Computational Fluid Dynamics to Predict Optimal Right Ventricular Outflow Tract Anatomy for Surgical Repair of Tetralogy of Fallot

Louvelle, Leslie 1 ;  Doyle, Matthew 2 ;  Van Arsdell, Glen 3 ;  Amon, Cristina 1, 2

1. Institute of Biomaterials and Biomedical Engineering, University of Toronto; 2. Department of Mechanical and Industrial Engineering, University of Toronto; 3. Division of Cardiac Surgery, Department of Surgery, University of Toronto

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart defect, accounting for 7-10% of all congenital heart disease. These patients require surgical repair of the right ventricular outflow tract (RVOT). Compared to traditional techniques, newer strategies such as infundibular patch placement (IPP) have shown improved long-term outcomes and increased freedom from intervention at 15 years postoperatively.

IPP involves placement of a patch to enlarge the cardiac infundibulum, the infravalvular, conical segment of the RVOT; unfortunately, success rates are variable. Patient-to-patient differences in RVOT anatomy could potentially account for this variability but there is minimal data linking anatomical factors with patient outcomes after TOF repair. Currently, physicians rely on surgical judgement when selecting a repair strategy; this decision carries significant risk of increased intraoperative challenges should the strategy fail. Consequently, newer techniques such as IPP are only employed in a minority of TOF cases.

In an effort to preoperatively predict successful implementation of IPP and increase its prevalence in TOF repair, this work seeks to develop an understanding of the relationship between infundibular anatomy and right heart function. It is hypothesized that computational fluid dynamics (CFD) simulations can be used to identify infundibular configurations which are optimal from a mechanical efficiency standpoint while avoiding hemolysis due to high wall shear stresses.

An idealized model of the RVOT was developed in SolidWorks (Dassault Systemes Inc., Waltham, MA, USA) and imported into ANSYS Workbench (ANSYS Inc., Canonsburg, PA, USA). The length and radius of the cardiac infundibulum were parameterized to allow for systematic adjustment and generation of 16 possible anatomical configurations. All other RVOT dimensions, including the pulmonary valve annulus and main pulmonary artery diameter, were kept constant to isolate effects from changes in infundibular geometry. For each of the 16 configurations, a CFD simulation of blood flow was generated with ANSYS Fluent and the mechanical efficiency was calculated based on the resultant pressures and flow rates.

Preliminary results reveal a logarithmic relationship between infundibulum radius and mechanical efficiency (R2 > 0.8 for all infundibulum lengths). Statistically significant effects were found for infundibulum radius with respect to the average (p < 0.001) and maximum (p < 0.001) wall shear stresses; smaller radii induced higher average and maximum shear stresses. Infundibulum length was insignificant.