Overview of Bidirectional Glenn Procedure or Hemi-Fontan
The bidirectional Glenn (BDG) and hemi-Fontan are types of heart surgeries used as a second step in a multi-stage repair process called the Fontan procedure. These surgeries are usually done in people who are born with only one working part of their heart (called a single ventricle), instead of the usual two. The single ventricle has to work extra hard to pump blood to both the body and the lungs until the heart can be fixed with surgery.
The goal of the BDG or hemi-Fontan procedure is to lighten the load on the single ventricle by changing the way blood flows in the body. This simplifies the final part of the Fontan procedure by making the heart’s work easier.
According to studies from several medical centers, people who have had the BDG or hemi-Fontan procedure before the final step of the Fontan procedure tend to have better outcomes. The Fontan procedure is a must for all people with a single ventricle. This surgery separates the blood flow to the lungs and the rest of the body. After the Fontan procedure, the blood flow is controlled by the pressure inside the major veins and changes in pressure inside the chest and relaxation of the heart ventricle.
As of 2018, it’s estimated that between 50,000 to 70,000 people in the world have had the Fontan procedure, and about 40% of them are adults. Each year, about a thousand more Fontan procedures are done in the United States.
Anatomy and Physiology of Bidirectional Glenn Procedure or Hemi-Fontan
The BDG (Bidirectional Glenn) procedure is a surgery for those people who have a condition where the blood from their body and lungs mix up. The aim of this surgery is to reroute the blood flow so that the blood from the body goes straight to the lungs, without having to pass through the heart. However, for the best results after the surgery, a few conditions must be met. These include healthy lung blood vessels, properly functioning heart valves, and a flexible heart.
In patients with HLHS (Hypoplastic Left Heart Syndrome), no blockage should be present in the wall dividing the two upper chambers of the heart, known as the atrial septum. The BDG operation helps to decrease the load on the heart, which in turn reduces the size of the ventricle (the larger, lower chamber of the heart) and prevents thickening of the heart wall muscles.
The best time for this surgery is as early as possible. Usually, the BDG operation is performed after an initial surgery like the Blalock-Taussig (BT) shunt or a pulmonary artery band. These procedures help to improve oxygen levels in the blood. In your abnormal heart, deoxygenated blood (blood that lacks oxygen) continues to mix with oxygenated blood. Therefore, the surgeon may need to make extra alterations to improve blood flow from the lungs or may need to remove the BT shunt or a pulmonary artery band.
Before proceeding to the final stage of repair, known as the Fontan completion, the surgeon must correct any existing complications, such as narrowing in the pulmonary arteries, blockages in the heart, leaking heart valves, and presence of additional blood vessels.
In essence, the goal of the BDG operation is to slowly remodel the heart over time, reducing the size and thickness of the heart’s walls. It also helps to increase oxygen levels in the blood without increasing the workload on the heart or raising the blood pressure in the lungs.
Why do People Need Bidirectional Glenn Procedure or Hemi-Fontan
A bidirectional Glenn or hemi-Fontan procedure are types of heart surgeries commonly done for conditions like hypoplastic left heart syndrome (where the left side of the heart is underdeveloped), tricuspid atresia (a valve in the heart, the tricuspid valve, is missing or abnormally developed), double inlet left or right ventricle, pulmonary atresia with an intact ventricular septum (a form of heart disease where the valve that controls blood flow from the heart to the lungs is missing or malformed), unbalanced atrioventricular canal defects (a type of heart defect), and congenitally corrected transposition of the great arteries (a rare birth defect of the heart), among others. These conditions can cause significant underdevelopment of either ventricle, which are the two lower chambers of the heart that pump blood out to the body.
Analysis from the Single Ventricle Reconstruction Trial showed that the bidirectional Glenn procedure is safest when performed between 3 to 6 months after the initial Stage I repair or Norwood procedure (another type of heart surgery). This procedure has the lowest risk of death during this window.
Among the 399 patients who lived through a bidirectional Glenn procedure, 87% survived for three years, and 68% lived without needing a heart transplant. Data from the National Pediatric Cardiology Quality Improvement Collaborative showed that patients who underwent this procedure after 5.1 months of age had a higher chance of death, demonstrating that it’s beneficial to have the surgery earlier. However, for infants who had this surgery before 4 months of age, there was also an increased risk of death, likely due to other existing health conditions and potential risks.
When a Person Should Avoid Bidirectional Glenn Procedure or Hemi-Fontan
Performing a BDG, a type of heart surgery, may not be advisable if a person has moderate-to-severe pulmonary hypertension (high blood pressure in their lungs). In the case that this type of heart surgery needs to be done, they might have to create bilateral bidirectional Glenn shunts, which are passages made for blood flow, especially if the person has a persistent left superior vena cava (a condition where they have an extra blood vessel in their heart).
Equipment used for Bidirectional Glenn Procedure or Hemi-Fontan
Transesophageal echocardiography (TEE) – which is a type of heart ultrasound taken from your esophagus – is used to spot the large vein (superior vena cava or SVC) that carries deoxygenated blood to your heart and its connections to the right lung artery. Special features of the ultrasound, such as pulsed Doppler and color-flow imaging, are used to check for any blockages or narrow spots at the connection site.
The doctors also make sure there’s no abnormal connection between the artery and vein in your lungs (called a pulmonary arteriovenous fistula) by injecting a special type of bubbly saline solution into your veins. They expect to see a gentle, smooth or two-phase blood flow, that increases during inhaling when you’re breathing on your own. Disturbed or chaotic blood flow at the connection site could show that there’s a blockage.
After the procedure, there’s a chance that a machine called Extracorporeal Membrane Oxygenation (ECMO) might be used for a short while. This machine oxygenates your blood outside your body, acting like an artificial lung, if there’s heart malfunction or severe high blood pressure in the lungs.
Who is needed to perform Bidirectional Glenn Procedure or Hemi-Fontan?
Getting a bidirectional Glenn shunt involves a team of different healthcare professionals. Before the operation, your case will be reviewed by heart specialists (cardiologists), specialist cardiologists who perform operations without major surgery (interventional cardiologists), and surgeons who operate on the heart (cardiothoracic surgeons). They will use heart ultrasounds (echocardiography) and a special x-ray that looks at flow of blood through the heart (cardiac catheterization) to decide if this operation is right for you.
The operation itself includes a whole team of individuals, including nurses who assist during surgery, anesthesiologists who help you sleep during the procedure, and perfusionists who manage the heart-lung machine during surgery.
After the operation, you’ll need to stay in intensive care for a week where specialists in critically ill patients (intensivists), nurses specialized in intensive care, and respiratory therapists will look after you. Sometimes, patients may need a treatment called Extracorporeal membrane oxygenation (ECMO) after surgery. This treatment acts like an artificial lung and heart outside your body. If you need this, a special ECMO team will be ready to care for you.
Preparing for Bidirectional Glenn Procedure or Hemi-Fontan
The procedure known as BDG, isn’t performed on babies younger than 2 months old. This is because their bodies have high PVR levels, which make it hard for blood to flow and oxygen to reach the body. The BDG procedure is sometimes needed earlier if a baby’s skin starts turning blue (cyanosis) after a stage I repair surgery, or if there’s a residual narrowing in the aorta (aortic coarctation). However, these babies might have a more difficult time after the surgery due to the high PVR.
Some babies might not need the stage I surgery and have BDG as their first procedure. Before having the surgery, doctors usually perform a cardiac catheterization or cardiac MRI. These tests help doctors understand the baby’s heart structure and how it’s functioning. They’re looking at things like the PVR level, the pressure in the heart when it’s relaxed (ventricular end-diastolic pressure), how the heart valves are working, and whether there’s a blood flow blockage at the atrial septum remnant– a leftover piece of tissue that can block flow of blood from one atrium to another.
There can also be variants – slightly unusual structures or connections in the heart. One example is abnormal connections between sinus venous drainage (one of the ways blood returns to the heart) and the heart muscle or IVC (the large vein that carries blood from the lower half of the body back to the heart). If these are present, they can lead to low oxygen levels after the operation because blood from the upper body doesn’t go through the lungs properly. Therefore, a thorough examination should be performed before the surgery, taking into account the baby’s overall health.
If the baby is being treated with medicines that prevent blood clots (anticoagulants) or platelet inhibitors, these should be stopped before surgery to avoid complications. Many hospitals will stop aspirin 7 to 10 days before surgery, even though it helps keep the BT shunt open. The BT shunt is a tube that is sometimes used temporarily to direct blood flow to the lungs.
How is Bidirectional Glenn Procedure or Hemi-Fontan performed
The procedure named BDG (Bidirectional Glenn procedure) involves the support of a machine called cardiopulmonary bypass (CPB). This machine helps to circulate the patient’s blood while their heart is stopped for surgery. The surgical team places tubes into major blood vessels – the aorta, superior vena cava (a blood vessel that brings deoxygenated blood from the body back to the heart), and the right atrium (one of the four chambers in the heart). To make the patient comfortable during the operation, their body temperature is slightly lowered and their heart is not ‘clamped’ (stopped and restarted).
The initial steps of the procedure include the inspection of earlier surgical works and their modification if necessary. Then, the major part of the operation requires cutting and sewing up the superior vena cava and right atrium (parts of the heart). This is carefully done to ensure that the natural pacemaker of the heart, known as the sinoatrial (SA) node, is not damaged.
Patients who have an underdeveloped pulmonary valve, a condition some of them are born with or develop due to earlier surgeries, may be at risk of serious complications. In these patients, the leaflets of the valve are sewn together to prevent the formation of blood clots. Moreover, for patients with a condition where part of the heart is too small to receive all the blood flow, there may be a need to maintain or get rid of extra blood flow to the lungs.
In the course of the BDG operation, other necessary surgical corrections may also be done. For instance, those with heterotaxy syndrome (a condition where organs are abnormally positioned in the body) may require the correction of other anomalies such as abnormal drainage of blood coming from the lungs to the heart. One striking part of their treatment procedure is known as the Kawashima procedure – a method to direct all blood flow to the lungs.
Another type of surgery instead of the standard BDG, called the hemi-Fontan procedure, may also be performed. In this procedure, the superior vena cava is connected directly to the right atrium and the pulmonary artery. This surgery might be easier to manage at a later stage. For high-risk cases, the BDG operation may be performed with partial use of a blood thinner (heparin) to minimize the chances of stroke or brain damage.
During the operation, the doctors will continuously monitor blood pressure, oxygen levels, and other important variables to ensure everything is going well. After the surgery, the monitoring continues to confirm that blood is flowing correctly, that the heart is pumping effectively, and that there are no complications such as leaks from the areas that were sewn up.
Post-operatively, the primary goal is to prevent the resistance in the blood vessels of the lungs from increasing, which can otherwise impede blood flow through the lungs. Proper care is also taken to prevent complications related to ventilation and oxygen supply to the patient. Doctors also aim to optimize blood pressure and blood flow variables to ensure the patient’s lungs and the rest of the body receive sufficient oxygen. In certain scenarios, the patient may require a pacemaker to maintain a normal heart rhythm. Ultimately, the aim is to have the patient recover as swiftly and safely as possible.
Possible Complications of Bidirectional Glenn Procedure or Hemi-Fontan
The bidirectional Glenn procedure is a type of heart surgery that balances the blood flow between the heart and lungs. It is usually a safe procedure with less than 2 percent of patients passing away due to the surgery. However, complications can occur in about 30 percent of patients after the surgery. These complications can include the need for emergency heart treatments (9%), the onset of nerve-related conditions (9%), another surgery (6%), a life-threatening irregular heart rhythm (3%), and feeding problems that require more procedures (15%).
Risk factors that can increase the likelihood of post-surgery complications include heart valve conditions (mitral stenosis, aortic atresia), being female, and poor health before surgery. In smaller patients, the surgery could be more challenging due to their size.
Blood loss after the surgery could be more in patients who are less than two years old, need a second surgery, have low oxygen levels in their blood, and had specific treatments during the surgery. Most patients who undergo this procedure will need to have their chests opened up for a second time, which can increase the risk of blood loss.
Following the surgery, low oxygen levels (hypoxemia) is one of the most common complications. This can be due to ventilation issues or a decrease in blood flow to the lungs. If oxygen levels do not improve, they may need to explore additional treatment options. Doctors recommend removing the breathing tube as soon as possible as it can enhance heart-lung-brain circulation. Positioning the head and neck correctly can also help prevent low oxygen levels.
The build-up of fluid in the lungs is another post-surgery complication, which can extend the hospital stay. This occurs in about 9% of child patients. In some cases, abnormal connections between blood vessels in the lungs may form, possibly due to the unique blood flow patterns caused by the surgery. This could lead to low oxygen saturation levels in the blood.
In some patients, the Glenn procedure’s effects may fail over time, leading to high pressure in the blood vessels, reduced blood flow to the lungs, poor oxygenation, and impaired blood flow away from the brain. This condition can result from the leakage of the heart valves, which decreases the efficiency of the heart’s output. In severe cases, the patient might experience seizures, bleeding in the brain, or a blocked blood vessel in the brain. If a patient’s condition after the Glenn procedure becomes critical, a life-support machine (ECMO) might be required. However, this comes with increased risks of kidney and nerve injuries, and stubborn acid levels in the body. Despite these, needing life-support does not necessarily increase the length of the hospital stay.
What Else Should I Know About Bidirectional Glenn Procedure or Hemi-Fontan?
The BDG (bidirectional Glenn) procedure is a complex heart operation that was created to help blue baby syndrome, a condition that is present in newborns with heart abnormalities. The creation of this procedure has taken a long time, with many different steps along the way.
Researchers started by exploring different ways to bypass the right side of the heart, primarily focusing on cases where the tricuspid valve doesn’t work properly. Out of all the methods they tried, some were particularly effective. The first successful bypass of the right heart was performed on dogs, by attaching the flap-like structure of the right atrium to the right pulmonary artery (which carries blood from the heart to the lungs) and tying off the main pulmonary artery. Another team of researchers increased blood flow to the lungs by using a vein to bypass the right heart, rather than an artery.
A team at Yale later tried a similar procedure with the right pulmonary artery but had limited success, with many animals experiencing complications such as fluid buildup in the chest and belly or blood clots. Despite the complications, they introduced us to the concept of tying superior vena cava (a large vein that carries blood from the upper body back to the heart) to the right or main pulmonary artery.
In 1964, the idea of the BDG procedure was introduced when the breakdown of how the veins and arteries were connected resulted in blood flowing to both lungs and minimised blockages. The first successful operation of this kind was carried out in 1958 on a seven-year-old boy who had a heart with only one ventricle (pumping chamber), and his heart vessels were in the opposite position they should be.
Once the operation is done, the heart becomes less bulky as it no longer needs to pump as much blood. The blood flow to the lungs becomes passive, not forced by the heart, and the baby remains blue as there is inadequate oxygen supply. The amount of oxygen in the blood remains at mid-80 levels. As the child grows older, these symptoms could increase when the child is active like while walking or crawling. If the heart function decreases, the risk of death increases, and a second operation called the Fontan completion maybe needed.
