Atrial Septal Defect (ASD) — #3 Sinus Venosus ASD
Overview
Sinus venosus atrial septal defect (SV-ASD) is an interatrial communication located outside the true atrial septum, at the junction of the superior or inferior vena cava with the right atrium. It accounts for roughly 5–10% of all ASDs and about 1% of congenital cardiac malformations overall.[1,2,9] A defining feature is its strong association with partial anomalous pulmonary venous return (PAPVR)—most commonly right upper (± right middle) pulmonary veins draining to the SVC or high right atrium, present in ~85–90% of cases.[1,9]
Because of this veno-venous anomaly, SV-ASD behaves less like a simple septal defect and more like a caval–pulmonary venous malformation. Effective repair must therefore address both the interatrial communication and the rerouting of anomalous pulmonary venous flow.
Anatomy and types
Morphologically, SV-ASD represents a deficiency of the caval wall rather than a hole in the fossa ovalis. The intact muscular rim of the oval fossa is “overridden” by the mouth of the SVC or IVC, and the posterior wall between the caval vein and right pulmonary veins is absent.[2,3] As a result, the pulmonary venous orifices and the caval lumen share a common chamber that communicates with the left atrium through a superior or inferior slot.
Two main variants are recognized:[1,3,4]
- Superior SV-ASD
- Located at the SVC–RA junction, above the fossa ovalis.
- Frequently associated with RUPV (± RMPV) draining to the SVC or high RA.
- Inferior SV-ASD
- Situated near the IVC–RA junction, below the fossa ovalis.
- Often associated with anomalous right lower pulmonary venous drainage toward the IVC–RA area.[4]
In both types, the true atrial septum is intact; the defect lies outside it. This anatomic distinction is critical for imaging interpretation and surgical planning.[2,3]
Pathophysiology and clinical features
Hemodynamically, SV-ASD produces a large left-to-right shunt at the atrial level, compounded by PAPVR: oxygenated blood from the right pulmonary veins returns to the SVC/RA, passes through the right ventricle, and recirculates to the lungs.[1,5] This leads to:
- Right atrial and right ventricular volume overload
- Increased pulmonary blood flow (Qp)
- Progressive pulmonary vascular remodeling and, in older or untreated patients, pulmonary hypertension
Clinically, patients present with findings similar to other significant ASDs—exercise intolerance, exertional dyspnea, frequent respiratory infections, and eventually atrial arrhythmias or right-sided heart failure in adulthood.[1,5] A typical clue is disproportionate right-sided enlargement on echocardiography in the absence of a large secundum ASD, prompting a search for SV-ASD and PAPVR by targeted imaging.
Diagnosis and imaging
High-quality transthoracic and transesophageal echocardiography are the mainstays of diagnosis. Multiplane TEE is particularly helpful in demonstrating:
- The intact fossa ovalis and superior or inferior defect at the venoatrial junction
- Entry of right pulmonary veins into the SVC or RA
- The relationship between the defect, sinus node region, and caval orifices[5]
Cardiac CT or MRI offers excellent delineation of pulmonary venous anatomy and is often used in older children and adults or when echo windows are limited.[4] These modalities are invaluable for pre-operative planning, especially when multiple anomalous pulmonary veins or complex caval anatomy are present.
Surgical objectives
Repair of SV-ASD is conceptually a two-stream reconstruction:
- Pulmonary venous pathway
- Reroute anomalous pulmonary venous flow to the left atrium via a wide, non-obstructed baffle.
- Systemic venous (caval) pathway
- Preserve or reconstruct an unobstructed SVC or IVC pathway to the right atrium while protecting the sinus node and its arterial supply at the SVC–RA junction.[1,6,7]
Simple patch closure of the interatrial communication is inadequate and risks pulmonary venous or caval obstruction. Contemporary strategies therefore combine intracardiac baffling with caval augmentation or reimplantation, tailored to the individual anatomy.
Superior SV-ASD with RUPV PAPVR
This is the most frequent presentation. Two main approaches are widely used.
1. Warden procedure
- The SVC is divided above the entry of the anomalous pulmonary veins.
- The distal SVC is anastomosed to the right atrial appendage, re-establishing caval drainage to the RA while avoiding the sinus node region.
- Within the atrium, an intracardiac patch baffle directs the RUPV (± RMPV) orifices and the proximal SVC segment through the defect into the left atrium.
This approach provides a generous pulmonary venous channel and moves the cavotomy away from the sinus node. Series focused on Warden and modified Warden techniques report low rates of SVC obstruction and acceptable sinus node preservation.[6,10]
2. Two-patch techniques
- The SVC–RA junction is left intact.
- A first (intracardiac) patch creates a tunnel from the RUPV–SVC/RA chamber across the defect to the left atrium, simultaneously closing the interatrial communication.
- A second (external) patch augments the SVC–RA wall to maintain caval lumen after the baffle encroaches on it.
Modified two-patch strategies, including the use of the right atrial appendage to enlarge the SVC, have been developed to minimize venous obstruction and sinus node dysfunction.[8]
Choice between Warden and (modified) two-patch repair depends on patient age and size, height of the pulmonary venous entry, SVC diameter, and surgeon preference. Recent institutional series suggest that a unified strategy relying primarily on single-patch intracardiac baffling or Warden repair can achieve excellent results with a high prevalence of normal sinus rhythm.[7]
Inferior SV-ASD
Inferior defects at the IVC–RA junction are less common but follow the same principles.[1,4] Repair typically involves:
- An intracardiac baffle directing anomalous right lower pulmonary venous flow to the left atrium, and
- Careful reconstruction of the IVC–RA junction to avoid narrowing or inadvertent inclusion of the IVC orifice within the baffle (which would shunt systemic venous blood to the LA).
Because of the close relationship to the hepatic veins and IVC, meticulous attention to patch orientation and size is essential to prevent hepatic congestion or systemic venous hypertension post-operatively.[4]
Outcomes and long-term considerations
Historical series already demonstrated good long-term survival after SV-ASD repair but highlighted concerns regarding sinus node dysfunction and venous obstruction.[1,6] Modern techniques have substantially reduced these complications.
A recent systematic review and meta-analysis of 1320 patients undergoing SV-ASD repair reported:[9]
- In-hospital mortality 0.24% and 30-day mortality 0.5%
- Long-term incidences of:
- atrial fibrillation ~3%
- sinus node dysfunction ~6–7%
- pacemaker implantation ~2%
- SVC obstruction ~2%
- pulmonary venous pathway obstruction ~1–2%
These pooled data confirm that surgical repair is highly safe and durable, establishing a benchmark for emerging transcatheter covered-stent strategies.[9]
From a practical standpoint, long-term follow-up should focus on:
- Pulmonary venous patency at the baffle–LA junction and reimplanted veins
- Caval pathway (SVC/IVC gradient, upper- or lower-body venous congestion)
- Sinus node function and atrial arrhythmias, particularly in patients with suture lines near the SVC–RA junction or prior atrial incisions[1,6,7]
When these aspects are carefully managed, most patients enjoy excellent functional status, regression of right-sided dilation, and normalization of pulmonary pressures.
References
[1] Attenhofer Jost CH, Connolly HM, Danielson GK, Bailey KR, Warnes CA, Tajik AJ. Sinus venosus atrial septal defect: long-term postoperative outcome for 115 patients. Circulation. 2005;112(13):1953-1958.
[2] McCarthy KP, Ho SY, Anderson RH. Defining the morphologic phenotypes of atrial septal defect and interatrial communications. Images Paediatr Cardiol. 2003;5(2):1-24.
[3] Li J, Al Zaghal AM, Anderson RH. The nature of the superior sinus venosus defect. Clin Anat. 1998;11(5):349-352.
[4] Crystal MA, Al Najashi K, Williams WG, Redington AN, Anderson RH. Inferior sinus venosus defect: echocardiographic diagnosis and surgical approach. J Thorac Cardiovasc Surg. 2009;137(6):1349-1355.
[5] Oliver JM, Gallego P, Gonzalez A, et al. Sinus venosus syndrome: atrial septal defect or anomalous venous connection? A multiplane transesophageal approach. Heart. 2002;88(6):634-638.
[6] 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.
[7] Stephens EH, Monge MC, Eltayeb O, et al. Evolution and current results of a unified strategy for sinus venosus surgery. Ann Thorac Surg. 2021;111(2):657-665.
[8] Elzein C, Abdulkarim M, Abbas U, Vricella L, Ilbawi M. Repair of superior sinus venosus atrial septal defect using a modified two-patch technique. Ann Thorac Surg. 2020;109(2):583-587.
[9] El-Andari R, Moolla M, John K, et al. Outcomes following surgical repair of sinus venosus atrial septal defects: a systematic review and meta-analysis. J Am Heart Assoc. 2024;13(12):e033686.
[10] Lin H, Yan J, Wang Q, et al. Outcomes of the Warden procedure for partial anomalous pulmonary venous drainage. Pediatr Cardiol. 2020;41(1):134-140.