4-D Flow in a Case of Scimitar Syndrome (QF_TH_030)

A 16 week old female was transferred from an outside hospital with Scimitar Syndrome (right sided pulmonary veins draining into the inferior vena cava), right lung sequestration/severe right pulmonary artery hypoplasia and dextroposition. The patient also had a patent ductus arteriosus (PDA), an atrial septal defect (ASD) with mostly left to right shunting, a left superior vena cava to coronary sinus. The patient had right ventricular dysfunction requiring intermittent milrinone use and severe pulmonary hypertension on dual pulmonary hypertension therapies (Bosentan & Sildenafil).

Patient was status post device occlusion of the right lung sequestration as well as status post PDA stent placement to relieve RV afterload. The echo after transfer suggested new findings of predominant left to right shunting at the PDA, increased flow from left lower pulmonary vein to left atrium concerning for possible pulmonary vein stenosis, and systemic right ventricular pressure.

In the setting of unknown pulmonary to systemic flow ratio (Qp:Qs) and unknown burden of pulmonary hypertension on the healthy left lung, a MRI was conducted to assess the hemodynamic burden of the PDA and ASD.

Diagnostic Techniques and Their Most Important Findings:

Cardiac MRI was performed to determine her Qp:Qs as well as venous anatomy. A 4-D flow analysis demonstrated a diminutive right pulmonary artery with no appreciable antegrade flow and the pulmonary flow split was calculated to be 90% through the left pulmonary artery and 10% through the right pulmonary artery. MRI also visualized a small Scimitar vein draining into the inferior vena cava-right atrium junction with no other obvious right-sided pulmonary veins (Fig 1). The Qp:Qs was 3:1 based on systemic/pulmonary venous drainage. Finally, the ASD shunt burden was 4L/min/m² and the stented PDA shunt burden was 2L/min/m².

Learning Points from this Case:

The MRI findings demonstrated hemodynamic significance of the ASD/PDA contribution to Qp:Qs. Instead of preserving the stented PDA to relieve RV afterload as posited before, the PDA was shown to have direct contribution to volume overload on the remaining healthy left lung. She subsequently had Piccolo device closure of the PDA which resulted in a Qp:Qs of 2.1:1 at the time of the cath. In the following weeks, she had improvement but remained symptomatic with increased right ventricular pressure. A follow-up 4-D flow study revealed a Qp:Qs of 1.3:1 from the remaining shunt across the ASD (Fig 2). This revealed that the ASD did not to contribute greatly to elevated right ventricular pressure, further guiding clinical decision making towards pulmonary hypertension management and away from surgically closing the ASD. CMR was shown in this case to provide effective hemodynamic assessment of venous anatomy with complex flow patterns in multiple decision-making points along the progression of treatment.