What are ostium primum and ostium secundum Atrial Septal Defects (ASDs), their differences, causes, and management strategies?

From the Guidelines

Atrial septal defects (ASDs) are congenital heart defects characterized by openings in the septum between the atria, with ostium primum and ostium secundum being the two main types, and their management strategy depends on the type, size, and symptoms of the defect, with transcatheter device closure preferred for secundum ASDs and surgical repair necessary for primum ASDs due to their complex nature. The key differences between ostium primum and ostium secundum ASDs are their location and associated defects, with primum ASDs typically being more complex and occurring at the lower portion of the atrial septum, often associated with atrioventricular canal defects and Down syndrome, resulting from incomplete fusion of the endocardial cushions during embryonic development 1. Ostium secundum ASDs, on the other hand, are the most common type, occurring in the middle portion of the atrial septum at the fossa ovalis, resulting from excessive resorption of the septum primum or inadequate development of the septum secundum 1. Both types cause left-to-right shunting of blood, leading to right heart volume overload, and symptoms may include fatigue, exercise intolerance, palpitations, and recurrent respiratory infections, though many patients remain asymptomatic until adulthood 1. Diagnosis involves echocardiography, ECG, and sometimes cardiac catheterization, and management depends on defect size and symptoms, with small defects (< 8mm) may close spontaneously and often require only monitoring, while larger defects typically require closure, either via transcatheter device closure or surgical repair 1. Some key points to consider in the management of ASDs include:

• Transcatheter device closure is preferred for secundum ASDs, while surgical repair is necessary for primum ASDs due to their complex nature 1
• Antibiotic prophylaxis is not routinely recommended except for 6 months after device placement 1
• Long-term follow-up is essential, particularly for patients with repaired primum defects who may develop atrioventricular valve regurgitation or conduction abnormalities later in life 1
• The presence of a sinus venosus ASD with anomalous pulmonary venous return can increase the left-to-right shunt and accelerate the onset of pulmonary hypertension, and therefore, it may be reasonable to pursue surgical closure in the presence of these ASDs regardless of other indications 1. The most recent and highest quality study recommends that adults with isolated secundum ASD causing impaired functional capacity, right atrial and/or RV enlargement, and net left-to-right shunt sufficiently large to cause physiological sequelae should undergo transcatheter or surgical closure to reduce RV volume and improve exercise tolerance, provided that systolic PA pressure is less than 50% of systolic systemic pressure and pulmonary vascular resistance is less than one third of the systemic vascular resistance 1.

From the Research

Definition and Types of Atrial Septal Defects (ASDs)

• Atrial Septal Defects (ASDs) are common congenital heart defects characterized by insufficient or absent tissue at the interatrial septum 2.
• There are four types of ASDs: ostium secundum, ostium primum, sinus venosus, and coronary sinus defects 3.
• Ostium primum and ostium secundum ASDs are two of the most common types of ASDs.

Differences between Ostium Primum and Ostium Secundum ASDs

• Ostium secundum defects are the most common type of ASD and are typically located in the middle of the atrial septum 3.
• Ostium primum defects are located in the lower part of the atrial septum and are often associated with other cardiac anomalies 2.
• Ostium secundum defects are usually amenable to percutaneous occlusion, while ostium primum defects typically require surgical correction 3.

Causes and Risk Factors

• ASDs are congenital heart defects, meaning they are present at birth 2.
• The exact cause of ASDs is not known, but they are thought to result from abnormal development of the heart during fetal development 4.
• Risk factors for ASDs include family history and certain genetic syndromes 4.

Management Strategies

• The primary indication for ASD closure is right heart volume overload, whether symptoms are present or not 4.
• Ostium secundum defects can be closed percutaneously using devices such as the Amplatzer® Septal Occluder (ASO) or surgically 3.
• Ostium primum defects typically require surgical correction 3.
• The choice of closure method depends on the type and size of the defect, as well as the patient's overall health and local clinical expertise 4.
• Severe pulmonary arterial hypertension is a contraindication to closure 2.