October 31, 2008
Dear Mayo Clinic:
At three, our son was diagnosed with subaortic membrane. He had annual checkups to track its growth and determine if it should be surgically removed. He is now six, and the membrane has not grown for three years, but our cardiologist says we should be prepared for surgery as the membrane will start to grow again. Can you tell us what we should expect? If the membrane is removed, will it grow back?
Answer:
Subaortic membrane is a ring of fibrous tissue located in the left side of the heart where blood flows to the aorta (left ventricular outflow tract). The aorta — the body’s largest artery — carries blood away from the heart to the rest of the body.
Depending on its size and location, subaortic membrane can cause serious complications. For example, it can hinder blood flow out of the heart, damage heart valves, and decrease the heart’s pumping efficiency. Surgery may be necessary to remove the membrane. But, if the condition is not causing problems, watchful waiting is a reasonable approach.
Most children who have subaortic membrane are diagnosed between the ages of 1 and 3. By disrupting the heart’s blood flow, subaortic membrane creates a distinctive heart murmur that a cardiologist can easily identify. The defect can be clearly seen and diagnosed with an echocardiogram, a test that uses sound waves to produce images of the heart. An echocardiogram will also show if the membrane is interfering with the aortic valve, which controls blood flow between the heart’s left pumping chamber (ventricle) and the aorta.
Because subaortic membrane interferes with the smooth flow of blood out of the left ventricle, the heart may have to work harder than normal to pump blood through the aorta and back to the body; this results in an elevated pressure in the left ventricle. A cardiologist can measure the difference between the pressure inside the ventricle and in the aorta (the gradient) to determine how much the membrane is obstructing blood flow.
Typically, surgery to remove a subaortic membrane is required if the membrane is located close enough to the aortic valve to affect its functioning, or if the blood flow obstruction creates a gradient of more than 30 millimeters of mercury (mm Hg).
The subaortic membrane might not grow much beyond the point at which it’s diagnosed. Over time, however, the blood flow obstruction can become more severe, or valve damage can reduce the left ventricle’s pumping effectiveness. Because these changes can happen, closely monitoring the condition over time, as your son’s cardiologist has done, is a wise course of action.
As your son grows, the probability that he will need surgery to remove the membrane decreases. Most people with subaortic membrane require surgery early in life, rather than later. Approximately 40 percent need surgery by 5 years of age. After that, only about 10 percent more need surgery. So, after age 5, chances decrease that the condition will require surgery.
If your son does have surgery to remove the membrane, the defect can grow back. Some research suggests that about 15 to 20 percent of patients need a second surgery for subaortic membrane. The risk of regrowth is higher for people who have a very severe obstruction prior to their first surgery, or require surgery before age 1. For most people, though, one surgery corrects the condition, and no further treatment is needed.
For your son’s situation, I’d recommend you continue what you have been doing: consistently monitor his condition with annual checkups to assess the membrane and evaluate his heart function. If you have specific questions or concerns about his condition or overall heart health, discuss them with his cardiologist.
Donald J. Hagler, M.D., Pediatric Cardiology, Mayo Clinic, Rochester, Minn.