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Atrial Septal Defects

A Hole Between the Upper Chambers of the Heart is a Common Defect

Jul 22, 2009 Kenneth Rosen

The human heart has two upper and two lower chambers. When the wall that divides the upper pair of chambers has a hole oxygen rich and oxygen poor blood can mix.

Congenital heart defects are surprisingly commonplace. They can range in severity from the minor to the life threatening. One of the most common congenital (present at the time of birth) heart defects is known as an atrial septal defect or ASD, a hole in the wall separating the atria, the two upper chambers of the heart.

The Heart Forms from a Tube

During embryonic development, the early heart begins to take shape as the heart tube, formed by specialized embryonic cells, begins to bend and fold. Important signaling interactions ultimately lead to the formation of the early heart with four distinct chambers but not yet containing any of the valves. The valves form later during embryonic development.

After the bending into place of the early heart tube structures, the upper chambers of the heart, the atria (also previously referred to as the auricles) are separated from the lower chambers of the heart, the ventricles. Ultimately, once completely formed, the ventricles will pump blood from the heart out to the structures of the body. The atria will serve to receive blood returning to the heart from either the lungs (into the left atrium) or from the rest of the body (the right atrium). They then pump the blood into the ventricles.

The Path of Blood Through the Heart and Circulatory System

Oxygenated blood flows from the lungs, where it receives the oxygen to replace the carbon dioxide that it has carried away from tissues in the body, through the pulmonary vein to the left atrium. Once there it is pumped into the left ventricle. The left ventricle contracts forcefully to send the blood into the aorta and ultimately to all the tissues of the body passing through arteries, then arterioles and finally through capillaries where the oxygen is exchanged for carbon dioxide. The deoxygenated blood flows back towards the heart through venules and then veins finally reaching the right atrium. It is then pumped into the right ventricle which promptly pumps it through the pulmonary artery to the lungs to be reoxygenated.

What Happens When There is a Hole Between the Atria

If the wall that separates the two atria does not completely close, an atrial septal defect results. Since the two atria receive blood, that in one is oxygenated and in the other is deoxygenated, mixing between the two circulatory paths can occur. This can lead to reduced oxygenation levels in the tissues of the body. Depending upon the size of the hole, stress on the ventricles can be greater or lesser. If the stress is great, owing to a larger hole, the ventricles can develop a difficult time pushing the blood throughout the body.

How This Type of Defect is Treated

For many of these defects, the hole is small enough that symptoms might not even be detected, and the hole can repair itself over the first few years of a child’s life. If symptoms are apparent interventions can be undertaken. For many of these symptomatic defects, a cardiac catheterization procedure (where a very thin, lighted tube is snaked up from a blood vessel in the groin all the way to the heart) can be used to deliver small devices such as specialized meshes that can allow the hole to be closed. In very serious septal defects, open heart surgery might be required.

The presence of an uncorrected atrial septal defect that has caused no detectable symptoms can cause other difficulties later in life if it does not close. Chief amongst these is an increased risk of stroke. Blood clots can form in the opening and if they were to break free they can move through the circulation and cause a stroke by blocking or restricting blood flow through blood vessels in the brain. Fortunately this does not happen that often.

To learn more about these types of heart defects visit the website of the US National Heart Lung and Blood Institute (NHLBI) at the National Institutes of Health.

The copyright of the article Atrial Septal Defects in General Medicine is owned by Kenneth Rosen. Permission to republish Atrial Septal Defects in print or online must be granted by the author in writing.

The Human Heart