Wrong Way Home: Variant Caval Return to the Left Atrium

Graphical abstract

Highlights

• •We report drainage of SVC and IVC to the LA with normal drainage of CS.
• •A defect in juxtaposed atrial appendages allowed flow from LA to RA.
• •TTE with agitated saline contrast study confirmed diagnosis.
• •CCT aided morphologic assessment and surgical planning.

Introduction

Congenital abnormalities of caval drainage and connections include benign common variants such as drainage of a left superior vena cava (SVC) to the coronary sinus (CS).¹ Abnormal caval drainage to the left atrium (LA) is less common.² Such defects can result in systemic desaturation and are clinically important. However, a high index of suspicion must be maintained by the clinical team given the infrequent occurrence and the fact that the degree of systemic desaturation can be mild. Herein we describe a case of anomalous drainage of the right SVC and the inferior vena cava (IVC) to the LA, which also received pulmonary venous return. Notably, the CS drained normally to the right atrium (RA). The only means of egress of blood into the RA was thus from flow through a defect between juxtaposed atrial appendages and venous return from the CS. We discuss (1) the unique anatomic findings of our case and its relationship to other cases of abnormal caval drainage reported in the literature; (2) the role of echocardiography in the diagnosis of abnormalities of caval drainage and surgical decision-making; and (3) the use of cardiac computed tomography (CCT) to facilitate three-dimensional conceptualization of the defects present in this case in anticipation of surgical repair.

Case Presentation

A patient with fetal diagnosis of a large perimembranous ventricular septal defect (VSD) and tricuspid and right ventricular hypoplasia was born at 36 weeks of gestational age. After birth, the patient was vigorous, with initial SpO₂ of 70% to 80%, which quickly rose to approximately 90% without need for supplemental oxygen. Postnatal transthoracic echocardiogram (TTE) confirmed the presence of a perimembranous VSD and otherwise showed mild tricuspid and right ventricular hypoplasia, an atrial septal defect with left-to-right shunting, normally related great arteries without significant aortic or pulmonary hypoplasia, and normal left and right ventricular systolic function. Follow-up TTE was notable for progressive left-sided chamber enlargement. During the patient’s hospital course, saturations were maintained predominantly just above 90% on room air, with this mild systemic desaturation felt to be attributable to pulmonary venous desaturation. Progressive tachypnea was noted, along with marginal weight gain. Consequently, diuretics were initiated for clinical heart failure symptoms. Despite optimization of medical therapy and nutrition, weight gain remained very poor, and the patient was transferred to our center at 6 weeks of age for consideration of surgical intervention. At the time of transfer, the patient was tachypneic with a respiratory rate of approximately 70 breaths per minute and had shown suboptimal weight gain, with an average daily weight gain of 16 g/day and a weight of 3.65 kg (<first percentile).

After transfer, TTE confirmed many of the previous findings, including presence of a large perimembranous VSD measuring approximately 16 × 7 mm and mild tricuspid valve hypoplasia with an annular dimension of 0.7 cm (Z score = –2.4). The right ventricle (RV) appeared qualitatively mildly hypoplastic, and the left ventricle measured moderately dilated, with a left ventricular end-diastolic dimension of 3.1 cm (Z score = 5.1). The great arteries were normally related, but there was abnormal caval drainage. Specifically, the TTE showed anomalous drainage of the right SVC, IVC, and hepatic veins to the LA. There was rightward anterior deviation of the superior atrial septum with a moderate defect noted allowing egress of blood from the LA into the RA. There was a leftward course of the right-sided atrial appendage such that it was juxtaposed with the left-sided atrial appendage. An agitated saline contrast study with an intravenous injection in the left foot showed dense initial opacification of the LA, confirming anomalous drainage of the IVC to the LA (Figure 1, Figure 2, Figure 3, Videos 1-6). Pulmonary veins were shown to drain normally to the LA.

Figure 1.

(A) Two-dimensional TTE, apical 4-chamber diastolic image, pediatric display, demonstrates a dilated LA, left ventricle, and hypoplastic right-sided chambers; (B) agitated saline contrast injection in the left foot demonstrates contrast in the LA and left ventricle.

Figure 2.

(A) Two-dimensional TTE, subcostal sagittal diastolic image, demonstrates the intrahepatic IVC entering the LA. (B) Two-dimensional TTE, subcostal sagittal diastolic image without (left) and with (right) color-flow Doppler, demonstrates the anomalous right SVC (arrow) coursing anterior to the right pulmonary artery and entering the LA.

Figure 3.

(A) Two-dimensional TTE, subcostal sagittal diastolic image without (left) and with (right) color-flow Doppler, demonstrates the intact atrial septum with flow entering into the RA from the defect (arrow) in the right-sided atrial appendage; (B) two-dimensional TTE, parasternal short-axis diastolic image, demonstrates the defect (arrow) between the leftward juxtaposed right-sided atrial appendage and LA.

Given the significant caval abnormalities, a CCT was completed to further evaluate the anatomy and assist with surgical planning. The CCT confirmed anomalous drainage of the SVC and IVC to the LA. The CS drained normally to the RA. The atrial shunt was well-defined as resulting from a moderate defect in the inferior mid-portion of the right-sided atrial appendage allowing egress of blood from the LA to the RA. The proximal aspect of the right-sided atrial appendage measured 7 × 9 mm in diameter and constituted the pathway for atrial shunting. Atrial appendage morphology assessment was limited by dilation of the left-sided atrial appendage and juxtaposition, but the right-sided atrial appendage was more elongated, suggestive of left atrial appendage morphology (Figure 4, Video 7). Notably, the exam also demonstrated normal lung and airway anatomy, with eparterial branching of the right bronchus and hyparterial branching of the left bronchus (Figure 5). An abdominal ultrasound confirmed abdominal situs solitus without the abnormalities of the liver, spleen, or gallbladder typically associated with left or right atrial isomerism.

Figure 4.

Cardiac computed tomography, multiplanar reformat, oblique sagittal display, demonstrates (A) the anomalous drainage of the right SVC and IVC into the LA and (B) the communication between the LA and RA (∗). (C) Three-dimensional volume-rendered reconstruction of the whole heart, posterior perspective, demonstrates the complex venous anatomy and the approximate level of the defect in the inferior aspect of the right-sided atrial appendage (∗); (D) three-dimensional transparent model of the volume-rendered CCT dataset demonstrates the caval return to the LA (blue arrows), the pulmonary venous return to the LA (red arrows), and the defect in the right-sided atrial appendage allowing shunting (purple arrow) from the LA (gray outline) to the RA (blue outline). LLPV, Left lower pulmonary vein; LUPV, left upper pulmonary vein; RAA, right-sided atrial appendage; RLPV, right lower pulmonary vein; RUPV, right upper pulmonary vein.

Figure 5.

(A) Cardiac computed tomography, multiplanar reformat, oblique coronal display, demonstrates the drainage of the CS (∗) to the RA and the defect between the right-sided atrial appendage and the superior aspect of the LA; (B) coronal display demonstrates the normal airway anatomy with eparterial branching of the right bronchus and hyparterial branching of the left bronchus.

The comprehensive imaging data were reviewed, with particular attention given to the size of the RV and tricuspid valve. Subjectively, the RV appeared mildly hypoplastic, but we noted that the relative difference in right and left ventricular size was magnified by left ventricular dilation in the setting of left-to-right intracardiac shunting. The RV was tripartite and had normal systolic function. Furthermore, the tricuspid valve annulus measured 0.7 cm with a Z score of –2.4, confirming only mild hypoplasia, and there was no significant tricuspid regurgitation. Taken together, we felt these findings indicated adequacy of right-sided structures to support a biventricular circulation. Clinically, there was no significant weight gain during hospitalization despite optimization of medical therapies and nutrition (weight of 3.63 kg prior to surgery), supporting an indication for inpatient surgical intervention.

After multidisciplinary discussion and review of recommendations with the family, the patient was taken to the operating room. There, the atrial septum was reconstructed to route the caval return to the RA. A small fenestration measuring 4 mm in diameter was intentionally created in the newly constructed atrial septum to allow for right-to-left atrial shunting as a popoff for periods when caval return might transiently exceed what the mild hypoplasic RV could support. This approach mirrored one that is commonly used for biventricular surgical repair of pulmonary atresia with intact ventricular septum.³ The VSD was closed. The patient tolerated the procedure well, with significant improvement in weight gain, averaging 31 g/day following recovery prior to discharge. The discharge TTE showed normal ventricular systolic function, no residual ventricular shunt, and right-to-left shunting at the atrial septum. The discharge SpO₂ was 90%. At most recent follow-up at 12 months of age, a TTE showed similar findings albeit with bidirectional atrial shunting. The patient was doing well clinically with satisfactory weight gain and systemic oxygen saturation of 98%.

Discussion

This case was remarkable for drainage of the near entirety of systemic venous return to the LA. A VSD was present, which allowed for augmentation of pulmonary blood flow via left-to-right shunting. This resulted in relatively mild systemic desaturation but also significant clinical congestive heart failure symptoms precluding growth, which necessitated early surgical treatment. This case raises several morphologic, physiologic, and clinical considerations. In the literature, cases of anomalous drainage of the right SVC to the LA and the spectrum of biatrial drainage of the SVC are well-described.² Various developmental theories have been suggested to explain this aberration, including abnormal orientation of the horn of the sinus venosus and/or underdevelopment of the partition between the right SVC and the right upper pulmonary veins as suggested by Van Praagh.⁴ Similar abnormalities encompassing isolated drainage of the IVC to the LA have also been described.⁵ Conversely, drainage of both the SVC and the IVC to the LA are more sparsely reported in the literature. Zhang et al.⁶ describe a patient with a similar anatomic configuration to ours, where the right SVC and IVC drained abnormally to the LA. Gupta et al.⁷ also described 2 patients at their center with anomalous drainage of the SVC, IVC, and CS to the LA. One of their reported cases occurred in the setting of left atrial isomerism. Importantly, in these cases and many other reported cases of “total anomalous systemic venous connection,” the CS also drains abnormally to the LA. In fact, in Gupta et al.'s review of over 20 prior case reports, all of those that commented on the CS indicated drainage of the CS to the LA when present.⁷ In contrast, in our case, the CS was shown by CCT to drain normally to the RA. We feel this constitutes a more unique aspect of the current case and were unable to identify a similar case in our review of the literature.

We speculate that our case may reflect a variant of left atrial isomerism. Variants of caval return in left atrial isomerism are well-described. Notably, a CS is frequently present.⁸ While there were no thoracic or visceral findings associated with left atrial isomerism in our case, this framework is supported by a more elongated appearance of the right-sided atrial appendage, suggestive of left atrial appendage morphology. Interestingly, one preoperative electrocardiogram in this patient showed ectopic atrial rhythm (Figure 6). While nonspecific, this finding might be compatible with some of the rhythm abnormalities encompassed by the spectrum of left atrial isomerism.

Figure 6.

Twelve-lead electrocardiogram demonstrates ectopic atrial rhythm.

An alternative consideration is whether findings could be primarily attributable to malposition of the atrial septum. However, malposition of the atrial septum is predominantly described as a source of abnormal drainage of pulmonary veins to the RA, despite normal anatomic connection to the LA and not being a source of abnormal caval drainage.⁹ Furthermore, abnormalities of the atrial septum are also well-described in cases of atrial isomerism, and hence our case might be better described with a unifying diagnosis of left atrial isomerism.

It is worth noting that there can be some confusion when describing caval or pulmonary venous anomalies as abnormalities of either drainage or connection. A full discourse on the semantics of these terms is beyond the scope of this report, but given some morphologic ambiguities, we have purposefully used the term drainage to describe the caval connections in our patient, which we believe is the vernacular that more accurately conveys physiologic and clinical considerations raised by the anatomy. While one can speculate about the morphologic underpinnings of this anatomy, we feel ultimately it is most important for the clinical imaging team in cases such as this to describe the venous pathways as precisely and accurately as possible so that the physiologic and clinical ramifications of the anatomy are clearly understood by all stakeholders.

From a diagnostic standpoint, TTE should be a primary modality of diagnosis of caval abnormalities. However, a high index of suspicion must be maintained by the clinical team as short sagittal clips showing caval return to atria may not clearly identify which atrium is receiving the vessels. The importance of careful sweeps through the anatomy with two-dimensional imaging and color-flow Doppler cannot be overemphasized. The need for a high index of suspicion is further underscored by the potential for relatively mild systemic desaturation, with SpO₂ greater than or equal to 90%, as was present in our case. This concept is further supported by literature reporting identification of cases of abnormal caval drainage in patients of all ages.⁷ Finally, this case also illustrates the power of agitated saline contrast to confirm abnormal connections and drainage. The clinical team should have a low threshold for performance of agitated saline contrast study if there is any ambiguity about caval abnormalities that could potentially result in systemic desaturation. Abnormal SVC drainage can be confirmed by agitated saline contrast injection in the upper extremities, while abnormal IVC drainage can be confirmed by agitated saline contrast injection in the lower extremities. Injection in the left upper extremity also has value when evaluating for rarer shunts such as presence of a levoatriocardinal vein or unroofed CS, which may not be identified with a right upper extremity injection.

Finally, this case illustrates the utility of CCT to confirm anatomic findings and visualize anatomy in 3 dimensions. This modality more accurately delineated the nature of the interatrial shunt, which was difficult to capture entirely in two-dimensional imaging clips. Interestingly, the functional atrial shunt in this case was attributable to a defect between the juxtaposed atrial appendages, which has been sparsely described.^10,11 We chose CCT rather than cardiovascular magnetic resonance given the higher spatial resolution available by CCT to delineate intracardiac anatomy and the relative ease of image acquisition in a small patient. Cardiovascular magnetic resonance can allow for a more detailed measurement of ventricular sizes, although in this case our team felt confident enough that TTE findings showed adequacy of right-sided structures to support biventricular repair.

We performed a nonsedated CCT using a dual-source computed tomography scanner and ultrafast high-pitch single-heartbeat protocol with manual timing to the arterial phase, followed by a second acquisition following a 15-second delay to better define the venous anatomy. The contrast was injected in an upper extremity, and visualization of the arterial and pulmonary venous anatomy was excellent with first-pass arterial timing; the IVC and CS imaging was excellent on the delayed imaging.

Conclusion

We describe a unique patient with abnormal drainage of the SVC and IVC to the LA with normal drainage of the CS to the RA. With the presence of atrial shunting and a VSD, systemic saturations were close to normal given the relatively high pulmonary blood flow, underscoring the need for a high index of suspicion for this diagnosis. We emphasize the importance of clear and precise descriptions of the venous connections so that the anatomy and physiology are fully understood. Abnormalities of caval connections and drainage can be readily made by TTE with two-dimensional and color-flow Doppler but benefit from complementary imaging with agitated saline contrast studies and CCT.

Ethics Statement

The authors declare that the work described has been carried out in accordance with The Code of Ethics of the World Medical Association (Declaration of Helsinki) for experiments involving humans.

Consent Statement

The authors declare that since this was a non-interventional, retrospective, observational study utilizing de-identified data, informed consent was not required from the patient under an IRB exemption status.

Funding Statement

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Disclosure Statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Supplementary Data

Video 1

Two-dimensional TTE, apical 4-chamber pediatric display sweeping from inferior to superior, demonstrates a dilated left heart, normal left and right ventricular systolic function, mild tricuspid and right ventricular hypoplasia, and a large perimembranous VSD.

Video 2

Two-dimensional TTE, apical 4-chamber pediatric display, demonstrates a dilated LA, left ventricle, and hypoplastic right-sided chambers with multiple bubbles first noted in the LA and then the left ventricle after injection of agitated saline contrast injection in the left foot, confirming anomalous drainage of the IVC to the LA.

Video 3

Two-dimensional TTE, subcostal sagittal image, demonstrates the intrahepatic IVC entering the LA.

Video 4

Two-dimensional TTE, subcostal sagittal image without (left) and with (right) color-flow Doppler, demonstrates the anomalous right SVC coursing anterior to the right pulmonary artery and entering the LA.

Video 5

Two-dimensional TTE, subcostal sagittal image without (left) and with (right) color-flow Doppler, demonstrates the intact atrial septum with flow entering into the RA from the defect in the right-sided atrial appendage.

Video 6

Two-dimensional TTE, parasternal short-axis image, demonstrates the defect between the leftward juxtaposed right-sided atrial appendage and the LA.

Video 7

Cardiac computed tomography, three-dimensional whole-heart reconstruction, rotational cine-image display viewed posteriorly, demonstrates the complex venous anatomy including the pulmonary vein anatomy and anomalous drainage of the right SVC to the LA in relation to the approximate level of the defect in the inferior aspect of the right-sided atrial appendage (∗). The aorta is red; the main and branch pulmonary arteries are blue. LAA, Left-sided atrial appendage; LLPV, left lower pulmonary vein; LUPV, left upper pulmonary vein; RLPV, right lower pulmonary vein; RUPV, right upper pulmonary vein.