Types of Atrial Septal Defect (ASD)

Atrial septal defects (ASDs) are common congenital heart anomalies, accounting for approximately 10–15% of congenital heart disease [1]. They represent interatrial communications that permit left-to-right shunting. Shunt magnitude and direction depend on defect size and relative atrial/ventricular compliances. Chronic shunting produces right-sided volume overload and pulmonary overcirculation, and if untreated, may lead to atrial arrhythmias, pulmonary vascular disease, paradoxical embolism, and eventual right heart failure [2,3]. Anatomically, ASDs are categorized by embryologic origin and their relationship to adjacent venous and valvar structures [4].

1) Secundum ASD

Anatomy & embryology. Defect in the fossa ovalis region due to deficiency of septum primum tissue and/or excessive resorption of the septum primum.

Epidemiology. Most common subtype (~70%) [1,4].

Associations. Multiple fenestrations, atrial septal aneurysm, or rarely part of a broader atrial communication spectrum.

Hemodynamics. Typically results in left-to-right shunt with right atrial and ventricular dilation, scaling with defect size and ventricular diastolic properties.

Natural history & management. Small defects may close spontaneously in childhood; closure is indicated when right-sided dilation or symptoms occur. Transcatheter occlusion is appropriate for most secundum ASDs with adequate rims, whereas surgical patch closure is indicated for deficient rims, very large/multifenestrated defects, or associated lesions [5].

2) Primum ASD (partial atrioventricular septal defect)

Anatomy. Located at the atrioventricular junction due to incomplete endocardial cushion fusion.

Defining features. Part of the atrioventricular septal defect spectrum. AV valves share a common plane and frequently have a cleft in the left AV (mitral) valve, leading to regurgitation.

Associations. Elongated LV outflow tract with “goose-neck” deformity; displaced conduction system.

Management. Surgical repair is required—patch closure of the primum defect and repair of the AV valve cleft. Device therapy is not applicable [6].

3) Sinus Venosus ASD

Anatomy. Deficiency of the posterior-superior (SVC type) or posterior-inferior (IVC type) atrial septal margin near venous entry, often outside the true septal plane.

Key association. Frequently accompanied by partial anomalous pulmonary venous return (PAPVR), especially right upper pulmonary veins draining into the SVC–RA junction in the superior type [7].

Imaging. Echocardiography, CT, or MRI is required to delineate anomalous pulmonary venous drainage.

Management. Surgical correction is standard (e.g., Warden or two-patch technique for SVC-type; baffling for IVC-type). Transcatheter closure is not feasible [7].

4) Coronary Sinus ASD (unroofed coronary sinus)

Anatomy. Partial or complete absence of the coronary sinus roof, creating communication between the coronary sinus and the left atrium.

Associations. Strongly linked with persistent left superior vena cava (PLSVC) draining into the coronary sinus, creating a right-to-left shunt with desaturation [8].

Management. Surgical repair tailored to the extent of unroofing and systemic venous anatomy, including rerouting or patch closure [8].

Diagnostic approach

• Transthoracic echocardiography: first-line to define location, size, and right heart dilation; color Doppler demonstrates shunt [1,4].
• TEE/3D echo: superior for rim assessment (secundum), cleft definition (primum), and venous connections (sinus venosus).
• CT/MRI: essential for delineating anomalous pulmonary venous return and complex venous anatomy [7,8].
• Hemodynamics: Cardiac catheterization for Qp:Qs or pulmonary vascular resistance when pulmonary hypertension is suspected [2,3].
• Clinical clues: Fixed, wide splitting of the second heart sound with pulmonary flow murmur is characteristic in unrepaired secundum ASDs [2].

Indications for closure

• Right atrial/ventricular dilation or symptoms attributable to shunt.
• Prior paradoxical embolism or systemic desaturation (e.g., coronary sinus ASD with PLSVC).
• Borderline pulmonary vascular resistance: consider fenestrated surgical strategies [5,6].

Surgical pearls & pitfalls

• Secundum: respect the triangle of Koch; avoid injury to the IVC rim and Eustachian valve; de-air carefully.
• Primum: meticulous cleft repair; preserve conduction tissue near the AV node; address LVOT geometry.
• Sinus venosus: ensure unobstructed SVC and pulmonary venous return after repair; consider sinus node location.
• Coronary sinus: plan for PLSVC rerouting; avoid obstruction of systemic venous pathways.

References

[1] Webb G, Gatzoulis MA. Atrial septal defects in the adult: recent progress and overview. Circulation. 2006;114(15):1645-1653.

[2] Bradley EA, Zaidi AN. Atrial septal defects in the adult: management and outcomes. Heart. 2020;106(15):1190-1199.

[3] Martin SS, Shapiro EP, Mukherjee M. Atrial septal defects—clinical manifestations, echo assessment, and intervention. Clin Cardiol. 2014;37(11):674-682.

[4] Kučera J. Atrial septal defects: classification, pathophysiology, and management. Cor Vasa. 2021;63(1):16-24.

[5] Rao PS. Current status of transcatheter closure of secundum atrial septal defect. Indian Heart J. 2017;69(5):566-574.

[6] Anderson RH, Webb S, Brown NA, Lamers W, Moorman A. Development of the heart: (2) Septation of the atriums and ventricles. Heart. 2003;89(8):949-958.

[7] Blom NA, Gittenberger-de Groot AC, DeRuiter MC, Poelmann RE, Ottenkamp J. Development of the pulmonary veins and its relevance to anomalous pulmonary venous connections. Heart. 2001;85(6):576-582.

[8] Quaegebeur J, Kirklin JW, Blackstone EH, Pacifico AD, Bargeron LM Jr. Surgical experience with unroofed coronary sinus. Ann Thorac Surg. 1985;40(4):378-386.