Dilated Coronary Sinus Causing Left Ventricular Inflow Obstruction: Decision on surgical intervention

Summary

Objectives: A significantly dilated coronary sinus causing left ventricular inflow obstruction presents a challenging dilemma during surgical repair of associated anomalies. We report a 5-month-old male infant was referred to a national heart centre in Muscat, Oman, in 2023 with a persistent left superior caval vein, dilated coronary sinus, partially anomalous pulmonary venous drainage and a large atrial septal defect, resulting in left ventricular inflow obstruction and low cardiac output. The dilated coronary sinus intensified a left-to-right shunt, leading to left ventricular underfilling and early heart failure symptoms. Although surgical correction was planned, direct intervention on the coronary sinus was deferred after intraoperative assessment, supported by virtual dissection of 2-dimensional computed tomography datasets. This non-invasive imaging provided detailed anatomical understanding, comparable to conventional dissection and guided the decision to leave the dilated coronary sinus untouched. Post-operative outcomes showed improved left ventricular filling and resolution of low cardiac output, supporting the chosen strategy. This case highlights the role of virtual dissection in complex surgical planning and decision-making.

1. Introduction

When the persistent left superior caval vein drains into the coronary sinus, the sinus itself is often dilated. Cochrane et al. proposed a novel relationship between left ventricular inflow obstruction and a persistent left superior vena cava with a dilated coronary sinus.¹ Over the past 3 decades, clinical experience has enhanced our understanding of this condition, revealing its association with other left heart obstructive lesions and prompting modifications in surgical approaches.² We present the case of an infant with low cardiac output and heart failure, in whom we strategically focused on redirecting an anomalous right pulmonary venous drainage to the left atrium and closing an atrial septal defect with no intervention to a dilated coronary sinus that was present in association with a persistent left superior caval vein. Post-operatively, the reduction in right atrial pressure led to a significant decrease in the size of the coronary sinus which contributed to improved left ventricular filling and resolution of the low cardiac output condition. This case report underscores the value of virtual dissection in surgical decision-making, offering critical anatomical guidance that can improve patient outcomes.

2. Case report

A 5-month-old male infant was referred to a national heart centre in Muscat, Oman, in 2023 with a history of recurrent respiratory tract infections, increased work of breathing and failure to thrive. A comprehensive transthoracic echocardiography and computed tomography (CT) with virtual dissection revealed usual atrial arrangements, a persistent left superior caval vein draining through a severely dilated coronary sinus, concordant atrioventricular and ventriculoarterial connections, and a large 14 mm defect in the oval fossa with anomalous connection of the right upper and middle pulmonary veins [Fig. 1,Fig. 2,Fig. 3]. Additionally, a parachute mitral valve with an annulus size of 12 mm (z-score: -0.6) was observed, albeit with no gradient observed across the valve. Notably, the left ventricle appeared underfilled compared to the severely dilated right ventricle [Supplementary Video-1, 2]. The course of the dilated coronary sinus was above the inferior annulus of the mitral valve, causing an external compression of the left atrial cavity in that region.

Fig. 1.

Preoperative transthoracic echocardiography images showing the large coronary sinus is small and underfilled left ventricle.

Fig. 2.

Virtual dissection of the 2-dimensional computed tomography data sets showing the location of the confluence of left pulmonary veins facing the atrial septal defect and the possible flow direction to the right atrium (red arrowhead) as well as the course of the dilated coronary sinus bulging above the mitral valve with no internal obstruction.

Fig. 3.

Virtual dissection of the 2-dimensional computed tomography data set showing the location of partially anomalous right pulmonary veins (red arrows) connecting to the superior caval vein (black arrow) with intact superior interatrial fold (blue arrow) and large defect in the oval fossa.

The patient underwent successful surgical correction via a median sternotomy using cardiopulmonary bypass at a temperature of 32°C. The orifices of the right upper and middle pulmonary veins were found at the junction between the superior caval vein and the right atrium. The walls of the dilated coronary sinus wall were partially covering the orifice of the mitral valve. The mitral valvar orifice, however, was adequate, taking a 12 mm Hagar dilator. There was no evidence of any internal obstruction of the mitral inflow and the left atrial cavity was noted to be small compared to that of the right atrium. Based on these findings, no surgical intervention was done on the dilated coronary sinus. Surgical repair involved only the baffling the anomalous right pulmonary veins to the left atrium with an autologous pericardial patch, which was also used to close the interatrial communication, albeit leaving a 4 mm fenestration. The patient was successfully separated from cardiopulmonary bypass and had an uneventful postoperative course. At the 6-month follow-up after surgery, the patient was in good condition, feeding well and gaining weight. Transthoracic echocardiography revealed good biventricular function, a good-sized left atrium and left ventricle, unobstructed baffling of the right upper and middle pulmonary veins and mitral valve with a mean gradient of 3 mm Hg [Fig. 4, Supplementary Video-3, 4].

Fig. 4.

Postoperative echocardiogram showing improvement of the left ventricle size (red arrows) and filling despite the presence of the large coronary sinus (yellow arrows).

3. Discussion

The relationship between a dilated coronary sinus and obstructed left ventricular inflow has been previously reported, though the underlying mechanism remains unclear.^1,2,3,4 One theory posits that the obstruction may result either from an internal blockage above the mitral valve or from impaired left atrial filling, which exacerbates left-to-right shunting across an atrial septal defect.¹ Studies have noted a significant pressure gradient above the mitral valve, which can be detected through echocardiography or cardiac catheterisation. This pressure gradient typically resolves after the surgical correction of the dilated coronary sinus and associated cardiac anomalies.^3,4 Upon reviewing previous cases, it was found that dilated coronary sinus-induced left ventricular inflow obstruction was primarily associated with defects causing left-to-right shunting. Therefore, the authors propose that increased right atrial filling pressure, resulting from left-to-right shunting, is transmitted to the coronary sinus, leading to further dilation. This dilation can cause external compression of the left atrium, thereby impeding its filling.

At the indexed time, the patient was in the intensive care unit with low cardiac output and was not stable enough for an invasive catheterisation. Although Doppler echocardiography showed no significant transmitral gradient, this was likely due to severe under-filling of the left ventricle. A large proportion of pulmonary venous return appeared to be shunted to the right atrium through an interatrial communication, potentially masking any gradient across the mitral valve. Cross-sectional imaging revealed a markedly dilated coronary sinus, initially raising concerns about functional mitral inflow obstruction due to posterior compression of the left atrium. However, intraoperative findings and the postoperative course confirmed that the coronary sinus was not the primary cause of obstruction and the absence of a preoperative mitral inflow gradient supports this conclusion.

In the current case, as shown by the virtual CT images and intraoperative findings, there was no evidence of internal obstruction of the mitral valve due to the dilated coronary sinus. This contrasts with cases involving a divided left atrium or a supramitral shelf, where internal obstruction is seen. The current case's findings suggest that the interaction between the expanding dilation of the coronary sinus and a small left atrium was the primary issue. Septation of the atrial chambers improved both left atrial and ventricular filling, demonstrating that direct intervention on the dilated coronary sinus was unnecessary.

Ramaswamy et al. reported that approximately one-third of patients with a dilated coronary sinus, identified via fetal echocardiography, had hypoplastic left ventricles and/or coarctations.⁵ They proposed a potential link between the dilated coronary sinus and mitral valve inflow obstruction, potentially originating during fetal development, owing to the proximity of the coronary sinus to the hinge of the mural leaflet of the mitral valve. In the current case, the dilated coronary sinus likely exacerbated left pulmonary vein shunting, especially considering its anatomical positioning opposite the atrial septal defect. This, combined with partially anomalous right pulmonary veins, resulted in significant left-to-right shunting and left ventricular underfilling. Reporting the location of the atrial septal defect in relation to the pulmonary veins is crucial, as it can influence the degree of left-to-right shunting and exacerbate the vicious cycle of coronary sinus dilation and impaired left atrial filling.

In the current case, through 2-dimensional CT projections, 3-dimensional digital models were created. Rapid segmentation and application of distinct color spectrums to specific ranges of Hounsfield units for tissue differentiation allowed the implementation of ‘virtual dissection’. This offered a highly detailed representation of intracardiac anatomy. Recent advancements in 3- and 4-dimensional cardiac CT have revolutionised the management of congenital heart malformations by providing detailed and precise anatomical information. Unlike traditional echocardiography, cardiac CT with virtual dissection offers unparalleled spatial resolution and advanced visualisation techniques, such as surface and volume rendering, which significantly enhance pre-procedural planning and simulation. Additionally, its faster scan speeds reduce the need for sedation, and optimised protocols minimise radiation exposure, making it a superior imaging modality for complex cardiac cases.⁶ While echocardiography remains a critical intraoperative tool for functional and dynamic assessment, it is often limited by acoustic windows, operator dependency and challenges in depicting complex 3-dimensional anatomical relationships. It should be noted however, that virtual dissection rather than replacing echocardiography evaluation, enhances preoperative understanding and facilitates more informed intraoperative decision-making, especially when conventional imaging is inconclusive.

The virtual dissection of 2-dimensional CT datasets provided a detailed 3-dimensional visualisation of the heart's anatomical structures, which was essential in assessing the complex congenital abnormalities. It revealed a persistent left superior caval vein draining into a severely dilated coronary sinus, an anomalous connection of the right upper and middle pulmonary veins and an underfilled left ventricle, along with external compression of the left atrial cavity by the dilated coronary sinus. These insights allowed for a precise understanding of the spatial relationships between the coronary sinus, mitral valve and pulmonary veins, guiding the decision to refrain from directly intervening on the coronary sinus. Instead, the surgical focus was on correcting the anomalous pulmonary venous drainage and closing the atrial septal defect. The virtual dissection effectively provided an ‘anatomical map’ of the heart, ensuring that the surgical approach was both targeted and minimally invasive.

This case report differs from the existing literature as it highlights a rare and significant left ventricular underfilling due to a markedly dilated coronary sinus, occurring in the context of a secundum atrial septal defect and partial anomalous right pulmonary venous connection, presenting early in infancy. While similar anatomical conditions have been described, the degree of ventricular underfilling observed in the current case, combined with this unique anatomical constellation, is not commonly reported in the literature. Furthermore, this report challenges the prevailing notion that intervention on the coronary sinus is necessary when it appears to obstruct left atrial inflow. In contrast to prior reports, this case demonstrates that despite initial imaging concerns about coronary sinus compression, the absence of a mitral inflow gradient and the patient's postoperative improvement without direct intervention on the coronary sinus support a more conservative approach in selected cases. This adds a new perspective to the management of such rare and complex congenital presentations. However, there are limitations to this case. Preoperative and postoperative cardiac catheterisation were not performed, which resulted in a lack of critical haemodynamic data that might have provided further insight into the physiological changes and pressures involved in this patient's condition.

4. Conclusion

This report's findings suggest that enhancing the size and filling of the left ventricle is achievable without directly targeting the dilated coronary sinus. When a dilated coronary sinus is encountered, the repair of associated cardiac lesions should be prioritised and left ventricular filling and pressure gradients should be re-assessed before contemplating interventions involving the coronary sinus. Furthermore, virtual dissection of 2-dimensional CT datasets proves to be a valuable tool in optimising surgical planning and decision-making.

Authors' Contribution

Hamood N. Al Kindi: Conceptualization, Methodology, Formal analysis, Resources, Writing - Original Draft, Writing - Review & Editing. Madan M. Maddali: Methodology, Formal analysis, Writing - Original Draft, Writing - Review & Editing. Justin Tretter: Resources, Data Curation, Visualization, Writing - Review & Editing, Final approval of the version submitted.

Ethics Statement

Written consent was obtained from the patient's parents to reproduce the images and publish the case report. This case report publication was also approved by the Institutional Review Board [MOH/CSR/CR/24/13].

Data Availability

Data is available upon reasonable request from the corresponding author.

Supplementary Data

Supplementary Video 1: Preoperative transthoracic echocardiogram of the apical 4 chamber showing severe under-filling of the left ventricle and compressed mitral valve inflow with a markedly enlarged coronary sinus.

Supplementary Video 2: Preoperative transthoracic echocardiogram of the parasternal long axis showing severe under-filling of the left ventricle and compressed mitral valve inflow with a markedly enlarged coronary sinus.

Supplementary Video 3: Postoperative transthoracic echocardiogram of the apical 4 chamber showing the improvement of the filling of the left ventricle and the mitral valve inflow without intervening on the coronary sinus.

Supplementary Video 4: Postoperative transthoracic echocardiogram of the parasternal long axis showing the improvement of the filling of the left ventricle and the mitral valve inflow without intervening on the coronary sinus.