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In the normal heart each ventricle does a separate job. The right ventricle pumps blood to the lungs, the left ,ventricle pumps blood to the body.
In a single ventricle heart, there is only one ventricle large enough to do the normal job of pumping blood. Thus, we need to configure the circulation to maximize the efficiency of this single ventricle.
This ultimately requires committing the single ventricle to doing the harder work of the heart, pumping blood to the body. The job of getting blood to the lungs must be done without a pump.
Whenever there is only one ventricle large enough to do a normal job of pumping blood, we need to configure the circulation to maximize the efficiency of this single ventricle without overworking it.
The “Fontan circulation” refers to this configuration where the single ventricle pumps blood returning from the lungs to the body, and the blood returning from the body travels to the lungs via direct blood vessel connections without a pumping chamber. In any individual child there may be different procedures needed to achieve this goal.
Operative stages for achieving a Fontan circulation
The type of operation needed in the newborn period is quite varied depending on the specific type of single ventricle cardiac defect. In some babies there is not enough blood flow into the lungs, resulting in cyanosis. In these babies, a tube graft is placed from an artery (usually the left subclavian or left innominate artery) to the pulmonary artery. This is called a systemic to pulmonary artery shunt or Blalock-Taussig (BT) shunt.
In other babies, the flow of blood into the lungs may be excessive, placing an extra burden on the ventricle and exposing the pulmonary arteries to dangerously high pressure. In these babies, a procedure will be performed to restrict blood flow to the lungs. This is done by placing a piece of material or a “band” around the pulmonary artery.
Other newborns have more complex heart disease and require more complex operations, such as the Norwood procedure for patients with hypoplastic left heart syndrome.
Rarely, a baby with a single ventricle anomaly will have “just right” flow into the lungs so that an equal amount of blood flows to the body and the lungs. These babies do not require intervention in the newborn period.
Whatever is needed in the newborn period, the aim is typically to balance the blood flow between the lungs and the body, achieving stable oxygen levels and adequate heart function.
The second stage for most children with single ventricle anomolies is undertaken around three to six months of age. The operation is called a “bi-directional Glenn” or sometimes a “hemi-Fontan.”
During the Glenn operation the large vessel that drains blood from the head and upper body back to the heart (the superior vena cava) is taken off the heart and sewn directly to the pulmonary artery. If a prior BT shunt was present, it is removed. If a pulmonary artery was previously placed, it may be removed but can also be left in place in some situations.
The Glenn operation has two major advantages in most children. First, because the connection is a direct one between two blood vessels, rather than made of artificial matter, it has the ability to grow with the child.
Second, it removes some of the work of pumping blood to the lungs from the single ventricle so that the ventricle will no longer have to pump all of the blood to the lungs in addition to all of the blood to the body, which places it at risk for early heart failure. In most cases this stage is tolerated the best of all the stages with a survival rate of 95 percent or better.
After the Glenn operation most children will have oxygen saturation levels of 75 percent to 85 percent.
The third and final stage in the reconstruction of a single ventricle heart defect is the Fontan completion operation. This operation is usually performed at 2 or 3 years of age, based on the child’s size and clinical status.
During the Fontan operation, blood returning to the heart from the lower half of the body (via the inferior vena cava) is connected directly the blood from the pulmonary arteries. Up until now this blood has bypassed the lungs resulting in oxygen levels lower than normal.
After a Fontan operation, oxygen levels will be nearly normal (90s). The two most common methods of performing the Fontan completion today are the “lateral tunnel” and the “extra-cardiac” techniques.
In the lateral tunnel method, a tunnel-like patch is placed inside the atrium so that blood returning from the inferior vena cava is directed through this tunnel. A connection is then made between the end of the tunnel / top of the right atrium and the underside of the pulmonary artery.
In the extra-cardiac method, the inferior vena cava is taken off of the heart and a synthetic tube, usually Gore-texTM, is sewn directly to the top of the inferior vena cava and to the underside of the pulmonary artery, routing the blood flow outside of the heart.
In either method, a hole or “fenestration” is often made between the Fontan circuit and the right atrium so that if pressures become very high in the Fontan circuit, there is a “pop-off” into the heart. Patients with fenestrations may have a more stable post-operative course with smaller and less prolonged plerual effusions (a common complication after Fontan surgery). Many fenestrations close spontaneously many months after surgery, but can also be closed during a cardiac catheterization procedure if deemed necessary.
Currently, when patients have been well prepared for Fontan completion, the success rates are 90 percent and higher.
Why do children need a Fontan Operation?
Affected children are blue (‘cyanosed’) because their arterial (red) and venous (blue) blood mix together. Such patients have one of several cardiac abnormalities that mean that the lung circulation cannot work independently from the body circulation. These problems may require a Fontan operation.
The main defects in this category are:
- Tricuspid Atresia
- Pulmonary Atresia with underdeveloped right ventricle
- Double inlet left ventricle
- Double outlet right ventricle with associated defects that prevent repair
- Hypoplastic left heart syndrome
- Other defects that cannot be fixed by other types of surgery
In all these situations, where a Fontan operation is recommended, the problems in the heart make it impossible or extremely hazardous to ‘repair’ the defect in a way that would allow two ventricles to support the two circulations separately.
The aim of the operation is to improve oxygen levels, by redirecting venous (blue) blood directly to the lungs. This produces two separate circulations and a decreased workload on the heart, but means that only one ventricle functions as the ‘pump’ (driving blood through the body circulation first and then into the lung circulation afterwards, before it returns to the ventricle to start again).
This operation works best if:
- there are good (normal) sized lung (pulmonary) arteries
- there is low pulmonary vascular resistance – allowing the blood to flow easily through the lung
- circulation with no need for high pressure to drive it
- there is a healthy / vigorous ventricle to pump blood round the circulation
- there is no valve dysfunction (leak) that allows blood to flow back across closed valves
Requirements for a child to be a good risk candidate for a Fontan circulation
For a heart with a Fontan reconstruction to work well, there are a few crucial features that must be maintained. These key factors must be kept in mind when planning the medical or surgical management of children with single ventricle defects from the first day of life onward.
The single ventricle must not be overworked for a long period of time, in terms of either having to pump too much blood or pump at too high a pressure.
The pulmonary arteries must grow well without stenosis (narrowing) and must remain low resistance (or be very relaxed). If the pulmonary arteries are narrow or if the resistance in these vessels is high, blood will not be able to flow into them without a pump, so the Fontan will not be successful.
Lastly, leaky or tight valves may adversely affect the function of the ventricle or the flow of blood to the lungs.
The decision for operation?
Many children or adults who are candidates for this type of surgery will have had previous surgery and / or catheter procedures. Before the Fontan operation can be performed they will need comprehensive review with several tests, probably including an up-to-date catheter test.
After the results have been discussed by the doctors and surgeons the patient / family will need to see the surgeon to learn more about the operation and what benefits it may achieve.
It is important that the family know that the Fontan operation is not a ëcureí and that patients after this surgery will need long-term follow-up.
The Fontan operation can be done in several different ways. At the Royal Children’s Hospital there have been three main ways of ensuring as much blood flow to the lungs as possible.
- Extracardiac Fontan
- The superior vena cava is connected to the right pulmonary artery (this may have been done at an earlier ‘bi-directional cavo-pulmonary shunt’ operation)
- The inferior vena cava is re-routed through a Gore-Tex tube (conduit), which runs outside the heart and is connected to the Pulmonary Arteries.
- The atrial septum is removed (this may have been done already at previous surgery).
- Blood returns via the pulmonary veins into the left atrium and may also pass to the right atrium freely > ventricle > Aorta > body.
- Venous return is redirected to the pulmonary artery and into the lungs by joining the uperior vena cava and the inferior vena cava by a large patch that creates a tunnel through the right atrium.
- The vena cavas are then connected directly to the pulmonary arteries above the heart.
- The atrial septum is removed.
- Blood returns via the pulmonary veins into the now independent left atrium > ventricle > Aorta > body.
- The right atrium is connected to the pulmonary artery.
- If the tricuspid valve is present it needs to be closed off with a patch (to prevent blood flowing into the ventricle).
- The atrial septal defect is closed.
- Blood now flows from the superior and inferior vena cava through the right atrium and into the pulmonary arteries.
- Blood returns via the pulmonary veins into the left atrium > ventricle > aorta > body.(No image here)
One or two days before surgery the patient will need to come to the cardiac ward, for preliminary tests.
While there he or she will have:
- a chest xray
- a cardiac echo scan
- blood tests
- height and weight measured
The family will be visited by:
Nurses from this ward take the family to visit the Intensive Care Unit, which introduces them to the area that the patient will return to after the operation.
The day of surgery
The anaesthetic and operation will take about 5 hours or longer.
After the operation the patient will be in the intensive care unit.
Because there is no separate ventricle to pump blood to the lungs it is important that blood flow to the pulmonary arteries is increased in every possible way! Such as…
- Being nursed with pillows under the head and two pillows under the legs to assist the flow of blood back to the heart.
- To help the heart contract, an infusion of a drug to strengthen the heart beat, such as ‘Dopamine’, may be needed. Drugs such as ‘phenoxybenzamine’ / ‘nitroprusside’ may also be used to open up blood vessels and reduce resistance in the circulation. These drugs allow blood to flow more easily and therefore reduce the effort required by the heart.
The intensive care team will make sure that the patient is breathing on his / her own as soon as possible (usually less than 12 hours). This will also assist venous return, as the need for an artificial ventilator (positive pressure ventilation) makes it more difficult for blood to return to the heart and ultimately, into the lungs and out again.
Heart function is also optimised by administering adequate fluid or blood to make sure that the pressure in the veins carrying blood back to the heart, and from there to the lungs, is maintained high enough to promote good blood flow through the lungs.
- Unfortunately because the pressures in the veins are higher than normal (inferior vena cava and superior vena cava), it also creates some problems.
While the body is trying to adjust to this the patient may be very prone to leakage of fluid into the sacs around the lungs or elsewhere, which can cause ëpleural effusionsí (fluid around the lungs), ascites (fluid in the abdomen) and liver congestion / enlargement.
Therefore the nurses are carefully noting the amount of fluid that is lost and is taken in. The absolute minimum of fluid intake is given during this early stage to try to minimise these problems.
- The family can be at the patient’s side as often as possible
- Hopefully he / she will be back in the ward within about 24 hours
- If he / she gets bored, the play or music therapist will provide some entertainment!!
Returning to the ward
- When all is well, the patient and family can return to the cardiac ward. The chest drain tubes may still be there, as will be the pressure lines and pacing wires.
- The patient may well be persistently thirsty!! He / she is still allowed only 50% of normal fluid intake (to decrease congestion and the risk of fluid collections around the lungs or elsewhere). This will be gradually increased but some restriction on fluid intake may even continue at home!
- Because of this fluid restriction, nutrition may suffer and therefore the patient can be more prone to infection.
To avoid this:
- The Dietitian makes sure that there are enough calories in the diet.
- The Physiotherapist visits twice a day to encourage deep breathing and coughing.
- The patient is weighed daily to help in fluid assessment.
- Nurses still watch closely for complications such as pleural effusions (fluid around the lungs), or pericardial effusion (fluid collection around the heart).
- The patient is commenced on ‘anticoagulant’ medications (Warfarin or Aspirin) to prevent blood clots forming too readily. This is because of more sluggish blood flow in the main veins and lung circulation, and an increased risk of blood clot in these areas or in the heart. While on these drugs it is important to remember that he or she may bruise easily or bleed for longer than normal after an injury. The patient may need to continue with these medications forever!
- The family can be in the ward as much as they like, Mum and Dad can even stay overnight.
- The hospital stay is at least two weeks after surgery and is often longer because of the fluid collections.
- When he / she leaves the hospital the patient will need to have a blood test once or twice a week at first and will need to be checked by the cardiologist.
- He / she will be on several medications that will be reduced gradually over the next two to three months.
- As the patient gradually gets back to normal and increases activity fluid intake will be allowed to return to normal and most of the medications can be ceased. This should only be done however as and when the cardiologist gives instructions.
- Most patients will be able to return to normal activity over the first three months or so.
- They should increase their activities gradually to a stage where they are engaging in regular light to moderate exercise. Moderate physical exertion is generally good for them, but they / their parents should seek advice from their cardiologist about what activities are suitable.
- Most Fontan patients will be free of ‘Cyanosis’ (blueness) and will have oxygen levels close to normal.
Will a child who has had a Fontan operation be able to function as well as a child with a normal, two-ventricle heart?
After a successful Fontan surgery, the reconstructed single ventricle heart has achieved its maximal efficiency in terms of ventricular work and near normal oxygen levels, but its capacity for work will usually not match that of a normal heart when examined using sophisticated testing.
The limitations children experience due to their heart defect, though, can vary greatly. At one end of the spectrum there are children with Fontan circulations who have participated in competitive sports such as swimming and gymnastics. Most children are on a blood thinner called coumadin after their Fontan to prevent clots from forming in the Fontan circuit. When a child is on a blood thinner, you must take extra careful to avoid falls or head trauma as they are at increased risk for internal bleeding.
Other children may have significant limitation in their capacity for exercise. Most children fall somewhere in between the extremes.
How long a heart with a single ventricle reconstruction can function is not known. It is now just over 30 years since the first successful Fontan operation was performed and many improvements in surgical technique and medical management have occurred over this time period.
Late complications including irregular rhythms and heart failure may be occur. Some speculate that most single ventricle hearts will not function efficiently beyond 30 to 40 years, but improvements in surgical technique and medical care may increase this age significantly. In some cases, if the ventricular function deteriorates significantly, heart transplantation may be considered.
Because of the possibility of late complications, continued regular follow-up with a cardiologist for the life of a patient with a single ventricle anomaly is essential.
The facts and opinions shown in this article are as accurate and up to date as possible, but are provided as general “information resources”, which may not be relevant to individual persons. This article is not a substitute for individual assessment and always take advice from a doctor who is familiar with the particular person.
Information taken from:
For more information click on the following URL’s:
Invasive Cardiology http://www.invasivecardiology.com/article/5068
This link goes to a webpage of a person who has had Fontan surgery: http://my.execpc.com/~markc/fontan.html