Atrial septal defect (ASD) is one of the most commonly recognized congenital cardiac anomalies and is sometimes known as “hole in the heart”. Find out more about the condition including its types, symptoms, causes, diagnosis and various treatment options.
It is a serious malformation of the heart marked by an abnormal opening in the interatrial septum – a partition that separates the right and left atrium. The condition may result in mixing of oxygenated blood from the left atrium with the deoxygenated one in the right atrium or vice-versa through this small opening. Such defects can be located in various spots on the interatrial septum and may vary in size.
The condition can be differentiated into several forms on the basis of other structures of the heart involved as well as the pattern of formation during early fetal development.
The major types of ASD are as follows:
Picture 1 – Atrial septal defect
It accounts for 6 to 10% of all cases of congenital heart disorders and is the most common form of ASD in infants.
Foramen ovale is an oval opening between the atria. It is a normal feature in newborns and usually closes by 3 months of age. However, in infants suffering from this form of ASD, this aperture becomes abnormally large and allows the passage of blood between the two upper chambers. It can also be an outcome of excessive absorption of septum primum- a wall that divides the embryonic heart into right and left chambers. Sometimes, the septum secundum, which is a membranous sheet, grows downward from the upper wall of the right atrium and may undergo incomplete fusion with the septum primum. This may give rise to an opening in the interatrial septum.
This particular form of ASD typically arises due to an incomplete closure of foramen ovale and is generally seen after birth. It has been found to be associated with migraine headaches.
In this form, there is a malformation of the ostium primum, which is an opening between the two atria present at the bottom of the interarterial septum. It is more often defined as an atrioventricular septal defect where there is a deficiency of atrioventricular septum that separates the right atrium from the left ventricle.
Superior vena cava (SVC) and inferior vena cava (IVC) are the two major veins of the heart. SVC transports deoxygenated blood from the upper part of the body to the right atrium of the heart. On the other hand, IVC carries deoxygenated blood into the right atrium from the lower part of the body. This particular form of ASD may occur near the superior vena cava or inferior vena cava and is associated with sinus venosus – a large cavity that precedes the right atrium. ASD, which is involved with SVC, causes the pulmonary veins to carry oxygenated blood from the lungs to the right atrium instead of the left upper chamber.
During fetal life, the heart fails to develop interarterial septum due to lack of formation of the septum primum and septum secundum. Only a large, common cavity behaves as a single atrium where the SVC and IVC as well as the four pulmonary veins drain deoxygenated blood into it.
The atrial septum is generally divided into 5 septal zones. Malformation occurring in 2 or more of these zones gives rise to ASD.
ASD accounts for 30-40% of all cases of congenital heart disorders. It is diagnosed in 1 infant per 1500 live births. PFO affects approximately 10-12% of the adult population.
About 70% of patients with uncorrected ASD begin to exhibit its symptoms by the age of 30. Smaller ASDs are generally asymptomatic. Severe cases are usually manifested by one or more of the following signs:
Although medical experts are still unclear about this type of a congenital defect, there could be certain factors associated with the condition. Defective development of the heart prior to birth can be a result of a mutational or genetic change, causing a block in the circulatory system.
The left chambers of the heart are normally prone to higher pressure than the right side. The left ventricle is responsible for pumping blood throughout the body. On the other hand, the right ventricle has to exert tremendous pressure to pump deoxygenated blood to the lungs.
Patients with large ASD may display left-to-right shunt where the blood flows from the left atrium to the right atrium. This causes both the right atrium and ventricle to become overloaded. If left untreated, it may lead to a heart failure.
In other cases, extreme pressure in the right atrium leads to a right-to-left shunt. Unlike the left-to-right shunt, here the blood flows from the right atrium to the left atrium, causing cyanosis.
Some of the common diagnostic procedures used for the detection of ASD include:
This is generally done as a part of physical examination where a stethoscope is used to listen to the internal sounds of the heart. Physicians can clearly detect a harsh-sounding murmur in individuals with ASD.
Detailed images of the heart and surrounding blood vessels may help in revealing any defect in the interatrial septum of the affected patients.
It is a standard echocardiogram (ECHO) used to facilitate the diagnosis of ASD. TTE involves a transducer generating high frequency waves that is placed on the chest wall and moved to different locations. A thorough evaluation of the four chambers of the heart is done. It also assesses the strength of the cardiac muscles and condition of the valves. The images are generally displayed on a monitor and recorded by a videotape. In some cases, Bubble contrast TTE is performed where agitated saline is injected into a vein, followed by imaging of the heart. Air bubbles can be seen moving from the right atrium to the left atrium during a right-to-left shunt. The technique is especially used to detect PFO.
It is an alternative method to perform an ECHO where a specialized probe containing an ultrasound transducer at its tip is injected into the esophagus of an affected patient. Several structures like pulmonary artery, aorta, atria and interatrial septum can be rendered as images and evaluated using the Doppler effect. TEE is a highly sensitive technique and gives better results as compared to TTE.
The test involves attachment of electrodes to the outer surface of the skin to evaluate the electrical activity of the heart. A device is placed in a position external to the body for tracing the heart activity. The time taken for the electrical impulses to travel from the sinus node through the atrioventricular node is long. This delay in the transmission of electrical pulses is due to the enlargement of the atria in severely affected patients.
In this procedure, a catheter is passed through a large vein that is threaded directly to the heart. A special contrast dye is then injected through the catheter to view the internal structures of the heart for any major defects using an X-ray camera.
This non-invasive process gives detailed images of the heart, including its major blood vessels and chambers. This method generally aids physicians in detecting any congenital malformation in infants.
ASD should be immediately corrected to avoid any serious consequences in future. Surgical mortality, after the closure of ASD, is generally lower in patients below the age of 25. The severity of the condition has to be determined before undergoing treatment. Right heart catheterization might be necessary for patients who are also suffering from pulmonary hypertension. Some of the common techniques used for closure of ASD include:
Picture 2 – Atrial septal defect Image
Individuals with Secundum ASD generally have to undergo this procedure during treatment. Anesthetic drugs are administered to patients to facilitate this process. A catheter, fitted with a small umbrella-shaped device inside, is infused into a vein in the groin and is threaded to the septum of the heart. Once it reaches the septum, the tiny device is pushed out of the catheter and placed in a proper manner to close the hole or defect. The device is kept in this position for about 6 months, after which normal tissue grows and covers it. It is a less invasive process than surgery and the outcome is generally very good.
In an open-heart surgery, a patch or plug is used to close the defect in the interatrial septum.
This minimally-invasive ASD involves use of Amplatzer Septal Occluder – a double disc device that comprises of Nitinol mesh filled with polyester fabric. It is designed in such a way that it can be placed next to the atrial opening and creates a platform for growth of tissues after implantation. However, there is chance of nickel toxicity, owing to the amount of nitinol in the device.
If left untreated, the condition may give rise to an array of complications in later life. The commonly associated complications observed in patients with ASD include:
A small Atrial septal defect does not require any treatment and normally closes on its own. Surgical repair becomes necessary if the condition persists for a longer time. Regular care and monitoring is essential even if an affected patient has undergone surgical closure. Call your health care provider if your child shows symptoms such as palpitation or Cyanosis.