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

Abstract

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.

A non-discrete method for computation of residence time in fluid mechanics simulations

“…7,8 Many prior studies report WSS as an important parameter for comparison of different anatomies and clinical scenarios. [9][10][11][12] This measure partly accounts for the time-history of red blood cell exposure to altered shear conditions. In this context, RT calculation is a measure of the degree of fluid entrapment in a specific region, providing a time scale for the thrombus formation process to occur.…”

The Influences of Swirl Flow on Fractional Flow Reserve in Mild/Moderate/Severe Stenotic Coronary Arterial Models

“…(3) [24]. The initial outlet coronary artery flow rate under hyperemic conditions was estimated as 5.2 ml/s from a 4-fold greater flow rate under basal conditions at 1.3 ml/s [24,29]. The physiological data, e.g., SBP, DBP, heart rate(HR) are listed in Table 1.…”

“…This was split in to the coronary arterial resistance, coronary capillary resistance, and coronary venal resistance, in dicated by   ,   and   , respectively. Values of   = 0.32·  ,   = 0.52·   , and Rcv = 0.16·  were imposed [19,29]. Total coronary capacitance,   , was split in to coronary arterial capacitance   and intramyocardial capacitance   , respectively.…”

Computational Simulation of the Adaptive Capacity of Vein Grafts in Response to Increased Pressure

“…CABG surgery is performed to revascularize diseased coronary arteries, using (in order of preference) arterial, venous, or synthetic grafts. Vein grafts, used in 70% of CABG procedures, have failure rates as high as 10-40% within 1 yr and more than 50% within 10 yr [1,2]. An increasing number of patients undergoing these procedures thus require repeat procedures, which carry higher morbidity and mortality rates [3,4].…”