Description:

Ajit Yoganathan, PhD
Wallace H. Coulter Distinguished Faculty Chair & Regents’ Professor
Associate Chair for Translational Research
Wallace H. Coulter Department of Biomedical Engineering
The Georgia Institute of Technology and Emory University
Host: Professor Michael Markl

Title:
“From Glass Models to a Virtual Surgery Platform: 20+ years of Fontan/Single Ventricle Translational Research”

Abstract:
For the past two decades, the Cardiovascular Fluid Mechanics Lab at Georgia Tech has fostered the collaboration between cardiac magnetic resonance imaging, engineering concepts, and fluid dynamic theories to better understand Fontan/single ventricle hemodynamics. Early in vitro Fontan studies utilized glass models of the total cavopulmonary connection (TCPC) to visualize the flow through two-dimensional idealized patient models. A flow-divider (“Optiflo”, US Patent #7811244) was also developed in order to improve the flow field of the TCPC. This development later evolved into a novel surgical approach connection known as the “Y-graft”. These early studies not only provided flow field visualization and engineering insights into the energetics of the TCPC but also established benchmark experimental validation data for computational fluid dynamic (CFD) simulations. Later, with the development of magnetic resonance imaging (MRI), including phase-contrast MRI, non-invasive analysis of anatomy and physiology became feasible. The patient-specific information obtained from clinical MR imaging are valuable inputs for CFD simulations, which can analyze detailed Fontan hemodynamics in a cost-efficient way. Additionally, with modern CFD capabilities, large-cohort investigations were carried out to quantify average TCPC hemodynamic metrics and identify TCPC geometric characteristics that may influence overall cardiovascular performance. The MRI-compatible supine bicycle ergometer, which allows patients to perform lower leg exercise, provided the technique to evaluate Fontan patient's exercise physiology. Limited exercise capacity, seen nearly universally among Fontan patients, has been linked to energy dissipation in the TCPC during exercise, which is also influenced by anatomic characteristics of the TCPC. Furthermore, the advent of real-time phase-contrast magnetic resonance (rtPCMR) imaging technologies and image processing techniques initiated a new era of assessing respiration during rest and exercise. The importance of respiratory effect was demonstrated not only on time variances of the blood flow in the TCPC but also by numerically assessing Fontan hemodynamics.
The knowledge we have gained from these studies and our collaborations have assisted clinicians in improving their surgical strategies for Fontan palliation. A cardiovascular surgical planning software (SURGEM) was collaboratively developed at Georgia Tech and is currently used to pre-operatively determine surgical options. This software provides a platform for clinicians to carry out virtual surgeries and gives the necessary data to engineers to assess three-dimensional TCPC hemodynamics. Evaluating surgical options pre-operatively by means of CFD affords surgeons the awareness of geometries that will or will not work on a patient-specific basis. With this virtual surgery platform, we have successfully predicted Fontan failures, remedied failing Fontan connections, and examined medical treatment options for failing Fontan patients.