Overview of Pulmonary Artery Banding
Pulmonary artery banding (PAB) is a surgical procedure used to alleviate certain birth heart defects. It is usually employed to control the flow of blood to the lungs when too much blood is being pumped there due to a large left-to-right shunt. This occurrence is when blood is diverted from the left side to the right side of the heart. In the early stages of treating heart defects, before more straightforward methods became standard, PAB was frequently the first surgery performed on some children with certain heart abnormalities. However, modern advancements in surgery have meant PAB is now mainly used for relieving symptoms in babies with complicated heart defects.
The goal of a PAB is to safeguard the lung’s blood vessels by limiting the amount of blood flow to the lungs and thereby reducing the pressure to the pulmonary bed, preventing harmful remodelling of the lung’s blood vessels and high blood pressure in the lungs. In other cases, the intention of a PAB is somewhat different and aims to “train” the left heart chamber – this means getting it ready for a series of specialised surgeries. This is the situation for babies who might be having intricate reconstructions that require the heart chamber to be prepared before it can operate efficiently at pumping blood to the entire body. More specific examples of these situations are explained further below.
Around 1951, Muller and Dammann performed the very first PAB on a five-month-old baby with a large opening in the wall separating the heart’s lower chambers (ventricular septal defect – VSD) and an excessive amount of blood being pumped to the lungs. Since then, multiple studies have shown the effectiveness of PAB to help patients with congestive heart failure caused by the absence of the tricuspid valve (tricuspid atresia), large VSDs, and defects in both the walls and the valves between the heart’s upper (atrial) and lower (ventricular) chambers (atrioventricular canal defects – AVC). Even though the use of PAB has decreased among heart surgeons, it remains a vital tool in their kit for treating complex birth heart defects.
Anatomy and Physiology of Pulmonary Artery Banding
Before thinking about a treatment called pulmonary artery banding, which is used to improve heart conditions, several body structures need to be carefully examined. It’s important to look at the main pulmonary artery’s length to ensure a band can be safely placed midway without impacting important structures above and below it. Typically, the lower part of the right pulmonary artery comes out slightly earlier from the main artery than the left one, and at a sharper angle. As a result, the right pulmonary artery has a greater chance of being distorted when the band is applied, although the left pulmonary artery may also be affected. Usually, the main pulmonary artery is larger and has thinner walls compared to the aorta, which increases chances of potential rupture during surgery.
Patients with a large hole in the wall separating the two lower chambers of the heart, called a ventricular septal defect, and low resistance to blood flow in the lungs, can eventually develop over-circulation in the lungs. This can lead to symptoms of congestive heart failure, which include rapid breathing, difficulty eating, and fluid in the lungs. Initially, these symptoms can be managed with medications to reduce fluid and improve heart function, and potentially additional feeding via a nasal tube. However, if left untreated in the long term, heavy blood flow in the lungs can lead to irreversible, harmful changes, such as thickening of the blood vessels and development of high blood pressure in the arteries supplying the lungs. This is especially likely with conditions that cause high pressure and high blood flow in the lungs.
A procedure called pulmonary artery banding reduces the blood flow in the lungs in order to prevent exposure to high pressures and bad vascular changes. This procedure places a band around the main pulmonary artery to narrow it, increasing resistance in the artery and reducing the blood flow from the left chamber of the heart to the right. This in turn results in increased blood output from the heart and blood pressure throughout the body. However, for specific heart defects that need a good mix of blood from the lungs and the rest of the body, this procedure might not be suitable, especially if there is a restricted opening in the wall separating the two upper chambers of the heart. In such cases, a surgical procedure or a balloon procedure might be needed to create a larger opening before the pulmonary artery banding is attempted.
Why do People Need Pulmonary Artery Banding
Pulmonary artery banding is a heart surgery done for two main purposes:
1) To reduce blood flow to the lungs when there’s too much due to left-to-right shunting, meaning blood is flowing from the left side of the heart to the right side instead of the usual direction. This is an initial treatment before a more permanent surgery is done later on.
2) To increase workload to the morphological left ventricle (which usually functions as a low-pressure lung artery). The aim here is to prepare or “train” this ventricle to become a main artery prior to a procedure known as an arterial switch in patients with a condition called transposition of the great arteries (TGA). In TGA, the two main arteries leaving the heart are reversed, affecting the circulation of blood.
In the following situations, blood flow to the lungs may need to be limited via pulmonary artery banding:
1) Muscular “Swiss cheese” ventricular defects (VSD) which may be detailed and difficult to repair and/or require surgeries in an infant.
2) Many or single ventricular defects with complicating conditions such as very low birth weight, infection in the bloodstream, pneumonia, bleeding inside the skull, or failure of more than one organ.
3) Unbalanced atrioventricular canal defect with small left ventricle, a preliminary treatment before opting for potential repair of both ventricles after more growth and development.
4) High-risk babies with weak left heart syndrome with PAB and a procedure to keep ductus arteriosus open for short-term treatment.
In the subsequent cases, pulmonary artery banding may be required for “training” the left ventricle:
1) Preparing the left ventricle in patients with D-TGA who are late (>1 month) for a further arterial switch operation, where the left ventricle has become “deconditioned” by functioning as the lung ventricle.
2) Preparing the left ventricle in patients with L-TGA for a further double switch procedure.
3) Reducing backflow of blood in the heart’s right ventricle in patients with L-TGA without VSD. In this case, the pressure load to the lung LV prompts a shift in the heart’s septum that enhances the closing of tricuspid valve flaps in the main artery’s right ventricle.
4) As an additional procedure in patients with single ventricle anatomy and direct blood flow to the lungs at the time of a particular shunt placement to maintain some direct flow but keep low the pressure in the main vein carrying deoxygenated blood to the heart from the upper half of the body.
When a Person Should Avoid Pulmonary Artery Banding
There are certain situations when doctors advise against a method known as pulmonary artery banding (PAB). This is a procedure used to limit the amount of blood flow to the lungs. Here are some situations in which PAB may be avoided:
1) Some babies with a specific type of heart defect (such as double inlet left ventricle or tricuspid atresia with TGA), can face a future risk of subaortic obstruction. This is a condition where the blood flow from the heart to the body’s aorta is blocked. The PAB can lead to an abnormal enlargement of the heart muscle, which worsens this blockage.
2) In patients who already have a high-pressure gradient (a sign of strong blood flow and resistance inside the blood vessels) in the systemic outflow tract/subaortic region, the PAB can further increase this pressure. It’s like putting two bands on a narrow hose, making it hard for both sides of the heart to pump blood out.
3) If there’s severe leakage of the heart valves (AV valve regurgitation), more pressure caused by the PAB could make the leakage worse. This situation is generally seen as a reason to avoid PAB.
4) In the case of truncus arteriosus, a rare type of heart defect, PAB can be difficult or less effective. This is due to a short artery present in the heart (MPA) and the need for balancing blood flow. Also, with continuous blood flow in this condition, putting a band may not efficiently limit the blood flow to the lungs. Hence, doctors generally avoid PAB for these patients due to these complex reasons.
Who is needed to perform Pulmonary Artery Banding?
A group of different healthcare professionals work together to plan, support and take care of you before, during, and after heart surgery. This team includes heart surgeons, children’s heart specialists, anesthesia doctors who specialize in heart procedures, nurses who assist in surgery and give intensive care, and perfusionists (experts who operate the heart-lung machine during surgery).
Preparing for Pulmonary Artery Banding
Before any heart operation, a patient will likely need to undergo an ultrasound of the heart, also known as an echocardiogram. This will give the doctors a detailed layout of the heart’s anatomy. There might be additional tests like MRI scans or cardiac catheterization to provide more information about the heart, especially when dealing with complex defects. However, these tests aren’t usually necessary for simple issues like a ventricular septal defect (VSD), which is a hole in the wall separating the heart’s chambers.
Before the operation, the goal will be to reduce the amount of blood flowing from the left side of the heart to the right, known as a left-to-right shunt. This can be achieved by reducing the pressure in the blood vessels and getting rid of excess fluid in the body, especially in patients who have symptoms of congestive heart failure such as fatigue, shortness of breath and swelling.
For patients with a severe overflow of blood to the lungs, it might be necessary to provide breathing support. This can be achieved by a machine, known as a ventilator, which helps ensure enough oxygen is getting into the lungs and removes carbon dioxide. This is crucial during a situation where the lungs are filled with fluid (known as pulmonary edema). However, care should be taken not to provide excessive oxygen. This is because high concentrations of oxygen can widen the blood vessels in the lungs and increase blood flow, which isn’t ideal in this instance.
How is Pulmonary Artery Banding performed
Pulmonary artery banding (PAB) is a surgical procedure that is used to help manage some heart conditions. It involves tightening a band around the artery that connects the heart to the lungs, known as the main pulmonary artery (MPA). There are three ways a surgeon can access the MPA to perform PAB: through an incision on the front left side of the chest, the left side of the chest, or down the middle of the chest (sternum).
Once the MPA is exposed, a band made from various materials, such as umbilical tape, is prepared for placement. Depending on different heart conditions, surgeons use a mathematical guide (the Trusler formula) to determine the right size for the band. The optimal size of the band is further refined based on different metrics related to the blood flow and pressure in the heart and lungs.
The band’s placement is crucial: it has to be positioned on MPA, avoiding contact with the pulmonary valve and the arteries branching from the MPA. Extra care is also taken to prevent the band from moving after the operation. This is done by carefully dissecting the tissue between the aorta (the main artery from the heart) and MPA and passing the band through this area.
After placement, the band is secured with a thread (usually a ‘polyethylene’ thread). Sometimes, doctors may make the band adjustable, allowing them to change its size depending on how the patient’s condition progresses post-surgery. They do this by adding or removing special metal clips (called ‘hemoclips’) that control the band’s tightness.
However, in some cases, the band may become loose over time. To prevent this from happening, sometimes, a small incision is made in the MPA, and the band is placed below this point.
Monitoring the patient’s vital signs, like oxygen saturation and blood pressure, after the surgery is crucial. In patients with certain heart conditions (single ventricle physiology), low oxygen levels are considered acceptable.
Once the treatment for the heart condition has progressed (usually after a series of surgeries), the band is often removed. This is done by carefully cutting away the scar tissue formed around the band. Sometimes, the removal of the band can result in a narrowing of the MPA. In such cases, additional surgical techniques are used to fix this issue, which might involve removing the narrowed bit of the artery or increasing its size by adding a patch.
Possible Complications of Pulmonary Artery Banding
There can be several complications associated with a medical procedure called pulmonary artery banding. This treatment involves placing a band around the pulmonary artery, which is the blood vessel that carries blood from the heart to the lungs, to regulate or restrict blood flow. Here, we explain some potential complications that might occur:
1. Stenosis or distortion of one or both branch PAs: This means that one or both of the branches of the pulmonary artery could become narrow (stenosis) or misshapen (distortion).
2. Alterations in the function of the pulmonary valve: The job of the pulmonary valve is to control the flow of blood from your heart to your lungs. This procedure could possibly make it not work properly.
3. Impingement of the circumflex artery: Circumflex artery is a branch of the main heart artery that supplies blood to the heart muscle. Impingement means that the artery might get squeezed, affecting proper blood flow.
4. Erosion of band into the pulmonary artery: Over time, the band that’s placed around the artery could wear away and dig into the pulmonary artery.
5. Pseudoaneurysm of the pulmonary artery: This means that a false aneurysm could develop in your pulmonary artery. A false aneurysm is like a weak spot in the artery that balloons out and could potentially burst.
6. Hemolysis: This is a condition where your red blood cells break down faster than your body can make new ones, which can make you feel tired and weak.
7. Thrombosis: This is when a blood clot forms and blocks blood flow in the pulmonary artery.
8. Ineffective band placement leading to irreversible changes to pulmonary vasculature causing pulmonary hypertension: If the band isn’t placed correctly, it might result in permanent changes to the blood vessels in the lungs, leading to high blood pressure in the lungs (pulmonary hypertension).
9. Local infection: Like with any surgery, there’s a risk that the area where the band was put in will become infected.
What Else Should I Know About Pulmonary Artery Banding?
If you’re suffering from congestive heart failure and have difficulty with your blood flow, a medical procedure called Pulmonary Artery Banding (PAB) might be suggested. This procedure often significantly improves heart performance, lessens the signs and symptoms of congestive heart failure, and improves blood flow in the lungs, as well as reducing the size of the lower chamber of the heart.
The risk of death for those undergoing PAB doesn’t mainly stem from the procedure itself, but often more from complex heart defects the patient may have. Particularly, patients who have PAB usually have it in preparation for a more complex heart surgery, meaning they’re generally considered high risk for such surgeries. Some early studies have even reported a 25% mortality rate from PAB.
That said, medical science has come a long way–improvements in surgical techniques, better planning for procedures, and advanced care after surgeries have greatly reduced the risk from PAB. Now, the mortality rate is only about 5%.