Atrial Septal Defect (ASD): Surgical Anatomy & Strategy

Atrial septal defect (ASD) is not a single lesion, but a group of interatrial communications that differ in embryologic origin, anatomic location, associated anomalies, and operative implications. For the surgeon, the key issue is not merely the presence of an atrial-level shunt, but the exact subtype of ASD, its relationship to the conduction system and atrioventricular valves, and whether anomalous systemic or pulmonary venous drainage is also present [1,2]. (PubMed)

Although most ASDs produce a left-to-right shunt and chronic right-sided volume loading, each subtype carries a distinct surgical logic. Secundum ASD is usually a defect of the fossa ovalis and is often suitable for transcatheter closure when the rims are adequate. Primum ASD belongs to the atrioventricular septal defect (AVSD) spectrum. Sinus venosus ASD is commonly associated with partial anomalous pulmonary venous return (PAPVR). Coronary sinus ASD represents an unroofed coronary sinus and is frequently associated with a persistent left superior vena cava (LSVC) [1-4]. (PubMed)

A practical approach begins with three questions:

1. Where is the defect located?
2. Which adjacent structures are at risk during repair?
3. Is the lesion isolated, or part of a broader atrial, venous, or AV junction malformation? (PubMed)

1. Secundum ASD

Secundum ASD is the most common type of ASD and is located at the fossa ovalis, within the true atrial septum. It is the classic central interatrial communication and, in anatomically suitable cases, transcatheter device closure is now considered first-line therapy. Surgical closure remains important when the defect is large, rim-deficient, associated with other lesions, or otherwise unsuitable for device treatment [1,3]. (PubMed)

From the operative standpoint, even a “simple” secundum ASD requires precise attention to adjacent landmarks. The inferior and posteroinferior margins lie near the triangle of Koch, bounded by the coronary sinus orifice, tendon of Todaro, and septal leaflet of the tricuspid valve. The AV node is located at the apex of this triangle. Conduction injury is uncommon in standard secundum ASD closure, but a careless low suture line near the coronary sinus region can place the conduction tissue at risk [4]. (PubMed)

Repair is performed by direct closure for small, tension-free defects or by patch closure for larger lesions. The patch should restore a smooth septal contour without distortion of adjacent atrial tissue, caval inflow, or the coronary sinus region. In practice, the geometry of the inferior margin matters as much as the size of the defect itself [1,4]. (PubMed)

2. Primum ASD

Primum ASD is not simply a low secundum defect. It is a defect of the inferior atrial septum adjacent to the AV valves and is best understood as a partial AVSD. Morphologically, it reflects deficiency of the endocardial cushion-derived AV septal structures and is commonly associated with a cleft in the left AV valve and varying degrees of left AV valve regurgitation [1,5]. (PubMed)

This subtype is particularly important because the conduction system is displaced. Ostium primum ASD has a higher risk of AV conduction disturbance than secundum ASD, and repair must follow AVSD principles rather than routine septal closure logic [4]. (PubMed)

In operative terms, the patch suture line should be planned with constant awareness of the abnormal position of the AV node and bundle. Sutures along the ventricular septal margin are deliberately placed to stay clear of the conduction axis, and the repair frequently includes closure of the left AV valve cleft or reconstruction of the regurgitant component. Thus, the operation is judged not only by elimination of the interatrial shunt, but also by preservation of AV valve competence and avoidance of heart block [4,5]. (PubMed)

Long-term surgical results for partial AVSD are generally favorable, but late reoperation is driven mainly by residual or recurrent left AV valve dysfunction and, less commonly, left ventricular outflow tract obstruction. In a large long-term series, closure of the left AV valve cleft was associated with better survival, underscoring that the valvar component is central to the lesion rather than incidental [5]. (PubMed)

3. Sinus Venosus ASD

Sinus venosus ASD is not a defect of the fossa ovalis septum. Rather, it is a malformation near the systemic venous inflow to the atria, occurring most commonly at the SVC-RA junction and less frequently near the IVC-RA junction. Its major surgical significance lies in its strong association with PAPVR, especially anomalous drainage of the right upper pulmonary veins into the SVC or right atrium [1,6]. (PubMed)

For this reason, sinus venosus ASD should be approached not as a simple septal hole, but as a venous rerouting lesion. Preoperative imaging must define the entry point of the anomalous pulmonary veins, the height of their connection within the SVC, the caliber of the SVC, and the anticipated risk of postoperative systemic or pulmonary venous obstruction. The goal of surgery is not simply closure of the defect, but restoration of correct pulmonary venous return to the left atrium while preserving unobstructed SVC drainage [1,6]. (PubMed)

Operative strategies

1) Warden procedure

The Warden procedure is particularly useful when anomalous pulmonary veins enter high into the SVC. The SVC is divided above the anomalous entry, the intracardiac pathway is baffled to direct pulmonary venous flow into the left atrium, and the cephalad SVC is reanastomosed to the right atrial appendage. This approach minimizes direct manipulation around the sinus node region and is often favored when the anatomy is suitable [7,8]. (PubMed)

2) Two-patch technique

The two-patch technique uses one patch to reroute anomalous pulmonary venous flow into the left atrium and a second patch to enlarge the SVC-right atrial pathway. It can be highly effective, but the balance between adequate baffling and avoidance of sinus node injury or caval narrowing remains critical [7]. (PubMed)

Contemporary outcomes

The strongest comparative outcome data among ASD subtypes currently exist for sinus venosus ASD repair. A 2024 systematic review and meta-analysis of 1,320 surgically repaired patients reported in-hospital mortality of 0.24%, 30-day mortality of 0.5%, and low long-term rates of atrial fibrillation (3.3%), sinus node dysfunction (6.5%), pacemaker implantation (2.23%), residual septal defect (1.34%), and SVC obstruction (1.76%) [6]. These data support the excellent overall safety and durability of surgical correction. (PubMed)

Technique-specific series further sharpen the operative message. Stewart and colleagues showed that late rhythm change from sinus rhythm to low atrial or junctional rhythm was significantly more frequent after the two-patch technique (55%) than after single-patch repair (24%) or the Warden procedure (0%) [7]. Likewise, Sojak and colleagues found that in patients with PAPVR draining into the SVC, the Warden procedure was associated with fewer new postoperative arrhythmias than intracaval baffling (23.1% vs 54.6%) [8]. Taken together, these studies support the view that when the pulmonary venous anatomy is high in the SVC, the Warden strategy is often advantageous because it reduces interference with the sinus node region while maintaining good venous pathways [7,8]. (PubMed)

Thus, the essential priorities in sinus venosus ASD repair are:

• complete pulmonary venous rerouting to the LA
• preservation of an unobstructed SVC pathway
• avoidance of sinus node dysfunction
• avoidance of residual interatrial shunting [6-8] (PubMed)

4. Coronary Sinus ASD

Coronary sinus ASD is an unroofed coronary sinus rather than a true septal defect of the fossa ovalis. In this anomaly, part or all of the wall separating the coronary sinus from the left atrium is absent, creating a communication that functionally behaves as an atrial-level shunt. It is a rare lesion and is frequently associated with persistent LSVC [1,9]. (PubMed)

Its importance lies in anatomy rather than frequency. The lesion may be diagnostically subtle, and the presence of LSVC can substantially alter operative planning. In complete forms, systemic venous return from the left upper body may be intimately involved in the abnormal communication, and failure to appreciate this preoperatively can lead to inappropriate repair or unexpected desaturation/venous pathway issues [9]. (PubMed)

The principle of repair is to re-establish the coronary sinus as a right-sided venous structure while eliminating the abnormal communication with the left atrium. Depending on the anatomy, this may be accomplished with direct closure or patch closure of the unroofed segment from the left atrial side. However, when LSVC drainage depends on the coronary sinus pathway, closure must be planned in a way that does not create systemic venous obstruction or misdirect venous return [9]. (PubMed)

Compared with sinus venosus ASD, robust comparative outcome data for coronary sinus ASD are limited. The literature is dominated by case reports and small series, so surgical decision-making remains heavily anatomy-driven [9]. (PubMed)

5. Hemodynamic and Clinical Perspective

Across all ASD subtypes, the basic physiology is usually a left-to-right atrial shunt with chronic right atrial and right ventricular volume overload. The magnitude of shunting depends not only on defect size, but also on ventricular compliance, pulmonary vascular resistance, and associated lesions. Over time, significant unrepaired shunts may lead to exercise intolerance, arrhythmia, right ventricular dysfunction, and pulmonary vascular disease [2,4]. (PubMed)

From a contemporary surgical perspective, ASD management is increasingly morphology-specific. The key distinction is no longer simply surgical versus catheter closure, but rather whether the lesion is a simple septal defect or a complex atrial/venous/AV junction malformation. Secundum ASD is often an occlusion problem. Primum ASD, sinus venosus ASD, and coronary sinus ASD are reconstructive problems [1,3,6,9]. (PubMed)

6. Practical Surgical Summary

Secundum ASD

• Fossa ovalis defect
• Often suitable for transcatheter closure
• Main surgical concern: inferior margin and protection of the AV nodal region [3,4] (PubMed)

Primum ASD

• Partial AVSD
• Frequently associated with a left AV valve cleft/regurgitation
• Main surgical concern: AV valve repair and avoidance of AV block [4,5] (PubMed)

Sinus venosus ASD

• Venous inflow malformation, usually with PAPVR
• Requires pulmonary venous rerouting, not just defect closure
• Main surgical concern: sinus node preservation, SVC patency, and pulmonary venous pathway geometry [6-8] (PubMed)

Coronary sinus ASD

• Unroofed coronary sinus
• Frequently associated with persistent LSVC
• Main surgical concern: restoration of proper coronary sinus/right atrial drainage without compromising systemic venous return [9] (PubMed)

References

[1] Grieshaber P, Jaschinski C, Farag M, Fonseca-Escalante E, Gorenflo M, Karck M, Loukanov T. Surgical Treatment of Atrial Septal Defects. Rev Cardiovasc Med. 2024;25(10):350.

[2] Le Gloan L, Legendre A, Iserin L, Ladouceur M. Pathophysiology and natural history of atrial septal defect. J Thorac Dis. 2018;10(Suppl 24):S2854-S2863.

[3] Rigatelli G, Gianese F, Zuin M. Secundum Atrial Septal Defects Transcatheter Closure: An Updated Reappraisal. Cardiovasc Revasc Med. 2022;44:92-97.

[4] Williams MR, Perry JC. Arrhythmias and conduction disorders associated with atrial septal defects. J Thorac Dis. 2018;10(Suppl 24):S2940-S2944.

[5] El-Najdawi EK, Driscoll DJ, Puga FJ, Dearani JA, Spotts BE, Mahoney DW, Danielson GK. Operation for partial atrioventricular septal defect: a forty-year review. J Thorac Cardiovasc Surg. 2000;119(5):880-889.

[6] El-Andari R, Moolla M, John K, Slingerland A, Campbell S, Nagendran J, Hong Y, Mathew A. Outcomes Following Surgical Repair of Sinus Venosus Atrial Septal Defects: A Systematic Review and Meta-Analysis. J Am Heart Assoc. 2024;13(12):e033686.

[7] Stewart RD, Bailliard F, Kelle AM, Backer CL, Young L, Mavroudis C. Evolving surgical strategy for sinus venosus atrial septal defect: effect on sinus node function and late venous obstruction. Ann Thorac Surg. 2007;84(5):1651-1655.

[8] Sojak V, Sagat M, Balazova E, Siman J. Outcomes after surgical repair of sinus venosus atrial septal defect in children. Bratisl Lek Listy. 2008;109(5):215-219.

[9] Chen C, Xu L, Xu Y, Li P, Liu S, You B. Unroofed Coronary Sinus Syndrome: An Easily Corrected Congenital Anomaly But More Diagnostic Suspicion Is Needed. Heart Lung Circ. 2018;27(6):731-738.