What Is Subaortic Stenosis?

Subaortic stenosis is an obstruction or narrowing at the outlet of the lower left chamber of the heart (the left ventricle), just below the aortic valve. In typical subaortic stenosis, the aortic valve itself is normal.

The normal heart has four chambers: two upper chambers called atria, which receive blood into the heart, and two lower chambers called ventricles, which pump blood out of the heart. Ordinarily, unoxygenated (blue) blood comes back from the body into the right atrium, moves into the right ventricle, and then is pumped out of the right ventricle through the pulmonary artery (the main artery to the lungs) to collect more oxygen. The now-oxygenated (red) blood returns from the lungs and enters the left atrium, moves into the left ventricle, and then is pumped through the left ventricle's outflow tract to the aortic valve and out to the body through the aorta (the body’s main artery).

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In a heart with subaortic stenosis, it is difficult for the left ventricle to pump the blood to the body due to the narrowed area in the outflow tract below the aortic valve.

Subaortic stenosis can cause two main problems for the heart:

  • The blockage can cause extra work for the left ventricle.
  • Turbulent blood flow created by the narrowing may damage the aortic valve, causing an otherwise normal valve to leak. This is called aortic valve insufficiency.

There are two kinds of subaortic stenosis:

  • Discreet subaortic stenosis, the more common form, occurs when a membrane composed of fibrous tissue forms an obstruction beneath the aortic valve.
  • Tunnel subaortic stenosis, a less common and more complex form, occurs when the pathway between the ventricle and valve is narrow for the entire distance.

What Are the Causes?

The causes of heart defects such as subaortic stenosis among most babies are unknown. Some babies have heart defects because of changes in their genes or chromosomes. A combination of environmental exposures and genetic factors are likely responsible, but little is known about the specific cause.

How Is It Diagnosed?

Doctors sometimes hear a heart murmur (an odd, whooshing sound heard via stethoscope) due to the turbulence of blood flow through the narrowed area, after which, further tests might reveal subaortic stenosis.

When the narrowing is severe, symptoms such as lethargy, lack of appetite and difficulty breathing may signal an obstruction in infants. Rarely, fainting or chest pain also may occur.

The following tests may be utilized to find more details:

  • An electrocardiogram (EKG or ECG) can check the heart’s electrical action to reveal enlargement of chambers.
  • Chest X-rays create images of the heart and lungs and can show structural changes.
  • Pulse oximetry, a small gadget placed painlessly on a finger, is used to measure oxygen level of the blood.
  • An echocardiogram (ECHO) uses sound waves (ultrasound) to produce images of the heart and vessels on a screen. That reveals information about structure and function of the heart.
  • A cardiac MRI (magnetic resonance imaging) uses radio waves, magnets and a computer to form three-dimensional images of the heart, which can reveal structural abnormalities.
  • Cardiac catheterization involves insertion of thin, long tubes (catheters) through blood vessels and guided into the heart to obtain further information and is sometimes performed to treat some cardiac defects without surgery.

How Is It Treated?

Surgery is usually done through a vertical incision in the middle of the chest. Repair requires open heart surgery; that is, the patient is -placed on the heart-lung machine.

The subaortic stenosis is repaired by opening the aorta just above the aortic valve. The subaortic membrane can be seen through the valve. The membrane can then be cut out, leaving the left ventricle's outflow tract open and smooth. This operation is called a subaortic resection.

It is uncommon to have major complications after a subaortic resection. It is possible to have a leftover membrane, though it is extremely unusual for that to cause any remaining obstruction. Other very uncommon complications include damage to the aortic valve itself, heart block (which is a problem with the electrical conduction of the heart), or creating a hole between the two pumping chambers (ventricular septal defect). Most patients who undergo a subaortic resection are able to be discharged with 3-4 days after surgery.

What Are the Long-Term Effects?

Surgery for subaortic stenosis typically has a high degree of success, and full recovery is usually expected unless there are initial complications. Subaortic stenosis may return a few years after effective surgery.

What Follow-Up Care Is Needed?

Children should have regular checkups with their pediatric cardiologist. Doctors may prescribe antibiotics before any dental or other surgery.

Why Choose the Children’s Heart Institute?

At Children’s Heart Institute at Children’s Memorial Hermann Hospital, patients with congenital or acquired heart disorders receive hands-on specialized care 24/7 from a team of affiliated physicians and specialty-trained nurses who aim to deliver the best possible outcomes.

Children’s Memorial Hermann Hospital was named one of the top children's hospitals nationally in Cardiology & Heart Surgery by U.S. News & World Report. In addition, Children’s Heart Institute is among the top congenital heart surgery programs in North America for patient care and outcomes, according to the Fall 2019 Society of Thoracic Surgeons (STS) Congenital Heart Surgery Database Report of 118 STS participating programs.

In collaboration with various subspecialties, the affiliated team provides comprehensive care for newborns, children and adolescents, with the ability to transition into adult congenital cardiac care. Team members have the experience and skills necessary to offer innovative treatment methods and specialized services, including, but not limited to:

  • Biventricular repairs and biventricular conversions
  • Congenital heart optimization
  • Full repairs for complex congenital heart defects in newborns
  • Hybrid catheterization and surgical procedures
  • Minimally invasive transcatheter pulmonary valve (TPV) therapy
  • Minimally invasive repairs
  • Treatment for adult congenital heart disease
  • Valve repairs and preservation

With the Level IV Neonatal Intensive Care Unit (NICU) and a dedicated Children’s Heart Institute Intensive Care Unit at Children’s Memorial Hermann Hospital, critical heart patients have access to quality, specialized care. By utilizing state-of-the-art techniques, the team at Children’s Heart Institute strives to offer patients with the most complex problems the greatest opportunity for a normal life.

Contact Us

If you have any questions, use the online tool below to help us connect with you. To refer a patient or schedule an appointment, please contact our clinic using the information below.

  • Pediatric Cardiology Clinic
    The University of Texas Health Science Center Professional Building
    6410 Fannin, Suite 370
    Houston, TX 77030
    Phone: (713) 486-6755 (Appointment Line)
  • Pediatric and Congenital Heart Surgery Clinic
    The University of Texas Health Science Center Professional Building
    6410 Fannin, Suite 370
    Houston, TX 77030
    Phone: (713) 500-5746

To contact Children’s Heart Institute at Children’s Memorial Hermann Hospital, please fill out the form below.


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The Children’s Heart Institute is a collaboration between the affiliated physicians at McGovern Medical School at UTHealth Houston and Children’s Memorial Hermann Hospital. Typically, patients are seen on an outpatient basis at a UT Physicians clinic with all inpatient procedures performed at Children’s Memorial Hermann Hospital.

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