Patient-Specific Multiscale Modeling of Blood Flow for Coronary Artery Bypass Graft Surgery

We present a computational framework for multiscale modeling and
simulation of blood flow in coronary artery bypass graft (CABG)
patients. Using this framework, only CT and non-invasive clinical
measurements are required without the need to assume pressure and/or
flow waveforms in the coronaries and we can capture global circulatory
dynamics. We demonstrate this methodology in a case study of a patient
with multiple CABGs. A patient-specific model of the blood vessels is
constructed from CT image data to include the aorta, aortic branch
vessels (brachiocephalic artery and carotids), the coronary arteries and
multiple bypass grafts. The rest of the circulatory system is modeled
using a lumped parameter network (LPN) 0 dimensional (0D) system
comprised of resistances, capacitors (compliance), inductors
(inertance), elastance and diodes (valves) that are tuned to match
patient-specific clinical data. A finite element solver is used to
compute blood flow and pressure in the 3D (3 dimensional) model, and
this solver is implicitly coupled to the 0D LPN code at all inlets and
outlets. By systematically parameterizing the graft geometry, we
evaluate the influence of graft shape on the local hemodynamics, and
global circulatory dynamics. Virtual manipulation of graft geometry is
automated using Bezier splines and control points along the pathlines.
Using this framework, we quantify wall shear stress, wall shear stress
gradients and oscillatory shear index for different surgical geometries.
We also compare pressures, flow rates and ventricular pressure-volume
loops pre- and post-bypass graft surgery. We observe that PV loops do
not change significantly after CABG but that both coronary perfusion and
local hemodynamic parameters near the anastomosis region change
substantially. Implications for future patient-specific optimization of
CABG are discussed.