A Methodology to Assess Geometry Complexity for Tetralogy of Fallot Patients

Leslie Louvelle (1), Matthew Doyle (2,3), Glen Van Arsdell (1,2), Cristina Amon (4,5)

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto

2. Department of Mechanical and Industrial Engineering, University of Toronto

3. Division of Vascular Surgery, University Health Network

4. Division of Cardiac Surgery, University of California Los Angeles

5. Division of Cardiac Surgery, University of Toronto

Tetralogy of Fallot (TOF) is the most common, cyanotic, congenital heart defect. During surgical repair of TOF, pulmonary valve preservation (preservative repair) has demonstrated improved long-term outcomes compared to repairs which incise into the valve annulus (non-preservative repair). Given the influence of geometry on hemodynamics, the success of preservative repair may be linked to the suitability of the preoperative patient geometry. However, the specific patient anatomies that may be predisposed to successful preservative repair are unknown due to significant interpatient variability in right ventricular outflow tract and pulmonary artery geometries, as well as the limitations in current methods of geometric analyses. As a first step towards understanding the link between geometry and hemodynamics in TOF patients, we present a methodology to characterize the TOF geometry from the right ventricular infundibulum to the left and right pulmonary arteries. Our process consists of segmentation of magnetic resonance images and analysis of cross-sectional slices of the geometries along the centerlines. Using this methodology, we quantify geometric parameters important in determining hemodynamic characteristics such as flow separation and recirculation, which can influence the degree of regurgitation. Specifically, we calculate the diameter along the length of the infundibulum, main pulmonary artery, and left and right pulmonary arteries, as well as the average diameter, length, and tortuosity for each segment. This methodology enables direct geometric comparisons within and among patients and allows for observation of the range in anatomic presentation. We have validated our methodology with a dataset of 11 postoperative TOF patients, repaired with both preservative and non-preservative surgical techniques. Applying this methodology to preoperative geometries, as we intend to do in future work, would yield measurements of geometric parameters that can be related to hemodynamic characteristics. We may then be able to determine the likelihood of success of preservative repair and enable patient-specific recommendation of the appropriate surgical repair strategy.