Ebstein's anomaly

Severe Ebstein's can be associated with the "Circular shunt physiology" (or "Circle of death"), a flow physiology by which blood flow goes from Right to Left atrium (via the ASD/inter-atrial shunt), to the Left ventricle, to the Aorta, to the Pulmonary artery (by the PDA) to the right ventricle (by pulmonary insufficiency), to the right atrium (via the tricuspid regurgitation), to the left atrium by the ASD.

Circular shunt physiology in Ebstein: Aorta → Ductus → Pulmonary artery → Pulmonary Insufficiency → Right Ventricle → Tricuspid insufficiency → Right atrium → Foramen Ovale → Left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta → Ductus arteriosus (Learn more here, and here). Some have described the use of maternal NSAIDs as a way to constrict the fetal duct in an attempt to address this fatal physiology for the fetus / newborn. Article here on "Surgical Management of Neonatal Ebstein’s Anomaly Associated With Circular Shunt".

Effective pulmonary blood flow is significantly reduced due to the following mechanisms: 

1. Low right ventricular (RV) output, resulting from decreased RV capacitance caused by atrialization of the RV. 

2. Severe pulmonary valve insufficiency, which leads to regurgitation and further reduces forward flow. 

As a result, the pulmonary artery (PA) is underfilled, and the ductus arteriosus (PDA) provides flow to the PA via a left-to-right shunt. However, this flow comes at the expense of systemic perfusion, effectively “stealing” blood from the systemic circulation. The PDA jet is directed toward the incompetent pulmonary valve, allowing blood to flow retrogradely from the PDA into the PA and back into the RV. Pulmonary vascular resistance (PVR) is typically elevated due to low pulmonary blood flow, which triggers reflex vasoconstriction in an attempt to preserve perfusion pressure. Additionally, hypoxemia and acidosis, which are often present, further raise PVR. This hemodynamic environment favors the abnormal circuit of flow: from the PDA to the PA, through the insufficient pulmonary valve, and into the RV. Some of the treatment strategies may involve: pulmonary vascular relaxation (iNO, oxygen exposure, titrated mechanical ventilation), restriction of the duct to break the circular shunt (NSAIDs or ligation), supporting the cardiac function in the context of acidosis, hypoxemia and likely low coronary perfusion pressure (high RA pressure in which the coronary sinus drains), while avoiding too much increase in PVR or SVR. As such, many of those infants require some low dose epinephrine, or milrinone (if the BP is not low). 

More on Ebstein's anomaly by clicking here (outside article).

More on fetal Ebstein and circular shunt physiology here.