Atrial septal defects (ASDs) are a group of rare disorders of the heart that are present at birth (congenital) and involve a hole in the wall (septum) that separates the two upper-chambers (atria) of the heart.
Normally the heart has four chambers: two upper chambers known as atria that are separated from each other by a fibrous partition known as the atrial septum and two lower chambers known as ventricles that are separated from each other by the ventricular septum. Valves connect the atria (left and right) to their respective ventricles. A small opening between the two atria (foramen ovale) is present at birth. Shortly after birth, the atrial septum gradually grows and seals this opening. In infants with atrial septal defects, the atrial septum may not close properly or may be malformed during fetal development. In these disorders, the opening (called patent foramen ovale) between the atria persists long after it should be closed, resulting in an increase in the workload on the right side of the heart and excessive blood flow to the lungs.
Initially, the symptoms associated with atrial septal defects may be absent or so mild that they may go unnoticed. Frequently this disorder is not recognized until school age or even adulthood. In adults with undetected atrial septal defects, various respiratory problems and/or heart failure may develop.
Several forms of atrial septal defects are recognized. They are classified according to their location in the septum. The term primum refers to defects that are in the lower part of the septum. The term secundum refers to defects that are located in the middle of the septum, and the term sinus venosus refers to defects in the upper part of the septum.
Ostium secundum atrial septal defect is the most common form of this group of heart defects. The middle portion of the atrial septum in the region of the foramen ovale fails to close during fetal development. The size of the opening may vary, along with the severity of the symptoms.
Ostium primum atrial septal defect is less common. The lower part of the atrial septum fails to develop normally, leaving an opening between the atria. Frequently, the valves that separate the atria from their respective ventricles (tricuspid and mitral) are also malformed, and the septum that divides the ventricles may also be deficient or malformed (atrioventricular septal defect). Another defect may have occurred during embryonic development in the tissue that forms the septum that divides the heart into atria and ventricles (endocardial cushion defect).
Sinus venosus, the least common form of atrial septal defect, occurs when there is an opening on the upper portion of the atrial septum. This defect is often associated with malformations of the vein that leads from the lungs into the heart (right pulmonary vein). One of the major veins of the body that returns blood to the heart (superior vena cava) may also be malformed.
Most children with atrial septal defects have no symptoms. A few affected individuals may be abnormally thin and experience mild growth delays as well as an increased susceptibility to respiratory infections. Other very severely affected children, especially those with ostium primum defects, may experience breathlessness, easy fatigability with exercise, and/or irregular heartbeats (arrhythmias).
A heart murmur is the most common sign and usually the only sign of ASD in children. There may also be a change in heart sounds that represents the closing of the valves of the heart.
Around the age of 40 years, people with atrial septal defects may experience symptoms related to an increase in pressure in the blood vessels of the lungs (pulmonary hypertension). Increased pressure in these vessels causes the blood to be propelled or “shunted” through the abnormal opening in the heart. Symptoms may include a bluish discoloration of the skin (cyanosis), clubbing of the fingertips, exercise intolerance, and/or an abnormal increase in the number of circulating red blood cells (polycythemia). Abscesses may also develop in the brain. Other symptoms may include swelling of the arms and legs and/or difficulty breathing.
Severe cases of atrial septal defects may lead to life-threatening complications such as chest pain, irregular heartbeats (arrhythmias), abnormal enlargement of the heart, a “fluttering” of the heart (atrial fibrillation), and/or heart failure. Females with atrial septal defects who become pregnant may be at risk for episodes of blood clot formation. These clots may detach from the walls of the blood vessels and travel through the systemic circulation (embolism).
Most cases of atrial septal defects occur on their own for no apparent reason (sporadically). The exact nature of the developmental defect or defects that may occur during embryonic development (embryogenesis) remain unclear.
Some cases of ASD appear to run in families. In such rare cases, the two forms, ostium primum and ostium secundum defects seem to be inherited as autosomal dominant genetic traits. To complicate matters further, genetic analysis suggests that there are at least two different genetic disorders involving ASD that are linked to mutations in a gene called
Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further sub-divided into many bands that are numbered. For example, “chromosome 6p21.3″ refers to band 21.3 on the short arm of chromosome 6. Similarly “chromosome 8p23.1-p22″ refers to a region between bands 22 and 23.1 on the short arm of chromosome 8. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.
Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.
Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25 percent with each pregnancy. The risk to have a child who is a carrier like the parents is 50 percent with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25 percent. The risk is the same for males and females.
All individuals carry 4-5 abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.
Atrial septal defects may also occur in association with a variety of other congenital heart defects, or in newborns that are relatively small or premature. Ostium primum defects occur frequently in individuals with Down syndrome or Ellis van-Creveld syndrome. (For more information on this disorder, choose “Down” or “Ellis van-Creveld” as your search term in the Rare Disease Database.)
Atrial septal defects are rare congenital heart defects that affect more females than males (2 or 3:1). Approximately 1 percent of all infants in the United States are born with a form of congenital heart defect. About 10 percent of these infants have atrial septal defects.
Although atrial septal defects can be diagnosed during infancy or in children between the ages of 6 months and 3 years, the disorder is usually diagnosed after the age of 40 years, when symptoms frequently appear. Symptoms may be noticed at an earlier age if the defects are very severe or if affected individuals live at high elevations (i.e., in the mountains). This is due to the slight narrowing of the arteries of the heart and lungs at higher altitudes.
Ostium primum atrial septal defects may occur in individuals with Down syndrome or in over 50 percent of people with Ellis van-Creveld syndrome. These defects may also occur in association with a variety of other disorders.
The diagnosis of atrial septal defects is confirmed by a thorough clinical examination and specialized tests that allow physicians to evaluate the structure and function of the heart. These tests may include an X-ray study, electrocardiogram (EKG), echocardiogram, and cardiac catheterization. X-ray studies may reveal abnormal enlargement of the heart or malformation of other heart structures. During an echocardiogram, ultrasonic waves are directed toward the heart, enabling physicians to study the motion and function of the heart. During cardiac catheterization, a small hollow tube (catheter) is inserted into a large vein and threaded through the blood vessels leading to the heart. This procedure allows physicians to determine the rate of blood flow through the heart, measure the pressure within the heart, and/or thoroughly identify anatomical abnormalities.
Treatment is usually surgical with the use of medications limited to the period during which the patient waits for a surgical procedure. In the case of the youngest patients “watchful waiting” is often sufficient as the opening closes while the child grows.
Surgery to close the opening of the heart was, until recently, the favored form of treatment. Open-heart surgery was designed to sew edges of the hole together (sutured) and close it. In some cases the hole might be patched and closed with a graft or prosthetic patch. The success rate is high for these surgical procedures. For ostium primum septal defects, surgery may be performed to repair or replace the atrioventricular valves. The success rate for this complex procedure is considerably lower. Surgery is optimally performed between the ages of 3 and 6 years.
In recent years a less traumatic way of closing the septal opening has been developed involving the use of catheters to which is attached a special device designed to close the opening(s) (septal occluder). A catheter is inserted into the heart through the groin and the surgeon “threads” a special fabric-covered wire frame to the heart. Half of the frame is positioned on each of the left and right side of the septal atrium. The surgeon then “wedges” the ASD between the two parts of the occluder. Over the next 6-8 weeks normal tissue grows around the device forming a stable and solid patch over the hole. The use of a catheter-closing device works best for those defects located in the middle of the dividing wall (secundum). There must be enough tissue left in other cases for the closure to take place.
Genetic counseling may be of benefit for some affected patients and their families. Other treatment is symptomatic and supportive.
Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.
For information about clinical trials being conducted at the National Institutes of Health (NIH) in Bethesda, MD, contact the NIH Patient Recruitment Office:
Tollfree: (800) 411-1222
TTY: (866) 411-1010
For information about clinical trials sponsored by private sources contact:
At the present time (June 2006) there are five clinical trials dealing with treatments for ASD. Two of these involve closure devices.
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