What is an Atrial Septal Defect?
An atrial septal defect (ASD) is a congenital defect, or birth defect of the heart. Congenital heart defects are the most common form of birth defects, occurring in approximately 1 per 150 children. An atrial septal defect is one of the more common congenital heart defects; the overall incidence is 2-3 per 1000. An ASD forms when the upper wall of the heart fails to properly close in the womb, leaving a hole.
Physiologically, an atrial septal defect allows for oxygenated blood (“red blood”) to pass from the left atrium to the right atrium, join with deoxygenated blood (“blue blood”), and return to the lungs. The effect of an ASD is therefore an increase in the total amount of blood that flows to the lungs. The amount is primarily determined by the size of the ASD. A large atrial septal defect can allow for a significant degree of blood flow to the lungs; a small ASD often results in a negligible increase.
Cause
The cause of most atrial septal defects is unknown. Some may be related to genetic disorders. Atrial septal defects are found relatively frequently in babies with certain syndromes, for example Down syndrome, trisomy 13, and trisomy 18. Other factors that may play a role include maternal alcohol exposure or drug use. A good portion of ASD's have no explainable cause whatsoever.
Signs and Symptoms
Symptoms from an atrial septal defect are actually quite uncommon. The majority of children, even those with large holes, rarely have any noticeable symptoms. Occasionally infants with large ASD’s may develop rapid breathing due to excess blood flow to the lungs. This may be more obvious during times of exertion, such as feeding. Other symptoms might include sweating or tachycardia. Adolescents and young adults may develop fatigue with exercise. Symptoms such as chest pain or palpitations are unusual.
Diagnosis
Diagnosis of an atrial septal defect can be made in a number of different ways. Occasionally an atrial septal defect may be identified or suspected on a fetal echocardiogram before birth. After birth, a child with an ASD often comes to attention due to the presence of a heart murmur. This simply refers to the sound that blood is making as it flows through the heart. There are many other different causes of heart murmurs, including normal causes. An echocardiogram uses sound waves to visualize the intracardiac structures and is the easiest means to show the size and location of an ASD. Occasionally a cardiac catheterization may be necessary to assess the lung blood pressures or the amount of blood flow through an atrial septal defect.
Treatment
There is a wide spectrum of treatment options for a child with an atrial septal defect. Small ASD's detected in the first few months of life often close spontaneously. Even in cases where a small ASD remains open, specific therapy is generally not needed. Medication is rarely necessary, even in the setting of large ASD's, due to the absence of symptoms in most children.
Atrial septal defect surgery is occasionally necessary. This often occurs in the setting of a large or moderate size hole. The most common indication for surgery is the presence of dilation of heart chambers, specifically the right ventricle, due to long-standing excess blood flow. Typically surgery is performed between 2 and 5 years of age, although it can easily be accomplished earlier if necessary. The risk of surgery for an ASD in this day and age is extremely low. The vast majority of children do very well with no significant long term problems.
A relatively new procedure has been developed in the last 10-15 years for ASD closure. This involves what is termed atrial septal defect device closure through a cardiac catheterization. A catheter (a long thin tube) is placed into the heart through a blood vessel in the leg. A device is then positioned in the ASD, effectively closing it from the inside. Advantages of this procedure over surgery include less discomfort and a shorter hospital stay. Disadvantages include the lack of long term follow-up on the safety and efficacy of device closure compared with surgery.
Outcomes
In general, the prognosis for a child with an atrial septal defect is very good. Even those children who go on to require surgery generally do well long-term. In most cases only a single surgery is necessary. The vast majority of children are cleared for full activity, including competitive athletics.
Certain children with congenital heart defects require antibiotics prior to dental or surgical procedures to minimize the risk of heart-related infection (SBE prophylaxis). This is not required for an isolated atrial septal defect.
In summary, although an atrial septal defect can cause alarm and concern in families, fortunately in almost all cases it is a very treatable condition.