Subaortic Stenosis

What is Subaortic Stenosis?

Subvalvular aortic stenosis, also known as subaortic stenosis, is a rare condition mostly seen in infants. It usually involves a kind of blocking wall, often made of muscle, located just below the heart’s aortic valve. This wall interrupts the normal flow of blood from the left ventricle, which is one of your heart’s main chambers. Even though this condition is considered a birth defect, it is not typically detected at birth or during infancy. Instead, it develops gradually and has a high chance of recurring after surgery, suggesting that it might actually be a condition that a child develops over time.

Here’s a bit of explanation about the heart structure involved in this condition. The mitral valve’s front leaflet and the fibrosa that’s inside the valve form the back right side boundary, while the muscular and membranous parts of the intraventricular septum (the wall separating the lower chambers of the heart) create the front and left borders of the left ventricle’s outflow tract.

Subvalvular aortic stenosis comes in various types and it can occur alone or coexist with other types. These include:

1. A thin, separate membrane: This is the most common type.
2. A fibromuscular ridge: A bulging line created by fibrous and muscular tissue.
3. A diffuse fibromuscular tunnel-like narrowing of the left ventricle’s outflow opening.
4. Unusual mitral valve tissue.

Most patients have a blocking wall that attaches to the septum of the ventricle or surrounds the left ventricle’s outflow tract. It could be positioned anywhere from just below the aortic valve to further down into the left ventricle. The aortic valve leaflets’ bases (the flaps that open and close to let blood flow) are often tightened by this subaortic tissue, which reduces their ability to move freely, thus adding to the obstruction.

The progression of subvalvular aortic stenosis is mostly slow and steady. It is rarely the only health issue that a patient presents with. Subvalvular aortic stenosis frequently occurs in combination with other congenital heart defects like a hole in the heart, a ductus arteriosus that remains open, a narrowing of the aorta, a bicuspid aortic valve, abnormal tissue in the left ventricle, a septal defect between heart’s chambers, and more. In most cases, subvalvular aortic stenosis is found incidentally while doctors check for other congenital heart defects.

What Causes Subaortic Stenosis?

Subvalvular aortic stenosis, a condition where the area below the aortic valve in the heart narrows, develops due to various factors. These include genetic factors, problems with blood flow due to other heart conditions, or an underlying shape of the outflow tract (the passage that allows blood to leave the heart) that makes the blood flow more turbulent.

Specific heart features like a narrow outflow tract, excessive aortic override (where the aortic valve extends more into the right ventricle), increased septation (partitioning) between the mitral and aortic valves, and a steep angle of the wall separating the atria (upper chambers of the heart), can lead to continuous disturbance in blood flow. These factors increase the stress on the wall separating the ventricles (lower chambers) due to fast-moving fluids, causing abnormal growth of the cells lining the blood vessels and muscle, resulting in the formation of a ridge made of fibrous and muscle tissue.

This ridge can be the cause of the narrowing under the aortic valve, a condition called subvalvular aortic stenosis. Additionally, any repair work done for related congenital heart defects might alter the outflow on the left side of the heart, potentially increasing turbulence and stress on the wall between the ventricles, adding to the development of subvalvular aortic stenosis.

Risk Factors and Frequency for Subaortic Stenosis

Subvalvular aortic stenosis (SAS) is a fairly rare heart disorder, typically seen in infants and newborns. Despite its rarity, it’s the second most common type of aortic stenosis. It accounts for around 1% of all heart defects present from birth, and 15-20% of all certain types of blockages in the left ventricle of the heart.

Among children with inborn aortic stenosis, 10-14% have SAS. It is more prevalent in males, making up 65-75% of all cases with a male to female ratio of 2:1. In terms of adult heart diseases that are present from birth, SAS makes up 6.5%.

In 50-65% of cases, SAS occurs alongside other heart problems. In a survey of 35 patients with SAS, the following additional conditions were found:

• Ventricular septal defect (VSD), a hole in the wall between the heart’s lower chambers, in 20% of cases.
• Patent ductus arteriosus, a persisting open blood vessel that normally should close after birth, in 34% of cases.
• Pulmonic stenosis, a narrowing of the heart’s pulmonary valve, in 9% of cases.
• Aortic coarctation, a narrowing of the large artery carrying blood from the heart to the rest of the body, in 23% of cases.
• Other different forms of heart lesions in 14% of cases.

Signs and Symptoms of Subaortic Stenosis

Subaortic stenosis is a heart condition usually detected at birth. Most babies with this condition don’t show any symptoms at birth, but can later exhibit signs such as shortness of breath during physical activity, chest pain, fainting or feeling lightheaded, night-time difficulty breathing, and even sudden cardiac death. Heart failure can occur in cases where the blood flow from the left ventricle of the heart is severely obstructed.

Shortness of breath during exertion is a common symptom in about 40% of patients with this condition. This is usually due to increased blood pressure in the lungs because the ventricle in the heart is not relaxing properly. If the blockage is severe, blood output from the heart may decrease, leading to a drop in blood pressure and less blood flow to the brain, which may result in fainting during exertion. Fainting and lightheadedness are less common in children and usually indicate an irregular heartbeat. Chest pain occurs in 25% of symptomatic patients because of a combination of reduced blood flow to the heart and increased demand for oxygen.

A physical examination is important in setting this condition apart from other similar heart disorders. Key findings include:

• Normal growth and development in children with this condition, apart from cases of severe obstruction of blood flow from the heart.
• A sensation of a heart rhythm in the carotid artery and on the left side of the chest wall found in one-third of patients with mild cases of this condition. Patients with moderate to severe cases might also have a strong heartbeat felt at the lower left part of the heart.

Also, it’s common for over half of the patients to develop a heart murmur in their first year of life. The murmur becomes more apparent and characteristic of this condition as the patient gets older, often heard in the upper part of the chest. The length of the murmur usually corresponds to the severity of the blockage. The murmur in this condition is different from that of aortic valve stenosis, another heart condition. A high-pitched murmur heard early when the heart relaxes is found in 30% to 50% patients. The intensity of the murmur usually decreases when the patient holds their breath after a deep breath in.

Testing for Subaortic Stenosis

Subvalvular aortic stenosis, a heart condition, isn’t diagnosed via typical blood tests. Instead, doctors use an imaging technique called an echocardiogram. This technique uses sound waves to produce images of the heart, allowing the doctor to view the heart’s structure and how well it’s functioning.

Through this method, doctors can evaluate various aspects of the heart, including potential blockages in the left ventricular outflow tract, the condition of the aortic and mitral valves, the definition and location of the stenosis, the degree of left ventricular hypertrophy (thickness or enlargement of the heart muscle), post-stenotic aortic dilatation (enlargement of the aorta), filling characteristics, any congenital heart defects, and the function of the left ventricle. Essentially, this information will help doctors understand the severity of the blockage and any related issues.

Although an echocardiogram provides a lot of valuable information, assessing the exact degree of obstruction is difficult. To solve this problem, doctors often use Doppler imaging, which uses sound waves to measure the speed and direction of blood flow. This technique helps determine the precise gradient (change in blood flow velocity) and the extent of obstruction.

Among echocardiographic techniques, 2D and 3D echocardiography enable doctors to have a closer look at the locations of the lesions, the extensiveness of the left ventricular outflow tract’s involvement, and any associated defects. Additionally, these techniques allow doctors to evaluate how stenosis relates to other heart structures and how close it is to the aortic valve.

Making a diagnosis can be complicated if a thickened heart muscle wall (the septum) hides the presence of the subaortic membrane, a problem frequently encountered with subvalvular aortic stenosis. In such scenarios, transesophageal echocardiography, which involves a probe being passed down the esophagus, can provide a clear image of the heart.

Additionally, other tests like an electrocardiogram may be useful. This test can show a varying degree of left ventricular hypertrophy in 50% to 80% of patients, which again indicates thickening or enlargement of the heart muscle. Additionally, a chest X-ray may be normal but can indicate mild heart enlargement or left ventricular prominence in some patients. While it’s not typically done, cardiac catheterization can be utilized to determine further details about the extent of obstruction, especially if multiple levels of obstruction are suspected.

Treatment Options for Subaortic Stenosis

Subvalvular aortic stenosis is a heart condition that often affects children and can get worse over time. Most kids who have this condition don’t show any symptoms, so doctors don’t usually recommend medication as a treatment; instead, they recommend surgery at some point to fix the problem, which involves removing the blockage inside the heart.

However, if a child’s condition worsens to the point where they experience heart failure or their heart doesn’t function effectively (known as left ventricular dysfunction), doctors will start them on medication until surgery can be done.

The best time to perform surgery for this heart condition is still a topic of debates. This is because early treatment often comes with risks such as the reappearance of the condition after surgery, the need for more surgeries, and the development of a new heart issue (aortic regurgitation).

Generally, kids and teenagers who show no heart strain, and who have a specific type of measurement on an ultrasound Doppler test (less than 30 mm Hg) will not require surgery but will need to be regularly checked by doctors.

Kids and teenagers whose Doppler measurements are 50 mm Hg or greater usually need surgery. For those with measurements between 30 and 50 mm Hg, surgery can be considered if they have symptoms such as chest pain, fainting, difficulty breathing when active, changes in their electrocardiogram (a test that measures heart activity), or they were diagnosed at an older age.

The worsening of a condition called aortic regurgitation alone doesn’t typically require surgery but if the condition advances to a severe stage, surgery may be needed.

Performing surgery for this condition necessitates using a heart-lung machine and removing the blocking membrane within the heart (an operation called a myomectomy). Some kids might require a heart valve repair or replacement simultaneously. For babies who are too sick for open-heart surgery, a procedure called percutaneous balloon dilatation can be done which can improve the symptoms for some months or even years until a proper operation can be performed.

There are several surgical techniques that can be used depending on the specifics of the person’s condition. Some might include enlarging parts of the heart or even replacing the heart valve with an artificial one. For repeated cases where the heart valve is normal, a modified procedure may be used that protects the valve.

The American Heart Association recommends that kids with subvalvular aortic stenosis don’t generally need antibiotics to prevent heart infection, except in specific situations such as those who had a prior heart infection or underwent surgery using artificial materials or devices.

What else can Subaortic Stenosis be?

Subvalvular aortic stenosis, a heart condition, often appears along with other heart-related issues. These include a hole in the wall between the lower chambers of the heart (ventricular septal defect), narrowing of the aorta (aorta coarctation), an unclosed blood vessel in the heart (patent ductus arteriosus), a two-leaflet aortic valve instead of the typical three (bicuspid aortic valve), and a hole in the center of the heart (atrioventricular septal defect).

Meanwhile, several other heart defects can hide the signs of subvalvular aortic stenosis, making it harder to diagnose. These conditions are:

• Hypertrophic cardiomyopathy (thickened heart muscle)
• Bicuspid aortic valve, as mentioned before
• Supravalvular aortic stenosis (narrowing just above the aortic valve)
• Valvular aortic stenosis (narrowing of the aortic valve itself)

What to expect with Subaortic Stenosis

Infants and children need to have regular check-ups (every 4 to 6 months) to track the progression of subvalvular aortic stenosis, a condition that progressively narrows the exit of the heart’s main pumping chamber.

Patients who have surgery to remove the narrowing in the heart’s outflow have an excellent chance of survival. However, they still need to continue regular check-ups because the narrowing can slowly redevelop over time. Therefore, long-term follow-up care after surgery is important. Most patients will need additional surgeries during their lifetime to manage the reoccurrence of this condition.

There are certain factors that increase the likelihood of needing additional surgeries. These are:

1. Being female
2. Increasing narrowing of the heart’s outflow over time
3. Difference between the narrowing of the heart’s outflow before and after surgery
4. Severe narrowing of the heart’s outflow (80 mm Hg or more) before surgery
5. Being diagnosed with this condition later in life (older than 30 years)

Possible Complications When Diagnosed with Subaortic Stenosis

After heart surgery, patients may face certain complications. These can include issues with your heart’s electrical signal (bundle branch or complete heart block), accidental damage causing a hole in the heart’s wall (iatrogenic ventricular septal defect), injury to the heart’s mitral valve, or a backflow of blood in the aorta (aortic regurgitation). In some cases, there may be incomplete relief or reoccurrence of the obstruction or the infection of the heart’s inner lining (infective endocarditis).

List of Post-Surgery Complications:

• Issues with heart’s electrical signal (Bundle branch or complete heart block)
• Accidental hole in heart’s wall (Iatrogenic ventricular septal defect)
• Mitral valve injury
• Backflow of blood in aorta (Aortic regurgitation)
• Incomplete relief or recurrence of obstruction
• Infection of heart’s inner lining (Infective endocarditis)

Recovery from Subaortic Stenosis

The level of physical activity a person can engage in safely is determined by the severity of their existing heart condition. Strenuous activities and competitive sports are generally to be avoided.

Specifically, if a person is in any of the following situations, they should refrain from intense sports, games, and workouts:

1. They have a significant blockage in the left ventricle of the heart (the pressure difference across this blockage is more than 50 mm Hg)

2. They show signs of considerable thickening of the left ventricle (a part of the heart responsible for pumping oxygen-rich blood to the body)

3. They have a significant irregular heart rate originating from the ventricles (the lower chambers of the heart) or supraventricular (the upper part of the heart)

4. There is more than a mild leakage from the aortic valve (the gate which controls the flow of oxygen-rich blood from the heart to the body).