Atrial Septal Defects (ASDs)

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 premium refers to defects that are in the lower part of the septum. The term second 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.

Types

The 4 types of atrial septal defects are:

  1. Ostium secundum defect – This defect occurs when there is increased reabsorption of the septum primum in the atrium’s roof, or the septum secundum does not occlude the ostium secundum. Ostium secundum defects are associated with pediatric syndromes such as Noonan, Treacher-Collins, and thrombocytopenia-absent radii syndrome.
  2. Ostium primum defect – The third most common defect of the atrial septum that occurs due to the failure of the septum primum to fuse with the endocardial cushions. Ostium primum defects result in atrioventricular communications and are best considered among the spectrum of atrioventricular septal defects.
  3. Sinus venosus defect – Superior and inferior defects occur, and neither involves the true membranous septum.

    • Superior defect: This occurs when the orifice of the superior vena cava overrides the atrial septum above the oval fossa (the remnant of the foreman ovale) and drains both the left and right atria. The superior sinus venosus defect and a partial anomalous connection of the right superior pulmonary vein to the superior vena cava often occur together.
    • Inferior defect: This occurs when the orifice of the inferior vena cava overrides both atria. The inferior sinus venosus defect and an anomalous connection of the right inferior pulmonary vein to the inferior vena cava can occur together.  The inferior defect is less common than the superior defect.
  4. Coronary sinus defect – The coronary sinus is a vessel that runs along the groove between the left atrium and left ventricle and collects veins that represent the venous return of the heart muscle.  It normally drains into the floor of the right atrium above the septal leaflet of the tricuspid valve. A defect or hole in the common wall between the left atrium and the coronary sinus (called “unroofing” of the coronary sinus) creates communication between the right and left atria.
  5. Secundum – This is the most common type of ASD. It occurs in the middle of the wall between the upper heart chambers (atrial septum).
  6. Primum – This type of ASD affects the lower part of the atrial septum and might occur with other congenital heart defects.
  7. Sinus venosus – This rare type of ASD usually occurs in the upper part of the wall separating the heart chambers. It’s also associated with other heart structure changes present at birth.
  8. Coronary sinus – In this rare type of ASD, part of the wall between the coronary sinus — which is part of the vein system of the heart — and the left upper heart chamber (left atrium) is missing.

Symptoms

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 the 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 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).

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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.

Atrial septal defect signs and symptoms can include:

  • Shortness of breath, especially when exercising
  • Fatigue
  • Swelling of legs, feet or belly (abdomen)
  • Irregular heartbeats (arrhythmias)
  • Sensation of a rapid, pounding heartbeat (palpitations) or skipped beats
  • Whooshing sound that can be heard through a stethoscope (heart murmur)

Severe cases of atrial septal defects may lead to life-threatening complications such as chest pain, irregular heartbeats (arrhythmias), abnormal enlargement of the heart, and 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).

Causes

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) remains 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

NKX2-5.

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 is 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 of 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.)

Diagnosis

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.=

  • Echocardiography – In transthoracic echocardiography, an atrial septal defect may be seen on color flow imaging as a jet of blood from the left atrium to the right atrium. If agitated saline is injected into a peripheral vein during echocardiography, small air bubbles can be seen on echocardiographic imaging. Bubbles traveling across an ASD may be seen either at rest or during a cough. (Bubbles only flow from right atrium to left atrium if the right atrial pressure is greater than left atrial). Because better visualization of the atria is achieved with transesophageal echocardiography, this test may be performed in individuals with a suspected ASD which is not visualized on transthoracic imaging.
  • Transcranial doppler bubble study – A less invasive method for detecting a PFO or other ASDs than transesophageal ultrasound is transcranial Doppler with bubble contrast.[rx] This method reveals the cerebral impact of the ASD or PFO.
  • Electrocardiogram – The ECG findings in atrial septal defect vary with the type of defect the individual has. Individuals with atrial septal defects may have a prolonged PR interval (a first-degree heart block). The prolongation of the PR interval is probably due to the enlargement of the atria common in ASDs and the increased distance due to the defect itself. Both of these can cause an increased distance of internodal conduction from the SA node to the AV node.
  • Transthoracic echocardiography/Doppler examination – an ultrasound image of the heart combined with measurements of blood flow to check the heart’s structure and see how well it is working.
  • Transesophageal echocardiography (TEE) Doppler examination – an ultrasound took through the esophagus is used to get a better picture of the atria and more details about the size and shape of the ASD. A TEE helps the doctor and can also be used to check the heart valves.
  • Intracardiac echocardiography (ICE)/Doppler examination – an ultrasound taken inside the heart. A tiny camera (echo probe) is sent to the heart through a peripheral vein. The test shows the size and shape of the defect and the direction of the blood flow across it. This study is often used during the percutaneous (nonsurgical) repair of the defect.
  • Right heart catheterization – a small, thin tube (catheter) is inserted into the heart through a peripheral vein. Pressures and the amount of oxygen in the blood (oxygen saturation) are measured in each chamber of the heart. The oxygen levels determine how much blood is flowing across the ASD. Your doctor may also use a tiny balloon at the end of the catheter or a special dye to check the size of the defect (atrial angiogram).
  • Left heart catheterization – during this procedure, a special dye is sent into the blood vessels of the heart through a catheter (angiography). The test can check for coronary artery disease (hard, narrow arteries).
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Treatment

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.

Surgical

Surgery to close the opening of the heart was, until recently, the favored form of treatment. Open-heart surgery was designed to sew the 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 sides 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.

ASD repair

Nonsurgical treatment

Nonsurgical (percutaneous) repair is the preferred treatment for most patients with secundum ASDs. If you have a different type of ASD, or the anatomy of your secundum ASD is not amenable to percutaneous closure, you may need surgery. Your doctor will let you know which type of repair is best for you.

This type of repair uses a device to close the hole in the septum.

Two different brands of closure devices are approved by the U.S. Food and Drug Administration for percutaneous ASD closure — the Amplatzer® Septal Occluder and the GORE HELEX® Septal Occluder.

The designs of the devices are different, but they work in similar ways.

The device is put in place using a long, thin tube called a catheter. The device is attached to the catheter, which is guided to your heart through a vein in your groin. When the device is released from the catheter, it opens up and seals the hole. Over time, tissue grows over the implant and it becomes part of the heart.

If your doctor recommends this type of repair, you will have a cardiac catheterization to check the size and location of the defect and measure pressures in your heart.

After the procedure, you will need to take a blood-thinning medication to keep clots from forming on the device. Your doctor will talk to you about the right type of medication for you and how long you need to take it.

Percutaneous Closure Devices for ASD Repair

AMPLATZER Septal Occluder

The AMPLATZER® Septal Occluder is a transcatheter closure device used to treat ASDs. It consists of two Nitinol wire mesh discs filled with polyester fabric. It is folded into a special delivery catheter, similar to the catheter used to cross the heart defect during catheterization.

The catheter is inserted into a vein in the leg, advanced into the atrial septum and through the defect. When the catheter is in the proper position, the device slowly is pushed out of the catheter until the discs of the device sit on each side of the defect, like a sandwich. The two discs are linked together by a short connecting waist that matches the size of the defect. The discs and the waist are filled with polyester fabric to increase the device’s closing ability. Over time, heart tissue grows over the implant, and it becomes part of the heart, permanently correcting the defect.

GORE HELEX® Septal Occluder

The GORE HELEX® Septal Occluder is a disc-like device that consists of ePTFE patch material supported by a single Nitinol wire frame. The device is put in place with a catheter and slowly pushed out until it covers the defect. The device bridges the septal defect.

Surgical repair

Surgery may be needed to repair large Secundum ASDs and other types of ASDs. In some cases, this can be done robotically or with a small incision.

A surgical repair usually involves using a tissue patch to close the ASD. The tissue often comes from your own pericardium (membrane around the heart). Some Secundum ASDs can be surgically closed with sutures alone.

Follow-up care

Follow-up visits

Your doctor will let you know how often you need to be seen for follow-up visits. A typical schedule is 3, 6 and 12 months after your procedure and once a year after that.

Activity

Your doctor will talk to you about activity restrictions related to recovery from the procedure.

Medications

Expect to take blood thinners for 6 to 12 months after surgery.

If you had a stroke, you may need to take this medication indefinitely. If you have another heart condition, you may need to take other medications.

You may need to take antibiotics before certain medical procedures for at least 6 months after your procedure to prevent an infection of your heart’s lining (endocarditis).

Genetic counseling may be of benefit to some affected patients and their families. Another treatment is symptomatic and supportive.

References