Atrial Septal Defect

An atrial septal defect is a congenital (“present from birth”) anomaly that affects a baby’s heart.  According to the US Centers for Disease Control (CDC), around 1,966 babies are born with ASD every year.

What Is An Atrial Septal Defect?

To properly understand ASD, we’ll first cover the heart’s normal development, and then explain how its formation differs in children with the condition.

The heart is a large organ made up of four separate chambers. On top are two spaces called the “atrium” and on bottom, two more spaces called “ventricles.”

How Blood Flows In A Healthy Human Heart

After birth, blood flows into the right atrium, descends to the right ventricle and then passes out toward the lungs. In the lungs, blood is filled with oxygen. Then it returns to the heart, entering now through the left atrium, passing downward through the left ventricle and then on to nourish the rest of the body with oxygen. After flowing through the body and releasing its supply of oxygen, blood returns to the right atrium where it repeats the process.

Crucially, each of the heart’s chambers have to be fully separated from one another for this process to work completely. We call the walls that divide chambers “septa.” “Septum” refers to one single wall.

How Blood Flows In A Fetus

But inside the womb, the process is different. Developing babies aren’t yet able to breath, and so their lungs won’t supply the oxygen their blood needs to fulfill its purpose. Instead, fetuses receive oxygen from their mother’s blood supply, which flows in through the umbilical cord.

In the meantime, the wall that will separate the heart’s upper chambers hasn’t closed fully. At this point, holes are a good thing.

Remember that after flowing through the body and delivering oxygen, blood returns to the right atrium. With a hole in place, the blood is allowed to flow right into the left atrium, down to the left ventricle and back out to the body. Blood doesn’t go towards the lungs, because it doesn’t yet need to be there. The baby is getting oxygen from its mother’s blood, not its own lungs.

For most babies, the atrias’ septum closes up shortly before birth. With a full wall separating the atria, blood can now flow down to the right ventricle and pass to the lungs for oxygen.

In babies with an atrial septal defect, this wall never completely formed, leaving a hole of varying size between the two chambers.

How An ASD Can Affect Blood Flow

As blood flows through the body, it releases oxygen. When it returns to the heart, we call it “deoxygenated” because it no longer carries this vital nutrient. Once a baby is born and breathing, deoxygenated blood will travel through the heart’s right side to reach the lungs for more.

But an atrial septal defect allows some of this deoxygenated blood to leak over into the right atrium. This chamber, which is normally filled only with oxygen-poor blood, now has a mixture of fluids: blood with and without oxygen. This mixture passes through the right ventricle and out to the lung, but it’s no longer able to absorb a full load of oxygen, and thus cannot properly nourish all the cells it needs to. As a result, the heart has to pump more, and harder, to adequately deliver nutrients.

Symptoms Of An Atrial Septal Defect

Now that we understand how an ASD works, understanding the symptoms of this defect will be easier.

But before we cover symptoms, it’s important to note that many babies and children will not experience any problems until later in life. Some people never do. The severity of complications vary widely based on how large the hole is, and how much blood it allows to flow right to left.

Large septal defects may become apparent at birth, through a number of possible symptoms:

  • Cyanosis – a blue tint to the skin and lips, caused by inadequate oxygen supply
  • Difficulty breathing
  • Tiring quickly during feeding
  • Heart murmurs – a sound (often described as “whooshing”) that can be heard when blood doesn’t flow properly through the heart. Doctors can hear this with a stethoscope.

In some cases, doctors can diagnose an atrial septal defect before birth. By using a fetal echocardiagram, a form of ultrasound, physicians can develop a picture of a baby’s heart before it’s outside the womb. This picture may be enough to reveal a structural anomaly prior to delivery.

Smaller holes might go unnoticed at birth. If the ASD causes problems later in life, the symptoms can include:

  • Labored breathing
  • Shortness of breath
  • Frequent respiratory infections
  • Heart palpitations – the feeling that your heart is beating faster or harder than normal, skipping beats or “fluttering.”

Does An Atrial Septal Defect Hurt My Child?

No. Beyond any associated symptoms, the presence of a congenital anomaly does not cause babies any pain.

What Causes ASD?

In relation to individual cases, doctors will probably never be able to determine what caused a child’s atrial septal defect. But researchers believe that most congenital defects are the result of genetic and environmental factors.

For its part, atrial septal defect seems to be hereditary, or passed from parents to children in genetic information. It can also be the result of an isolated genetic mutation, and may be contributed to by certain chemicals when ingested by an expectant mother.

For a more detailed look at the causes of heart defects, click here.

How Common Is Atrial Septal Defect?

Based on statistics released by the CDC, atrial septal defect appears to be the second most common congenital heart defect in America, behind only atrioventricular septal defect in frequency.

With that being said, it’s difficult to arrive at accurate numbers in relation to any birth defects, since only 13 states and Puerto Rico track congenital anomalies at birth.

Assuming an estimated total of 4 million live births per year, one out of every 2,035 babies are born with an atrial septal defect in the US.

According to a study published in Circulation: Journal of the American Heart Association, atrial septal defect is “the most common congenital heart [defect] encountered in adults.”

Risks & Complications Of ASD

Without adequate treatment, babies born with atrial septal defects commonly experience difficulty breathing. Over time, an ASD can contribute to hypoxemia, a conditioned characterized by low levels of oxygen in the blood. Without enough oxygen, organs, including the brain, can suffer permanent damage.

But most babies do not suffer complications directly after birth. More likely, symptoms will only appear after years of improper blood flow and heightened stress to the heart.

It’s crucial to note that ASD can be treated effectively, and as reported by the University of California San Francisco’s Department of Surgery, around half of all ASD close on their own without treatment.  In fact, about 20% of the atrial septal defects that will close of their own accord, do so before the affected baby reaches one year of age.

When left untreated, the long-term effects of an ASD may include:

  • Pulmonary hypertension – high blood pressure that specifically affects vessels in the lungs. Over time, pulmonary hypertension can thicken these veins and make them hard, which in turn forces the heart to work even more to pump an adequate amount of blood.
  •  Stroke – Small blood clots sometimes form on the heart’s right side. Usually, the lungs filter these clots out before they reach the heart’s left atrium and are carried to the body. In hearts with an atrial septal defect, clots can pass directly from the right atrium where they form to the left atrium, where they can be pumped directly into the body. If the clot eventually reaches arteries that supply the brain with oxygen, it can block blood flow and cause a stroke.
  • Right heart failure – atrial septal defects force the heart to work harder, and specifically the heart’s right side. After years of extra effort, the right side may lose its ability to pump effectively.
  • Arrhythmia – abnormal heart rhythms

You can find more information on the potential complications of a congenital heart defect here.

How Are Atrial Septal Defects Treated?

ASD was first effectively treated with open-heart surgery in 1953. Since then, the procedure has become so advanced that the prognosis for a full recovery is nearly 100%. Generally, this surgery requires the use of a cardiopulmonary bypass, a machine that temporarily takes over heart and lung functions while the heart is opened.

Again, doctors will monitor a child’s heart using an echocardiagram before suggesting surgical intervention. Many smaller ASDs close up by themselves. In the meantime, a regimen of medications can be prescribed to alleviate symptoms and avoid complications, including:

  • Beta blockers reduce the risk of developing an arrhythmia
  • Anticoagulants can prevent blood clots from forming

An alternative to open-heart surgery that has become increasingly common involves a catheter. Catheters are thin tubes and medical devices can be attached to their tips.

To repair an atrial septal defect, a small patch will be placed on the catheter’s tip and then the tube will be thread through a blood vessel in the patient’s grown. Using imaging devices, surgeons can guide the catheter through the vein and into the heart. After placing the patch to cover the defect, the catheter is removed. Cardiac tissue eventually grows over the patch.

For more information on how doctors treat congenital heart defects, click here.

How Will ASD Affect My Child’s Life?

Most children won’t need to restrict their activities after having an atrial septal defect repaired, although only your own doctor can tell you what is and is not healthy for your child.

While vigorous physical exercise is usually a concern for people with heart conditions, kids born with an ASD are usually able to live happy, active lives. Children and adults with associated complications, like pulmonary hypertension or other heart defects, may need to limit exercise on the advice of a cardiologist.

Heart defects, along with certain methods that repair them, can alter the surface of cardiac tissue, creating new places for bacteria to gather. Infective endocarditis is an infection in heart tissue, but people who were born with an ASD are at a very low risk of getting it.