Atrial Septal Defect (ASD) — #4 Coronary Sinus ASD
Overview
Coronary sinus atrial septal defect (ASD) is the clinical expression of unroofed coronary sinus (UCS), a rare congenital anomaly in which part or all of the wall separating the coronary sinus (CS) from the left atrium (LA) is absent. The lesion creates a direct communication between the LA and the CS, which normally drains into the right atrium (RA), and therefore functions as an interatrial shunt at the level of the CS.[1,2] UCS represents the rarest subtype of ASD, accounting for <1% of all atrial septal defects and an even smaller proportion of congenital heart disease overall.[3,4] (JTCVS)
A recent systematic review confirmed that most reported patients are managed invasively and that outcomes after repair are excellent, but the lesion is frequently missed or diagnosed late, often during evaluation for unexplained right-sided dilation, cyanosis, or paradoxical embolic events.[2,5] (PubMed)
Anatomy and classification
In the normal heart, the CS courses in the posterior atrioventricular groove and opens into the RA via a discrete ostium guarded by the Thebesian valve. A complete muscular “roof” separates the CS from the LA, so that all coronary venous return drains exclusively to the RA.[1] (JTCVS)
In coronary sinus ASD, a segment of this roof is missing, and the CS lumen communicates with the LA cavity. The CS ostium to the RA is usually intact, so the CS becomes a short conduit connecting the LA and RA. The magnitude and direction of shunting depend on the size and length of the unroofed segment and the relative atrial pressures.
Multiple morphologic schemes have been proposed. A CT-based classification that is practical for surgeons divides UCS into four main types according to the location and extent of the roof defect, each with “a” and “b” subtypes depending on the presence of a persistent left superior vena cava (LSVC)[4]: (Journal of Thoracic Disease)
- Type I – Completely unroofed CS
- Ia: complete unroofing with LSVC draining to the CS/LA.
- Ib: complete unroofing without LSVC.
- Type II – Partially unroofed proximal CS
- Type III – Partially unroofed distal (terminal) CS
- Type IV – Localized communications between CS and LA wall
Across published cohorts, Type Ia (complete unroofing with LSVC) is the most common phenotype, representing roughly half of all reported cases.[2,4] (PubMed)
Coronary sinus ASD is frequently associated with other anomalies—particularly persistent LSVC, additional ASDs, AV septal defects, and heterotaxy syndromes.[1,4,6] (PubMed)
Pathophysiology
The fundamental hemodynamic consequence is an atrial level shunt through the CS–LA communication. In the typical situation without LSVC, oxygenated blood from the LA enters the CS via the unroofed segment and then drains to the RA through the CS ostium, resulting in a left-to-right shunt with RA and right ventricular (RV) volume overload and increased pulmonary blood flow—essentially mimicking a conventional ASD.[1,3] (JTCVS)
When a persistent LSVC draining into the CS is present, systemic venous blood from the LSVC reaches a chamber that now communicates with both atria. Depending on the relative resistances and pressure gradients, three patterns are possible:
- LSVC blood flows preferentially into the LA, producing a right-to-left component and systemic desaturation (Raghib complex).
- LA blood passes into the CS and then the RA, augmenting the left-to-right shunt.
- Bidirectional flow within the CS, with complex streaming and mixture of coronary venous and LSVC blood.[4,7] (Journal of Thoracic Disease)
Clinically, patients may present with exertional dyspnea, fatigue, or reduced exercise tolerance due to chronic right-sided volume loading, or with cyanosis, stroke, or brain abscess when a significant right-to-left component is present.[3,5] (PMC)
Diagnostic evaluation
Because the defect is posterior and often small relative to the size of the CS, UCS can be challenging to identify by routine transthoracic echocardiography, and historically many cases were diagnosed only at surgery or autopsy.[1,3] (JTCVS)
Modern imaging strategies include:
- Transthoracic and contrast echocardiography, which can demonstrate CS dilation, direct LA–CS communication, abnormal LSVC drainage, and associated lesions. Combined standard and contrast echo correctly classify most cases and is often the first-line diagnostic tool.[1,8] (PubMed)
- Transesophageal echocardiography, particularly valuable in adults with suboptimal transthoracic windows.
- CT angiography or cardiac MRI, which provide high-resolution, 3-dimensional definition of the CS, LA, LSVC, and neighboring structures, and allow precise assignment of UCS type relevant to surgical planning.[4,9] (Journal of Thoracic Disease)
A high index of suspicion is warranted in patients with disproportionate right-sided enlargement, dilated CS, or unexplained desaturation, especially when LSVC is present or the interatrial septum appears intact on initial imaging.[3,4] (JTCVS)
Surgical objectives and techniques
The overarching goals of repair are to:
- Abolish the pathological communication between LA and CS, eliminating shunting.
- Maintain or restore unobstructed venous drainage of the CS and any LSVC to the RA.
- Avoid injury to adjacent structures, particularly the left circumflex coronary artery, AV node, and His bundle near the CS ostium.[1,3] (JTCVS)
Isolated coronary sinus ASD without LSVC
In patients without LSVC—or with an LSVC that can be safely ligated because of a robust innominate vein—the operation is usually straightforward:
- The LA is opened, and the unroofed segment is closed from the LA side using direct sutures for small defects or a pericardial patch for larger or elongated segments.
- The CS roof is thus reconstructed, re-establishing the CS as a right-sided venous channel draining solely to the RA through its native ostium.[1,6] (JTCVS)
Coronary sinus ASD with persistent LSVC
When a PLSVC–CS–LA complex is present, operative planning becomes more nuanced. Options include[3,4,6]: (JTCVS)
- Intracardiac baffle: reconstructing a tunnel within the LA/CS that directs LSVC and coronary venous blood to the RA while patch-closing the LA communication.
- Extracardiac rerouting of the LSVC to the RA or right atrial appendage (e.g., modified Warden-type procedures) when CS geometry or extent of unroofing precludes an adequate intracardiac tunnel.
- Selective LSVC ligation in carefully evaluated cases where a large bridging vein ensures safe decompression of the left head and neck veins.
Across contemporary surgical series, an intracardiac baffle is the most frequently employed strategy, followed by direct/patch repair of the unroofed segment, together accounting for more than half of reported operations.[2,6] (PubMed)
Emerging transcatheter approaches
Although surgery remains the standard of care, isolated defects with suitable rims have recently been treated with percutaneous device closure or covered stents, guided by multimodality imaging.[2,10,11] Early reports suggest that transcatheter closure can be safe and effective in highly selected adult patients, particularly when surgery carries increased risk, but long-term experience is limited and these techniques are not yet widely adopted. (PubMed)
Postoperative and long-term outcomes
Pooled data from a large contemporary systematic review encompassing more than 300 patients showed that 95% of individuals with UCS ultimately underwent invasive management, predominantly surgical repair.[2] Early outcomes are excellent, with reported in-hospital mortality around 2–3%, and most modern series report no late deaths attributable to the repair itself.[2,6] (PubMed)
Important late issues include:
- Residual or recurrent shunt, which is uncommon (≈0.5%) when the entire unroofed segment is recognized and closed.[2] (PubMed)
- Venous pathway obstruction, particularly LSVC or CS narrowing after complex baffle reconstructions; careful imaging follow-up is recommended in patients with extensive intracardiac tunneling.[6] (Wiley Online Library)
- Atrial arrhythmias, including atrial fibrillation or flutter, reported in a small minority of patients (≈3%) in adult cohorts.[2,5] (PubMed)
When the lesion is recognized and repaired before the development of advanced pulmonary vascular disease, right-sided chamber dimensions regress, symptoms improve, and long-term survival approaches that of the general congenital heart disease population.[2,6] (PubMed)
References
[1] Xie MX, Yang YL, Cheng TO, Wang XF, Li K, Ren PP, et al. Coronary sinus septal defect (unroofed coronary sinus): echocardiographic diagnosis and surgical treatment. Int J Cardiol. 2013;168(2):1258-1263.
[2] Slingerland A, Mathew A, et al. Invasive management of unroofed coronary sinus: a systematic review. Cardiol Young. 2025;(in press).
[3] Ootaki Y, Yamaguchi M, Yoshimura N, Oka S, Yoshida M, Hasegawa T, et al. Unroofed coronary sinus syndrome: diagnosis, classification, and surgical treatment. J Thorac Cardiovasc Surg. 2003;126(5):1655-1656.
[4] Zhi AH, Sun L, Guo JJ, Li J, Sun ZY, Sun LZ, et al. CT angiography for diagnosis and subcategorization of unroofed coronary sinus syndrome. J Thorac Dis. 2017;9(10):3781-3791.
[5] Osei FA, Kenny D, Kenny A, McCrindle BW, Lee KJ. Isolated coronary sinus septal defect and the challenges it presents: a case report and review of the literature. CASE (Phila). 2021;5(6):341-346.
[6] Shi H, Yan J, Wang Q, Hua Z, Li S, Zhang J. Surgical management of unroofed coronary sinus syndrome: a 20-year single-center experience. J Card Surg. 2021;36(2):589-595.
[7] Raghib G, Ruttenberg HD, Anderson RC, Amplatz K, Adams P Jr, Edwards JE. Termination of left superior vena cava in left atrium, atrial septal defect, and absence of coronary sinus; a developmental complex. Circulation. 1965;31:906-918.
[8] Sun L, Zhang N, Yang Y, Xie M. Evaluation of unroofed coronary sinus syndrome using cardiac CT. AJR Am J Roentgenol. 2018;210(2):341-349.
[9] Kim H, Choe YH, Park SW, Kang IS, Kim YH, Kim HS, et al. Partially unroofed coronary sinus: MDCT and MRI findings. AJR Am J Roentgenol. 2010;195(5):W331-W336.
[10] Linjawi HT, Vonder Muhll I, Noga M, Mathew A. Multimodality image-guided percutaneous device closure of an unroofed coronary sinus shunt. JACC Cardiovasc Interv. 2022;15(1):107-109.
[11] Roy M, Gordon E, Johnson M, Hijazi ZM. Transcatheter closure of coronary sinus atrial septal defect using covered stents in an adult. Catheter Cardiovasc Interv. 2017;90(7):1170-1174.