What is Supravalvar Aortic Stenosis?
Supravalvular aortic stenosis (SVAS) is a birth defect that affects the heart. SVAS involves narrowing of a segment of the aorta, the main blood vessel that carries blood from the heart to the rest of the body, specifically the part just above the heart’s aortic valve. It’s important to note that SVAS represents 8% to 14% of all cases of aortic stenosis that are present from birth.
There are three identified types of the SVAS: the hourglass type, the membranous type, and the hypoplasia of aortic arch type. The hourglass type is the most frequent one. The membranous type happens due to a fibrous (tissue made of fibres) or fibromuscular (muscle and fibrous tissue) semi-circular layer with a small gap in the middle that is stretched across the inside of the aorta. The third type, hypoplasia of the ascending aorta, involves the underdevelopment or small size of the ascending aorta.
What Causes Supravalvar Aortic Stenosis?
Supravalvular aortic stenosis (SVAS) can be found in people with certain genetic conditions, as well as in those without. One such condition is Williams syndrome, also known as Williams-Beuren syndrome, which is typically inherited from one parent. This condition is usually due to a change on a specific part of our genetic code, called chromosome 7q11.23.
The non-familial or non-inherited types of SVAS are caused by changes in, or in people with Williams syndrome, the removal of, a specific gene called the ‘elastin’ gene located on the same chromosome. The removal in Williams syndrome goes beyond just the elastin gene. It also includes other genes, like the LIM-kinase gene which is thought to be behind the issues with visual-spatial awareness that lead to the other aspects of the disease.
A rare genetic disorder where someone gets two copies of a specific gene (one from each parent), called homozygous familial hypercholesterolemia, also has SVAS as one of its features.
Risk Factors and Frequency for Supravalvar Aortic Stenosis
Congenital heart defects, or heart problems present at birth, are not uncommon – about 8 in every 1000 babies are born with them. A specific type of this problem, known as Left Ventricular Outflow Tract (LVOT) obstructive lesions, makes up about 6% of all congenital heart diseases. SVAS, another specific defect, is quite rare, making up less than 0.05% of all congenital heart defects, but contributes to 8% to 14% of all aortic stenosis cases, a condition where the heart’s aortic valve narrows. There are different types of SVAS, with the sporadic form being more common than the form that’s inherited through families (autosomal dominant).
Signs and Symptoms of Supravalvar Aortic Stenosis
Supravalvar aortic stenosis (SVAS) is a condition that differs from other types of narrowing of the aortic valve. It’s often seen in newborns with a disorder called Williams syndrome. This is a complex disease that affects many systems in the body, including the heart. It can cause problems with calcium and vitamin D metabolism.
Babies with Williams syndrome may fail to grow at the expected rate due to difficulties with feeding and digestive issues such as vomiting and constipation. Other symptoms to look out for include slight intellectual delay, distinctive facial features (such as a high forehead, starry or lacy patterns in the eyes, and wide-set teeth), and personality traits similar to being the life and soul of a party. Heart-related problems can also occur, like the narrowing of certain arteries and misalignment of the eyes.
If these features are identified in infancy, it should raise a flag to doctors about the potential presence of a more widespread disease. In Williams syndrome, SVAS typically worsens over time as the aorta, a major blood vessel, doesn’t grow as it should.
The physical signs of SVAS can look a lot like those of another heart-related issue, aortic valve stenosis. However, there are key differences. These include an exaggerated sound when the aortic valve closes, no audible ejection click, and the lack of a specific type of vibration and sound travelling into the area near the collarbone and along the major blood vessels in the neck. One unique feature of SVAS is that the blood pressure in the right arm is typically higher than that in the left arm. This can result from turbulent blood flow sticking to the sides of the blood vessels and being directed more towards one artery than the other.
Also, it’s important to note that SVAS can occur alongside other heart and blood vessel abnormalities that could further complicate the symptoms. These may include narrowing of the aorta and openings of other arteries, unusual structure of the aortic valve, narrowing of the coronary arteries, and narrowing of the artery supplying lung tissue with blood.
- Associated with Williams syndrome
- Problems with calcium and vitamin D metabolism
- Failure to thrive due to feeding issues and gastrointestinal problems
- Distinctive facial features
- Possibility of heart-related problems
- Progressive worsening of SVAS
- Silent ejection click
- Higher blood pressure in the right arm
- May occur with other heart and blood vessel abnormalities
Testing for Supravalvar Aortic Stenosis
If your doctor suspects you have supravalvular aortic stenosis (SVAS), they will likely confirm with an echocardiogram. In some cases, an MRI with angiography may be used for a more precise understanding of the condition. Below are some tests doctors use for diagnosing SVAS.
* EKG (Electrocardiogram): This test measures the electrical activity of your heart. Patterns seen in this test can show if there’s an unusual thickening of your heart muscle. If the blood vessels leading to your lungs are narrowed, it might result in a more conspicuous thickening pattern.
* Chest X-Ray (CXR): Normally, the results would come back normal. However, depending on how much the blood vessel is narrowed, your heart might appear larger than normal on this X-ray.
* Echocardiogram: This is like an ultrasound for your heart. It would reveal the narrowing of the blood vessels and show us what type it is. It can show if the areas around your heart valves are ballooned out (dilated) or if the outlet of your heart that leads to the rest of your body is smaller than the part where your heart pumps blood from.
* Doppler examination: This exam uses sound waves to measure how fast blood is flowing. However, it might sometimes overestimate the severity of the blockage compared to that found during cardiac catheterization, which is a more invasive procedure.
In a nutshell, cardiac angiography is an essential part of a thorough evaluation to accurately measure the pressure difference across different parts of your heart and to check the health of your coronary arteries, which are the blood vessels supplying your heart with blood and oxygen.
Treatment Options for Supravalvar Aortic Stenosis
In cases of aortic stenosis, which is a condition where the aortic valve in the heart narrows, making the heart work harder to pump blood to the rest of the body, a surgical procedure is often carried out. This procedure is usually performed before the obstruction becomes too severe as a way to prevent it from progressing. The decision to do so is made by experts, as there aren’t many studies on this specific situation. Furthermore, it’s important to note that how quickly the condition could worsen depends on the initial severity of the valve’s narrowing and is typically slower in adults compared to children.
Surgery for aortic stenosis is generally a reliable solution and is advised for individuals who show symptoms and have a specific measurement (or “gradient”) of aortic stenosis which is higher than 30 mmHg, verified through a procedure called cardiac angiography that allows doctors to see the heart’s blood vessels.
The surgery often has successful outcomes for the long term. It usually involves a process called the Ross procedure, where the affected aortic valve is replaced with the patient’s pulmonary valve, which is another heart valve. There are also other surgical methods like utilizing a Y patch and performing a procedure known as an end to end anastomosis which involves connecting two sections of a blood vessel. However, it’s important to note that the surgical risk is higher for patients if they also suffer from widespread disease of the blood vessels (diffuse arteriopathy) or a blockage in the pathways that allow blood to exit the heart chambers (biventricular outflow obstruction).
Apart from the surgery, there’s also another effective alternative therapy which is the placement of a stent, a small tube that can be permanently placed to keep the blood vessels open. This can be particularly beneficial for patients with involvement of smaller branches of the aorta, making it another valuable treatment option to consider.
What else can Supravalvar Aortic Stenosis be?
There are several conditions that may look like the one your doctor suspects. These also need to be considered in the diagnosis process:
- Subvalvular aortic stenosis
- Valvular aortic stenosis
- Hypertrophic obstructive cardiomyopathy
What to expect with Supravalvar Aortic Stenosis
The results following surgical correction depend on the type of narrowing (stenosis) and whether there are other heart conditions present. Factors that can make the outcome worse and often require more surgeries include the presence of widespread (diffuse) lesions compared to pinpoint (discrete) narrowing, or if there’s also disease in the aortic valve.
