Evaluation of an Unbalanced Right Dominant Atrioventricular Canal in an Unrepaired Neonate with a Single 4D Flow Dataset

Presenting Author(s)

• SR

  Stephen C. Ream, MD

  Pediatric Cardiology Fellow
  SSM Health Cardinal Glennon Children's Hospital

Primary Author(s)

• SR

  Stephen C. Ream, MD

  Pediatric Cardiology Fellow
  SSM Health Cardinal Glennon Children's Hospital

Co-Author(s)

• LS

  Laura Schoeneberg, MD

  Clinical Assistant Professor of Pediatrics
  Children's Mercy Kansas City
• WK

  Wilson King, MD

  Assistant Professor of Pediatric Cardiology
  Saint Louis University

Description of Clinical Presentation: A 7-day old was diagnosed prenatally with a right dominant unbalanced atrioventricular canal and coarctation of the aorta. Postnatal echocardiogram confirmed the diagnosis. The cardiology and surgical teams were faced with the challenge of which surgical options were most appropriate to offer the patient and family. Options included aortic arch reconstruction with pulmonary artery banding, Stage I Norwood/Sano shunt, or Stage I Norwood/Hybrid. Each could then potentially proceed toward a biventricular or single ventricle repair with varying degrees of associated technical difficulty. The key clinical question was whether the left ventricle was adequate for a biventricular repair. It was not entirely clear how small the left ventricle was based on transthoracic echocardiography. Previous data has suggested that left ventricular volumes as small as 20 mL/m2 can safely undergo biventricular repair. Cardiac MRI was utilized to help define anatomic and physiological constraints, including obtaining an accurate size of the left ventricle.

Diagnostic Techniques and Their Most Important Findings: A cardiac MRI was performed utilizing a 3T 750W scanner and 16 channel GEM large wrap coil with Ferumoxytol (3 mg/kg) contrast infused over 15 minutes. The patient was intubated, anesthetized, and paralyzed. A single 4D flow sequence was performed with an acquired resolution of 1.2 x 1 x 1 mm, reconstructed to 0.6 x 0.86 x 0.86 mm with 20 ms resolution with 25 reconstructed phases. The scan was completed in 23 min and 50 seconds. Complete ventricular volume and all flow data were obtained from the 4D flow sequence. Myocardial borders were sharp and easy to contour, increasing confidence that the volumetric analysis was accurate. The left ventricle was significantly hypoplastic, with the left ventricular end-diastolic volume measured 18 mL/m2, and an LVEDV/RVEDV ratio of 0.15:1.  The left AV valve was hypoplastic with a 4 chamber measurement of 7 mm with z-score of -2.4, a left AV valve to total AV valve cross-sectional area 0.23:1, and a left AV valve to right AV valve inflow ratio by 4D flow of 0.3:1.  4D flow also confirmed significant pulmonary overcirculation with a Qp:Qs of 5.5:1 by branch pulmonary arteries to aortic flow comparison and 7:1 comparing pulmonary vein flow to caval flow. The inlet ventricular septal defect was moderate in size, measuring 4.6 mm in the 4 chamber view.

Learning Points from this Case: Cardiac MRI precisely quantified the size of the left ventricle and left AV valve size, suggesting that candidacy for biventricular repair seemed less likely at the current time. The VSD was also smaller than the surgeon originally thought, making arch repair and PA band less attractive.   Based on MRI and echo data, the patient underwent a Stage I Norwood/Sano repair and did well. The case illustrates how a single 4D flow dataset can be used to accurately obtain structure, function, and flow information in a clinically impactful manner, all in a single acquisition in less than 25 minutes.

A. 4 chamber inverse surface reconstruction during mid-diastole with preferential inflow into the right ventricle B. En face view of the AV valves with 4D flow demonstrating disproportionate flow commitment to the right ventricle

A. 4 chamber 2D reconstruction during end-diastole highlighting the hypoplastic left ventricle B. 4 chamber inverse surface reconstruction during end-diastole

A. 3D surface reconstruction of the hypoplastic aortic arch and large patent ductus arteriosus B. 4D flow through the hypoplastic aortic arch and large patent ductus arteriosus