What is an Atrial Septal Defect?
Atrial septal defects (ASD) are basically holes in the wall that separates the left and right atrium, i.e. the upper chambers of the heart. Usually atrial septal defects are a congenital condition, which means people are born with them. The defect allows blood to mix between the upper chambers of the heart. A big enough hole can be a problem for two reasons, firstly it can allow oxygen-rich blood to mix with oxygen empty blood leading to lower oxygen levels, and secondly it can cause enlargement of the right side of the heart. We will review the indications to close the atrial septal defects later in this article. There are several different kinds of atrial septal defects and it’s important to know which is which because different defects have different management strategies. Many of you will have heard of a PFO, (patent foramen ovale) and I have discussed that in detail in another article linked here.
What an ASD Looks Like Up Close
What an ASD Looks Like from Afar
Prevalence of ASD
Atrial septal defects are one of the most common types of congenital heart disease. It’s estimated that an atrial septal defect is present in up to 100 per every thousand live births. Most people have a defect called a secundum defect. There is an increased risk of an atrial septal defect in families with a history of congenital heart disease, especially with a history of an atrial septal defect.
Causes of ASD
Most cases of atrial septal defect have no identifiable cause, so basically people are just born with them. Researchers have identified some possible patterns of inheritance or genetic abnormalities, however this does not appear to be the cause in the majority of cases.
Atrial septal defects are known to be more common in those with genetic syndromes. The best example is Downs Syndrome where atrial septal defects are seen in up to 2/3rds of cases. There is some research that suggests associations between exposure so substances such as alcohol, cigarettes or certain medications during pregnancy. There are also associations between atrial septal defects and advanced maternal age and diabetes.
What are the Different Types of Atrial Septal Defect?
Patent Foramen Ovale, aka PFO
This is the most common ‘hole in the heart.’ It is written about in detail in this linked post. It is basically a channel between the right and left side of the heart that is needed during fetal life to make sure oxygen rich blood from the mother can be delivered to the baby. In 3 out of every four people this hole closes naturally after birth. In the other quarter it remains and is known as a PFO.
Septum Secundum Atrial Septal Defect
This is the most common of the true atrial septal defects. Unlike the PFO, which is a channel. The septum secundum ASD is a true absence of tissue in the atrial septum with a resultant hole between the upper chambers of the heart. It is usually in the middle area of the wall that separates the left and right upper heart chambers. The size can vary from just a few mm to several cm. This type of defect can usually be closed using minimally invasive keyhole techniques avoiding the need for open-heart surgery.
Septum Primum Atrial Septal Defect
This defect is generally considered more complex and is often associated with other defects such as abnormal heart valves. The septum Primum defect typically can’t be closed through catheter based techniques, and requires heart surgery to fix it.
Sinus Venosus Atrial Septal Defect
In this defect there is absence of tissue in the area where the great vein known as the vena cava enters the heart. It is often associated with a further abnormality whereby the veins that usually drain in to the left side of the heart can now drain in to the right side of the heart.
Coronary Sinus Atrial Septal Defect
In this uncommon defect, the vein that drains blood from the left side of the heart to the right side, the coronary sinus, has a hole in it known as unroofing allowing communication of oxygen rich and oxygen-depleted blood.
What Problems Can it Lead to?
Typically, an atrial septal defect results in blood going from the left upper chamber of the heart to the right upper chamber known as shunting of blood. The amount of blood that shunts is typically related to the size of the defect.
When the size of the defect is less than 1cm, then the shunt is generally fairly small and does not lead to heart enlargement. With larger defects, the shunt is more significant and leads to heart enlargement. Larger ASD defects also associated with increased pressures and damage to the vessels of the lung. Because the shunt is from left to right thereby increasing the amount of blood in the right side of the heart, the right side of the heart becomes enlargement. This leads to right-sided heart failure and increased pressures in the lung vessels that can lead to irreversible damage. Untreated large atrial septal defects need to be repaired; otherwise, they can greatly shorten a person’s life expectancy.
Symptoms of an ASD
Even when defects are relatively large, most people do not have symptoms at a young age and symptoms will typically develop into adulthood with large enough defects. Most commonly the defects will be picked up due to the presence of a heart murmur, an abnormal echocardiogram, or abnormal EKG tracing.
When symptoms develop they may start as shortness of breath on exercise, fatigue, palpitations or passing out. In more advanced disease, people may experience turning blue and swelling of the lower limbs.
Diagnosis of ASD
Physical Examination
The heart sounds may be abnormal, with a pattern known as splitting of the 2nd heart sound. A murmur may be present during contraction of the heart as blood is shifted through the defect and also relaxation of the heart as the extra blood travels through the right-sided heart valve. In more advanced disease, swelling, blue tinge, and irregular heartbeat may be noted.
EKG
Right bundle branch block, right axis deviation and p wave abnormality patterns may be noted.
This is an ultrasound scan of the heart that can show the defect and its size, and the degree of heart enlargement and heart pressures.
Heart Catheterization
This is a test where small tubes are inserted into the heart to measure pressures and see the effect on the heart and help to determine the significance of the defect.
When Should an ASD be Closed?
The strongest indication for closing an atrial septal defect is a defect that has a significant effect on the circulation leading to right-sided heart enlargement. There is extra blood in the right-sided circulation through the lungs because of the blood that goes through the hole. When the extra blood is 1.5 times that of the left sided system that is generally considered significant and an indication for closure. Other indications for closure include suspicion of a clot traveling through the defect or the presence of breathing difficulty attributed to the defect. In some instances of large defects with severe effects on the heart, closure can worsen symptoms and the possibility of this should be ruled out prior to proceeding. Sometimes procedures such as the mitraclip procedure require creation of a small atrial septal defect although these usually don’t need closing.
How is an Atrial Septal Defect Closed?
Open Heart Surgery
One option is open-heart surgery. This is a tried and tested option with good outcomes. It has declined in recent years due to the popularity and success of minimally invasive catheter based closure. Although the most common defects can be closed by catheter, the others generally cannot and therefore require surgery.
Robotic Heart Surgery
Even complex defects can be closed by robotic surgery if performed in the right hands. The advantage to robotic surgery is the minimal invasive aspect. Someone experienced in robotic, in which case even the most complex of defects can be closed, should perform the surgery.
Catheter-Based Repair
For suitable defects this is considered the preferred approach. Typically the defect can be closed through a small hole through which a tube is advanced from the leg vessels to the heart. Success rates are excellent for suitable defects and patients can typically go home the next day. Structural heart specialists perform this procedure.
How Can Cardiologists Close a Heart Defect Through a Tiny Hole?
This technique is known as percutaneous (through the skin) or catheter based repair. The procedure is painless as the area is numbed up and also the patients are sedated. A small tube called a catheter is placed into a leg vein. The veins provide a route to the heart. A wire is passed through the vein and up to the heart and passed through the hole in the heart. We see the wire under x-ray and also ultrasound guidance. A device is advanced over the wire and placed across the defect, sealing it. Once the device is secured into place the tubes and wires are removed. The patient can go home the next morning. Typically we prescribe blood-thinning medication for a period of a few months after the procedure.
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