developed during the person’s lifetime. People with congenital heart disease are born with that condition.  TOF is a congenital heart disease.

Tetralogy of Fallot is extremely rare.  For example, there are only 20,000 babies born with this condition every year in America.  People with this type of heart disease are born with hearts having four distinct defects. These are:

  • Pulmonary valve stenosis
  • Ventricular septal defect
  • Overriding aorta
  • Right ventricular hypertrophy


These defects and treatments needed to correct them will be discussed in more detail below.


Pulmonary valve stenosis

People whose hearts have this condition have hearts with narrow pulmonary valves.  The pulmonary valve is which the heart’s lower chamber (right ventricle) from the heart’s main blood vessel going to the lungs (pulmonary artery).   When the pulmonary valve is narrowed, blood has a harder time traveling to the lungs, and its flow is lessened. The muscle below the pulmonary valve may be weaker as well.  Some people with severe forms of TOF may have a malformed or incomplete pulmonary valve. This is referred to as pulmonary atresia and causes less blood to go to the lungs.


Ventricular septal defect

Normal hearts have a wall which separates their two lower chambers.  This is referred to as the septum. The two lower chambers of the heart are the left and right ventricles.  People with TOF have a hole in the septum. Blue blood in the right ventricle is able to travel to the lungs to be oxygenated through this hole.  It does this by flowing through the left ventricle to mix with blood which the lungs have just infused with oxygen.

When people have ventricular septal defect (VSD) they face another issue because blood from their left ventricle flows back through to the right ventricle rather inefficiently.  Less oxygenated blood flows through the body because of VSD. In extreme cases, VSD can weaken the heart.


Overriding Aorta

The aorta is the main artery which oxygenated blood travels out of the heart to the body through.  In normal hearts, it branches off of the left ventricle. For people with TOF however, the aorta is formed slightly to the right of the heart and rests directly above the VSD.  The aorta is in an abnormal position in this instance. Oxygen rich blood from the left ventricle, and deoxygenated blood from the right ventricle mix and result in purple blood which is then pumped out to the rest of the heart.  The result can be bad for the person.


Right Ventricular Hypertrophy

If a person has TOF, his or her heart is working extra to pump blood.  The muscular wall of his or her heart’s right ventricle may thicken over time.  This causes the right ventricle to become less efficient. It can also cause the heart to stiffen, weaken, and fail over time.  This can result in premature death in extreme cases.


It is not uncommon for people with TOF to have other heart defects.  These can include a hole between the heart’s upper chambers, also referred to as atrial septal defect (ASD).  People with TOF can also have abnormal or dysfunctional coronary arteries, or a right aortic arch.


Some facts about TOF

Tetralogy of Fallot is the most common congenital heart disease.  In America alone, approximately 5 out of every ten thousand babies are born with it.  People who develop TOF develop it very early in utero. This occurs when the heart is first developing.  When the heart starts to develop, it begins as a simple tube which divides into two equal sides. In babies with TOF, the tube starts to divide into two unequal sides with the right side being much smaller than the left.  The result is the development of the four heart problems mentioned above as the heart begins to develop.


This heart condition was named after the famous French doctor Etienne Louis Arthur Fallot.  He was the one who first noticed the disease and gave it a name.


How and why is TOF caused?

As with all major congenital heart diseases, not much is known regarding the causes of TOF.  since it happens as the fetus’s heart is forming, doctors are not sure how to prevent it. However, certain factors and conditions are thought to increase the fetus’s risk of developing it in the pregnant woman.  These factors are:

  • A virus during pregnancy.  A good example is rubella
  • Drinking excessive alcohol when pregnant
  • Not eating right during pregnancy
  • Having advanced maternal age when pregnant (being over age 40)
  • The pregnant woman having TOF
  • The fetus having another genetic anomaly like Down Syndrome or DiGeorge Syndrome


How long can people with TOF live?

Most people with TOF have average life expectancies.  While some people with TOF only live into their mid-forties or early fifties, most people can expect to live into their 60’s, 70’s, and 80’s.  The first life saving surgery for babies with TOF was pioneered in 1944. It was called the Blalock-Taussig procedure. It allows these babies’ hearts to pump enough oxygenated blood to their bodies.  Most people who had this procedure are still alive.


Approximately 10 years later, life saving open heart surgery was pioneered which could repair, but not fix, TOF.  


How can doctors tell if a newborn has TOF?

The most obvious sign of TOF in a newborn is cyanosis or a heart murmur.  A heart murmur is caused by irregular blood flow and is characterized by an abnormal ‘whooshing’ sound.  Of course, since visual diagnosis by itself is not enough for a doctor to determine if a newborn really has TOF, he or she (doctor) will use several tests and do a physical exam to confirm TOF.


Tests used to determine TOF

Echocardiography:  These produce echocardiograms which work by producing accurate and very visible pictures of the heart with high-pitched sound waves.  The pictures are actually moving images of the heart which the doctor can see on a video screen.


Echocardiograms are primarily used to diagnose TOF in newborns because they allow the doctor to see if their hearts have a VSD, its location (if a VSD exists), the structure of the pulmonary valve and artery.  Newborn hearts with TOF will have malformed or partially formed pulmonary valves and arteries. Echocardiograms also tell the doctor if the right ventricle is functioning the way it should, and if the the aorta is positioned the way it should be.  They also indicate other serious and not so severe heart defects. Once the doctor fully understands the nature and extent of TOF, he or she can use the echocardiogram to map out a treatment plan for the newborn.


Electrocardiogram:  This test records the electrical movements of the heart as it functions (contracts).  A technician will place patches with electrodes (wires which record heart function) on the newborn’s chest, wrists, and ankles.  The heart’s function is recorded on a special piece of paper as a line which shows its electrical activity. An electrocardiogram is casually referred to as an EKG.  It is valuable for doctors because it can detect right ventricular hypertrophy (enlargement of the right ventricle), the nature of the heart’s rhythm (whether or not it is regular), and enlargement of the right atrium.


Chest X-ray:  This test uses radioactive energy to help draw an image which shows the heart and lungs structure.  Newborns with TOF usually have an enlarged right ventricle. Their heart looks like a boot as a result.


Pulse oximetry:  a technician places a small sensor on one of the newborn’s fingers or toes.  This sensor detects the levels of oxygen saturation in the newborn’s blood stream.


Heart catheterization:  This test will indicate the heart’s structure to the doctor.  Once the doctor knows more about the structure of the newborn’s heart, he or she can formulate an effective treatment plan.  The doctor places a thin, flexible tube into the heart through the newborn’s groin, artery, arm, or neck. A special dye is injected into the tube which will paint an accurate picture of the heart’s structure.  Heart catheterizations are also useful in letting the doctor know the pressure and oxygen saturation levels of the heart’s chambers and blood vessels.


Treatment plans

The only effective long-term treatment for newborns with TOF is surgery.  A newborn can get one of two types of surgery: an intracardiac repair, or a temporary procedure using a shunt.  The intracardiac repair is most commonly used in newborns, babies, and young kids.


The condition of the heart and the severity of TOF in the newborn, baby, or young kid largely determines the type of surgery to be performed and its date.  


Some newborns, babies, and kids need to take medicines to keep the two large arteries in the heart open wide enough to allow enough blood to flow to and from the heart.  This maintains the function and structure of the heart before the intracardiac repair.


Intracardiac repair

This is major open heart surgery which is done before the baby turns one.  This procedure is rarely done on adults who had no surgery as newborns or babies.  The surgeon will patch the VSD to close it. This allows blood to flow through the heart more efficiently and at a regular pace.  TOF babies have a narrow pulmonary valve. If not corrected, it can cause problems for them later on in life. The pulmonary valve is either replaced or repaired to allow more blood to flow to the lungs.


The right ventricle is not worked as much.  It becomes much thinner and goes back to the size which it is in people with a normal heart.  Oxygen saturation in the blood increases and symptoms either become less severe or temporarily disappear after the surgery.


Temporary surgery

Some babies with TOF need temporary surgery before their intracardiac surgery to make sure that more blood flows to the lungs.  Premature babies, or those who were born with under/undeveloped pulmonary arteries tend to require this surgery.

The surgeon creates a shunt between the large artery which separates the aorta and the pulmonary artery.  The shunt is removed before the intercardiac surgery.


Long-term outlook

Most babies who get either type of surgery do fairly well as adults and can live fairly long and productive lives.  However, since these surgeries are not a ‘fix,’ most people with TOF tend to have complications later on in life – even after these life saving surgeries.  Common complications for with people with TOF are:

  • Chronic pulmonary regurgitation.  This is a condition which results in blood leaking back into the right ventricle through the pulmonary valve.  People with this complication have much lower ejection fractions.
  • People with TOF can develop major heart problems.  One of these includes blood leaking into the right ventricle through the tricuspid valve.  This can result in a lowered ejection fraction and heart failure. It is referred to as tricuspid regurgitation.
  • VSDs which may leak throughout the person’s life.  These holes often need to be re-repaired because the patches can become damaged or wear away.  This results in continued or new leakage even after surgery.
  • A dysfunctional left ventricle or an enlarged right ventricle.  This results in a much lower ejection fraction which can eventually lead to heart failure.
  • Arrhythmias – these are irregular heartbeats.  They can lead to heart malfunction if not treated
  • Coronary heart disease
  • Dilation of the ascending aorta
  • The person with TOF can die suddenly and prematurely.  Though not common, it is not unheard of for people with TOF to die in their mid-forties to early fifties.


These complications mean that most people with TOF will require additional surgeries throughout their lives even after the initial life saving surgery.  They need to visit their cardiologist at least once a year for a a regular cardiac checkup. The cardiologist can determine if another surgery or usage of medicines are needed.  Many adults with TOF suffer from leakage in the repaired pulmonary valve. They may need open heart surgery to have their pulmonary valve replaced with a prosthetic or animal artificial valve.  These tend to have a life expectancy of 10-15 years.


Adults with TOF commonly experience arrhythmias which are usually only correctable with medication.  They may need ablations (a procedure which freezes part of the heart) to treat the arrythmias. They may also need a pacemaker to adjust the heart’s natural rhythm.  This pacemaker is referred to as a defibrillator.


Adults with TOF may need to take blood thinners to treat blood clots.  They may also need antibiotics because they are more prone to develop life threatening infections.


Sometimes these adults are advised not to exercise heavily or exert themselves excessively physically to put less stress on their hearts.


In conclusion…

While not a death sentence, TOF is a heart condition which is treatable and manageable with the right medical intervention.  Many people with TOF live fairly healthy and happy lives.






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