Tetralogy of Fallot – ToF
We’re now getting to a more complicated condition called the Tetralogy of Fallot – or ToF, for short. The diseases discussed until now had just one abnormality in the heart – Atrial Septal Defect (ASD) or Ventricular Septal Defect (VSD) or Patent Ductus Arteriosus (PDA).
As the name tetralogy implies, there are FOUR abnormalities combined together in this complex heart defect. ToF is also commonly called the “blue-baby” disease.
In this article, you’ll learn:
- What are the components of ToF?
- Why is it called “Blue Baby Disease”?
- What exactly happens in ToF?
- What is a “cyanotic spell”?
- What happens if ToF is left uncorrected?
- What are the surgical options?
- How is a single stage intra-cardiac repair done?
- Variations in ToF needing modified repair
- What is an “outflow patch”?
- When is an intracardiac repair NOT possible?
- What are the palliative operations for ToF?
- The Blalock-Taussig shunt
- Other systemic-pulmonary shunt procedures
- What is the outcome after a total correction operation?
- What is the future course after a shunt procedure?
Basics of Tetralogy of Fallot
What are the four components of ToF ?
1. The first is a Ventricular Septal Defect – or VSD.
2. Next is a narrowing of the Pulmonary Valve, which guards the junction of the right ventricle with the pulmonary artery. This narrowing is called Pulmonary Stenosis (PS).
3. The third feature is a thickening of the wall of the right ventricle (RV). This increases the strength of the right ventricle and helps it pump blood more forcibly. This thickening is called RV Hypertrophy.
4. And the last component is an over-riding aorta.
As you know already, the aorta normally arises from the left ventricle. In ToF, the aorta is moved away from its normal position so that it arises partly from the right ventricle too. Since there is a wall – or ventricular septum – between the two ventricles, it is obvious that the aorta must be positioned right above this wall – or in other words, the aorta over-rides the ventricular septum.
Why is ToF called “Blue Baby Disease” ?
Because a baby with ToF is “blue”. No kidding! The child has a bluish color, most obvious on the tongue, lips, finger tips and toes. Although ToF is not the only disease to cause this blue color – called “cyanosis” – it is the most common one.
What causes this blue color ?
Blood contains a “pigment” – or coloring substance – called “hemoglobin”. This hemoglobin has a special property – it can carry oxygen. You can imagine hemoglobin to be a sort of pick-up truck. It travels on the highway of the blood-vessels, and reaches the lungs, where oxygen is loaded onto it.
It then continues along arteries to different parts of the body, where it unloads its oxygen. The oxygen is converted into energy, which is used by different organs to do their work. The “empty” hemoglobin then returns to the lung to pick up its next load.
When hemoglobin is carrying oxygen, it is bright red in color. That’s why we call the “pure” blood of the arteries “red blood”. When it has given up its oxygen load, hemoglobin changes color. It beomes blue or purple. That is why we refer to “impure” blood that returns to the heart in the veins as “blue blood“.
Normally, the two kinds of blood are separated by the wall between the two ventricles. But in ToF, the aorta arises above this wall, and is connected partly to the right ventricle too. So “impure” blue blood from the veins mixes with “pure” red blood from the left ventricle, before entering the aorta.
The mixed blood is not bright red, but has a bluish hue. When this blood is pumped to all parts of the body, a “blue” tinge is visible. This is obvious in places where the skin is thin, and the color of blood flowing in the arteries is visible through it – like the tongue, nail beds and lips. Because ToF causes this blue color (called cyanosis), it is a cyanotic congenital heart disease.
What exactly happens in ToF ?
It is quite difficult to explain (so please excuse me if I seem vague), but there are basically TWO major problems with ToF.
- First, due to the narrowing of the pulmonary valve, less blood is allowed to flow to the lungs. The lungs are the organs where “impure” blood is mixed with oxygen and “purified”. When less blood flows to the lungs, the blood cannot be purified completely.
- Second, there is a problem called veno-arterial mixing.
What is Veno-arterial mixing ?
In ToF, and a few other defects too, the “impure” blood returning through the veins to the right ventricle mixes with the arterial blood. This mixing decreases the amount of oxygen in the blood reaching the aorta.
Blood from the aorta reaches all organs of the body. So all organs – brain, kidneys, liver, muscles – now get a lesser amount of oxygen, which is the life-giving gas. As a result, they are not able to work normally. In older children, this is shown by a limitation in work and play.
Children with ToF cannot play strenuous games. They often “squat” down in a typical position after some time to relieve their giddiness and tiredness.
Other problems also exist. Due to a narrow pulmonary valve, less blood enters the blood vessels of the lung – the pulmonary arteries. Because of this low blood flow, these arteries do not grow in size as the child grows older. In severe cases, the pulmonary arteries may not develop at all, and may be absent. This condition is called Pulmonary Atresia. The size and development of the pulmonary artery is very important in deciding about the timing of an operation, and the choice of procedure.
Another complication is Paradoxical Embolism. Strokes and infection of the brain (called Cerebral Abscess) can occur because of this.
By far the most dangerous complication of ToF is the Cyanotic Spell. During a cyanotic spell, the child develops very rapid deep breathing and sweating. The bluish color becomes deeper. The child may become limp and lose consciousness.
Seizures – or “fits” – may also occur. Rarely, a spell may be fatal. This is why the presence of multiple frequent spells makes early surgery necessary. Spells occur most frequently in the first six months of life. They most often occur after feeding or crying, especially when the child has just woken up from deep sleep.
What causes a spell ?
There may be “spasm” or contraction of a band of muscle in the right ventricle just under the pulmonary valve. When this muscle contracts, it further narrows the channel for blood flow into the lungs. As a result, oxygen delivery becomes further reduced. This causes a spell. Luckily, after some time, this muscle relaxes. Once again, blood flow into the lungs is restored, and oxygen supply increases. The spell is “broken”.
What happens if ToF is untreated ?
A lot depends on the severity of the defect. With severe narrowing of the pulmonary valve (pulmonary stenosis), where little or no blood flows into the lungs, the chances of survival beyond one year of life without surgery are remote. In milder forms, children live longer.
But without treatment, the “life expectancy” is less than normal. The risk of stroke and brain abscess increase with age. Heart failure may occur later. Constant exposure of heart muscle to blood with lesser oxygen content makes it weak, and it “fails”. This condition is called Cyanotic Cardiomyopathy.
When should ToF be repaired ?
Many factors have to be analyzed before a decision is reached about timing and type of operation. It might be easier if we begin by describing the operative and non-operative options available, and how exactly they are beneficial to the child with ToF.
What are the surgical options ?
Surgery for ToF can be grouped under two major heads.
The first is called Intra Cardiac Repair (ICR) – previously called a “Total Correction”. Of course, all open heart operations are intra-cardiac repairs, but then I never said we surgeons are logical when it comes to naming! In this method, all the four defects of ToF are corrected in the same operation.
The other group is called Palliative Operations. These are operations which correct the abnormalities of ToF in a “staged” manner, by operations spread out over a few months or years.
Hold on! Why would anyone decide to have a palliative procedure, when all the defects can be corrected at one go with the intra-cardiac repair ?
An intra-cardiac repair is a difficult and stressful operation. Not all patients are capable of withstanding it. Sometimes, children are too sick, or their hearts are too badly diseased, for a single-stage operation to succeed.
It is in this group that the surgeon and cardiologist will decide to proceed carefully, in stages. When a cautious approach is followed, the ultimate outcome is better than when a rash attempt is made at heroic one-stage repair.
Surgery for Tetralogy of Fallot
Lets see what an Intra-cardiac repair of ToF – also called a Total Correction operation – is all about.
What is done in an Intra-Cardiac Repair for ToF ?
To refresh your memory, ToF has four defects – a VSD, pulmonary valve narrowing (stenosis), thickening of the right ventricle, and an aorta over-riding the wall between the two ventricles.
So how does the surgeon correct these defects all at once ?
Repair of ToF is an open heart operation.
The patient is hooked up to the heart and lung machine, and the heart is stopped. The surgeon may approach the area of repair by one of many routes, which depend on the arrangement of the different structures. The repair may be done through the right atrium, the right ventricle, the pulmonary artery, or maybe even a combination of more than one of these.
The surgeon makes a suitable opening in the chamber, and looks at the defect, to decide
- Whether a one-stage repair is possible ? and
- How to proceed with it ?
The actual steps of the one-stage intra-cardiac repair are
- To “open up” the narrowed pulmonary valve
- To divide and sometimes remove a portion of the thickened muscle of the right ventricle, particularly a band below the pulmonary valve. This thick muscle band (or “infundibulum“) blocks blood flow into the pulmonary artery.
- To close the ventricular septal defect (VSD) using a synthetic “patch” made of fabric like Dacron or PTFE (Poly tetra-fluoro ethylene). The surgeon places the patch so that the aorta is now connected only to the left ventricle. This restores the normal pattern of blood flow, and prevents veno-arterial mixing.
Sometimes variations occur which require the surgeon to modify the operation to fit the patient. I will describe some of the common variations.
We saw how “opening up” a narrow pulmonary valve can relieve obstruction to blood flow into the lungs. In addition, if a muscle band in the right ventricle (infundibulum) is causing obstruction, it may be divided or removed.
In rare cases, even this may not be enough to adequately reduce the obstruction to blood flow into the pulmonary artery. The reasons for this may be
- the “ring” or annulus to which the pulmonary valve is attached is itself very narrow – a condition called “Annular Hypoplasia“.
- there may be additional narrowing ABOVE the pulmonary valve. This may be because
- the pulmonary artery itself is small (Hypoplasia of the main pulmonary artery)
- the branches or divisions of the pulmonary artery are narrow (pulmonary artery “branch stenosis“)
- the branches or divisions of the pulmonary artery have not developed at all (a condition called Pulmonary Atresia)
What is an “Outflow Patch”? When is it needed ?
The passage or tunnel leading from the right ventricle into the pulmonary artery is called the “outflow tract” of the right ventricle. Through this blood flows OUT of the right ventricle.
When this tract is narrowed, due to a small pulmonary valve annulus (or ring) – pulmonary annular hypoplasia – a special operation is required to relieve the obstruction. A vertical (length-wise) cut is made in the wall of the right ventricle and extended into the pulmonary artery ACROSS the narrow pulmonary annulus. This adequately “opens up” the narrow outflow tract.
But the problem now is the opening in the wall of the outflow tract. This defect is closed using a “patch” of Dacron or PTFE, so that it does not become narrow again. The natural covering of the heart – called the pericardium – may be used for the outflow patch too. Because this patch goes across the outflow tract of the right ventricle, it is called an “Outflow Patch”.
When there is obstruction even above the pulmonary valve – in the main pulmonary artery trunk, or in one of its branches or divisions – further modification of the outflow patch repair is needed.
The outflow patch is tailored to be longer. The vertical incision in the right ventricle is extended even further, right across the pulmonary artery and its branches, until it has crossed the area of narrowing. When the obstruction has thus been relieved, the defect in the wall of the pulmonary artery is now repaired using the tailored patch.
However, in the very severe case where pulmonary arteries are not formed at all – pulmonary atresia – this repair is not possible. I will explain this in another section.
Though it relieves the obstruction of blood flow into the pulmonary artery very effectively, there are some problems with an outflow patch.
First, the pulmonary valve becomes “leaky” and blood flowing into the lungs can easily return back into the right ventricle. This is called Pulmonary Regurgitation. As a consequence of this, the right ventricle has to pump a larger amount of blood. Over the years the right ventricle may become weak and “fail”.
In an attempt to avoid this, some surgeons place an artificial valve in the outflow patch. A “monocusp valve” may be created by simply sewing on a flap of fabric or pericardium to the inside of the outflow patch. Another choice is to use a “homograft” patch with a valve cusp. This monocusp valve, though not perfect, may reduce the amount of blood leaking back into the right ventricle. In theory, this should reduce the chance of right ventricle failure.
Another problem with the outflow patch is that calcium may get deposited on it, making it rigid and hard. It may also be weakened by the forceful contraction of the right ventricle, and balloon out – a condition called “aneurysmal dilatation“. After many years, a second operation to repair or replace the outflow patch may be required sometimes.
Palliation for Tetralogy of Fallot
When is an Intra-Cardiac Repair not feasible for ToF ?
There are many such situations.
If, for instance, the pulmonary artery branches are not at all developed (Pulmonary Atresia), a one-stage total correction operation is impossible. For then, where would blood from the right ventricle go ?
Somewhat similar is the condition where the outflow tract of the right ventricle is VERY narrow at any portion – at the valve, or above it, or in one of the branches. Here, even with repair and widening of the narrowed area, significant block to blood flow will persist. If a one-stage operation is performed, then all the blood from the right ventricle would be forced to travel through the repaired, yet narrow outflow tract.
What happens then ?
The right ventricle has to work harder to pump blood through a narrow passage – it is like packing all your clothes into a very small suitcase, you have to push harder to get it all in! And the right ventricle cannot do this forever. It gets tired, and “fails”. If a palliative operation is done first, this problem can be avoided.
Then again, there are some babies who are too small. They would not be able to tolerate a difficult operation. Or there may be many other coexisting birth defects (multiple VSDs,abnormal coronary arteries). The presence of such defects would greatly increase the risk of a direct repair.
What are the palliative operations for ToF ?
The significant problem in ToF is REDUCED blood flow into the lungs. This results in reduced oxygen delivery to the body.
The operations designed to increase blood flow into the lungs are called Systemic-Pulmonary Shunts. These are connections between the aorta or one of its branches (the “systemic” arteries) and the pulmonary artery. The principle underlying these shunts is that a portion of blood flow from the arteries will be directed across the shunt into the pulmonary artery and its branches.
This has two effects.
- First, by increasing the total lung blood flow, the amount of oxygen available for distribution to the rest of the body is increased.
- Second, the increasing amount of blood flowing into the pulmonary artery and its branches stimulates them to grow in size. The narrow portions may become wider. So, later, when an operation for total correction is performed, there is little or no obstruction to lung blood flow.
What are the types of systemic – pulmonary shunts ?
1. The BLALOCK – TAUSSIG SHUNT.
This shunt was the first of its kind, and revolutionised the treatment of “blue-baby” disease. Dr.Helen B.Taussig was a famous cardiologist, who studied heart disease in children in great detail. She thought of the idea of diverting blood from the subclavian artery, which is a branch of the aorta, to the pulmonary artery. (The subclavian artery is so named because it lies under – “sub” – the collar bone or clavicle – “clavian“).
By improving the amount of lung blood flow, and increasing the oxygen content, it would relieve the cyanosis – or bluish discoloration.
In Dr.Alfred Blalock, she found a surgeon both highly skilled and daring enough to attempt this procedure on sick children. After practising many times on experimental animals, Dr.Blalock performed the first “shunt” operation on September 23rd, 1944 at Johns Hopkins Hospital, Maryland, USA.
The results were dramatic. At the end of the operation, when the clamps on the artery were released, the blue color of the child disappeared. Instead, the child turned a healthy pink – and the operating room personnel burst into spontaneous applause!
Ever since, the Blalock-Taussig shunt, or its “modified” version, have been used in the palliation of thousands of children with ToF, with great success.
How is this shunt created ?
Through an opening on one side of the chest, the surgeon has to first identify and free the pulmonary artery and the subclavian branch of the aorta.
Clamps are applied on both vessels to allow better visualisation. The subclavian artery is divided, turned down and then sewed to an opening in the side of the pulmonary artery using fine hair-like thread made of polymers like polypropylene.
Although widely performed, this shunt has a few problems. The isolation and division of the subclavian artery is a time consuming and difficult procedure. Also, it carries a risk of injury to nerves that supply the hand and arm muscles, and to the blood supply of the upper limb.
In the modified version, which is most commonly performed now, the subclavian artery is not divided. Instead, an artificial tube made of material like PTFE (Poly tetra-fluoro ethylene) is used to create the shunt. The PTFE tube is sewn to the subclavian artery on one side and to the pulmonary artery on the other, using fine surgical sutures. In this way, the same effect is achieved, without interrupting either artery and with lesser risk.
The effects of a Blalock-Taussig shunt are immediate, and usually last long.
The severity of cyanosis (“blueness”) is reduced. However, it is only a temporary measure. It aims to improve oxygen supply and promote growth of the pulmonary artery branches. Once these have been achieved, an intra-cardiac repair can be performed safely.
How safe is a Blalock-Taussig shunt operation ?
A Blalock-Taussig shunt is a reasonably safe procedure. Complications are rare and include:
- Blockage of the shunt. This causes the blue color to return. Clot dissolving medication, or even repeat operation may be required.
- Infection. Since the PTFE tube is a “foreign” material, it may become a site of implantation for bacteria that cause infection.
- Excessive lung blood flow. This happens rarely when an inappropriately large PTFE tube is used. If left uncorrected, this may cause thickening and hardening of the lung blood vessels which compromise later corrective surgery.
- Distortion of the pulmonary artery. As a child grows, the point at which the PTFE graft is attached to the artery may not grow, causing a bend or kink in the pulmonary artery at that point.
What are the other types of “Shunt” operations ?
Instead of choosing the subclavian artery, other branches or even the aorta itself may be used in a shunt.
2. In the POTTS shunt, a direct connection is made between the lower part of the aorta (on the left side of the chest) and the left branch of the pulmonary artery. This operation was popular earlier, but has more or less been given up now. This is because of certain drawbacks, both in its function, and in the difficulty of closing it during the time of the total correction operation.
3. In the WATERSTON – COOLEY shunt, a connection is made between the back of the aorta and the right branch of the pulmonary artery. Though still popular in some hospitals, it is a difficult operation to perform perfectly.
4. In the DAVIDSON shunt, a short tube of PTFE is used to create a shunt between the aorta and the pulmonary artery through an opening in the middle of the chest.
Outcome After Treatment For Tetralogy
So now you know quite a bit about surgical treatment of the Tetralogy of Fallot.
There is still one major issue which I have deliberately left to the end. It was first brought to my notice by a parent, who said it was most important to her to know what her child’s chances were with the different treatment options, and what were the risks in the periods between the different stages.
This is a highly uncertain topic.
Surgical treatment is like an orchestra. A great soloist alone cannot make a great performance. The smallest contributor to the surgical process has just as important a role as the more glamorous heart surgeon! And just as with any other technical matter, practice makes perfect.
Differences are tremendous between hospitals. The best approach would be to gather information from the specific center where you are planning to undergo surgery, about the outcomes at their hospital.
What is the outcome after a one-stage intra-cardiac repair ?
In the best centers, a one-stage intracardiac repair – or total correction – is usually possible in most cases, with a mortality risk of 2 to 5 percent.
Are these patients then CURED ?
Once again, this is a difficult question to answer. The longest “follow-up” in studies of operated ToF patients is about 30 years. Analysis of these results show that around 90% of the survivors live upto 20 years of age.
Even after this, the life expectancy is almost normal. When this is compared with the fact that 90% of un-operated patients with ToF are dead by 30 years of age, the benefits of operation are unquestionable.
And again, much remains unknown. Maybe in another 30 years, medicine will have advanced enough to provide better alternatives which will eliminate even this small added late risk!
Is there a risk of later operations?
After a total correction operation, a few patients may also need a second operation for complications. The most frequent complications are incomplete relief of pulmonary stenosis causing residual obstruction, and incomplete closure of the VSD with a residual leak across the patch.
Other less frequent ones include disturbances of heart rhythm, aneurysmal dilation or hardening of the outflow patch and severe pulmonary valve leak.
Overall, nearly 40% of corrected ToF patients will need re-operation over the next 10 years.
And what about the “shunted” patient ?
By its very nature, a shunt makes a later total correction operation necessary. Usually this is done within 6 to 18 months, provided the conditions are then ideal for correction.
What happens in the intervening period ?
If the shunt is well performed, the cyanosis (blue color) becomes less or disappears entirely. The child grows and is more active, and most importantly, is free from cyanotic spells which may be life-threatening. Uncommonly, one of the complications mentioned earlier – infection, shunt obstruction – may occur.
In very rare cases, conditions never become suitable for repair, and a intra-cardiac repair operation for Tetralogy of Fallot cannot be safely performed. In such cases, the patient may survive on a shunt alone, although results are not as good as with a corrective operation.