Ebstein anomaly is characterized by failure of normal TV leaflet delamination during embryonic development. Its anatomical features include a sail-like anterior leaflet, apical displacement of the septal and inferior leaflet hinge points, and atrialized portion of the right ventricle (RV). These anatomical abnormalities often result in significant tricuspid regurgitation and RV dysfunction.¹ There is a wide spectrum of clinical presentations in Ebstein anomaly. Late presentation in childhood or adulthood is associated with a better prognosis because the TV may be amenable to surgical repair or replacement whereas neonatal or prenatal presentation often carries a poor prognosis, with perinatal mortality ranging from 45% to 85%.^2,3 Severe neonatal presentation is characterized by inadequate anterograde pulmonary blood flow, resulting in profound cyanosis and a reliance on ductus arteriosus flow to supply the pulmonary circulation.¹

The infant in this scenario was exhibiting evidence of a rare but severe phenomenon seen in Ebstein anomaly: a circular shunt. This phenomenon can occur during gestation or shortly after birth, when there is significant pulmonary regurgitation with little or no anterograde flow through the pulmonary valve and elevated pulmonary vascular resistance (PVR), causing blood from the aorta to travel through the ductus arteriosus into the RV, where it then flows retrograde through the TV, to the RA, and then right to left across the atrial-level shunt to the left atrium. The blood is then again ejected from the left ventricle (LV) to the aorta and back in a circular manner through the ductus arteriosus into the RV, never reaching the lungs for oxygenation (Figure 1).^2,4,5

Figure 1: Ebstein Anomaly With Circular Shunt

Modified from Konstantinov IE, Zubritskiy A, Jaques CH, Fricke TA, Moscoso B. Surgical management of neonatal Ebstein anomaly with a circular shunt. J Thorac Cardiovasc Surg. 2024;168(2):325-328. doi:10.1016/j.jtcvs.2023.10.057.
ASD = atrial septal defect; PDA = patent ductus arteriosus; LV = left ventricle; RA = right atrium; RV = right ventricle.

Although pulmonary regurgitation and inadequate systemic output are components of a circular shunt, circular shunt itself is the most complete description. Pulmonary hypertension may be present as the result of pulmonary compression from cardiomegaly; however, it would not explain this patient's clinical picture. In a circular shunt, hypercarbia and hypoxia result from ineffective pulmonary blood flow and poor alveolar ventilation in the setting of recirculating flow and pulmonary compression. A circular shunt was the reason for his inability to oxygenate, ventilate, and perfuse, and most completely explains his physiology.

Circular shunts can lead to low cardiac output, cyanosis, a large volume load to the heart, severe dilation of the heart chambers, elevated filling pressures, and, if present during gestation, pulmonary hypoplasia due to lung compression by the enlarged heart.² The fraction of the circular shunt can be variable, creating a spectrum of clinical presentation.² Fetuses with Ebstein anomaly and a circular shunt are almost twice as likely to experience fetal demise or neonatal death as are those without a circular shunt.³

According to the American Association for Thoracic Surgery (AATS) 2024 expert consensus document on the Management of Neonates and Infants With Ebstein Anomaly, hemodynamically unstable neonates with Ebstein anomaly and a circular shunt who show signs of low cardiac output and metabolic acidosis should have emergent interruption of the circular shunt.⁵ Decompressing the RV, relieving compression of the LV, and ensuring adequate pulmonary blood flow are also important.⁴ These steps may be achieved with a Starnes procedure if an operating room and cardiopulmonary bypass are immediately available.⁵ With a Starnes procedure, the RV is excluded by patch closure of the TV at the anatomical annulus, with the coronary sinus retained on the atrial side of the patch.¹ A fenestration is made in the patch, the patent foramen is enlarged if needed to ensure unobstructed interatrial blood flow, and an RA reduction is performed.¹ If significant pulmonary regurgitation is present, the main pulmonary artery and duct are ligated, and a source of pulmonary blood flow is provided via a modified Blalock-Thomas-Taussig shunt.¹

Alternatively, the circular shunt may be interrupted via ligation of the main pulmonary artery and placement of bilateral pulmonary artery bands while maintaining pulmonary blood flow through the ductus arteriosus.⁵ With this strategy, a more definitive procedure may be needed within 2-3 days if LV outflow tract obstruction develops due to the dilated RV.⁵ Extracorporeal membrane oxygenation (ECMO) support with occlusion of the PDA is another option.^2,5 A short trial of ECMO support may help facilitate remodeling of the RV as the PVR decreases.² If, after a week, the RV still fails to produce forward flow, the Starnes procedure can be considered.^2,5 Venoarterial ECMO alone in this scenario is insufficient because it does not address the circular shunt and still places the patient at risk of low cardiac output. Neonates with Ebstein anomaly and a circular shunt who are hemodynamically stable and have estimated RVSP >20-25 mm Hg may undergo an attempt at medical closure of the PDA.⁵

Given the high mortality of fetuses and infants with severe Ebstein anomaly and a circular shunt, fetal interventions to interrupt the circular shunt at the ductus arteriosus have been trialed by administering nonsteroidal anti-inflammatory drugs (NSAIDs) or hyperoxygenation to the pregnant patient. Studies using NSAIDs have demonstrated approximately 80% of fetuses achieved ductal constriction with higher rates of live births and survival to hospital discharge.^3,4 However, NSAIDs carry risks of oligohydramnios, kidney dysfunction, postpartum hemorrhage in the birthing parent, and potential persistence of elevated PVR.^6,7 Due to the high risks of NSAIDs, one case study explored chronic hyperoxygenation in the pregnant patient during late gestation and demonstrated constriction of the ductus arteriosus.⁷ Hyperoxygenation in the birthing parent may also reduce PVR and promote anterograde pulmonary blood flow⁶; however, further study is needed to determine the best options for prenatal management.

References

1. Kumar SR, Kung G, Noh N, et al. Single-ventricle outcomes after neonatal palliation of severe Ebstein anomaly with modified Starnes procedure. Circulation. 2016;134(17):1257-1264. doi:10.1161/CIRCULATIONAHA.115.021241
2. Elzein C, Subramanian S, Ilbawi M. Surgical management of neonatal Ebstein's anomaly associated with circular shunt. World J Pediatr Congenit Heart Surg. 2019;10(1):116-120. doi:10.1177/2150135117704615
3. Peña FL, Emanuelson TW, Todman SH, Jones RC, Mahajan S. Fetal circular shunt in Ebstein's anomaly and non-steroidal anti-inflammatory treatment. J Neonatal Perinatal Med. 2024;17(1):63-69. doi:10.3233/NPM-230040
4. Konstantinov IE, Zubritskiy A, Jaques CH, Fricke TA, Moscoso B. Surgical management of neonatal Ebstein anomaly with a circular shunt. J Thorac Cardiovasc Surg. 2024;168(2):325-328. doi:10.1016/j.jtcvs.2023.10.057
5. Konstantinov IE, Chai P, Bacha E, et al. The American Association for Thoracic Surgery (AATS) 2024 expert consensus document: management of neonates and infants with Ebstein anomaly. J Thorac Cardiovasc Surg. 2024;168(2):311-324. doi:10.1016/j.jtcvs.2024.04.018
6. Mustafa HJ, Aghajani F, Bairmani ZA, Khalil A. Transplacental non-steroidal anti-inflammatory drugs versus expectant management in fetal Ebstein anomaly with circular shunt: systematic review and meta-analysis. Prenat Diagn. 2024;44(6-7):773-782. doi:10.1002/pd.6446
7. Arunamata A, Axelrod DM, Bianco K, Balasubramanian S, Quirin A, Tacy TA. Chronic antepartum maternal hyperoxygenation in a case of severe fetal Ebstein's anomaly with circular shunt physiology. Ann Pediatr Cardiol. 2017;10(3):284-287. doi:10.4103/apc.APC_20_17