Atrial Septal Defect: Understanding the Most Common Congenital Heart Condition
Congenital heart disease refers to abnormalities in the development of the heart and major blood vessels during the fetal stage. These conditions are present at birth and are among the most common types of birth defects. According to current statistics, the incidence rate is approximately 0.6 to 1.4 percent among all live births. With current birth rates, it is estimated that around 150,000 children with some form of congenital heart disease are born each year. Given its high prevalence and impact on families, this article series aims to provide a deeper understanding of congenital heart conditions, starting with one of the most prevalent types — atrial septal defect (ASD).
Types of Atrial Septal Defects
Atrial septal defect is one of the most common congenital heart conditions diagnosed in adults. When the defect is small, it may have minimal impact on hemodynamics, allowing patients to live a normal lifespan without noticeable symptoms. This is why many cases are often discovered incidentally during routine physical exams in adulthood.
There are three primary types of ASD: ostium primum, ostium secundum, and sinus venosus. The ostium primum type is more severe and anatomically classified as a partial atrioventricular septal defect. It is often associated with malformations of the mitral and tricuspid valves. Ostium secundum, the most common form, is typically a simple defect located in the central portion of the atrial septum. The sinus venosus type is further classified into superior and inferior variants, depending on the location of the defect near the superior or inferior vena cava.
Pathophysiology of Atrial Septal Defect
In patients with ASD, blood flows from the left atrium to the right atrium due to the pressure difference between the two chambers. The degree of hemodynamic impact depends largely on the size of the defect and the resulting volume of shunted blood. Larger defects can significantly burden the right side of the heart and increase pulmonary blood flow.
If left untreated over time, chronic left-to-right shunting can lead to increased pressure on the right heart, pulmonary hypertension, and eventually right heart failure. In the late stages of the disease, the pressure in the right heart may surpass that of the left, reversing the shunt direction to right-to-left. This causes cyanosis — a bluish discoloration of the skin due to reduced oxygen levels — and marks the terminal phase of the condition.
Clinical Presentation and Symptoms
Small ASDs often do not cause symptoms in early life and are usually detected during routine physical exams. In children, however, symptoms may include reduced exercise tolerance and frequent respiratory infections. Most patients begin to experience symptoms in adulthood, such as arrhythmias (especially atrial flutter and atrial fibrillation), shortness of breath during physical activity, and swelling in the lower extremities.
During a physical examination, a physician may detect a systolic murmur at the pulmonary valve area, along with an increased and fixed split second heart sound — a classic sign of atrial septal defect.
Diagnostic Tools and Imaging
The primary diagnostic method is echocardiography, which can clearly visualize the defect, confirm the presence of a left-to-right shunt, and assess the size of the right heart chambers. In more advanced cases, it may also reveal pulmonary hypertension or a right-to-left shunt.
Additional tests include electrocardiography (ECG), which may show right axis deviation or right bundle branch block, and chest X-ray, which can demonstrate right heart enlargement and increased pulmonary blood flow.
Treatment Options and Prognosis
Treatment strategies depend on the patient's age, symptoms, and the specific type of ASD. Patients with primum or sinus venosus defects, those with associated cardiac anomalies, pulmonary hypertension, or right-to-left shunting typically require surgical repair.
Ostium secundum defects, however, have a high chance of spontaneous closure, especially in infants. Studies show that about 87 percent of these defects close naturally. Defects smaller than 3 mm in infants under 3 months old usually close by 18 months of age. Those between 3 and 8 mm have an 80 percent chance of spontaneous closure within the same period. Larger defects, however, are less likely to close on their own.
For patients requiring intervention, timely treatment before the age of 24 has been shown to result in survival rates comparable to those of the general population. Minimally invasive closure via catheter-based devices is often an option for secundum-type ASDs. This procedure is typically recommended for patients aged around 3 years with defects measuring between 5 and 36 mm, no right-to-left shunting, and who meet other procedural criteria.