bubble_chart Overview

Atrial septal defect (ASD) is caused by congenital developmental abnormalities of the interatrial septum. There are two types: primum and secundum defects, and it is one of the most common congenital heart diseases. The primum defect results from incomplete development of the primary septum during embryonic development, failing to fuse with the endocardial cushion, and is often associated with endocardial cushion developmental disorders. Therefore, it is now mostly classified under the category of endocardial cushion defects. This section refers only to secundum atrial septal defects. This type is caused by incomplete development of the secondary atrial septum or excessive absorption of the primary atrial septum. Based on the location of the defect, it can be divided into four types:

1. The fossa ovalis defect type (central defect) is the most common, accounting for about 80%.
2. The superior vena cava type (high-position defect) is relatively rare, accounting for only 3–4%.
3. The inferior vena cava type (low-position defect) is the second most common after the central type, accounting for about 12%.
4. The mixed type, where two or more malformations coexist, accounts for about 5%.

Due to the left-to-right shunt at the atrial level, pulmonary blood flow increases, and pulmonary artery pressure and right ventricular pressure may rise. During this period, relative pulmonary valve stenosis creates a certain pressure gradient, and the systolic murmur in this condition is produced by excessive blood flow passing through the normal pulmonary valve. Antagonism: blood flow through the atrial septal defect, due to the small pressure gradient and slow velocity between the left and right atria, does not form turbulence and thus does not produce a murmur. However, due to the large pulmonary blood flow, pulmonary hypertension may also occur. In advanced stages, right-to-left shunting may appear due to pulmonary vascular obstruction.

bubble_chart Clinical Manifestations

Symptoms: This condition is the most common single cardiac malformation. During childhood, it generally does not pose a life-threatening risk. Small defects with minimal shunting may remain asymptomatic for a long time. Those with larger defects may experience lack of strength, shortness of breath, and susceptibility to respiratory infections during school age, though most symptoms are not pronounced.

Sign: Physical development may present as a slender build, and those with significant shunting may have lower body weight compared to normal children of the same age. Murmurs are usually not obvious before the age of 3 and are often mistaken for innocent murmurs. In two-thirds of cases, the murmur is most prominent at the first and second intercostal spaces along the left sternal border, presenting as an ejection systolic murmur, typically only grade 2 with limited radiation. A few cases may reach grade 3 (often accompanied by pulmonary stirred pulse stenosis). There is fixed splitting of the second heart sound. In cases with significant shunting, a diastolic intermediate stage [second stage] filling murmur may be heard at the tricuspid area. Those with mitral stenosis (referred to as Lutembacher syndrome) exhibit a diastolic murmur and an opening snap at the cardiac apex.

bubble_chart Auxiliary Examination

1. X-ray examination: Small defects may show no changes, while moderate or larger ones may present with increased pulmonary blood flow, bulging of the pulmonary artery segment, a small main pulmonary artery, and enlargement of the right atrium and right ventricle.
2. Electrocardiogram: Right axis deviation and right ventricular hypertrophy, with QRS complexes in V3R and V1 showing an rsR' pattern. Approximately 10% of cases may exhibit prolonged P-R intervals, and about 25% may show elevated P waves.
3. Echocardiography: The four-chamber view may reveal a continuous echo interruption in the atrial septum, enlargement of the right atrium and right ventricle, and synchronous movement of the interventricular septum and the posterior left ventricular wall. Pulsed Doppler can detect a diastolic turbulent flow spectrum on the right atrial side of the atrial septum, while color Doppler may show a multicolored flow jet from left-to-right shunting during diastole in the right atrium. The diagnosis is usually confirmed clinically through the above non-invasive examinations.
4. Cardiac catheterization and angiography: The catheter can easily pass through the defect to reach the left atrium. Oxygen saturation results from right heart catheterization also have diagnostic value. The average oxygen content in the right atrium is >1.9 vol% higher than in the superior vena cava, or >1.5 vol% higher than the average caval oxygen content, or >1.0 vol% higher than in the inferior vena cava. Typical cases may not require this examination.

bubble_chart Treatment Measures

The possibility of natural closure of an atrial septal defect is extremely small. As the natural course progresses, the left-to-right shunt volume may gradually increase, and the heart chambers may also enlarge. However, heart failure rarely occurs during elementary school age. By adulthood, pulmonary hypertension, arrhythmias, and congestive heart failure may develop, with surgical risks being higher than in childhood. Therefore, any child with clinical symptoms and a pulmonary-to-systemic flow ratio >1.5:1 should undergo surgical treatment. The surgical mortality rate is below 1%, with minimal residual shunting. The optimal age for surgery is during the preschool years.