Atrial Septal Defect (ASD): Definition and Epidemiology

Atrial Septal Defect (ASD): What Is It?

Atrial septal defect is a common congenital heart disease characterized by a defect in the septum separating the two atria due to embryological developmental failure, resulting in incomplete closure and allowing blood to pass between the left and right atria. The shunt occurs due to right ventricular compliance, and the direction of the shunt is from left to right.

What Are the Causes of (ASD) Atrial Septal Defect?

ASD is the second most common congenital heart disease seen in childhood. Approximately 30-50% of children with congenital heart disease have ASD as part of their cardiac malformations. Approximately 70% of all ASDs are secundum type lesions and occur 2 times more frequently in girls than in boys. ASD is reported in approximately 2 out of every 1,000 live births. Most defects are isolated and occur sporadically. Atrial septal defect is reported as an isolated defect in 5-10% of all congenital heart diseases. ASD is the most common congenital cardiac anomaly encountered in the adult age group. This is because most patients lack significant symptoms, leading to missed diagnosis of the defect.

Most familial secundum defects follow heterogeneous inheritance patterns, primarily autosomal dominant. The risk of secundum defect increases in families with a history of ASD in siblings or other congenital heart disease. On the other hand, diabetes mellitus, non-diabetic mothers with elevated glycemic index, and advanced maternal age (≥35 years) are other maternal risk factors for ASD. ASD types are divided into different subgroups according to the localization of the defect. In order of frequency from most to least common, they are classified into four groups: secundum, primum, sinus venosus, and coronary sinus type. Besides these, patent foramen ovale (PFO), which causes communication between the left and right atria, is not considered an atrial septal defect.

Types of ASD

Atrial septal defects can be defined as holes in the septum separating the upper two chambers of the heart and are among the most commonly seen congenital heart defects. They are divided into four main types according to their localization:

• Secundum type (Fossa ovalis) ASD: The most common type, located in the middle portion of the septum.
• Primum type ASD: Located in the lower portion of the septum and can often be seen with other congenital cardiac anomalies such as atrioventricular valve defects.
• Sinus venosus type ASD: A rarely seen type, generally located in the upper portion of the septum.
• Coronary sinus type ASD: Another rare type, located in the lower portion of the septum and can be seen with other cardiac anomalies.

Clinical course may vary depending on the type and size of the defect; small defects may be asymptomatic, while large defects may show more prominent clinical findings.

Symptoms and Diagnosis of (ASD) Atrial Septal Defect

Most infants and children with ASD are asymptomatic. Because symptoms show late clinical manifestations and physical examination findings may not attract the physician's attention, diagnosis is often delayed in patients. Approximately one-quarter of patients are diagnosed after the first decade of life. Patients are generally diagnosed when a murmur is heard on physical examination or incidentally during echocardiography (ECO) performed for another reason.

Recently, infants with heart murmurs on physical examination have been referred to pediatric cardiologists at earlier stages, resulting in earlier detection of ASD. Asymptomatic patients without heart failure or pulmonary hypertension but with weight or height (z) values <-1 showed z value increases of 0.5 within 2 years after surgery at an average age of 4 years.

In cases diagnosed early and managed in a timely manner, favorable life expectancy and quality of life may be expected, though outcomes can vary between individuals. However, in cases operated on at advanced ages, life expectancy may be shorter compared to patients of the same age. Most patients diagnosed with ASD are asymptomatic. Rarely, congestive heart failure may develop in ASD cases during infancy.

If large defects are not treated, pulmonary hypertension and heart failure may develop in adulthood (20s-30s). Atrial arrhythmias may be seen in these cases in adulthood. Infective endocarditis does not typically occur in isolated ASD; therefore, prophylaxis is generally not necessary in these cases. Bacterial endocarditis can develop in secundum type defects. For this reason, prophylaxis may be applied as recommended by the physician. Cerebrovascular events caused by paradoxical embolization are a rare complication in the pediatric age group.

Depending on the type and size of the defect, symptoms may vary; particularly in small defects, no findings may be apparent. Notable findings in the clinical course include the following:

• Shortness of breath, especially during exertion
• Weakness and fatigue
• Palpitations
• Swelling of the feet and ankles
• Stroke (cerebrovascular event) in the adult age group

The severity and intensity of these findings vary according to defect size; some patients may show no symptoms, while large defects may show more prominent manifestations. It should be remembered that these findings may be due to causes other than ASD, and medical consultation is recommended if such complaints are present.

When Should You See a Doctor?

It is appropriate to see a doctor in the following situations, especially if these findings are newly developed or severe:

• Shortness of breath during exertion
• Excessive weakness and fatigue
• Palpitations
• Swelling of the feet and ankles

Medical evaluation is also important in the following situations:

• Presence of ASD or other heart disease history in the family
• History of stroke or heart attack or other cardiovascular disease in the individual
• Pregnancy or pregnancy planning

Diagnosis is confirmed with physical examination findings of a murmur along with echocardiography, electrocardiography, or cardiac catheterization if necessary; these evaluations help determine the type and size of the defect.

Risk Factors

ASD develops during the heart's development in the womb; although its exact cause is not fully known, some factors thought to increase risk are listed below:

• Rubella infection during pregnancy: Rubella infection, especially during the first three months of pregnancy, is considered an important risk factor.
• Some chronic diseases in the mother: Chronic diseases such as diabetes and lupus can increase the risk of ASD in the baby.
• Alcohol or substance use during pregnancy: Use of these substances can increase risk.
• Advanced maternal age: Maternal age of 35 years or older increases risk.
• Family history: Presence of ASD history in the family increases risk.

The presence of one or more of these risk factors does not mean the baby will definitely have ASD, and the absence of these risk factors does not mean ASD will not develop. Regular medical follow-up during pregnancy can help identify possible problems early.

Complications

Small ASDs, especially when diagnosed early and appropriately evaluated, usually do not lead to significant complications. However, large defects or ASDs not diagnosed early may develop certain complications over time:

• Pulmonary hypertension: An increase in pressure in the vessels carrying blood from the heart to the lungs; progressive pulmonary hypertension can lead to heart failure.
• Stroke: Especially in adults, stroke may develop when blood clots pass through the defect into circulation and reach the brain.
• Heart failure: In large or early undiagnosed defects, the heart may be unable to pump adequate blood to the body.
• Cardiac arrhythmias: Rhythm disturbances such as atrial fibrillation may occur, and this condition increases stroke risk.

ASD and Pregnancy

Small and asymptomatic ASDs generally do not cause problems during pregnancy. However, in large defects or cases not diagnosed early, there is reported increased risk of certain complications during pregnancy:

• Pulmonary hypertension: Can lead to heart failure, negatively affecting maternal and fetal health.
• Stroke: Blood clots passing through the heart defect into circulation can reach the brain and cause stroke.
• Premature birth: Risk of premature birth may increase due to ASD.

Women with ASD diagnosis who are pregnant or planning pregnancy should consult their physician to assess potential risks and management of the pregnancy process. Regular medical follow-up during pregnancy, healthy nutrition, regular physical activity, and avoidance of harmful habits such as smoking and alcohol are recommended general approaches.

Prevention

Although there is no definitive method to completely prevent ASD, some general recommendations to reduce risk are as follows:

• Supporting general health through folic acid supplementation, healthy nutrition, and regular physical activity before pregnancy
• Vaccination before pregnancy for women without immunity to rubella
• Maintaining healthy weight during pregnancy
• Avoiding smoking, alcohol, and substance use during pregnancy
• Regular medical follow-up of pregnancy

In pregnancies with family history of ASD or other heart disease, the physician may recommend additional tests if deemed necessary.

Treatment of (ASD) Atrial Septal Defect

Currently, transcatheter closure of ASD cases has provided an alternative to open surgery. The first successful closure of secundum ASD with a "double umbrella" by King in 1976 was a milestone. Despite many technological innovations in this field, most are not practical. Among these, the Amplatzer Septal Occluder has become a widely used option.

The Amplatzer septal occluder received Food and Drug Administration (FDA) approval in 2001, and the Helix occluder in 2006. The natural course of ASD depends on patient factors, anatomic type of ASD, and size. In sinus venosus and primum type lesions, the shunt is usually hemodynamically significant, the defect size does not decrease, and surgical closure is often necessary. It has been reported that the probability of spontaneous closure of ASD and the time of closure are proportional to the shunt diameter detected on echocardiography performed before the third month of life. Since spontaneous closure may occur in defects, careful evaluation of patients with ASD diagnosis is necessary before deciding on surgical repair before age two.

Primum, sinus venosus, and coronary sinus type atrial septal defects are generally recommended for surgical closure. Secundum type atrial septal defects can be closed by either surgical or percutaneous transcatheter method with a closure device, depending on the physician's assessment.

Can ASD Close Spontaneously?

In small-sized ASDs, especially in young children, the defect may close spontaneously. Some sources report that some small-diameter defects close spontaneously by age 10. However, since most defects do not close spontaneously, treatment may become necessary. In defects that do not close spontaneously and are untreated, complications such as pulmonary hypertension or stroke may develop over time; therefore, surgical or catheter closure of the defect is evaluated by the physician.

What Is the Recovery Process After Closure Procedure?

The recovery process varies depending on the treatment method used:

• Transcatheter (percutaneous) closure: A small closure device is placed at the defect with the help of a catheter inserted through the groin or arm. In this method, the recovery process is generally shorter.
• Open heart surgery: The heart is accessed through an incision made in the chest wall, and the defect is closed with sutures or a patch. The recovery process may be longer with this method.

Following physician recommendations during the recovery process, using prescribed medications as directed, adequate rest, healthy nutrition, and regular physical activity are recommended general approaches. After closure procedures, infections, bleeding, or delayed wound healing may rarely occur; medical consultation is important in such situations.

How Are Treatment Options Determined?

Two fundamental methods are used in ASD treatment:

• Transcatheter closure: A small closure device is inserted through a catheter introduced from the groin or arm to close the opening in the defect.
• Open heart surgery: The heart is accessed through an incision made in the chest, and the defect is closed with sutures or a patch.

The method to be applied is determined by the physician based on the size and location of the defect, the patient's general health status, and age. Not all ASD types are suitable for transcatheter closure; for example, in primum, sinus venosus, and coronary sinus type defects, surgical closure is usually preferred, while in secundum type defects, both methods can be considered depending on suitability. Rare complications following performed procedures include infection, bleeding, wound healing problems, damage to surrounding tissues, and incomplete defect closure; in such cases, additional evaluation or intervention may be needed. Treatment decisions are made by the treating physician after evaluating each patient's individual situation, and patients are encouraged to discuss their specific circumstances with their hekim.